SYNTHESIS OF ALLYLNICKEL ARYLOXIDES AND ARENETHIOLATES - STUDY OF THEIR DYNAMIC ISOMERIZATION AND 1,3-DIENE POLYMERIZATION ACTIVITY

A new family of allylnickel(II) complexes, [Ni(eta3-allyl)(mu-X)]2 (X = ArO, ArS), have been synthesized by anion metathesis of the sodium o r lithium salts of aryloxides or arenethiolates with[Ni(eta3-allyl)(mu -Br)]2. The complexes are proposed to be dimeric and to consist of a m ixture of cis and trans isomers. A dynamic process rapidly equilibrate s the cis and trans isomers of the pentafluorophenoxide, 2,6-difluorop henoxide, and 3,5-bis(trifluoromethyl)phenoxide complexes on the H-1 N MR time scale. The 2,6-dimethylphenoxide, 2,6-diisopropylphenoxide, 2, 4,6-tris(trifluoromethyl)phenoxide, and pentafluorothiophenoxide compl exes are static at room temperature. A variable-temperature NMR study of the 3,5-bis(trifluoromethyl)phenoxide complex provided activation e nthalpy and entropy values of 12.9 kcal/mol and -6.6 cal/(K mol), resp ectively. Allyl rotation or cleavage of one of the mu-X bridges is pro posed as the mechanism for the isomerization. The pentafluorophenoxide , 3,5-bis(trifluoromethyl)phenoxide, and 2,4,6-tris(trifluoromethyl)ph enoxide complexes initiate the rapid polymerization of 1,3-cyclohexadi ene and 1,3-butadiene to form high-molecular weight, 1,4-linked polyme rs.