Reactivity patterns and catalytic chemistry of iridium polyhydride complexes

Article abstract of DOI:10.1016/0022-328X(90)85230-V

(1, P=PPrⁱ3) reacts autocatalytically with CF3COOR (R=CH2CF3) in cyclo-C6D12 at 60 deg C according to: 1 + CF3COOR -> (2) + ROH (4) (eq.1).The rate-law, -d<1>/dt=k<1>^1/2<2>^1/2<4>^-1/2 (k=1.25*10^-4 M^-1/2 sec^-1), is consistent with the mechanism, 1 + 2 <-> 2 (5) + 4 (rapid equilibrium); 5 + CF3COOR -> > (6) (rate determining); 6 -> 2 + CF3CHO; 5 + CF3CHO -> 2. 2 reacts rapidly with H2 (25 deg C, 1 atm) according to: 2 + 2H2 -> 1 + 4 (eq.2).Although the combination of reactions 1 and 2 constitute a catalytic cycle for the hydrogenation of CF3COOR (CF3COOR + 2H2 -> 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 and <(IrH3P2)2N2> which are related through the labile equilibrium, <(IrH3P2)2N2> + N2 <-> 2 (Keq ca. 1.5 at 35 deg C).