WO2012122605A1 - Iridium based complex for water splitting - Google Patents

Abstract

In a general form, there is provided a cyclometalated iridium complex, which in one application can be used as a catalyst for water splitting. In one form, the cyclometalated iridium complex includes bandgap lowering ligands, for example aryl quinoline. In another form, the cyclometalated iridium complex includes bandgap widening ligands, for example aryl triazole. In a particular example, one or more additional linking groups are included to improve solubility of the complex. In another particular example, one or more additional linking groups are included to improve attachment of the complex to a semiconductor or an electrode. According to a specific example, there is a cyclometalated iridium complex having the structure wherein, Ar is an aryl group, or a fused or heterocyclic arene or ring.

Description

IRIDIUM BASED COMPLEX FOR WATER SPLITTING

Technical Field

[001] The present invention generally relates to water splitting, and also relates to water oxidation or water photolysis. More specifically, the present invention relates to a complex or a catalyst for water splitting.

Background

[002] Increasing worldwide energy demands, and concerns that such demands and fossil fuel reliance may prove unsustainable or ecologically detrimental have induced research into alternative energy sources. Solar energy is a renewable alternative to fossil fuels and many different systems for harnessing solar energy have been proposed. However, as the intensity of solar energy is variable, for example depending on the time of day or geographic location, many solar energy systems rely on forms of energy storage in order to provide suitable or steady power.

[003] Photoinduced water splitting which produces hydrogen is one such example. Hydrogen produced by light-driven water splitting can be directly used for combustion, used in fuel cells, or stored, for example in the form of liquid fuel. Photoinduced water splitting is a topical area of research as water is the most accessible source of hydrogen on Earth.

[004] In nature, photoinduced water splitting is a finely balanced process, overcoming the energetic barrier of O-H bond cleavage and 0-0 bond formation by a complex photo synthetic reaction cascade. The energy required to spontaneously dissect water into its elemental constituents at 298 K is 237 kJ/mole. Although the energy needed to directly cleave water using sunlight is available, the absorbance of solar energy by water at such wavelengths is insufficient. One aspect of current research in photoinduced water splitting focuses on designing catalysts to facilitate H-H and 0-0 bond formation. Additionally, current research strives to design catalysts that operate in the visible light spectrum to induce water splitting. [005] In currently known work, ruthenium complexes have been proposed as molecular catalysts to oxidise water to dioxygen (see Llobet et ah, Angew. Chem. Int. Ed 2009, 48, 2842). Relatively recent work has also been performed on iridium(III) [i.e. Ir(III)] complexes as catalysts for water oxidation. Since the catalytic process is carried out in an oxidative, and often, either acidic or basic water environment, particularly robust and water soluble catalysts are required. Such requirements can strongly influence suitable types of organic ancillary ligands for a metallic centre, and which can often result in a decrease of catalytic activity over time due to oxidative degradation of organic ligands. A known cyclometalated Ir(III) complex is provided by Thomas et ah, (Inorg. Chem. 2005, 44, 5677). Ir(III) based materials are continuing to be explored as catalysts in photoinduced water splitting. However, there is significant scope to produce new Ir(IIl) complexes that provide improved catalytic activity, efficiency, stability, etc.

[006] Research into electron transitions involving Ir(III) complexes demonstrate the complexity of the charge transfer system. Two principle transitions, or a combination thereof, are observed being metal-to-ligand charge transfer (MLCT) in which an electron is promoted from a metal orbital to a vacant orbital on one of the ligands, and ligand-centred (LC) transitions in which an electron is promoted between orbitals on one of the coordinated ligands. Generally, the electron excitation is not pure MLCT but an admixture of MLCT and LC. Strong spin orbit coupling from the Ir(III) centre facilitates intersystem crossing between energetically similar states. In current research, it is sought to tune excited states in an Ir(III) complex to thus provide desirable photo-electro-chemical behaviour which can promote or induce water splitting. There is a need to provide new Ir(III) complexes that can beneficially modify energy bandgaps for use in a photoinduced water splitting system, for example that promotes generation of oxygen gas by the formation of a bond between two oxygen atoms originating from water molecules. Efficient and stable catalysts for oxygen evolution are an important challenge to be addressed for photoinduced water splitting technologies to become more efficient and commercially viable.

[007] There is a need for a new type of catalyst, such as a new iridium complex, arid/or a method for producing such a complex, which addresses or at least ameliorates one or more problems inherent in the prior art. In a particular example, there is a need for more efficient water splitting catalysts. In another particular example, there is a need for improved water soluble catalysts for water splitting. In another particular example, there is a need for catalysts that provide for or otherwise enable to improve attachment to or association with an electrode used for water splitting.

[008] The reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Brief Summary of the Invention

[009] In various example embodiments there are provided novel catalysts, or families of catalysts, also referenced herein as complexes, for photoinduced water splitting, for example which promote or otherwise improve oxygen evolution, and/or hydrogen evolution.

[010] In a general form, there is provided a cyclometalated iridium complex. In one form, the cyclometalated iridium complex includes bandgap widening ligands, for example, aryl triazole, aryl benzimidazole. In another form, the cyclometalated iridium complex includes bandgap lowering ligands, for example, aryl quinoline, aryl pyrazine, aryl quinoxaline. [01 1] Example advantageous effects of the catalysts or complexes can include tuneable photo-absorption characteristics to enhance efficiency, and/or functional linker moiety that allows the catalysts and/or complexes to anchor to an electrode or a semiconductor. Significant improvements are observed as a result of the catalysts and/or complexes in more efficient water splitting.

[012] In a particular example, one or more additional linking groups are included to improve solubility of the complex. [013] In another particular example, one or more additional linking groups are included to improve attachment of the complex to a semiconductor and/or an electrode, for example an electrode used in water splitting and/or photon-driven devices. [014] In a more specific example, there is provided a cyclometalated iridium complex comprising the structure of formula I:

o_r lb

wherein, Ar is an aryl group, or a fused or heterocyclic arene or ring. [015] In a particular example, the shown pyridine ring in formula I contains more than one nitrogen, derived such as from carbazole, pyrimidine, pyrazine, pyridazine, quinoline, quinoxaline, pyrrole, imidazole, triazine, and/or triazole.

[016] In a particular example, A and/or B are initially part of an electrolyte or a solvent. In another particular example, A and/or B are OH₂, OH, O, bipyridyl, OTf, N0₃, SO4, PF₆, CI, or a halo. In another example form, Ar is an aryl ring, or a fused or a heterocyclic arene.

[017] In a particular example, A and/or B are a bidetate ligand, for example diamine, bipyridyl, picolinic acid, picolinamide, quinolone carboxylic acid and/or their derivatives, with an optional counter ion selected from, for example, OH, O, OTf, NO3, SO4, PF6, CI, or a halo.

[018] In another example, the cyclometalated iridium complex further comprises the structure of formula II:

Ha or ' ^■ . lib

wherein, C is one or more linking groups and C is provided on any part of the ligand rings, on either part of the ligand rings, or on the two ligand rings. [019] In another particular example, C is a water hydrophilic group or an anchor group. C can be derived from, for example, phosphonic acid, carboxylic acid, hydroxamide, amine, ether and/or alcohol.

[020] In another example form, C facilitates or improves the attachment of the complex to a semiconductor and or an electrode.

[021 ] In yet another particular example, Ar has the following structure:

wherein X, Y and Z are individually selected from the group consisting of: hydrogen, a halogen, an organofluorine, a trifluoromethyl, an alkyl, a nitro, a cyanide, C_nF_2n+i, COOR, C(0)R, OR, an arene, and/or an heteroarene.

[022] Optionally: ^'

X = H, Y = H, Z = H;

X = F, Y = H, Z = H;

X = F, Y = F, Z = H;

X = F, Y = H, Z - CF₃;

X = F, Y = F, Z = CF₃; or

X = H, Y = H, Z = CF₃

[023] Also optionally, Ar can be selected from the group consisting of: phenyl, a fused arene, for example naphthene, pyrene, fluorene, dibenzofuran, dibenzothiophene, coumarine, anthracene, indole, benzimidazole, quinazoline, phthalimide, phenanthridine, or a heteroarene, such as pyridine, quinoline, carbazole, pyrimidine, pyrazine, pyridazine, pyrrole, imidazole, triazine, and/or triazole. [024] In another form, the ligands, attachments and/or linking groups are used to alter or tune the energy bandgap.

[025] In example forms, the cyclometalated complex can be used as a catalyst, photocatalyst, photosensitizer and/or a precursor of active catalytic species in a water splitting device. In a preferred form, there is provided a photoinduced water splitting catalyst including one or more of the cyclometalated complexes and/or one or more of the iridium complexes to act as an active catalytic species or a precursor to promote water splitting. [026] In another form, an embodiment is directed to the use of one or more of the cyclometalated complexes in a light-driven opto-electronic device.

Brief Description of Figures

[027] Example embodiments should become apparent from the following description, which is given by way of example only, of at least one preferred but non-limiting embodiment, described in connection with the accompanying figures.

[028] Fig. 1 illustrates comparative sacrificial agent, eerie ammonium nitrate (CAN), consumption measurement results from water splitting using novel complexes according to the present invention against a known complex Al at different concentrations;

[029] Fig. 2 illustrates further comparative CAN consumption measurement results from water splitting using novel complexes according to the present invention; [030] Fig. 3 illustrates further comparative CAN consumption measurement results from water splitting using novel complexes according to the present invention; [031] Fig. 4 illustrates comparative oxygen measurement results from water splitting using novel complexes according to the present invention against a known complex Al , where oxygen formation was confirmed by GC; [032] Fig. 5 illustrates further comparative oxygen measurement results from water splitting using novel complexes according to the present invention;

[033] Fig. 6 illustrates comparative absorption spectra of the novel complexes B1-B3 and E1-E3, and known complex Al , showing the blue-shifted and red-shifted absorption from bandgap increasing and decreasing ligands, respectively (inset shows an expansion of the absorption spectra);

[034] Fig. 7 illustrates comparative absorption spectra of the novel complexes E5-E8, with intense red-shifted absorption spectra (inset shows an expansion of the absorption spectra);

[035] Fig. 8 illustrates results of the measured photocurrents from photoinduced water splitting, showing when complex Bl is present, as a light source was cycled on and off; [036] Fig. 9 illustrates results of measured photocurrents from photoinduced water splitting, showing when the indicated novel catalysts Bl-4 are present, as a light source was cycled on and off;

[037] Fig. 10 illustrates results of measured photocurrents from photoinduced water splitting, when complex Bl is continuously irradiated with a light source;

[038] Fig. 11 illustrates results of measured photocurrents from photoinduced water splitting, showing increased photocurrents from the indicated novel metal complex attached to a semiconductor, Ti0₂ nanoparticles, as a light source was cycled on and off, compared to those of in the absence of the novel catalyst.

Preferred Embodiments [039] The following modes, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments. [040] Water splitting can be achieved by electrolysis which consumes electric power. The free energy of the reaction is 1.23 eV with an activation energy of greater than about 1.85 eV. For photolysis, this energy range is within the visible light spectrum. However, water molecules do not absorb solar radiation effectively in this range. Additionally, the products of the reaction are thermodynamically unfavourable and several bonds are required to be broken and formed. One approach to simplify this complex bond rearrangement is to split the reaction equation into oxidation and reduction half reactions as follows in Scheme 1.

Scheme 1: water splitting process (Ox: sacrificial oxidant, Red: sacrificial reductant, cat:

catalyst).

Types of photochemical cells have been proposed to split water, for example containing two catalysts, two electrodes, an electron relay and a photosensitiser. A photosensitiser initiates the redox reaction by transferring excited electrons after photon absorption. There are two major known types of water oxidation catalysts, inorganics and organometallics.

[041] Unlike inorganic water oxidation catalysts, organometallic catalysts consist of one or more organic ligands coordinating to a transition metal. An early coordination complex that was discovered to catalyse water oxidation is a ruthenium blue dimer, [(bpy)₂(H₂0)Ru(IIl)ORu(III)(H₂0)(bpy)₂]⁴⁺ (Gersten, et al., J. Am. Chem. Soc. 1982, 104, 4029). Over the last two decades, ruthenium catalysts ranging from monomelic to dimeric and more recently tetrameric have been intensively studied (e.g. Zong, et al., J. Am. Chem. Soc. 2005, 127, 12802; Concepcion, et al., J. Am. Chem. Soc. 2008, 130, 16462; Sartorel, et al., J. Am. Chem. Soc. 2008, 130, 5006; Xu, et al., Angew. Chem. Int. Ed. 2010, 49, 8934).

