Addition of L = carbon monoxide or aryl isocyanides to the Grubbs second-generation carbene complexes Ru(H(2)IMes)(CHR)(PCy3)Cl-2 (H(2)IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene; R = Ph, Me, H, CH=CMe2) triggers carbene insertion into an aromatic ring of the N-heterocyclic carbene supporting ligand, forming Ru(l-mesityl-3-(-7'-R-2',4',6'-trimethylcycloheptatrienyl)-4,5-dihydroim idazol-2-ylidene)L2(PCY3)CI2. Insertions are also promoted for other PR3 substituted complexes by carbon monoxide and aryl isocyanides, and for the phosphine-free Hoveyda-Blechert complex Ru(H21Mes)(CH(i-PrOC6H4))CI2 by aryl isocyanicles 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 (PPh3) and carbene (CH(OC6H4-p-NO2) ligands are both present. Insertion depends on the added ligand, the carbene substituent, and to a lesser degree on the PR3 ligand trans to the N-heterocyclic carbene.