Activation of molecular hydrogen in cobalt-catalyzed hydroformylation

Abstract

The mechanism of the activation of molecular hydrogen in cobalt-catalyzed hydroformylation of olefins has been studied by high pressure IR spectroscopy using HCo(CO) 4 ( 1) under 100 bar H 2 (or D 2) in the absence or presence of CO at room temperature. The treatment of 1 with 100 bar H 2 resulted in the formation of CO 2(CO) 8 ( 2) and a small amount of Co 4(CO) 12 ( 3), and the transient formation of HCo 3(CO) 9 ( 4). In the reaction of 1 with one equivalent of 3,3-dimethyl-butene-1 under 100 bar H 2 both hydrogenation and hydroformylation occur, but the former is much faster. In the presence of large amounts of 1 the predominant path for the hydrogenation of the olefin involves the reaction of two equivalents of 1 with the olefin even under 100 bar of H 2. Under a very low partial pressure of CO the stability of 1 is increased and the hydrogenation significantly slowed down. The preferred path of the hydroformylation of the olefin involves the addition of H 2 and CO from gas phase even in the presence of large amount of HCo(CO) 4 ( 1) under 100 bar H 2 and 2.3 bar COat room temperature. The studies reveal that the mechanism of H 2 activation in the presence of HCo(CO) 4 ( 1) is highly dependent on the reaction conditions. Under 100 bar H 2 and at room temperature the activation of molecular hydrogen starts at a coordinatively unsaturated acyl cobalt carbonyl, yielding an aldehyde and an unknown cobalt species. It is believed that this species is a coordinatively unsaturated hydrido cobalt carbonyl like {HCo(Co) 3}, and can activate and catalytically hydroformylate the olefin.