New decomposition pathways for formyl complexes of ruthenium(II)

Abstract

The preparation of trans-[Ru(CHO)(CO)(dppb)₂][SbF₆][dppb = 1,2-bis(diphenylphosphino)benzene] from hydridic reduction of trans-[Ru(CO)₂(dppb)₂][SbF₆]₂ is described. The formyl complex decomposes with first-order kinetics (t_½= 28 min) at 30 °C to give exclusively trans-[RuH(CO)(dppb)₂][SbF₆]. Detailed studies of the decomposition reaction including the observation of initiation of free-radical polymerization of methyl methacrylate during the reaction lead to the postulation of rate-determining homolytic cleavage of the Ru–CHO bond. The low rate of initiation of polymerization, together with the high isotope effect for the decomposition (k_H/k_D= 2.3) and the failure to observe cross-over products during co-decomposition of trans-[Ru(¹³CHO)(¹³CO)(dppb)₂][SbF₆] and trans-[Ru(CDO)(CO)(dppb)₂][SbF₆], lead to the conclusion that another decomposition pathway, involving concerted H migration and CO loss in a six-co-ordinate complex, operates. These results are compared with those obtained for trans-[Ru(CHO)(CO)(dppe)₂][SbF₆][dppe = 1,2-bis(diphenylphosphino)ethane].