Ligand-Promoted Carbene Insertion into the Aryl Substituent of an <i>N</i>-Heterocyclic Carbene Ligand in Ruthenium-Based Metathesis Catalysts

Abstract

Addition of L = carbon monoxide or aryl isocyanides to the Grubbs second-generation carbene complexes Ru(H(2)IMes)(CHR)(PCy(3))Cl(2) (H(2)IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene; R = Ph, Me, H, CH=CMe(2)) triggers carbene insertion into an aromatic ring of the N-heterocyclic carbene supporting ligand, forming Ru{1-mesityl-3-(-7'-R-2',4',6'-trimethylcycloheptatrienyl)-4,5-dihydroimidazol-2-ylidene}L(2)(PCy(3))Cl(2). Insertions are also promoted for other PR(3) substituted complexes by carbon monoxide and aryl isocyanides, and for the phosphine-free Hoveyda-Blechert complex Ru(H(2)IMes)(CH(i-PrOC(6)H(4)))Cl(2) by aryl isocyanides and small phosphites but only after initial displacement of the coordinated ether. Heteroatom substituted carbenes do not undergo CO-promoted insertion unless poorer electron donor phosphine (PPh(3)) and carbene (CH(OC(6)H(4)-p-NO(2)) ligands are both present. Insertion depends on the added ligand, the carbene substituent, and to a lesser degree on the PR(3) ligand trans to the N-heterocyclic carbene.