[042] The first aqua Ir(III) complex, [Ir(ppy)2(H₂0)2]⁺, shown below as complex Al, where ppy is phenylpyridine, was synthesised and characterised in 1994, with a structure being determined as the carbon-iridium bond trans to the iridium-water coordination. However, the catalytic behaviour on water oxidation using these aqua Ir(III) complexes (A 1-5) was not appreciated and investigated until 2008 (McDaniel et al., J. Am, Chem. Soc. 2008, 130, 21

wherein, OTf is inflate or trifluoromethariesulfonate, -OSO2CF3.

[043] The Applicant has produced one or more novel families of Ir(III) complexes with surprisingly high catalytic activity in water splitting, for example by being ligated with aryl triazole, or aryl quinoline, or aryl pyrazine, aryl quinoxaline, or benzo[&]quinoline ligands.

[044] It is believed the aryl triazole and aryl quinoline ligands, as examples, lead to larger (i.e. wider) and smaller (i.e. narrower) bandgaps, respectively. Furthermore, the Applicant has been able to advantageously influence catalytic activity by tuning of oxidation potentials of the Ir(III) complexes by attaching electron withdrawing groups on one or both of the ligands, such as a ligand phenyl ring, for effective water oxidation. It is believed the addition of one or more electron withdrawing groups, such as for example a fluorine or a trifluoromethyl group to the ligand phenyl ring increases the oxidation potentials of the aqua Ir(III) complexes. Moreover, the Applicant has been able to advantageously influence catalytic activity by tuning of electron density of the Ir(III) complexes by attaching electron donating groups on one or both of the ligands, such as a ligand phenyl ring, for effective water oxidation. It is believed the addition of one or more electron donating groups, such as for example an alkyl or aryl amino group to the ligand rings, increases the electron density of the aqua Ir(III) complexes for fast oxygen release.

Aryl triazole iridium(III) complexes

[045] The Applicant has discovered unexpected effects of widened bandgap aqua Ir(III) complexes on improving water oxidation, and synthesised a family of aqua Ir(III) complexes based on aryl triazole ligands, an example of which is shown below as complex B.

[046] ' Referring to Scheme 2, compound C was formed in two steps (Lo et al., Chem. Mater. 2006, 18, 51 19) from respective benzoyl chloride by first treating with ethyl butyrimidate hydrochloride in presence of triethylamine to give the corresponding N- benzoylbutanimidic acid ethyl ester, which was then reacted with methylhydrazine immediately to give the desired aryl triazole compound C.

compound C complex D complex B

C1 : X=H, Y=H, Z=H D1 . X=H, Y=H, Z=H B1 : X=H, Y=H, Z=H

C2: X=F, Y=H, Z=H D2: X=F, Y=H, Z=H B2: X=F, Y=H, Z=H

C3: X=F, Y=F, Z=H D3: X=F, Y=F, Z=H B3: X=F, Y=F, Z=H

C4: X=F, Y=H, Z=CF₃ D4: X=F, Y=H, Z=CF₃ B4: X=F, Y=H, Z=CF₃

Scheme 2: Synthesis of aryl triazole ligands and analogues. Example reagents and conditions: (i): Ir(HI) chloride trihydrate, 2-ethoxyethanol, water, heat, Ar^. (ii): silver trifluoromethanesulfonate, CH2CI2, methanol, water, heat. [047] The chloro-bridged iridium dimer Dl was prepared in about 78% yields as a yellow solid by cyclometallation of iridium trichloride with compound C in 2-ethoxyethanol and water (Lo et ai, Chem. Mater. 2006, 18, 51 19). [048] Different methods have been reported for the preparation of the known Ir(III) complex A from a corresponding chloro-bridged iridium dimer in the presence of silver triflate, for example carried out in dichloromethane (DCM) and methanol at room temperature for 1 hour, or heating in ethanol and water at reflux for 16 hours. [049] Both methods were used to prepare complex Bl, however, the conversion was unsatisfactory mainly due to the low solubility of compound Dl in methanol or ethanol (and also the presence of water). The incompletion of the reaction made the isolation of complex Bl problematic due to its poor solubility in most organic solvents and contamination together with compound Dl .

[050] To overcome this, the known method was modified by using excess silver triflate (1.5 equivalents). After removal of the excess of silver triflate by water extraction, complex Bl was obtained in about a 64% yield. Complexes B2-4 were similarly prepared under the same conditions from the corresponding chloro-bridged iridium dimers, D2 - D4.

[051] Mass spectrometry of the synthesised aqua Ir(III) complexes showed major fragmentation peaks at 591.3, 629.1 and 665.1 for Bl, B2 and B3, respectively by losing two water ligands and a counter ion, OTf.

Aryl quinoline iridium(III) complexes

The Applicant has also discovered that aqua Ir(III) complexes based on decreased bandgap ligands can provide unexpected improvements in water oxidation, and synthesised another family of aqua Ir(III) complexes based on aryl quinoline ligands.

[052] In an example form there is provided a cyclometalated iridium complex comprising the structure of:

wherein, 'Ar' is an aryl group, such as any functional group or substituent derived from a simple aromatic ring, for example phenyl, a fused ring, for example naphthene, pyrene, fluorene, dibenzofuran, dibenzothiophene, coumarine, anthracene, indole, benzimidazole, quinazoline, phthalimide, phenanthridine, or heteroarene, such as pyridine, quinoline, carbazole, pyrimidine, pyrazine, pyridazine, pyrrole, imidazole, triazine, and/or triazole;

and wherein, A and/or B are OH₂, OTf, OH, O, PF₆, N0₃, and/or a halo such as F, CI, Br, I, and/or a bidetate ligand, for example diamine, bipyridyl, picolinic acid, picolinamide, quinolone carboxylic acid and/or their derivatives, with an optional counter ion selected from, for example, OH, O, OTf, NO3, SO₄, PF₆, CI, and/or a halo.

[053] As used herein, an aryl group, typically a Ce-20 aryl group, refers to any functional group or substituent derived from a simple aromatic ring. An aryl group may be unsubstituted or substituted at any position. Typically, it carries 0, 1 , 2 or 3 substituents. References to an aryl group include fused ring systems in which an aryl group is fused to a carbocyclyl, heterocyclyl or heteroaryl group. The carbocyclyl, heterocyclyl or heteroaryl group to which the aryl group is fused may itself be fused to a further aryl, heteroaryl, carbocyclyl or heterocyclyl. Accordingly, the term aryl encompasses aryl groups such as phenyl when fused to other monocyclic or polycyclic ring systems.

[054] For the avoidance of doubt, while cyclometalated complexes are shown as bearing ligands, the complexes may comprise further ligands which are not shown for the sake of clarity. For example, the complexes may comprise a further ligand of the same structure.

[055] In a more specific example form there is provided a cyclometalated iridium complex comprising the structure of:

[056] In another example form Ar is a heterocyclic aromatic ring, for example including nitrogen. In another example form Ar has the following structure:

wherein, X, Y and Z can be individually selected from the non-exclusive group of hydrogen, a halogen (such as fluorine providing a strong electron withdrawing attachment), a halo, a trifiuoromethyl, an alkyl, a nitro, a cyanide, C_nF_2n+i, COOR, C(0)R,

OR, an arene, and/or an heteroarene.

[057] In another specific example, Ar has a structure using:

X = H, Y = H, Z = H;

X = F, Y = H, Z = H;

X = F, Y = F, Z = H;

X = F, Y = H, Z = CF₃;

X = F, Y = F, Z = CF₃; or

X = H, Y = H, Z = CF₃

[058] In still another example the cyclometalated iridium complex can include one or more hydrophilic group in any part of the ligand ring. The hydrophilic group can be derived from, for example, phosphonic acid, carboxyiic acid, hydroxamide, amine, ether and/or alcohol linking group to improve solubility. Additionally or alternatively, the cyclometalated iridium complex can include one or more linking group C to improve attachment to or association with a semiconductor material or an electrode. [059] Further example aqua Ir(HI) complexes based on aryl quinoline ligands are shown below as complex E. It should be noted that various anions could be used, for example O ^', PF₆ ^", and/or NO3^*. In another form, the anion can act as a counter ion.

[060] Referring to Scheme 3, the synthesis of aryl quinoline ligands, e.g. compound G, was carried out under Suzuki-Miyaura cross-coupling reaction conditions using 2-chloro- 4-methylquinoline with corresponding arylboronic acids. The synthesis of complex E involves cyclometallation with iridium trichloride hydrate with corresponding ligand, and followed by ligation with water ligand and anionic exchange.

compound F compound G complex E

F1 : X= H, Y=H, Z=H G1 : X= H, Y=H, Z=H El : X= H, Y=H, Z=H F2: X=F, Y=H, Z=H G2: X=F, Y=H, Z=H E2: X=F, Y=H, Z=H F3: X=F, Y=F, Z=H G3: X=F, Y=F, Z=H E3: X=F, Y=F, Z=H F4: X=F, Y=H, Z=CF₃ G4: X=F, Y=H, Z=CF₃ E4: X=F, Y=H, Z=CF₃

Scheme 3: Synthesis of aryl quinoline ligands and analogues. Reagents and conditions: (i): 4-chloro-4-methylquinoline, tetrakis(triphenylphoshine)palladium(0), sodium carbonate, toluene, ethanol, water, heat. Ar _g). (ii): Ir(III) chloride

trihydrate, 2-ethoxy ethanol, water, heat, Ar<_g) followed by silver trifluoromethanesulfonate, CH2CI2, methanol, water, heat.

[061] Further example complexes of family E having fused arylquinoline ligands were additionally produced as presented below.

complex E7

[062] Referring to Scheme 4, the synthesis of the aryl quinoline ligands, e.g. compound J, was carried out under Suzuki-Miyaura cross-coupling reaction conditions using 2-chloro- 4-methylquinoline with corresponding arylboronic acids, which can be available commercially or prepared from the corresponding bromoarenes. The synthesis of complexes E5-8 involves cyclometallation with iridium trichloride hydrate with the corresponding ligand, and followed by ligation with water ligand in presence of silver triflate.

compound H compound I compound J complex K complex E

HI : Ar=naphthalene 11 : Ar=naphthalene Jl : Ar=naphthalene I : Ar=naphthalene E5: Ar=naphthalene H2: Ar=pyrene 12: Ar=pyrene J2: Ar=pyrene K2: Ar=pyrene E6: Ar=pyrene

H3: Ar=carbazole 13: Ar=carbazole J3: Ar=carbazole 3: Ar=carbazole E7: A =carbazole H4: Ar=phenanthrene 14: Ar=phenanthrene J4: Ar=phenanthrene 4: Ar=phenanthrene E8: Ar=phenanthrene

Scheme 4: Synthesis of aryl quinoline ligands and analogues. Reagents and conditions: (i):a. n-BuLi, THF, Ar^.b. B(OMe)3, c. HCl(_aq). (ii): 4-chloro-4- methylquinoline, tetrakis(triphenylphoshine)palladium(0), sodium carbonate, toluene, ethanol, water, heat. Ar^. (Hi): Ir(III) chloride

trihydrate, 2-ethoxyethanol, water, heat, Ar^. (iv): silver trifluoromethanesulfonate, CH2CI2, methanol, water, heat.

[063] The aqua aryl quinoline Ir(III) complexes E were prepared from the ligands via a two step approach, first a cyclometallation to give the chloro-bridged iridium dimer and then the introduction of water ligands under the same conditions as for the aryl triazole family. Notably, all the aryl quinoline Ir(III) dimers were found to have limited solubility in many organic solvents such as dichloromethane, chloroform, acetone, toluene and dimethyl sulphoxide. Hence Ή NMR signals of the chloro-bridged iridium dimers were weak. Nevertheless, the presence of several broadened peaks around 6.0-7.0 ppm could be identified as the phenyl protons ortho to an Ir-C bond, supporting the formation of chloro- bridge iridium dimers. The next step to form a target aqua Ir(III) complex E was carried out under the same conditions as described for the formation of aqua lr(III) complexes B using silver triflate in yields of about 50-60%. Unlike the chloro-bridged dimers and Ir(III) complexes B, the so-formed aqua Ir(III) complexes E showed a dramatic improvement in solubility, being more soluble in DC but less soluble in acetone.

