Activation of molecular hydrogen in cobalt-catalyzed hydroformylation

Article abstract of DOI:10.1016/0022-328X(91)80161-C

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 H2 (or D2) in the absence or presence of CO at room temperature.The treatment of 1 with 100 bar H2 resulted in the formation of Co2(CO)8 (2) and a small amount of Co4(CO)12 (3), and the transient formation of HCo3(CO)9 (4).In the reaction of 1 with one equivalent of 3,3-dimethyl-butene-1 under 100 bar H2 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 H2.Under a very low partial pressure of CO the stability of 1 is increased and the hydrogenation significant slowed down.The preferred path of the hydroformylation of the olefin involves the addition of H2 and CO from gas phase even in the presence of large amount of HCo(CO)4 (1) under 100 bar H2 and 2.3 bar CO at room temperature.The studies reveal that the mechanism of H2 activation in the presence of HCo(CO)4 (1) is highly dependent on the reaction conditions.Under 100 bar H2 and at rom 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 hydriodo cobalt carbonyl like (HCo(CO)3>, and can activate and catalytically hydroformylate the olefin.