Synthesis of allylnickel aryloxides and arenethiolates. Study of their dynamic isomerization and 1,3-diene polymerization activity

Article abstract of DOI:10.1021/om00017a073

A new family of allylnickel(II) complexes, [Ni(η³-allyl)(μ-X)]₂ (X = ArO, ArS), have been synthesized by anion metathesis of the sodium or lithium salts of aryloxides or arenethiolates with [Ni(η³-allyl)(μ-Br)]₂. The complexes are proposed to be dimeric and to consist of a mixture of cis and trans isomers. A dynamic process rapidly equilibrates the cis and trans isomers of the pentafluorophenoxide, 2,6-difluorophenoxide, and and 3,5-bis(trifluoromethyl)phenoxide complexes on the ¹H NMR time scale. The 2,6-dimethylphenoxide, 2,6-diisopropylphenoxide, 2,4,6-tris(trifluoromethyl)phenoxide, and pentafluorothiophenoxide complexes are static at room temperature. A variable-temperature NMR study of the 3,5-bis(trifluoromethyl)phenoxide complex provided activation enthalpy and entropy values of 12.9 kcal/mol and -6.6 cal/(K mol), respectively. Allyl rotation or cleavage of one of the μ-X bridges is proposed as the mechanism for the isomerization. The pentafluorophenoxide, 3,5-bis(trifluoromethyl)phenoxide, and 2,4,6-tris(trifluoromethyl)phenoxide complexes initiate the rapid polymerization of 1,3-cyclohexadiene and 1,3-butadiene to form high-molecular weight, 1,4-linked polymers.