Aqua aryl quinoxaline and aryl pyrazine iridium(HI) complexes

[064] The Applicant has also discovered that decreased bandgap aqua Ir(III) complexes can provide unexpected improvements in water oxidation, and synthesised another families of aqua Ir(III) complexes based on aryl pyrazine, or aryl pyrazine, or aryl quinoxaline, or aryl

wherein, X can be selected from the non-exclusive group of hydrogen, a halogen

(such as fluorine providing a strong electron withdrawing attachment), a halo, a trifluoromethyl, an alkyl, a nitro, a cyanide,C_nF_2n+i, COOR, C(0)R, OR, an arene, and/or an heteroarene. [065] 'Ar' is an aryl group, such as any functional group or substituent derived from a simple aromatic ring, for example phenyl, a fused ring, for example naphthene, pyrene, fluorene, dibenzofuran, dibenzothiophene, coumarine, anthracene, indole, benzimidazole, quinazoline, phthalimide, phenanthridine, or heteroarene, such as pyridine, quinoline, carbazole, pyrimidine, pyrazine, pyridazine, pyrrole, imidazole, triazine, and/or triazole.

[066] Referring to Schemes 5, the synthesis of aryl quinoxaline ligands, e.g. compound O, was carried out under dehydration reaction using diamines with corresponding diketones (e.g. compound N), which could be prepared from the respective alkynes (e.g. compound M) after oxidation. The synthesis of complex L involves cyclometallation with iridium trichloride hydrate with corresponding ligand, and followed by ligation with water ligand and anionic exchange.

compound M compound N com ound O complex P complex L

M l : X=H Nl : X=H 01 : X=H P1 : X=H L1 : X=H

M2: X=F N2: X=F 02: X=F P2: X-F L2: X=F

M3: X=CF₃ N3: X=CF₃ 03: X=CF₃ P2: X=CF_j L3: X=CF₃

Scheme 5: Synthesis of aryl quinoline ligands and analogues. Reagents and conditions: (i):a. KMnOj fii): 1 ,2-diaminobenzene. (Hi): Ir(III) chloride

trihydrate, 2-ethoxyethanol, water, heat, Ar_(g). (iv): silver trifluoromethanesulfonate, CH₂CI₂, methanol, water, heat.

[067] Referring to Scheme 6, the synthesis of aryl pyrazine ligands, e.g. compound 00, was carried out under Suzuki cross coupling reaction [i.e. using compound NN with 2- chloropyrazine in the presence of tetrakis(triphenylphoshine)palladium(0)], The synthesis of complex LL involves cyclometallation with iridium trichloride hydrate with corresponding ligand, and followed by ligation with water ligand and anionic exchange.

compound NN compound 00 complex PP complex LL

NNI : X=H 001 : X=H PP1 : X=H LL1 : X=H

NN2: X=F 002: X=F PP2: X=F LL2: X=F

NN3: X=CF₃ 003: X=CF₃ PP2: X=CF₃ LL3: X=CF_j

Scheme 6: Synthesis of aryl pyrazine ligands and analogues. Reagents and conditions: (i)2-chloropyrazine, tetrakis(triphenylphoshine)palladium(0), sodium carbonate, toluene, ethanol, water, heat. Ar^. (ii): Ir(III) chloride

trihydrate, 2-ethoxyethanol, water, heat, Ar^. (Hi): silver trifluoromethanesulfonate, C C , methanol, water, heat.

compound OOO complex PPP complex LLL

Scheme 7: Synthesis of benzofhjquinoline ligand and analogues. Reagents and conditions: (i): Ir(IH) chloride trihydrate, 2-ethoxyethanol, water, heat, Ar^. (ii): silver trifluoromethanesulfonate, CH2CI2, methanol, water, heat.

[068] Thus, new families of aqua cyclometalated Ir(III) complexes based on aryl triazole, aryl quinoline and aryl quinoxaline ligands have been successfully synthesised. X-ray crystallography indicates that the triflate anion can alternatively coordinate to the Ir(III) metal in the aqua iridium complexes such as El. Compared with a known complex Al,0 UV-visible absorption spectra shows a blue-shift in absorption for iridium complexes B based on aryl triazole, while iridium complexes E based on aryl quinoline or quinoxaline show a red-shift in absorption. For all novel families of aqua Ir(III) complexes, fluorination on the ligand phenyl rings also blue-shifts the absorption spectra. S Aqua iridium(III) complexes with hydrophilic and/or linking groups

[069] Solubility (hydrophilicity) of a catalyst is another important factor for consideration. A phosphonic acid linking group, as used in complex Q, has been identified as having the ability to improve solubility of the catalysts of type E. Improved performance of a sample of complex Q has been presented in Figs. 2 and 5. Improved performance of0 samples of other complexes Q for different linking groups has been shown in Figs. 2 and 5.

[070] In another example form there is provided a cyclometalated iridium complex comprising the structure of:

5

wherein, A and/or B are OH₂, OTf, OH, O, PF₆, N0₃,or a halo such as F, CI, Br, I; C is one or more linking groups on any part of the ligand rings or on both ligand rings. C is selected from a functional group derived from, for example, phosphonic acid, carboxylic acid, hydroxamide, amine, ether and/or alcohol. Additionally or alternatively, the ligand of the cyclometalated iridium complex can include one or more halo such as F, CI. Additionally or alternatively, the cyclometalated iridium complex can include one or more linking group C to improve and/or facilitate attachment to or association with a semiconductor material or an electrode in a photon driven device. dium

wherein A is a ligand such as OH₂, OTf, OH, O, PF₆, N0₃,or a halo such as F, CI, Br, I. C is one or more linking groups on any part of the ligand ring. C is selected from a hydrophilic group derived from, for example, phosphonic acid, carboxylic acid, hydroxamide, amine, ether and/or alcohol. Additionally or alternatively, the ligand of the cyclometalated iridium complex can include one or more halo such as F, CI. Additionally or alternatively, the cyclometalated iridium complex can include one or more linking group C to improve attachment to or association with a semiconductor material or an electrode in a photon driven device. [072] The following further example complexes QI - QIX, including examples of hydrophil

complex QVa complex QVb

complex QVIII

complex QIX

wherein, A can be a selection from OH₂, OTf, OH, O, PF₆, NO3, S0_4> or a halo such as F, CI, Br, I as a ligand or as a counter ion while ligated with a solvent such as water, MeOH, MeCN, THF, NEt3, or an electrolyte.

compound R compound S complex T complex Qla

Scheme 8: Synthesis of aryl quinoline ligands and analogues. Reagents and

conditions: (i).: SOCl₂, MeOH, Ar_(g). (ii): Ir(III) chloride trihydrate, 2-ethoxyethanol, heat, Ar(_g). (iii):a. LiOH, MeOH, THF; b. HOTf(_aq).

compound S compound U complex V complex QII

Scheme 9: Synthesis of aryl quinoline ligands and analogues. Reagents and conditions: (i):NaBH₄, EtOH, heat, (ii): Ir(III) chloride trihydrate, 2-ethoxyethanol, heat,

Ar(_g). (Hi): silver trifluoromethanesulfonate, methanol, water, heat.

compound S complex T complex QUI

Scheme 10: Synthesis of aryl quinoline ligands and analogues. Reagents and conditions: (i): Ir(III) chloride trihydrate, 2-ethoxyethanol, heat, Ar^. (ii): silver trifluoromethanesulfonate, CH2CI2, methanol, water, heat.

Scheme 11: Synthesis of aryl quinoline ligands and analogues. Reagents and conditions: (i): NBS, l. l-azobis(cyclohexanecarbonitrile), CH2CI2, water, light, heat, (ii): P(OEt)i, heat. (Hi): Ir(III) chloride trihydrate, 2-ethoxyethanol, water, heat, Ar^. (iv): silvertrifluoromethanesulfonate, CH2CI2, methanol, water, heat, (v): HCl(_aq), heat.

[073] Electrochemistry of complexes B and E shows reversible oxidation with the oxidation potential higher than water. By fluorination of the ligand phenyl ring, systematic increases in oxidation potential were observed. While the cyclometalated Ir(III) complexes may have either two aqua ligands with triflate counter ion in salt form or single aqua ligand with triflate ion coordinating to iridium directly, the coordination of the triflate ion to Ir(III) seems not to hinder catalytic activity for water oxidation. Water oxidation tests show best results for the aryl quinoline Ir(III) complexes providing a relatively fast oxygen formation rate.

Water Oxidation Performance οϊ Example Complexes ^'

[074] Importantly, water splitting with significant oxygen generation and photocurrents using the new metal complexes developed by the Applicant has been achievable. [075] Referring to Figs. 1 and 2, there are shown comparative CAN consumption measurement results from water splitting catalysed by the novel complexes Bl-3, El -3, E5, E7 and L against the known complex Al under the same conditions: In the CAN consumption tests, 4 mL of aqueous CAN solution (2.0 mM) containing 0.1 M HNO3 was mixed with 20 μί, of the catalyst solution in acetonitrile (from 0.25 mM to 4 mM) in a cuvette. CAN consumption was studied by monitoring the absorbance change of Ce(IV) at 340 nm. The concentration of CAN employed was 2 mM whereas the concentrations of the Ir(III) complex catalysts ranged from 1.32 to 21.04 μΜ. It can be seen that the example complexes exhibited substantial improvements in performance over a known complex Al .

[076] Referring to Fig. 3 there are shown further CAN consumption measurement results from water splitting using other novel complexes bearing with a hydrophilic group as indicated in the figures. Substantial improvements in water oxidation can be observed. [077] Referring to Fig. 4 there are shown comparative oxygen generation measurement results from water splitting catalysed by the novel complexes El -3, E5, and E7 against the known complex Al under the same conditions. In a transparent reactor at 28 °C was water (2 mL), CAN (2 g, 3.6 mmol), and the iridium complex catalyst (0.1 μιηοΐ, ca. 0.05-0.1 mg, depending on the molecular weight) being tested. Results are presented for a 'dark' scenario (reactor wrapped in Al foil) and a Might' scenario (reactor exposed to visible light from two LED lamps, each 6 W). It can be seen that the example complexes exhibited substantial improvements in performance over a known complex Al .

[078] Referring to Fig. 5 there are shown further oxygen generation measurement results from water splitting using other novel complexes (Q) bearing with a functional group as indicated in the figures. Substantial improvements in water oxidation can be observed.

[079] Referring to Fig. 6 there are shown comparative absorption spectra of novel complex El and a . known complex Al . Compared are UV-vis absorption spectra of complexes A 1, Bl-3 (for blue shifted absorption), and El -3 (for red-shifted absorption) in methanol, with the inset showing an expansion of the absorption spectra. [080] Referring to Fig. 7 there are shown comparative absorption spectra of the novel complexes E5-8. Compared are UV-vis absorption spectra of complexes E5-8 in methanol, with the inset showing an expansion of the absorption spectra. [081] Referring to Fig. 8 there are illustrated controlled potential electrolysis at different potentials vs Ag/AgCl with alternate 25 seconds of illumination (275-750.nm) for complex Bl - with Nafion glassy carbon electrode (diameter 3 mm) in contact with 0.1M Na₂S0₄.

[082] Referring to Fig. 9 there are shown comparative net photocurrents for complexes B 1 -4 in 0.1 M Na₂S0₄ at different potentials vs Ag/AgCl.

[083] Referring to Fig. 10 there is illustrated controlled potential electrolysis at 1,100 mV vs Ag/AgCl with continuous illumination (275-750 nm) for 32,000 seconds for complex Bl - with Nafion glassy carbon electrode (diameter 3 mm) in contact with 0.1M Na₂S0₄.

[084] Referring to Fig. 11 there are illustrated resulting measured currents from photoinduced water splitting, showing both scenarios for no catalyst and when the indicated novel catalyst is present, as a light source was cycled on and off. As can be seen, there is very little measured current when the catalysts are not present and that the presence of the catalysts substantially improve the measured current resulting from incident light in a water splitting device.

[085] In another example embodiment, a separate photosensitiser and catalyst can be combined as a single 'photocatalyst' material provided by forms of the complexes of type E or Q. Example photocurrent results using a photocatalyst are presented in Table 1. An LED light source is incident on a transparent reactor having a working electrode and a platinum electrode, with the photocurrent measured between the electrodes.

[086] It is believed that a linker group provided with one of the complexes of type E or Q (or alternatively B) mediate direct attachment of an iridium complex to a semiconductor such as titanium dioxide, or a photoanode for photo-driven charge injection to a dye and/or a Ti0₂ semiconductor. Light Source Sample Working Electrode Photocurrent (μΑ)

LI Ti0₂ 0.6

LED L2 TiCVcomplex QIa 11

L3 TiCVcomplex QlVa 12

Table 1. Sample results for sensitised "water splitting using a photocatalyst. Different samples LI - L3 are trialled, with LI being a background test. A 6 W LED light source is incident on a transparent reactor having a working electrode and a platinum electrode in

0. lMNa₂S0₄ or 0.1 M NaOAc/HOAc.

