Synthesis and dynamic behaviour of a dimeric ruthenium benzylidene complex bearing a truncated N-heterocyclic carbene ligand

Described herein is the reaction of the first-generation Grubbs catalyst RuCl2(PCy3)(2)(-CHPh) (GI) with free IMe4 (1,3,4,5-tetramethylimidazol-2-ylidene), in which the N-mesityl groups commonly present in Ru-NHC metathesis catalysts are truncated to N-Me (NHC = N-heterocyclic carbene). Treatment of GI with IMe4 (1-2.1 equiv) effects displacement of both PCy3 ligands, but does not terminate at the monoruthenium species RuCl2(IMe4)(2)(= CHPh) Ru-3. Instead, dimerization occurs to afford [Ru-2(mu-Cl)(3)(IMe4)(4)(=CHPh)(2)] Cl Ru-4, the structure of which was confirmed by crystallographic analysis. A molecular dynamics study of Ru-4 indicated rapid rotation of both the NHC and the benzylidene ligands, accounting for the observation of multiple benzylidene signals in the solution 1H NMR spectrum of Ru-4. (C) 2017 Elsevier B.V.All rights reserved.