Syntheses and spectroscopic studies of new cobalt(I) complexes

The new Co(I) complexes [Me3SnCo(Co)3L] (L = PPh3, P(OPh)3, AsPh3) are prepared by reductively cleaving the dimers [Co(Co)3L]2 on a sodium amalgam, followed by the addition of Me3SnCl. A synthetic procedure is developed to prepare and purify these compounds on a large scale. A previous report that [Co(Co)3AsPh3]2 cannot be reductively cleaved without decomposition is proved wrong. The new products prove sufficiently stable to enable them to be studied by ir, nmr (1H, 13C[1H], 119Sn[1H]) and mass spectroscopy. The compounds [Me3SnCo(Co)3L] (L PPh3, P(OPh)3, AsPh3) are shown to be non-susceptible towards nucleophilic substitution. Attempted displacement of a carbonyl ligand by an isocyanide ligand (using an excess of the latter) after treatment with the labilising agent Me3No, leads to a variety of products of which only the major one can be identified as trans-[Co(CNR)3L2][PF6] (R = t-Bu, Ph, 2,6-dimethylphenyl; L = PPh3, P(OPh)3, AsPh3). Except for the case where R = t-Bu, L = PPh3, the products are extremely unstable oils and cannot be characterised properly. The new Co(I) bis(phosphine) complexes are prepared by reacting dppm (bis(diphenylphosphino)methane) and dppe (bis(diphenylphosphino)ethane) with [(π-RC3H4)Co(Co)3] (R = H, Me). The reaction with dppm leads to the isolation of [(π-RC3H4)Co(Co)2(η1-dppm)] (R = H, Me) which are the first examples of Co(I) complexes with a monodentate dppm ligand. These extremely air-sensitive compounds are moderately stable and do not decompose below -20 deg C in the solid state. The reaction with dppe results in the formation of the bridged dimers [(π-RC3H4)Co(Co)2]2(μ-dppe) (R = H, Me) which are stable at room temperature. The dppm as well as the dppe compounds are studied with ir and nmr (1H, 13C[1H], 31P[1H]) spectroscopy and prove not to be fluxional. 19 figs., 30 tabs., 98 refs