Examples - Preparation of Ligands and Complexes

[087] The following further examples discuss various methods of preparing example ligands or complexes. These examples are intended to be merely illustrative and not limiting to the scope of the present invention.

[088] Complex Dl (Lo, et al, Chem. Mater. 2006, 18, 5119) (200 mg, 0.319 mmol) was dissolved in a mixture of dichloromethane (5 mL) and methanol (5 mL). Silver triflate (122 mg, 0.478 mmol) in aqueous solution (2 mL) was added and the mixture was refluxed at 50 °C for 5 h under argon. After cooling, the solid suspension was removed through filtration and all solvent was removed to give a solid film. The solid was redissolved in acetone (10 mL) and diluted with hexane (30 mL). The precipitated product was collected and purified by recystallisation through evaporation in dichloromethane (300 mL) to give Bl (158 mg, 64% yield) as a yellow solid. X™_ax(MeOH)/nm: 262 (loge/dm³ mol^"1 cm^"1 4.45), 277 (4.60), 332 (4.22), 346 (4.18), 394 (3.64), 441 (3.58), 534 (2.86). Ή NMR (300 MHz, acetone-d₆ + drops of D₂0): δ 0.96 (t, J=8.7, 6H), 1.80 (m, 4H, Pr-H), 2.93 (m, 4H, Pr-H), 4.38 (s, 6H, Me), 6.32 (d, J=4.2, 2H, Ph-H), 6.68 (t, J=5.1, 2H, Ph-H), 6.84 (t, J=5.1 , 2H, Ph-H), 7.58 (d, J=4.8, 2H, Ph-H). mlz [ESI⁺]: 593.1 (M⁺-OTf-2H₂0).

D2 B2

[089] Complex B2 was prepared following the same procedure as for complex Bl . Yield: 48%. MeOH)/nm: 251 (loge/dm³ mol^"1 on ¹ 4.39), 296 (3.77), 332 (3.45), 385 (3.39), 436 (2.03). Ή NMR (300 MHz, acetone- ^ + drops of D₂0) δ 0.95 (t, J=8.8, 6H), 1.80 (m, 4H, Pr-H), 2.94 (m, 4H, Pr-H), 4.39 (s, 6H, Me), 5.92 (d, J=6.0, 2H, Ph-H), 6.64 (m, 2H, Ph-H), 7.67 (m, 2H, Ph-H). mlz [ESf ] : 629.1 (M⁺-OTf-2H₂0).

[090] Complex B3 was prepared following the same procedure as for complex Bl . Yield: 58%. WMeOH)/nm: 250 (loge/dm³ mol^'1 cm^"1 4.45), 290 (3.86), 320 (3.59), 360 (3.46), 422 (2.08). Ή NMR (300 MHz, acetone-d* + drops of D₂0) δ 0.98 (t, J=7.4, 6H, Pr-H), 1.80 (m, 4H, Pr-H), 2.96 (m, 4H, Pr-H), 4.35 (d, J=7.1, 6H, Me), 5.79 (d, 7=9.1, 2H, Ph- H), 6.55 (d, J=5.4, 2H, Ph-H). mlz [ESI⁺]: 665.1 (M⁺-OTf-2H₂0).

Example 4: Preparation of 4-methyl-2-phenylquinoline (compound Gl)

[091] 2-Chloro-4 methylquinoline (600 mg, 3.39 mmol), phenyl boronic acid (620 mg, 5.08 mmol) and sodium carbonate (636 mg) were dissolved in a mixture of toluene (10 mL), ethanol (3 mL) and water (3 mL). The mixture was deoxygenated before and after the addition of tetrakis(triphenylphosphine)palladium(0) (275 mg, 0.23 mmol). The mixture was heated at reflux for 16 h under argon. When cooled, water (15 mL) was added and the two layers were separated. The aqueous layer was extracted with diethyl ether (3 x 15 mL). All the organic portions were combined, washed with brine (10 mL), dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed in vacuo to give a yellow oil. The oil was purified by column chromatography over silica using ethyl acetate-hexane (1 :50) as eluent to give compound Gl (628 mg, 84%) as a colourless oil, which solidified on standing. Ή NMR (300 MHz, CDC1₃)6 2.78 (d, 7=0.9, 3H, Me), 7.41-7.57 (m, 4H, Ph-H), 7.73 (t, =6.9, 2H, Qui-H), 7.99 (d, 7=8.4, 1H, Qui-H), 8.13-8.19 (m,^'3H, Qui-H). ¹³C NMR (125 MHz, CDC1₃) 519.06, 1 19.83, 123.69, 126.10, 127.63, 127.63, 128.86, 128.86, 129.27, 129.39, 130.41 , 139.95, 144.85, 157.15. mlz [ESI⁺]: 220.1 (M⁺).

[092] 2-Chloro-4-methylquinoline (3.00 g, 16.9 mmol), 4-fluorophenyl boronic acid

(3.55 g, 25.3 mmol) and sodium carbonate (3.18 g) were dissolved in a mixture of toluene

(45 mL), ethanol (15 mL) and water (15 mL). The mixture was deoxygenated before and after the addition of tetrakis(triphenylphosphine)palladium(0) (1.37 g, 1.18 mmol). The mixture was refluxed at 1 10 °C for 16 h under argon. When cooled, water (45 mL) was added and the two layers were separated. The aqueous layer was extracted with diethyl ether (3 x 40 mL). All the organic portions were combined, washed with brine (40 mL), dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed in vacuo to give a yellow oil. The oil was purified by column chromatography over silica using ethyl acetate-hexane (1 :50) as eluent to give G2 (2.67 g, 66%) as a colourless oil, which solidified on standing. Ή NMR (300 MHz, CDC1₃) δ 2.76 (d, J=0.9, Me), 7.23-7.15 (m, 2H, Ph-H), 7.54 (t, J=8.3, 1H, Qui-H), 7.66 (d, J=0.9, 1H, Qui-H), 7.72 (t, J=8.4, 1H, Qui-H), 7.73 (d, J=8.9, 1H, Qui-H), 8.20-8.00 (m, 3H, Qui-H). ^,3C NMR (125 MHz, CDCI3) δ 19.16, 1 15.87, 1 15.90, 1 19.52, 123.76, 126.21 , 127.28, 129.45, 129.51, 129.57, 130.33, 136.07, 136.10, 145.10, 148.21, 156.08, 163.86 (d, J=197.8). mlz [ESI⁺]: 238.1 (M⁺).

[093] 2-Chloro-4-methylquinoline (2.01 g, 11.3 mmol), 2,4-difluorophenyl boronic acid (2.66 g, 16.9 mmol) and sodium carbonate (2.12 mg) were dissolved in a mixture of toluene (30 mL), ethanol (10 mL) and water (10 mL). The mixture was deoxygenated before and after the addition of tetrakis(triphenylphosphine)palladium(0) (910 mg, 0.79 mmol). The mixture was refluxed at 110 °C for 16 h under argon. When cooled, water (30 mL) was added and the two layers were separated. The aqueous layer was extracted with diethyl ether (3 x 30 mL). All the organic portions were combined, washed with brine (30 mL), dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed in vacuo to give a yellow oil. The oil was purified by column chromatography over silica using ethyl acetate-hexane (1 :50) as eluent to give G3 (2.83 g,

98%) as a colourless oil, which solidified on standing. Ή NMR (300 MHz, CDCI3) δ 2.77 (d, J=0.9, Me), 6.94 (m, 1H, Ph-H), 7.04 (m, 1H, Ph-H), 7.58 (t, J=8.3, 1H, Qui-H), 7.69 (d, J=2.1 , 1H, Qui-H), 7.73 (d, J=8.4, 1H, Qui-H), 8.20-8.00 (m, 3H, Qui-H). ^I3C NMR (100 MHz, CDCI3) 6 19.04, 104.48 (t, J=26.6), 112.13 (dd, J=20.9 & 3.6,), 122.89 (d, J=8.0), 123.79, 124.57 (dd, J=12.4 & 3.9), 126.56, 127.39, 129.53, 130.35, 132.84 (m), 144.66, 148.24, 152.96 (d, J=1.6), 160.95 (dd, J=250.7 & 11.9), 163.64 (dd, J=249.7 & 11.9). m/z [ESf]: 256.1 (M⁺). Example 7: Preparation of iridium complex El

Gl El

[094] A mixture of compound Gl (406 mg, 1.85 mmol), iridium trichloride hydrate (296 mg, 0.84 mmol), 2-ethoxyethanol (16 mL) and water (8 mL) was heated at 1 10 °C under argon for 40 h. When cooled, water (40 mL) was added to reaction mixture to give red solid precipitation. The precipitation was filtered and washed with water (3 x 30 mL) and hexane (3 x 150 mL). The dried chloro-bridged dimer was suspended in dichloromethane (30 mL) and methanol (15 mL). An aqueous solution (15 mL) of silver inflate (190 mg, 0.74 mmol) was added and the mixture was heated at 50 °C for 16 h. After cooled, water (30 mL) was added and organic and aqueous layers were separated. Aqueous layer was extracted with dichloromethane (3 15 mL). The dichloromethane extracts were combined with organic layer. Insoluble suspension was removed through filtration and a red solid (complex El) was obtained (340 mg, 51%) after removal of solvents. λ™3χ( βΟΗ)/^ηπι: 262 (loge/dm³ mol^'1 cm^'1 4.45), 277 (4.60), 332 (4.22), 346 (4.18), 394 (3.64), 441 (3.58), 534 (2.86). Ή NMR (300 MHz, CDC1₃) δ 3.00 (s, 6H, Me), 6.33 (d, J=7.2, 2H), 6.59 (t, J=6.3, 2H), 6.92 (t, J=8.4, 2H), 7.62 (m, 4H), 7.73 (d, J=6.6, 2H), 7.94 (s, 2H), 8.05 (m, 2H), 8.69 (m, 2H). mlz [ESI⁺] : 629.1 (M^-OTf-FbO).

Example 8: Preparation of iridium complex E2

[095] Complex E2 (orange solid) was prepared following the same procedure as for complex El . Yield: (69%). WMeOH)/nm: 261 (logs/dm³ ι^ηοΓ¹ crn ¹ 4.57), 277 (4.59), 323 (4.22), 339 (4.18), 384 (3.78), 426 (2.66), 518 (2.63). Ή NMR (300 MHz, CDC1₃) δ 3.01 (s, 6H, Me), 5.96 (d, J=6.8, 2H), 6.69 (td, J=12.6 & 2.49, 2H), 7.65 (m, 4H), 7.72 (m, 2H), 7.87 (s, 2H), 8.05 (m, 2H), 8.61 (m, 2H). m/z [ESI⁺]: 665.1 (M⁺-OTf -H₂0).

Example 9: Preparation of iridium complex E3

[096] Complex E3 (orange solid) was prepared _. following the same procedure as for complex El . Yield: (55%). WMeOH)/nm: 261 (lc½e/dm³ mol^'1 cm^'1 4.58), 272 (4.58), 341 (4.20), 383 (3.71), 421 (3.69), 516 (2.54). Ή NMR (300 MHz, CDC1₃) δ 3.01 (s,6H, Me), 5.76 (d, J=6.7, 2H), 6.46 (td, J=12.7 & 2.4, 2H), 7.69 (m, 4H), 8.08 (m, 2H), 8.36 (d, J=2.25, 2H), 8.61 (d, J=9.45, 2H). m/z [ESI⁺]: 701.1 (M⁺-OTf -H₂0).

