Catalytic reactions involving butadiene: III. Oligomerisation with cationic bis(triphenylphosphine)(η3-allyl) complexes

The bis(triphenylphosphine)(η³-crotyl)nickel cation is a catalyst precursor for the oligomerisation of butadiene to cyclic or linear dimers. Polymers and oligomers are also produced in variable amounts. The product distributions depend strongly on the type of solvent used and on the nature of co-catalysts. In the aprotic polar solvent DMF, the starting complex undergoes disproportionation, leading finally to a zerovalent nickel-phosphine catalyst. In protic solvents (alcohols) a cationic hydridonickel-phosphine catalyst is produced, but addition of sodium methoxide induces the formation of the zerovalent nickel-phosphine, therefore accounting for the changes in product selectivities.