The reaction of tetramethyldiphosphine with butadiene

Abstract

Exclusive 1,4-addition of tetramethyldiphosphine to butadiene occurs slowly above 100°; the reaction is catalysed by azobis(isobutyronitrile). The formation of cis- and trans-1,4-bis(dimethylphosphino)but-2-ene is discussed in terms of a dimethylphosphino-radical addition involving an allyl radical intermediate, the more reactive primary carbon atom of which abstracts Me₂Ṗ from the diphosphine. The isomers have been identified by a comparison of their ¹H n.m.r. spectra with that of the independently prepared trans-compound. The i.r. spectra of the isomers are recorded. Complexes of both isomers with Pt^II are apparently polymeric; they have been separated by use of their solubility difference.