[097] A mixture of compound Jl (303 mg, 1.24 mmol), iridium trichloride hydrate (164 mg, 0.47 mmol), 2-ethoxyethanol (18 mL) and water (6 mL)was heated at 120 °C under argon for 36 h. When cooled, water (40 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (100 mL), methanol (50 mL) and diethyl ether (250 mL). After completely dried, 266 mg (74%) of solid (complex Kl) was obtained. The chloro-bridged dimer Kl (153 mg, 0.10 mmol) was suspended in dichloromethane (15 mL) and methanol (15 mL). An aqueous solution (3 mL) of silver triflate (62 mg, 0.24 mmol) was added and the mixture was heated at 60 °C for 24 h. After cooled, water (30 mL) was added and dichloromethane and methanol were removed under vacuum. The crude product was then extracted by dichloromethane (2 x 30 mL) and washed by distilled H₂0 (2 x 15 mL). A dark red solid (complex E5) was obtained (135 mg, 74%) after filtration of the insoluble solid and removal of the solvents. Ή NMR (400 MHz, CDC1₃) δ 3.06 (s, 6H), 6.44 (d, J=8.6„2H), 7.36 (t, J=6.9, 2H), 7.54- 7.63 (m, 6H), 7.68 (d, .7=7.4, 2H), 8.07 (dd, J=8.2 &1.6, 2H), 8.48 (d, J=8.2, 2H), 8.59 (s, 2H), 8.69 (d, J=8.6, 2H). ^,3C NMR (75 MHz, Acetone-d^O) δ 19.41 ,122.28, 122.65, 124.22, 125.43, 126.81, 127.12, 127.70, 127.85, 129.19, 130.15, 131.82, 132.31, 132.53, 133.78, 141.69, 149.07, 149.24, 149.37, 170.92. mlz [ESf]: 729.2 (M⁺-OTf-2H₂0). Anal. Cal. For C₄iH₃₂F₃IrN₂0₅S: C, 53.88; H, 3.53; N, 3.06. Found: C, 53.19; H, 3.24; N, 2.99.

g, 4.20 mmol) and sodium carbonate (2.06 g) were dissolved in a mixture of toluene (30 mL), ethanol (10 mL) and water (10 mL). The mixture was deoxygenated before and after the addition of tetrakis(triphenylphosphine)palladium(0) (233 mg, 0.20 mmol). The mixture was refluxed at 100 °C for 48 h under argon. When cooled, water (50 mL) was added and the two layers were separated. The aqueous layer was extracted with diethyl ether (3 x 30 mL). All the organic portions were combined, washed with brine (30 mL), dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed in vacuo to give a yellowish solid. The crude solid was purified by column chromatography over silica using ethyl acetate-hexane (1 :20) as eluent to give compound J2 as a light yellow solid (950 mg, 99%).. Ή NMR (300 MHz, CDC1₃) δ 2.85 (s, 3H), 7.66 (dt, J=6.87 & 1.26, IH), 7.71 (s, IH), 7.81 (dt, J=6.9 & 1.4, IH), 8.00-8.14 (m, 5H), 8.21-8.32 (m, 5H), 8.45 (d, J=9.3, IH). ^,3C NMR (125 MHz, DMSO-d6) δ 19.04, 123.92, 124.60, 125.00, 125.04, 125,26, 125.29, 125.31 , 125.54, 126.20, 126.55, 127.16, 127.62, 127.88, 128.10, 128.26, 129.04, 129.69, 130.53, 131.1 1, 131.56, 131.69, 136.28, 144.56, 148.33, 159.62. mlz [ESf]: 344.1 (M+H⁺). Anal. Cal. For C₂₆H|₇N: C, 90.93; H, 4.99; N, 4.08. Found: C, 90.65; H, 5.05; N, 4.03.

[099] A mixture of compound J2 (384 mg, 1.12 mmol), iridium trichloride hydrate (164 mg, 0.47 mmol), 2-ethoxyethanol (18 mL) and water (6 mL) was heated at 120 °C under argon for 36 h. When cooled, water (40 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (100 mL), methanol (100 mL) and diethyl ether (250 mL). After completely dried, a solid (200 mg, 47%) was obtained as complex K2. The chloro-bridged dimer, K2 (111 mg, 0.06 mmol) was suspended in dichloromethane (15 inL) and methanol (15 mL). An aqueous solution (3 mL) of silver triflate (38 mg, 0.15 mmol) was added and the mixture was heated at 60 °C for 24 h. After cooled, water (30 mL) was added and dichloromethane and methanol were removed under vacuum. The crude product was then extracted by dichloromethane (2 x 30 mL) and washed by distilled H₂0 (2 x 15 mL). A red solid product was obtained as complex E6 (89 mg, 70%) after filtration of the insoluble solid and removal of the solvents. Ή NMR (500 MHz, DMSO-d^) δ 3.22 (s, 6H), 6.70 (s, 2H), 7.25 (d, .7=9.1 , 2H), 7.78-7.85 (m, 6H), 7.89 (t, J=7.5, 2H), 8.07 (d, J=7.3, 2H), 8.22 (d, J=7.3, 2H), 8.27 (d, J=9.6, 2H), 8.35 (dd, J=8.5 & 1.55, 2H), 8.80 (s, 2H), 9.00 (d, J=9.5, 2H), 9.13 (d, J=8.5, 2H). ^I3C NMR (125 MHz* DMSO-d^) δ 19.73, 119.99, 122.03, 122.94, 123.00, 124.94, 125.60, 125.85, 126.47, 126.88, 126.93, 127.61, 127.76, 129.46, 129.51, 129.57, 130.24, 131.28, 131.39, 131.64, 136.14, 141.12, 141.60, 149.34, 149.43, 170.59. [MALDI-TOF]: 1062.6 (M⁺), 877.4 (M⁺-OTf-2H₂0). Anal. Cal. For C₅₃H₃₆F₃IrN₂0₅S: C, 59.93; H, 3.42; N, 2.64. Found: C, 58.60; H, 3.10; N, 2.59.

Example 12: Preparation of compound J3 and iridium complex E7

[0100] 2-Chloro-4-methylquinoline (500 mg, 2.81 mmol), 9-methyl-9H-carbazol-3-yl-3- boronic acid (1.10 g, 4.89 mmol) and sodium carbonate (2.06 g) were dissolved in a mixture of toluene (30 mL), ethanol (10 mL) and water (10 mL). The mixture was deoxygenated before and after the addition of tetrakis(triphenylphosphine)palladium(0) (233 mg, 0.20 mmol). The mixture was heated for reflux at 100 °C for 20 h under argon. When cooled, water (50 mL) was added and the two layers were separated. The aqueous layer was extracted with diethyl ether (3 x 30 mL). All the organic portions were combined, washed with brine (30 mL), dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed in vacuo to give a yellowish solid. The crude solid was purified by column chromatography over silica using ethyl acetate- hexane (1 :20) as eluent to give compound J3 (858 mg, 91%) as a pure white solid. Ή NMR (500 MHz, CDClj) δ 2.81 (s, 3H), 3.91 (s, 3H), 7.28 (t, =1.0, 1H), 7.43 (d, 7=8.2, 1H), 7.51-7.55 (m, 3H), 7.73 (t, 7=6.9, 1H), 7.89 (s, 1H), 8.01 (d, 7=8.3, 1H), 8.23 (t, 7=7.95, lH), 8.36 (d, 7=8.55, 1H), 8.93 (s, 1H). ¹³C NMR (125 MHz, CDC1₃) 6J9.21 , 29.38, 108.76, 108.78, 119.41, 119.88, 119.97, 120.78, 123.33, 123.42, 123.77, 125.65, 125.69, 126.07, 127.14, 129.39, 130.12, 130.86, 141.69, 141.96, 144.69, 148.38, 157.90. mlz [ESI⁺]: 323.2 (M+H⁺). Anal. Cal. For C₂₃H,₈N₂: C, 85.68; H, 5.63; N, 8.69. Found: C, 85.86; H, 5.42; N, 8.47.

[0101] A mixture of compound J3 (480 mg, 1.44 mmol), iridium trichloride hydrate (212 mg, 0.60 mmol), 2-ethoxyethanol (12 mL) and water (4 mL) was heated at 130 °C under argon for 16 h. When cooled, water (40 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (100 mL), methanol (100 mL) and diethyl ether (250 mL). After completely dried, a solid (340 mg, 63%) was obtained as complex K3. The chloro-bridged dimer, 3 (270 mg, 0.15 mmol) was suspended in dichloromethane (15 mL) and methanol (15 mL). An aqueous solution (3 mL) of silver triflate (93 mg, 0.36 mmol) was added and the mixture was heated at 60 °C for 6 h. After cooled, water (30 mL) was added and the sovlent evaporated. The crude product was then extracted with dichloromethane (2 x 30 mL) and washed with distilled H₂0 (2 x 15 mL). A red solid (complex E7) was obtained (252 mg, 82%) after filtration of the insoluble solid and removal of the solvents. Ή NMR (300 MHz, CDC1₃) δ 3.05 (s, 6H), 3.19 (s, 6H), 6.33 (s, 2H), 7.1 1-7.18 (m, 4H), 7.33 (t, J=7.1, 2H), 7.56 (m, 4H), 8.04-8.07 (m, 4H), 8.15 (s, 2H), 8.67 (b, 2H). ^I3C NMR (100 MHz, CDC1₃) δ 19.58, 28.83, 108.59, 114.70, 117.43, 1 18.47, 1 19.24, 119.33, 1 19.53, 123.72, 124.53, 12117, 126.10, 126.79, 127.46, 131.32, 135.12, 137.68, 140.81 , 142.42, 147.83, 148.29, 169.16. mlz [ESI⁺]: 835.2 (M⁺-OTf-2H₂0). Anal. Cal. For C₄₇H₃₈F₃lrN₄0₅S: C, 55.34; H, 3.75; N, 5.49. Found: C, 56.07; H, 3.66; N, 5.52.

Example 13: Preparation of iridium complex E8

[0102] A mixture of compound J4 (250 mg, 0.78 mmol), iridium trichloride hydrate (108 mg, 0.31 mmol), 2-ethoxyethanol (18 mL) and water (6 mL) was heated at 120 °C under argon for 36 h. When cooled, water (40 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (100 mL), methanol (50 mL) and hexane (250 mL) and dried to give complex K4 (70 mg, 26%). The dried chloro-bridged dimer (44 mg, 0.025 mmol) was suspended in dichloromethane (10 mL) and methanol (10 mL). An aqueous solution (1 mL) of silver triflate (15 mg, 0.058 mmol) was added and the mixture was heated at 60 °C for 24 h. After cooled, water (30 mL) was added and dichloromethane and methanol were removed under vacuum. The crude product was then extracted with dichloromethane (2 x 30 mL) and washed by distilled H₂0 (2 x 15 mL). A dark red solid was obtained after filtration of the insoluble solid and removal of the solvents as complex E8 (37.5 mg, 72%). Ή NMR (500 MHz, DMSO-de) δ 2.96 (s, 6H), 6.09 (d, J=8.35, 2H), 6.36 (t, J=6.95, 2H), 7.12-7.17 (m, 4H), 7.34 (t, J=6.90, 2H), 7.49 (d, J=8.55, 2H), 7.66 (t, J=7.10, 2H), 7.82 (t, J=8.20, 2H), 8.01 (d, J=8.25, 2H), 8.44 (d, J=8.45, 2H), 8.74-8.76 (m, 4H), 8.90 (d, J=8.25, 2H). mlz [MALDI-TOF]: 1015.2 (M+H⁺), 829.7 (M⁺-OTf-2H₂0). Example 14: Preparation of iridium complexes LLL

[0103] Benzo[/i]quinoline (150 mg, 0.84 mmol) and iridium trichloride trihydrate (123 mg, 0.35 mmol) were dissolved in a mixture of 2-methoxyethanol (2.25 mL) and water (0.75 mL). The mixture was heated at 125 °C under argon for 16 hours. When cooled, water (40 mL) was added to the reaction mixture to precipitate a yellow solid. The precipitate was filtered and washed thoroughly with water (100 mL), methanol (50 mL), diethyl ether (100 ml) and dried to give PPP (131 mg, 64%) as a light yellow powder, mp: >300 °C. Ή NMR (300 MHz, CDCI3) δ 5.96 (d, J=7.0, IH), 6.79 (t, J=7.6, IH), 7.21-7.10 (m, 2H), 7.69 (dd, J=21.7, 8.7, 4H), 8.26 (dd, J=8.0, 1.2, IH), 9.34 (dd, J=5.3, 1.2, IH). The chloro-bridged dimer PPP (100 mg, 0.085 mmol) was suspended in dichloromethane (15 mL) and methanol (15 ml). An aqueous solution (1.5 mL) of silver triflate (70 mg, 0.27 mmol) was added to the suspension and the mixture was heated at 60 °C for 18 hours. After cooling to room temperature, dichloromethane and methanol were removed under vacuum. The crude product was extracted with dichloromethane (2 x 30 ml) and washed with distilled water (2 x 15 ml) to give LLL as a dark yellow solid (89 mg, 71%). mp: 250 °C (decompose). MS (MALDI-TOF: DCTB): m/z 549 (100%, M⁺-OTf-2H₂0). Ή NMR (400 MHz, DMSO-de) 6 5.91 (d, J=7.2, IH, Ph-H), 7.11 (t, J=7.6, IH, Ph-H), 7.54 (d, J=7.8, IH, Ph-H), 7.96 (q, J=8.8, 2H, Ph-H), 8.12 (dd, J=8.0, 5.6, IH, Qui-H), 8.91 (d, J=8.0, IH, Qui-H), 9.89 (d, J=5.4, IH, Qui-H). ¹³C NMR (101 MHz, DMSO-d₆) δ 122.59, 123.95, 124.80, 127.91, 128.04, 129.50, 129.57, 133.65, 138.37, 139.65, 144.00, 152.00, 155.69. max(MeOH)/nm: 255 (log ε/dm³ mor¹ cm^"1 4.49), 255 (4.49), 330 (4.12), 358 (4.01), 435 (3.56).

