Ir(ppy)3

Technical Specifications

Product Description & Scientific Applications

fac-Ir(ppy)3 is a neutral, homoleptic cyclometalated iridium(III) complex: three 2-phenylpyridine ligands bind the metal through carbon and nitrogen in the facial geometry. The three strongly electron-donating cyclometalating ligands raise the metal-centred orbitals and make the complex a powerful photoreductant. Photoexcitation populates a triplet metal-to-ligand charge-transfer state that phosphoresces green, with an emission maximum of 494 nm in a 1:1 ethanol/methanol glass at 77 K. In acetonitrile at room temperature the excited state is long-lived, with a lifetime of 1900 ns. The redox potentials (acetonitrile, versus SCE) place the ground-state Ir(IV)/Ir(III) couple at +0.77 V and the Ir(III)/Ir(II) couple at −2.19 V; the excited state is a strong reductant at −1.73 V (M+/M*) and a mild oxidant at +0.31 V (M*/M−). The very negative excited-state reduction potential is the defining feature: photoexcited *Ir(ppy)3 reduces substrates directly at E1/2(IV/*III) = −1.73 V versus SCE, a more strongly reducing excited state than the heteroleptic cationic catalysts of this family reach.

Applications

As a visible-light photoredox catalyst fac-Ir(ppy)3 operates at loadings near or below 1 mol%, and it also serves as a phosphorescent OLED emitter:

• OLED green dopant — a phosphorescent green emitter used as a dopant in organic light-emitting diodes; the roughly spherical facial complex adopts an isotropic transition-dipole orientation in vacuum-deposited host films.
• Reductive dehalogenation — reduces alkyl, alkenyl, and aryl iodides that are otherwise difficult to reduce, using a tributylamine/Hantzsch ester or formic acid reductant system.
• Enantioselective α-benzylation of aldehydes — paired with an imidazolidinone organocatalyst, the reducing excited state converts electron-deficient benzyl halides to benzyl radicals.
• Atom-transfer radical addition — adds trifluoromethylated tertiary bromides to aliphatic alkenes.
• Radical dearomative cyclisation — at loadings as low as 0.1 mol%.
• Difluoroacetylation/cyclisation — converts chromone-tethered alkenes to tetrahydroxanthones in yields up to 85%.
• Radical difunctionalisation of alkenyl ketones — to tetralones and cyclopropanes.
• Triplet-energy-transfer photosensitisation — beyond single-electron transfer, for example in a cobaloxime-coupled synthesis of phenanthrenols.
• CO2-to-CO photoreduction — as a visible-light photosensitiser with an earth-abundant nickel carbene catalyst, driving selective reduction of CO2 to CO with turnover numbers reaching 98,000; with N-heterocyclic-carbene gold catalysts it sustains CO2-to-CO photoreduction for over 100 hours.
• Oxygen-tolerant aqueous photoredox — within micellar nanoparticles it drives photoredox catalysis in aerated aqueous solution under visible light near 500 nm, activating nitroso precursors to release nitric oxide.

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