An investigation of the asymmetric synthesis of 3‐phenyl‐1‐butene by the Grignard cross‐coupling reaction is presented. The reaction is catalysed by nickel complexes of bisphosphane and 3‐diphenylphosphanylpyrrolidine‐type ligands. A comparison of the results obtained with our P,N monophosphane ligands with those obtained with the most effective known amino acid derived P,N ligands shows a similar enantioselectivity but an inverse sense of optical induction. An X‐ray structural analysis of the 1‐phenylethyl Grignard compound is reported. Quantitative analysis and the determination of enantiomeric composition of the catalytic samples is accomplished using a novel enantioselective GLC separation. Compared to the popular model reaction that uses a chloride‐containing Grignard compound and vinyl bromide as starting compounds, we obtain improved enantioselectivities of P,N monophosphane catalysts by substituting vinyl bromide with vinyl chloride. With two of the new P,N ligands we find a nonlinear dependence of enantioselectivity on the enantiomeric purity of the ligands (asymmetric amplification). Catalytic results subject to such nonlinear effects show a dependence on the ligand to nickel ratio.
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Nagel et al. (1997) studied this question.