DECOMPOSITION OF (NiRR'L2) COMPLEXES INDUCED BY BROMINE OR ANODIC OXIDATION

Article abstract of DOI:10.1016/0022-328X(86)80013-4

A study has been made of the decomposition of the compounds t-(NiRR'L2) (L=PMe2Ph and PEt3; R=aryl or vinyl groups) and (Ni(mes)(o-tol)bipy) (mes=mesityl) oxidatively induced either by electrochemical means or by bromine.No organometallic compound of Ni(III) was isolated in the above reactions, but a pentacoordinate intermediate of Ni(III) is postulated.Breakdown takes place readily after the Ni(III) intermediate is formed.If the decomposition is induced is induced electrochemically, the intermediate decomposes giving only the coupling product R-R'.When bromine is used as the oxidizing agent, the Ni(III) intermediate is only formed if coordination to the central atom is allowed by the volume of the ligands.Thus, (Ni(C2Cl3)(mes)(PMe2Ph)2) dos not decompose at all, and only (Ni(C2Cl3(mesBr2)(PMe2Ph)2) is obtained.The intermediate ' Ni(III)RR'BrL2' undergoes reductive elimination to give R-R', RBr and R'Br.The formation of the products R-R'is increasingly favoured the greater the electronegativity of the organic ligands.The reductive elimination giving RBr takes place more readily the greater the electronegativity of the organic ligand R.The product of the reductive elimination reaction is 'Ni(I)Br', 'Ni(I)R', or 'Ni(I)R'', which in the presence of bromine give Ni(2+), (NiBr(RBr)L2), phosphonium salts, RBr, and R'Br.