Model compounds of ruthenium-alkene intermediates in olefin metathesis reactions

The development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis is reported. Upon addn. of 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 another. Characterization of these complexes as well as other Ru-alkene adducts bearing NHCs will be presented.