Nickel catalysed cross-coupling reactions of grignard reagents with di-, tri- and polychlorobiphenyls

Abstract

In the presence of catalytic amounts of NiCl 2(dppp) (dppp = bis(diphenylphosphino)propane), alkyl and aryl Grignard reagents RMgX (X = Br, I) readily undergo cross-coupling reactions with 4,4'-dichloro-biphenyl ( 1) under mild conditions to give dialkylated products. The reactivity increases in the order R = Me < Et < n-Bu < Ph. AlMe 3 and MgMe 2 are ineffective, while n-BuLi as the alkylating agent or 4,4'-dibromobiphenyl instead of the chloro analogue gives mixtures of alkylation and reduction products. Analogous palladium complexes are inactive as catalysts. 3,5,4'-Trichlorobiphenyl is peralkylated in high conversion and selectivity; the initial alkylation step is slower than subsequent steps, and even at incomplete conversion the completely dechlorinated product predominates. For commercial PCB mixtures (Aroclor 1242, 42% Cl) up to 52% dechlorination was observed under these conditions.