Example 15: Preparation of iridium complexes LI & L2

compound M compound N com ound O complex L

M1 : X=H N1 : X=H OI : X=H PI : X=H LI : X=H

M2: X=F N2: X=F 02: X-F P2: X-F L2: X=F

[0104] A mixture of Ml (100 mg, 0.56 mmol), potassium permanganate (532 mg, 3.30 mmol), tetrabutylammonium bromide (75 mg, 0.23 mmol), and acetic acid (0.25 mL) was heated at 50 °C under argon for 5 hours. The reaction was cooled and transferred to a separating funnel before sodium metabisulfate (5 g in 100 ml water) was added until no more potassium permanganate colouration was visible. The aqueous layer was separated and extracted with dichloromethane (3 x 50 mL). All the dichloromethane extracts were combined and washed with brine (50 mL) before passing through a silica plug to give Nl (81 mg, 69%) as a yellow solid, mp: 93-95 °C. Ή NMR (300 MHz, CDC1₃) δ 7.96 (dd, 7=8.2, 1.0, 4H), 7.65 (t, .7=7.4, 2H), 7.50 (t, J=7.6, 4H).

[0105] A mixture of Nl (900 mg, 3.60 mmol), o-phenylenediamine (470 mg 4.00 mmol), acetonitrile (4.5 mL) and iodine (1 10 mg) was stirred at room temperature for 2 hours. The yellow brown mixture was passed through a silica plug using dichloromethane as eluent and the solvent was removed under vacuum to give 01 (733 mg, 73%) as a yellow solid, mp: 123-125 °C. Ή NMR (500 MHz, DMSO-d₆) 5 7.42-7.31 (m, 6H), 7.47 (dd, J=8.1, 1.6, 4H), 7.89 (dd, J=6.4, 3.4, 2H), 8.16 (dd, 7=6.3, 3.4, 2H). ?unax(MeOH)/nm: 244 (log ε/dm³ mol^"1 cm^"1 4.68), 344 (4.16). [0106] A mixture of 01 (700 mg, 2.50 mmol), iridium trichloride trihydrate (360 mg, 1.00 mmol) 2-ethoxyethanol (44 mL) and water (15 mL) was heated at 130 °C under argon for 16 hours. When cooled, water (40 mL) was added to the reaction mixture to give precipitate a red solid. The precipitate was filtered and washed thoroughly with water (100 mL), methanol (100 mL) and diethyl ether (250 mL) and dried to give PI (540 mg, 68%) as a dark brown powder, mp: >300 °C. Ή NMR (300 MHz, DMSO-d₆) δ 6.20 (d, =7.5, 1H), 6.54-6.38 (m, 2H), 6.88-6.81 (m, 1H), 7.66 (d, 7=3.1, 3H), 7.97-7.69 (b, 4H), 8.16 (dd, 7=8.1, 1.3, 1H), 9.00 (d, 7=8.1, 1H). [0107] The chloro-bridged dimer PI (540 mg, 0.50 mmol) was suspended in dichloromethane (123 -mL) and methanol (123 ml). An aqueous solution (10 mL) of silver triflate (430 mg, 1.70 mmol) was added and the mixture was heated at 60 °C under argon for 18 hours. After being cooled, dichloromethane and methanol were removed under vacuum. The crude product was passed through filter paper and the product was washed with acetone and dried under vacuum to give LI as a dark brown powder (894 mg, 95%). mp: >300 °C. MS (MALDl-TOF: DITH): m/z 755 (100%, M⁺-OTf-2H₂0). Ή NMR (300 MHz, DMSO-do) δ 6.21 (dd, J=6.0, 3.1, 1H), 6.61-6.50 (m, 2H), 6.82 (dd, J=6.4, 3.4, 1H), 7.65 (dd, .7=5.1 , 1.7, 3H), 7.85-7.73 (m, 2H), 8.08-7.90 (m, 2H, Qx-H), 8.31-8.22 (m, 1H, Qx-H), 8.85 (d, J=9.9, 1H, Qx-H). ^,3C (100 MHz, DMSO-d,,) δ 1 15.9, 1 19.1, 121.7, 122.3, 122.3, 125.9, 129.1, 129.2, 129.4, 129.8, 130.1, 130.2, 130.9, 131.77, 135.2, 139.3, 140.5, 140.8, 145.1, 153.2, 163.4. Xmax(MeOH)/nm: 265 (log ε/dm³ mof' cm^{-1 "}4.49), 286 (4.25), 293 (4.32), 379 (4.19), 491 (3.45). [0108] A mixture of M2 (386 mg, 02.50 mmol), ground potassium hydroxide pellets (2.80 g, 50 mmol) and toluene (15 mL) was degassed under vacuum and purged with argon, which was repeated three times. The reaction was heated at 70 °C under argon overnight until the yellow solution became a red colour. l-Fluoro-4-iodobenzene (0.35 mL, 3.00 mmol), tetrakis(triphenylphosphine)palladium(0) (200 mg, 0.18 mmol), and copper(I) iodide (48 mg, 0.30 mmol) were added to the reaction mixture. The reaction was further degassed and purged with argon for three times. The reaction was heated at 70 °C for five days, monitoring from TLC for when the reaction was complete. The solvent was removed under vacuum and the mixture was separated by column chromatograph over silica using hexane as eluent to give N₂ as a white solid. (331 mg, 62%). mp: 94-95 °C. Ή NMR (300 MHz, CDC1₃) 6 7.09-6.96 (m, 4H), 7.53-7.42 (m, 4H).

[0109] A mixture of potassium permanganate (4.70 g, 30.0 mmol), dichloromethane (50 mL), tetrabutylammonium bromide (750 mg, 0.20 mmol), acetic acid (2.5 mL) and M2 (1.07 g, 0.50 mmol) was heated at 50 °C under argon for 5 h. The reaction was cooled and passed through a silica plug to give N2 as a yellow crystalline solid (1.16 g, 94%) after removing the solvent, mp: 1 19-120 °C. Ή NMR (300 MHz, CDC1₃) δ 7.21 (dd, J=9.0, 8.3, 4H), 8.08-7.96 (m, 4H). [0110] A mixture of N2 (1.01 g, 4.10 mmol), o-phenylenediamine (460 mg 0.50 mmol), acetonitrile (5 ml) and iodine (100 mg, 0.40 mmol) was stirred at room temperature for 2 hours under argon. After five minutes an orange colour could be seen. The resultant brown/green mixture was passed through a silica plug using dichloromethane as the eluent to give 02 (1.22 g, 94%) as a cream coloured solid after the removal of solvents by vacuum, mp: 133-134.9 °C. Ή NMR (300 MHz, CDC1₃) δ 7.04 (t, J=8.7, 4H, Ph-H), 7.49 (dd, J=8.8, 5.4, 4H, Ph-H), 7.77 (dd, J=6.4, 3.4, 2H, Qx-H), 8.14 (dd, 7=6.4, 3.5, 2H, Qx- H). max(MeOH)/nm: 243 (log ε/dm³ mol^"1 cm^-1 4.51), 346 (4.00). [0111] 02 (750 mg, 2.35 mmol) and iridium trichloride trihydrate (346.5 mg, 0.98 mmol) were dissolved in 2-methoxyethanol (1 1.25 mL) and water (3.75 mL). The mixture was heated at 125 °C under argon for 16 h. When cooled, water (40 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (300 mL), and a mixture of methanol (100 mL) and water (50 mL) and fully dried to give P2 as a red powder (712 mg, 85%). mp: >300 °C. Ή NMR (300 MHz, CDCI3) δ 5.26 (dd, .7=9.4, 2.5, 1H), 6.24 (td, J=8.8, 2.6, 1H), 6.67 (ddd, .7=8.6, 7.0, 1.4, 1H), 6.89 (dd, J=9.0, 5.8, 1H), 7.33 (b, J=28.2, 20.2, 3H), 7.68 (dd, J=8.3, 1.4, 1H), 7.94 (b, 1H), 8.16 (b, 1H), 8.24 (d, J=8.4, 1H). [01 12] The chloro-bridged dimer P2. (300 mg, 0.17 mmol) was suspended in dichloromethane (35 mL) and methanol (35 mL). An aqueous solution (3.5 mL) of silver triflate (180 mg, 0.70 mmol) was added and the mixture was heated at 60 °C under argon for 18 hours. After being cooled, dichloromethane and methanol were removed under vacuum. The crude product was extracted with dichloromethane (2 x 30 mL) and washed with distilled water (2 x 15 mL). The organic layer was combined and passed through filter paper. The solvent was removed under vacuum and the crude was recrystallised from dichloromethane and hexane. The precipitate was collected and fully dried to give L2 as a dark brown powder (347 mg, 98%). mp: >300 °C. (MALDI: DITH): m/z 827 (100%, M⁺- OTf-2H₂0). 1H NMR (300 MHz, methanol-d,) δ 5.93 (dd, J=9.5, 2.5, 1H, Ph-H), 6.45 (td, J=8.8, 2.6, 1H, Ph-H), 7.04 (dd, J=9.0, 5.8, 1H, Ph-H), 7.38 (t, J=8.8, 2H, Ph-H), 7.93- 7.85 (m, 2H, Ph-H), 8.04-7.93 (m, 2H, Qx-H), 8.31 (d, J=8.0, 1H, Qx-H), 8.70 (d, J=8.3, 1H, Qx-H). ¹³C NMR (101 MHz, methanol-d δ 109.48 (d, J=23,0), 1 16.27 (d, J=22.0), 1 19.06, 121.59 (d, J=18.2), 122.26, 125.42, 129.37, 130.65, 131.48 (d, J=8.6), 131.8, 132.27 (d, 7=9.7), 135.53 (d, 7=3.2), 140.38 (d, 7=14.0), 141.36, 147.52 (d, 7=7.5), 152.21, 159.91, 161.78, 162.49 (d, J=7.9), 164.24. Xmax(MeOH)/nm: 262 (log ε/dm³ mol^'1 cm^'1 4.32), 286 (4.25), 379 (4.04), 464 (3.48).

[01 13] A mixture of compound S (400 mg, 1.50 mmol), iridium trichloride hydrate (220 mg, 0.63 mmol), 2-ethoxyethanol (6 mL) (note: O should be avoided) was heated at 120 °C under argon for 20 h. When cooled, water (20 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (100 mL), methanol (50 mL) and diethyl ether (250 mL). The dried chloro-bridged dimer (complex T) (150 mg, 0.10 mmol) and LiOH (29 mg, 1.20 mmol) were dissolved in a mixed solvent of THF (30 mL) and EtOH (10 mL). The mixture was stirred at room temperature for 2 h. H₂0 (15 mL) was added to the mixture. The solution was heated at 80 °C for 24 h. The reaction was cooled to room temperature and solvent was completely removedto leave a solid. The solid was dissolved in H₂0 (50 mL) and 0.1 M HOTf aqueous solution was dropped to the solution until pH=3. The precipitation was collected, washed with H₂0 thoroughly and dried in the air to give complex QIa (1 13 mg, 75%). Ή NMR (400 MHz, DMSO-de) δ 6.10 (d, J=8.05, 1H), 6.22 (d, J=7.45, 1H), 6.51 (t, J=7.35, 1H), 6.61 (t, J=7.35, 1H), 6.91 (m, 2H), 7.56 (t, 7=7.9, 1H), 7.71 (t, 7=7.9, 1H), 7.85 (t, 7=7.9, 1Ή), 8.00-8.08 (m, 3H), 8.29-8.66 (m, 4H), 8.78 (d, 7=8.8, 1H), 8.83 (d, 7=8.05, 1H). ^I3C NMR is not measured due to the very low solubility, mlz [MALDI-TOF]: 81 1.5 (M⁺-COOH), 712.1 ([M+Na]⁺-OTf-H₂0), 689.3 (M⁺-OTf-H₂0), 645.2 (M⁺-OTf-H₂0- COOH).

