A sterically demanding nucleophilic carbene: 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Thermochemistry and catalytic application in olefin metathesis

The sterically demanding nucleophilic carbene ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2 (IPr, 4) has been synthesized. The reaction of [Cp*RuCl](4) (5; Cp* = eta*-C5Me5) with this ligand affords a coordinatively unsaturated Cp*Ru(IPr)Cl (6) complex. Solution calorimetric results in this system provide information concerning the electron donor properties of the carbene ligand. Steric parameters associated with this ligand are determined from the X-ray crystal structure study. The carbene ligand reacts with RuCl2(=C(H)Ph)(PCy3)(2) (1) to yield a mixed carbene-phosphine ruthenium complex RuCl2(=C(H)Ph)(IPr)(PCy3) (9). A single-crystal X-ray diffraction study has been performed on 9. The thermal stability of 9 has been studied at 60 degrees C and its catalytic activity has been evaluated for the ring closing metathesis of diethyldiallylmalonate. (C) 2000 Elsevier Science S.A. All rights reserved.