[Ir[dF(CF3)ppy]2(dtbbpy)]PF6

Technical Specifications

Product Description & Scientific Applications

Ir[dF(CF3)ppy]2(dtbbpy)PF6 is a cationic, heteroleptic cyclometalated iridium(III) complex: two 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine ligands and one 4,4′-di-tert-butyl-2,2′-bipyridine ligand surround the metal, with hexafluorophosphate as counter-ion. The electron-withdrawing fluorine and trifluoromethyl substituents lower the metal-centred orbitals, so that, unlike the electron-rich tris-cyclometalated and non-fluorinated heteroleptic congeners, the excited state is a strong single-electron oxidant. Photoexcitation populates a long-lived triplet metal-to-ligand charge-transfer state; in acetonitrile at room temperature the excitation maximum is 380 nm, the emission maximum is 470 nm, and the lifetime is 2300 ns (2.3 µs). The redox potentials (acetonitrile, versus SCE) place the ground-state Ir(IV)/Ir(III) couple at +1.69 V and the Ir(III)/Ir(II) couple at −1.37 V, while the excited state combines a mild reducing potential of −0.89 V (M+/M*) with a powerful oxidising potential of +1.21 V (M*/M−). This strongly oxidising excited state is the defining feature. The complex also carries an excited-state triplet energy of 61 kcal/mol, close to the ~60 kcal/mol triplet energy of styrenes, which lets it act as a triplet-energy-transfer sensitiser as well as an electron-transfer catalyst.

Applications

As a visible-light photocatalyst Ir[dF(CF3)ppy]2(dtbbpy)PF6 is exploited along both redox channels of its excited state and the energy-transfer manifold:

• PMB ether deprotection (reducing channel) — the excited state (−0.89 V vs SCE) donates an electron to bromotrichloromethane, which is thereby reduced and serves as the stoichiometric oxidant, deprotecting para-methoxybenzyl (PMB) ethers as a mild alternative to oxidative or acidic conditions.
• Energy-transfer [2+2] cycloaddition — its 61 kcal/mol triplet energy sensitises cyclisation: where a radical-cation pathway would deliver a [4+2] adduct from a styrene, energy transfer instead gives the cyclobutane as the exclusive product, switching the reaction outcome.
• Nickel metallaphotoredox cross-coupling (oxidising channel) — its +1.21 V oxidising excited state, paired with a supersilanol reagent, single-electron oxidises the derived silanolate to a silyl radical that abstracts halogen atoms, enabling C(sp3)–C(sp3) cross-electrophile coupling of aliphatic bromides, including the union of two secondary carbon centres. The long excited-state lifetime and high oxidation potential make it a standard photocatalyst for such dual photoredox/nickel cross-coupling.

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