Monophenylation accompanied by partial reduction of 1,1-dihalogeno-2-phenyl-1-alkenes in the presence of a nickel-phosphine complex

Reaction of 1,1-dihalogeno-2-phenyl-1-alkenes (I) with phenylmagnesium bromide in the presence of NiCl2(dppp) in THF has been studied. Mono-cross-coupling accompanied by partial reduction gave (E)-1,2-diphenyl-1-alkenes (III) as the major products. Use of a large excess of Grignard reagent increased the yields of III and the (Z)-isomers (II), with a decrease in the yield of double cross-coupling products, 1,1,2-triphenyl-1-alkenes (IV). The highest ratio of the sum of the yields of the monophenylation products to the yield of the double cross-coupling product, (II + III)/IV = 36.5, was found for the reaction of PhMgBr with 1,1-dibromo-2-phenylpropene (Ib) in a 12.0/1 molar ratio. A possible reaction mechanism is described.