Example 17: Preparation of compound U and iridium complexes V & OH

U QII

[0114] A solution of compound S (263 mg, 1 mmol), sodium borohydride (1 13.5 mg, 3 mmol) in 30 mL of absolute ethanol was heated at reflux for 3 h, before being cooled to room temperature. H₂0 (30 mL) was added to the mixture. The ethanol was evaporated and the resulting suspension was extracted with diethyl ether (3 x 20 mL). The combined organic layer was dried over anhydrous MgS0₄, and filtered. The filtrate was collected and the solvent was removed. The crude was purified by column chromatography over silica using dichloromethane/methanol (20:1) as eluent to give compound U (200 mg, 85%). Ή NMR (300 MHz, acetone-d₆) δ 4.98 (b, 1H), 5.24 (s, 2H), 7.44-7.56 (m, 4H), 7.74 (dt, J=6.9 & 1.4, 1H), 8.01 (d, J=8.04, 1H), 8.15-8.20 (m, 2H), 8.27-8.30 (m, 2H). ^I3C NMR (75 MHz, acetone-d_fi) δ 60.73, 115.35, 123.12, 125.00, 126.12, 127.30, 128.69, 129.27, 129.33, 130.05, 139.58, 148.02, 148.37, 156.51. mlz [ESf]: 236 QM+H]⁺). [0115] A mixture of compound U (428 mg, 1.82 mmol), iridium trichloride hydrate (268 mg, 0.76 mmol), 2-ethoxyethanol (10 mL) and water (3 mL) was heated at 120 °C under argon for 20 h. When cooled, water (40 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with- water (100 mL),.dichloromethane (50 mL) and diethyl ether (100 mL). After completely dried, 420 mg (79%) of complex V was obtained. The chloro-bridged dimer (complex V) (111 mg, 0.08 mmol) was suspended in methanol (20 mL). An aqueous solution (2 mL) of silver triflate (50 mg, 0.19 mmol) was added and the mixture was heated at 70 °C for 36 h. After completion, all solvents were removed under vacuum. The crude product was then dissolved in 30 mL of methanol and kept overnight. The insoluble solid was filtered off and complex QII was obtained (90 mg, 67%) after removal of methanol. Ή NMR (300 MHz, methanol-d,) δ 5.47 (s, 4H), 6.11 (d, J=7.8, 2H), 6.54 (t, J=7.3, 2H), 6.89 (t, J=7.6, 2H), 7.71-7.88 (m, 6H), 8.18 (d, 7=8.1, 2H), 8.43 (s, 2H), 9.03 (d, J=8.85, 2H). ¹³C NMR (75 MHz, methanol-d,) δ 61.49, 114.93, 123.70, 125.04, 127.00, 127.21, 127.33, 128.03, 130.64, 132.38, 135.49, 138.64, 148.36, 149.70, 153.05, 170.95. mlz [MALDI-TOF]: 661.1 (M⁺-OTf-2H₂0).

[01 16] A mixture of compound S (400 mg, 1.50 mmol), iridium trichloride hydrate (220 mg, 0.63 mmol) and 2-ethoxyethanol (6 mL) (note: H2O should be avoided)was heated at 120 °C under argon for 20 h. When cooled, water (20 mL) was added to the reaction mixture to give red solid precipitation. The precipitation was filtered and washed thoroughly with water (100 mL), methanol (50 mL) and diethyl ether (250 mL). The dried chloro-bridged dimer (150 mg, 0.10 mmol) was suspended in dichloromethane (10 mL) and methanol (10 mL). An aqueous solution (3 mL) of silver triflate (62 mg, 0.24 mmol) was added and the mixture was heated at 60 °C for 16 h. After cooled, water (30 mL) was added and dichloromethane and methanol were removed under vacuum. The crude product was then extracted with dichloromethane (2 x 20 mL) and washed with distilled H₂0 (2 x 15 mL). A dark red solid product was yielded after filtration of the insoluble solid and removal of the solvents to give complex QUI (128 mg, 71%). Ή NMR (400 MHz, methanol-^) δ 4.19 (s, 6H), 6.1 1 (d, J=7.8, 2H), 6.64 (t, J=7.3, 2H), 6.97 (t, J=7.4, 2H), 7.82 (t, J=7.8, 2H), 7.89 (t, J=8.0, 2H), 7.94 (d, 7=7.7, 2H), 8.71 (s, 2H), 8.83 (d, J=8.2, 2H), 9.06 (d, J=8.7, 2H). ¹³C NMR (100 MHz, methanol-d₄) δ 53.84, 1 19.23, 124.27, 126.18, 127.08, 127.77, 128.06, 129.34, 131.46, 133.14, 135.50, 138.60, 140.75, 147.44, 150.87, 167.06, 171.22. m/z [MALDI-TOF]: 717.4 (M⁺-OTf-2H₂0). · Anal. Cal. For C35H₂gF₃IrN₂0₉S: C, 46.61; H, 3.13; N, 3.1 1. Found: C, 45.32; H, 2.73; N, 2.71. <

Example 19: Preparation of compounds Wl & XI and complexes YL Z. OI Va & QVa

QlVa Z QVa

[0117] l ,l-Azobis(cyclohexanecarbonitrile) (ABCN, 194 mg, 0.80 mmol) was added to a mixture of compound Gl (1.74 g, 7.95 mmol) N-bromosuccinimide (NBS, 1.71 g, 9.54 mmol), dichloromethane (75 mL) and H₂0 (75 mL). The mixture was vigorous stirred,exposed to a 150 W halogen lamp and heated at reflux for 5 h. The mixture was then cooled to room temperature. The organic layer was collected and the water layer was extracted with dichloromethane (2 x 50 mL). The combined organic layer was then washed with brine, dried over anhydrous MgSC>4 and filtered. The filtrate was collected and the solvent was removed under vacuum. The crude was purified by column chromatography over silica using dichloromethane-hexane (1 : 1) as eluent to afford compound Wl as a colourless solid (1.94 g, 71%). Ή NMR (300 MHz, CDC1₃) δ 4.92 (s, 2H), 7.45-7.57 (m, 3H), 7.63 (dt, J=6.9 & 1.3, 1H), 7.76 (dt, J=8.4 & 1.5, 1H), 7.91 (s, 1H), 8.1 1 -8.18 (m, 3H), 8.23(dd, J=8.5 & 0.7, 1H). ¹³C NMR (125 MHz, CDCI3) δ 28.83, 1 19.36, 123.17, 124.86, 126.75, 127.49, 128.90, 129.61, 129.92, 130.62, 139.03, 142.90, 148.78, 157.08. mlz [ESI⁺]: 298.0 (M+H⁺). Anal. Cal. For C,₆Hi₂BrN: C, 64.45; H, 4.06; N, 4.70. Found: C, 64.31 ; H, 4.03; N, 4.97.

[01 18] A mixture of compound Wl (596 mg, 2 mmol) and triethylphosphite (2.5 mL) was heated at 100 °C overnight. The excess triethyl phosphite was then removed by distillation at 80 °C under high vacuum. The crude product was purified by column chromatography over silica using dichloromethane-hexane (2:1) and then dichloromethane -methanol (20:1) as eluent to give compound XI as a colorless oil (631 mg, 89%). Ή NMR (300 MHz, CDCI3) δ 1.16 (t, J=7.05, 6H), 3.65 (d, J =22.7, 2H), 3.95-4.02 (m, 4H), 7.44-7.57 (m, 4H), 7.70 (dt, J=6.9 & 1.35, 1H), 7.87 (d, J=3.6, 1H), 8.07 (dd, J=8.4 & 1.0, 1H), 8.14- 8.19 (m, 3H). ^,3C NMR (.125 MHz, CDCb) δ 16.1 1 (d, J=6.1), 30.37 (d, J=137.0), 62.20 (d, J=7.0), 120.54 (d, J=7.0), 123.78 (d, .7=1.6), 126.07, 126.11, 126.14, 127.25, 128.58, 129.17, 129.34, 130.16, 138.67, 138.74, 139.06, 148.36 (d, J=1.65), 156.29 (d, J=3.55). mlz [ESI⁺]: 356.1 (M+H⁺). Anal. Cal. For C₂oH2₂N0₃P: C, 67.60; H, 6.24; N, 3.94. Found: C, 67.26; H, 6.21 ; N, 3.92.

[01 19] Compound XI (470 mg, 1.33 mmol) and iridium trichloride hydrate (195 mg, 0.55 mmol) were dissolved in a mixture of 2-ethoxyethanol (12 mL) and water (4 mL). The mixture was heated at 130 °C under argon for 24 h. When cooled, water (40 mL) was added to the reaction mixture to precipitate a red solid. The precipitation was filtered and washed with water (3 x 30 mL) and hexane (3 x 150 mL). After completely dried, complex Yl (334 mg, 65%) was obtained. The chloro-bridged dimer (complex Y, 247 mg, 0.13 mmol) was suspended in dichloromethane (15 mL) and methanol (15 mL). An aqueous solution (3 mL) of silver triflate (339 mg, 1.32 mmol) was added and the mixture was heated at 50 °C for 16 h. After cooled, water (30 mL) was added. The solvent was removed under vacuum. The crude product was extracted by dichloromethane (2 x 30 mL) and washed by distilled H₂0 (2 x 15 mL). A red solid (130 mg, 46%) was yielded as complex Z after complete removal of the solvent. Ή NMR (300 MHz, CDC1₃) δ 1.19-1.22 (m, 12H), 3.74 (d, J=22.4, 4H), 4.02 (m, 8H), 6.32 (d, J=7.8, 2H), 6.59 (t, J=7.5, 2H), 6.93 (t, J=6.3, 2H), 7.56-7,69 (m, 6H), 8.03 (s, 4H), 8.85 (b, 2H). ¹³C NMR (100 MHz, CDC1₃) δ 16.66 (d, J=5.8), 30.45 (d, J=127.4), 62.41 (t, J=5.7), 1 19.53, 122.40, 122.82, 126.59, 127.01, 127.24, 127.28, 129.81, 131.61, 134.58, 141.34, 144.72 (d, J=9.4), 147.08, 148.91, 169.08. mlz [ESf]: 901.1 (M⁺-OTf-2H₂0).

[0120] Complex Z (109 mg, 0.1 mmol) was added to 15 mL of aqueous HC1 solution (5.7 M) and refluxed at 100 °C for 24 h. After cooled to room temperature, crude complex Z was obtained by removing the solvent as a yellow solid. Complex Z was dissolved in 2 mL methanol and purified by column chromatography over Sephadex LH-20 using methanol as eluent to give complex QlVa (29.2 mg, 30%). A™_x(MeOH)/nm: 233 (loge/dm³ mol^"1 cm^{' 1} 4.54), 260 (4.54), 280 (4.53), 294 (4.43), 324 (4.23), 360 (4.00), 410 (3.76), 438 (3.60). Ή NMR (400 MHz, methanol-d,): δ 3.90 (d, 6H, J=22.9), 7.00 (t, 2H, J=6.3), 7.11 (t, 2H, J=7.8), 7.58 (d, 2H, J=7.8), 7.66 (t, 2H, J=7.0), 7.73-7.81 (m, 4H), 8.03 (d, 2H, J=3.5), 8.11 (d, 2H, J=8.3), 9.59 (d, 2H, J=7.9). ¹³C NMR (100 MHz, MeOD) δ 30.78 (d, J=131.31), 1 17.72 (d, J=6.81), 121.59, 124.98, 125.28, 125.65, 125.99 (d, J=4.53), 126.920, 128.40, 130.27, 132.85, 134.31, 143.24 (d, J=9.40), 147.61, 150.24 (d, J=1.94), 171.88(d, J=3.35). mlz [ESI⁺]: 893 (M⁺-P0₃H₂). mlz [MALDI-TOF]: 627.04 (M⁺-OTf- 2H₂0-2P0₃H₂).

[0121] Complex Y (187.3 mg, 0.1 mmol) was added to 20 mL of aqueous HC1 solution (5.7 M) and heated at reflux for 24 h. After cooled to room temperature, the crude product was obtained by removing the solvent. The resulted yellowish solid was dissolved in 3 mL of methanol and purified by column chromatography over Sephadex LH-20 using methanol as eluent to give complex QVa (48.8 mg, 29%).

