Synthesis of Allylnickel Aryloxides and Arenethiolates: Study of Their Dynamic Isomerization and 1,3-Diene Polymerization Activity
A new family of allylnickel(I1) complexes, [Ni(η^3-+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(η^3-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 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(trifluoromethy1)phenoxide complexes initiate the rapid polymerization of 1,3-cyclohexadiene and 1,3-butadiene to form high-molecular weight, 1,4-linked polymers.
© 1994 American Chemical Society. Received November 1, 1993. We gratefully acknowledge Prof. Robert H. Grubbs for many helpful discussions. The Air Force Office of Scientific Research is acknowledged for providing financial assistance to J.P.C. We thank Dr. Roger Assink and Ralph H. Hunkins at Sandia National Laboratories for providing ^(13)C-CPMAS NMR spectra of poly(CHD). We acknowledge the NSF Chemical Instrumentation Program for providing a low-field NMR spectrometer.
Supplemental Material - om00017a073_si_001.pdf