Interference by phosphine decomposition in oxidative additions of aryl halides to methyl-, and trimethylsilyl-tris(triphenylphosphine)cobalt

The oxidative addition of aryl halides, ArX, to [Ph₃P]₃CoCH₃ yield ArAr and ArCH₃ when Ar = 4-CH₃C₆H₄, but exclusively ArCH₃ for 1- and 2-bromo-naphthalene and 4-bromobiphenyl. Decomposition of the phosphine ligand in [Ph₃P]₃CoCH₃ interfers with these reactions to varying extents depending on the relative rates of the reactions; ArCl mostly gives PhPh with some ArPh and ArAr; ArI gives mostly ArAr; ArBr shows intermediate behaviour. Other cobalt compounds such as [Ph₃P]₃CoSi[C₃]₃, [Ph₂PCH₃]₃CoCH₃, [Ph₂PCH₃]₃CoPh and [Ph₂PGe(CH₃)₃]₃CoCH₃ and several other organic halides examined show a low activity in the oxidative addition.