Reactions of octacarbonyldicobalt with tetraphenyl derivatives of Group 5A, including tetraphenyldibismuthane. Synthesis and crystal and molecular structure of tricarbonyl(diphenylbismuthido)(triphenylphosphine)cobalt(I), [Co(BiPh2)(CO)3(PPh3)]

Abstract

Tetraphenyldibismuthane reacts with [Co₂(CO)₈] to give the product of oxidative addition, [Co(BiPh₂)(CO)₄], which was isolated as its triphenylphosphine adduct, [Co(BiPh₂)(CO)₃(PPh₃)]. [Co(BiPh₂)(CO)₃(PPh₃)] crystallises in the orthorhombic space group Pbca, with a= 26.105(13), b= 21.066(10), c= 10.845(3)Å, Z= 8, R= 0.0522, and R′= 0.0497. The molecular structure consists of discrete [Co(BiPh₂)(CO)₃(PPh₃)] units, the geometry around cobalt being that of a distorted trigonal bipyramid with three equatorial carbonyl groups and the BiPh₂ and PPh₃ ligands occupying the axial positions. The reactivity of [Co₂(CO)₈] towards E₂Ph₄ was compared along the series from E = arsenic to bismuth. Oxidative addition (E = Bi) and substitutive oxidative addition (E = As or Sb) reactivity patterns were encountered. No tendency of terminal BiPh₂ to become bridging with CO substitution was observed. The unique behaviour of BiPh₂ as a ligand is explained in terms of the low availability of the second lone pair on bismuth for bonding, in spite of the considerable σ-donation from bismuth to cobalt suggested for terminal BiPh₂ by the i.r. spectra.