Ir(3,4,7,8-Me 4phen) (CH 2CH 2) 2Cl]: A very active catalyst precursor for hydrogen transfer from alcohols to unsaturated organic substrates

Abstract

Some new complexes of the type Ir 1chel(CH 2CH 2) 2Cl (chel = bipy; 4,4′-Me 2bipy; 4,4′-Ph 2bipy; phen; 5,6-Me 2phen; 4,7-Ph 2phen; 3,4,7,8-Me 4phen) behave as catalyst precursors for the hydrogen transfer from alcohols to ketones and Schiff bases. The most active of the complexes is the 3,4,7,8-Me 4phen derivative, which, at 83°C, gave turnovers of up to 2850 cycles/min with cyclohexanone, 2700 cycles/min with 4-tert-butylcyclohexanone and 5000 cycles/min with benzylidenaniline, at a catalyst concentration of 4 X 10 −5 M and a KOH (cocatalyst) concentration of 8 X 10 −4 M. Good catalytic activity was observed also at room temperature. Some catalytic activity was found at low substrate concentrations, even in the absence of KOH. The maximum stereoselectivity reached in the reduction of 4-tertbutylcyclohexanone was 97%, the trans-alcohol being formed.