Synthesis, characterization, and norbornene polymerization of η 3-benzylnickel(II) complexes of N-heterocyclic carbenes

Abstract

Neutral η 1-benzylnickel carbene complexes, [Ni(η 1-CH 2C 6H 5)(I iPr)(PMe 3)(Cl)] ( 3) (I iPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) and [Ni(η 1-CH 2C 6H 5)(SI iPr)(PMe 3)(Cl)] ( 4) (SI iPr = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-ylidene), were prepared by the reaction between [Ni(η 3-CH 2C 6H 5)(PMe 3)(Cl)] and an equivalent amount of the corresponding free N-heterocyclic carbene. The preparation of η 3-benzylnickel carbene complexes, [Ni(η 3-CH 2C 6H 5)(I iPr)(Cl)] ( 5) and [Ni(η 3-CH 2C 6H 5)(SI iPr)(Cl)] ( 6) were carried out by the abstraction of PMe 3 from 3 and 4 by the treatment of B(C 6F 5) 3. The treatment of AgX on 5 and 6 produced the anion-exchanged complexes, [Ni(η 3-CH 2C 6H 5)(NHC)(X)] ( 7, NHC = I iPr, X = O 2CCF 3; 8, NHC = I iPr, X = O 3SCF 3; 9, NHC = SI iPr, X = O 2CCF 3; 10, NHC = SI iPr, X = O 3SCF 3). The solid state structures of 3 and 10 were determined by X-ray crystallography. The η 3-benzyl complexes of I iPr ( 5, 7, and 8) alone, in the absence of any activators such as borate and MAO, showed good catalytic activity towards the vinyl-type norbornene polymerization. The catalyst was thermally robust and the activity increases as the temperature rises to 130 °C.