Decomposition reactions of square-planar bis-aryl-cobalt(II) complexes

The organocobalt complexes [CoR₂L₂], with (a) L = PEtPh₂ and R = 2,3,5,6- C₆HCl₄, 2,4,6-C₆H₂Cl₃ and 2,6-C₆H₃Cl₂; and (b) R = 2,4,6-C₆H₂Cl₃ and L = PEt₃, PEt₂Ph, $\text{1}\text{2}$ dpe, 3,5-lut and $\text{1}\text{2}$ bipy, have been obtained by reaction of RMgX with [CoCl₂L₂] or by ligand exchange from [CoR₂(PEtPh₂)₂]. The decompositions in benzene and carbon tetrachloride, and under oxidative conditions have been studied. In benzene solutions, the stability decreases with decrease in the number of chlorine atoms in R. A mixture of RH and RR is obtained in a ratio which depends on the nature of L, the configuration of the complex, and the presence of oxidants. The thermal decomposition takes place through a tricoordinate intermediate “CoR₂L”, when L = phosphine, or directly from [CoR₂L₂] when L = amine. The oxidatively induced decomposition takes place through a cobalt(III) intermediate, which gives RR when L = phosphine or RX (X = H, Br) when L = amine. The process is intramolecular in all cases.