233 (logs/dm³ moP¹ cm^"1 4.44), 260 (4.44), 280 (4.42), 294 (4.30), 324 (4.1 1), 360 (3.89), 410 (3.61), 438 (3.51). Ή NMR (300 MHz, methanol-d₄): δ 3.89 (d, 6H, J=23.49), 7.02 (t, 2H, J=6.99), 7.1 1 (t, 2H, J=6.75), 7.58 (d, 2H, J=7.80), 7.67 (t, 2H, J=7.32), 7.75-7.84 (m, 4H), 8.05 (s, 2H), 8.13 (d, 2H, J=8.31), 9.58 (d, 2H, J=8.76). ¹³C NMR (75 MHz, methanol^) δ 30.76 (d, J=131.87), 1 17.70 (d, J=6.81), 121.56, 124.96, 125.26, 125.62, 125.98 (d, J=4.35), 126.90, 128.37, 130.24, 132.83, 134.29, 143.23 (d, J=9.05), 147.60, 150.25, 171.85. mlz [MALDI-TOF]: 842.13 (M⁺), 788.99 (M⁺-C1-H₂0), 710.04 (M⁺-C1-H₂0-P0₃H₂), 663.04 (M⁺-H₂0-2P0₃H₂), 629.08 (M⁺-C1-H₂0-2P0₃H₂+2H).

[0122] l,l-Azobis(cyclohexanecarbonitrile) (ABCN, 292 mg, 1.20 mmol) was added to a mixture of compound G2 (2.83 g, 11.9 mmol), N-bromosuccinimide (2.55 g, 14.3 mmol), dichloromethane (75 mL) and H₂0 (75 mL). The mixture was vigorously stirred, exposed to a 150 W halogen lamp and heated at reflux for 5 h. The mixture was then cooled to room temperature. The organic layer was collected and the water layer was extracted with dichloromethane (2 x 100 mL). The combined organic layer was then washed with brine, dried over anhydrous MgS0₄ and filtered. The filtrate was collected and the solvent was removed under vacuum. The crude was purified by column chromatography over silica using dichloromethane-hexane (1 :1) as eluent to give compound W2 as a colourless solid (12.19 g, 58%); mp 124 °C. Ή NMR (300 MHz, CDC1₃) δ 4.88 (s, 2H), 7.18-7.27 (m, 2H), 7.62 (dt, .7=1.295 & 6.87, 1H), 7.76 (dt, J=1.41 & 6.90, 1H), 7.83 (s, 1H), 8.08-8.22 (m, 4H). ¹³C NMR (75 MHz, CDC1₃) δ 28.67, 1 15.81 (d, 7=21.62), 1 18.97, 123.14, 124.75, 126.80, 129.34 (d, J=8.46), 130.02, 130.52, 135.20 (d, J=3.16), 143.04, 148.73, 155.98, 163.90 (d, J=248.00). mlz [MALDI-TOF]: 316.0 (M+H⁺). Anal. Cal. For CieHnBrFN: C, 60.78; H, 3.51 ; N, 4.43. Found: C, 60.75; H, 3.42; N, 4.46.

[0123] A mixture of compound W2 (2.35 g, 7.4 mmol) and triethylphosphite (10 mL) was heated at 100 °C overnight under argon. The excess triethyl phosphite was removed by distillation. The crude product was purified by column chromatography over silica using dichloromethane-hexane (1 :1) and dichloromethane-methanol (20:1) as eluent to give X2 as a colourless oil (2.87 g, 100%). Ή NMR (300 MHz, CDC1₃) 6 1.15 (dt, J=0.33 & 6.87, 6H), 3.62 (d, J=22.65, 2H), 3.91-4.03 (m, 4H), 7.12-7.18 (m, 2H), 7.49-7.55 (m, 1H), 7.68 (dt, J=1.35 & 8.37, 1H), 7.80 (d, J=3.60, 1H), 8.04(dd, J=1.05 & 8.46, 1H), 8.09-8.16 (m, 3H). ^,3C NMR (75 MHz, CDCI3) δ 16.16 (d, J=5.99), 30.45 (d, J=137.12), 62.34 (d, J=6.71), 1 15.57 (d, J=21.41), 120.34 (d, J=6.97), 123.81 (d, J=1.41), 126.10 (d, J=4.90), 126.22, 129.22 (d, J=8.34), 129.57, 130.13, 135.28 (d, J=3.08), 138.98 (d, J=8.97), 148.34 (d, J=2.26), 155.35 (d, J=3.59), 163.67 (d, J=247.59). m/z [MALDI-TOF]: 374.1 (M+H⁺). Anal. Cal: For C₂₀H₂iFNO₃P: C, 64.34; H, 5.67; N, 3.75. Found: C, 63.98; H, 5.67; N, 3.75.

[0124] A mixture of X2 (896 mg, 2.4 mmol), iridium trichloride hydrate (353 mg, 1.0 mmol), 2-ethoxyethanol (12 mL) and water (4 mL) was heated at 130 °C under argon for 20 hours. When cooled, water (40 mL) was added to the mixture to give red solid precipitation. The precipitation was filtered off and washed with water (3 x 30 mL). After being dried, the obtained solid was suspended in a mixture of 10 mL of HC1 (2 M) solution and 10 mL acetone and stirred overnight. The precipitate was filtered and dried to give Y2 (757 mg, 78%). A mixture of Y2 (537 mg, 0.28 mmol), 20 mL aqueous HC1 solution (6 M) was heated at reflux (100 °C) for 42 h. After being cooled to room temperature, the solvent was removed by evaporation to give a crude product as a yellow solid. The solid was dissolved in 2 mL methanol and purified by column chromatography over Sephadex LH- 20 using methanol as eluent to give QVb as a red solid (210 mg, 42%). Ή NMR (500 MHz, methanol^) δ 3.89 (d, 4H, J=23.49), 7.02 (dd, 2H, J=10.10 & 2.50), 7.62 (d, 2H, J=6.30), 7.63 (d, 2H, J=5.95), 7.76 (dt, 2H, J=6.90 & 1.15), 7.81 (d, 2H, J=3.60), 8.00 (d, 2H, J=7.70), 9.53 (d, 2H, J=8.75). ¹³C NMR (100 MHz, MeOD) δ 32.01 (d, J=I31.43), 109.79 (d, J=23.37), 1 19.30 (d, J=6.89), 1 19.76 (d, J=18.96), 126.43, 126.91, 127.17 (d, J=4.25), 127.99, 128.49 (d, J=9.74), 131.65, 138.72 (d, J=7.53), 144.58 (d, J=9.22), 145.36, 151.42 (d, J=1.96), 162.84 (d, J=250.13), 172.13 (d, J=3.43). mlz [MALDI-TOF, using dithranol as matrix]: 663.22 (M⁺-C1-2H₂0-2P0₃H₂), 825.17 (M⁺-C1-2H₂0), 884.28 ([M-Cl+Na]⁺), 896.29 [M*]. mlz [MALDI-TOF, using 4-dimethylamino-pyridine as matrix]: Anal. Cal. For C₃₂Hi₉F₂IrN₂0₄P₂: 786.1 (59%), 787.1 (21%), 788.1 (100%), 789.1 (35%), 790.1 (7%). Found: 786.3 (46%), 787.3 (25%), 788.3 (100%), 789.3 (48%), 790.3 (38%). (M⁺-OTf-2H₂0-2H₂0-H). WMeOH)/nm: 265 (loge/dm³ mol^"1 cm^"1 4.40), 278 (4.37), 294 (4.25), 322sh (4.03), 358sh (3.87), 404 (3.61), 428sh (3.52), 487sh (2.67), 527sh (2.43).

[0125] Optional embodiments of the present invention may also be said to broadly consist in the parts, elements and features referred to or indicated herein, individually or collectively, in any or all combinations of two or more of the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. [0126] Although a preferred embodiment has been described in detail, it should be understood that various changes, substitutions, and alterations can be made by one of ordinary skill in the art without departing from the scope of the present invention.

Claims

The claims:

1. A water splitting catalyst, comprising a cyclometalated iridium complex including bandgap lowering ligands.

2. The water splitting catalyst of claim 1, wherein the ligands are aryl quinoline ligands.

3. The water splitting catalyst of claim 1, wherein the ligands are derived from aryl pyrazine or aryl quinoxaline.

4. The water splitting catalyst of any one of claims 1 to 3, wherein one or more additional linking groups are included to improve solubility of the complex. 5. The water splitting catalyst of any one of claims 1 to 3, wherein one or more additional linking groups are included to improve attachment of the complex to a semiconductor or an electrode. cyclometalated iridium complex, comprising the structure of formula I:

la lb wherein, Ar is an aryl group, or a fused or heterocyclic arene or ring.

7. The cyclometalated iridium complex of claim 6, wherein the represented pyridine ring further comprises two or more nitrogens derived from the group consisting of carbazole, pyrimidine, pyrazine, pyridazine, quinoline, quinoxaline, pyrrole, imidazole, triazine, and triazole.

8. The cyclometalated iridium complex of claim 6 or 7, wherein A and/or B are initially part of an electrolyte or a solvent.

9. The cyclometalated iridium complex of claim 6 or 7, wherein A and/or B are initially part of an electrolyte, which can be ligated to a metal or act as a counter ion.

10. The cyclometalated iridium complex of claim 6 or 7, wherein A and/or B are selected from the group consisting of OH₂, OH, O, OTf, S0₄, NO3, PF₆₎ CI, and a halo.

1 1. The cyclometalated iridium complex of claim 6 or 7, wherein A and/or B are selected from the group consisting of a bidentate ligand, diamine, bipyridyl, picolinic acid, picolinamide, quinolone carboxylic acid, and a derivative thereof.

12. The cyclometalated iridium complex of any one of claims 6 to 1 1, further comprising the structure of formula II:

Ha lib

wherein, C is one or more linking groups and C is provided on any part of the ligand rings, on either part of the ligand rings, or on the two ligand rings.

13. The cyclometalated iridium complex of claim 12, wherein C is a hydrophilic group or an anchor group.

14. The cyclometalated iridium complex of claim 12, wherein C is derived from the group consisting of phosphonic acid, carboxylic acid, hydroxamide, amine, ether and alcohol.

15. The cyclometalated iridium complex of claim 14, wherein C facilitates the attachment of the complex to an electrode or semiconductor.

16. The cyclometalated iridium complex of any one of claims 6 to 15, wherein A and/or B are initially part of an electrolyte or a solvent.

17. The cyclometalated iridium complex of any one of claims 6 to 16, wherein Ar has the following structure:

and wherein X, Y and Z are individually selected from the group consisting of hydrogen, a halogen, an organofluorine, a trifluoromethyl, an alkyl, a nitro, a cyanide, C_nF_2n+i, COOR, C(0)R, OR, an aryl, and an heteroarene.

18. The cyclometalated iridium complex of claim 17, wherein:

X = H, Y = H, Z = H;

X = F, Y = H, Z = H;

X = F, Y = F, Z = H;

X = F, Y = H, Z = CF₃;

X = F, Y = F, Z = CF₃; or

X = H, Y = H, Z = CF₃.

19. The cyclometalated iridium complex of any one of claims 6 to 18, wherein Ar is selected from the group consisting of phenyl, a fused ring, for example naphthene, pyrene, fluorene, dibenzofuran, dibenzothiophene, coumarine, anthracene, indole, benzimidazole, quinazoline, phthalimide, phenanthridine, or heteroarene, such as pyridine, quinoline, carbazole, pyrimidine, pyrazine, pyridazine, pyrrole, imidazole, triazine, and triazole.

20. The cyclometalated iridium complex of any one of claims 6 to 19, wherein the cyclometalated complex is used as a catalyst, photocatalyst, photosensitizer and/or a precursor of active catalytic species in water splitting.

21. The cyclometalated iridium complex of any one of claims 6 to 20, wherein the cyclometalated complex is used in a light-driven or photon-driven opto-electronic device.

22. A water splitting catalyst, comprising a cyclometalated iridium complex including bandgap widening ligands.

23. The water splitting catalyst of claim 22, wherein the ligands are aryl triazole or aryl benzimidazole ligands.

24. The water splitting catalyst of claim 23, including substitution groups to alter the energy level and energy bandgap.

25. The water splitting catalyst of any one of claims 22 to 24, further including one or more linking groups to improve the solubility of the complex.

26. The water splitting catalyst of any one of claims 22 to 24, further including one or more linking groups to improve the attachment of the complex to a semiconductor or an electrode used in a water splitting or photon-driven device.