Kinetics and mechanism of the transfer hydrogenation and double bond migration of 1-hexene catalyzed by molybdenum complexes

Abstract

The mechanism of the transfer hydrogenation and double bond migration of 1-hexene catalyzed by trans-Mo(N 2) 2(dpe) 2 (dpe = Ph 2PCH 2CH 2PPh 2) has been studied. The stoichiometric reaction of 1-hexene with MoH4(dpe)2 suggests that the active species for the hydrogenation is MoH 2(dpe) 2 and that for the double bond migration it is Mo(dpe) 2. The double bond migration is suppressed in the hydrogenation of 1-hexene by molecular hydrogen, with the formation of a moderate amount of hexane. The result of the reaction of Mo(C 2H 4) 2(dpe) 2 with 2-propanol suggests that dual pathways may be available for the transfer hydrogenation. The kinetics of the hydrogen transfer from 2-propanol to 1-hexene, however, indicate that the predominant pathway involves the reaction of the catalyst with 2-propanol, giving the hydride, followed by 1-hexene coordination. The double bond migration which occurs in the presence of 2-propanol is inferred to proceed by a σ-alkyl mechanism which is different from that in the absence of 2-propanol.