Reactivity patterns and catalytic chemistry of iridium polyhydride complexes

[IrH₅P₂] (1, P PPrⁱ ₃) reacts autocatalytically with CF₃COOR (R CH₂CF₃) in cyclo-C₆D₁₂ at 60°C according to: 1 + CF₃COOR → [IrH₂P₂(OR)] (2) + ROH (4) (eq. 1). The rate-law, - d[1] dt = k[1] ^{1 2}[CF₃COOR][2] ^{1 2}[4]^{- 1 2} (k = 1.25 × 10^-4 M^{- 1 2} sec^-1), is consistent with the mechanism, 1 + 2 ⇌ 2 [IrH₃P₂] (5) + 4 (rapid equilibrium); 5 + CF₃COOR → [IrH₂P₂{OCH(OR)CF₃}] (6) (rate determining); 6 → 2 + CF₃CHO; 5 + CF₃CHO → 2. 2 reacts rapidly with H₂ (25° C, 1 atm) according to: 2 + 2 H₂ → 1 + 4 (eq. 2). Although the combination of reactions 1 and 2 constitute a catalytic cycle for the hydrogenation of CF₃COOR (CF₃COOR + 2 H₂ → 2 (4), catalyzed by 1), such catalytic hydrogenation does not occur, presumably because H₂ suppresses reaction by rapidly converting the catalytic intermediates, 2 and 5, to 1. However, 1 was found to be effective as a catalyst or catalyst precursor for transfer hydrogenation, e.g. CH₂CHC(CH₃)₃ + (CH₃)₂CHOH → CH₃CH₂C(CH₃)₃ + (CH₃)₂CO. While not directly detected, IrH₃P₂ could be trapped at low temperatures by N₂ to yield the complexes [IrH₃P₂(N₂)] and [(IrH₃P₂)₂N₂] which are related through the labile equilibrium, [(IrH₃P₂)₂N₂] + N₂ ⇌ 2 [IrH₃P₂(N₂)] (K_eq ∼ 1.5 at 35° C).