Synthesis of ruthenium-olefin complexes as models of olefin metathesis reaction intermediates

The development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis has been reported recently. Upon addn. of the ligand precursor 1,2-divinylbenzene to (H2IMes)(py2)(Cl)2Ru=CHPh (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. Based on 1H NMR spectroscopy expts. and X-ray crystallog. anal., these complexes are assigned as side-bound isomers in which the olefin and H2IMes ligands are coordinated cis to each other. Exploration of the generality of these observations through variation of the N-heterocyclic carbene ligand and the ligand precursor and will be presented.