Exchange reactions and decomposition pathways of organocobalt(II) square-planner complexes

A number of compounds of the type [Co(C₆Cl₅)₂L₂] (L PEtPh₂, PEt₂Ph, PEt₃, py, β-pic, λ-pic, 3,5-lut, or L₂ dpe and bipy) have been prepared by reacting C₆Cl₅MgX with [CoCl₂L₂] or by adding the stabilizing ligand to a solution of "Co(C₆Cl₅)₂". Ligand exchange reactions show that a more basic displaces a less basic ligand. The compounds with L PEt₂Ph, PEt₃, dpe, and bipy remain unaltered in boiling benzene, but when L PEtPh₂ and 3,5-lut, partial decomposition occurs. The decompositions give only C₆HCl₅ when L py, β-pic, λ-pic, and 3,5-lut, but a mixture of C₆H_1+nCl_5n and C₁₂H_nCl_{10 n} is obtained when L PEtPh₂; the coupling occurs after the dissociation of the ligand. Decomposition in benzene in the presence of bromine gives C₆BrCl₅ when L is an amine, but C₁₂H_nCl_10n when L is a phosphine.