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Reactivity patterns and catalytic chemistry of iridium polyhydride complexes

1990; Elsevier BV; Volume: 382; Issue: 1-2 Linguagem: Inglês

10.1016/0022-328x(90)85230-v

1872-8561

Alan S. Goldman, Jack Halpern,

Organometallic Complex Synthesis and Catalysis

[IrH5P2] (1, P  PPri3) 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]12[CF3COOR][2]12[4]−12 (k = 1.25 × 10−4M−12 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. CH2CHC(CH3)3 + (CH3)2CHOH → CH3CH2C(CH3)3 + (CH3)2CO. 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)] (Keq ∼ 1.5 at 35° C).