Selected reactions of cobalt carbonyl complexes placed under vacuum conditions

There are two main equilibrium reactions involving Co-2(CO)(8) which illustrate the sensitivity of the chemico-physical behavior of cobalt carbonyls to small changes in their immediate environment, such as change in CO partial pressure, addition of hydrogen, presence of a base or application of a vacuum. The first, is the equilibrium reaction of Co-2(CO)(8) with H-2 to yield HCo(CO)(4). Both the kinetics and the equilibrium of this reaction are strongly influenced by the relative pCO in the system. The second is the equilibrium decomposition of Co-2(CO)(8) to Co-4(CO)(12). This work examines these reactions and the behavior of some cobalt carbonyls under more drastic conditions, such as vacuum or partial vacuum conditions. The results are discussed as to their possible relevance and role in the mechanism of the hydroformylation (OXO) reaction. Specifically, the formation of the trinuclear cobalt carbonyl hydride, HCo3(CO)(9), is described and analyzed under conditions which may arise in the semi-stoichiometric OXO reaction, i.e. at low pCO or in the absence of CO. The consequences of the presence of small quantities of HCo3(CO)(9) in solution on the mechanism of the semi-stoichiometric OXO reaction are discussed. In addition, the decomposition reaction of Co-2(CO)(8) to Co-4(CO)(12) is examined in the absence of CO, and some pertinent, previously unreported, thermodynamic parameters are calculated. (C) 1999 Elsevier Science S.A. All rights reserved.