On the structure of tetracoordinated organocobalt complexes of the type [CoR₂L₂]

A series of square-planar organocobalt complexes of the type [CoR₂L₂] (R = 2,3,4,6-C₆,HCl₄ and 2,3,6-C₆H₂Cl₃, L = PEtPh₂, PEt₂Ph, and PEt₃; R = 2,3,5,6-C₆HCl₄, and 2,6-C₆H₃Cl₂, L = PEt₂Ph, PEt₃, and 1 2dpe) have been prepared in which the electronegativities of the ligand R vary progressively. The reaction of o-C₆H₄ClMgBr with [CoCl₂L₂] (L = PEtPh₂ PEt₂Ph, γ-pic or 1 2bipy) did not give air stable compounds at room temperature, but the solutions obtained at -78°C appear to contain square-planar species for L = PEtPh₂, PEt₂Ph, and γ-pic, and tetrahedral for L₂ = bipy. The tendency towards square-planar or tetrahedral structures for the compounds [CoR₂L₂] depends on the following factors in order of importance: (i) when the neutral ligand is a phosphine a square-planar structure is adopted; (ii) when L is an aromatic amine, bulky ortho substituents on R favour a square-planar structure; and (iii) a tetrahedral geometry is favoured by bidentate amine ligands. The electronegativity of the organic group R seems to be less important.