Trnka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T. - L.; Ding, S.; Day, M. W.; Grubbs, R. H. Synthesis and Activity of Ruthenium Alkylidene Complexes Coordinated with Phosphine and N-Heterocyclic Carbene Ligands. Journal of the American Chemical Society 2003,
125(9), 2546-2558.
Abstract
The prepn. and characterization of a variety of ruthenium complexes coordinated with phosphine and N-heterocyclic carbene (NHC) ligands are reported. Ligand Ph3Tri (2,4-dihydro-2,4,5-triphenyl-3H-1,2,4-triazol-3-ylidene) was prepd. in the form of its MeOH adduct Ph3Tri(H)(OMe) (2,4-dihydro-3-methoxy-2,4,5-triphenyl-3H-1,2,4-triazole) by one-pot condensation of N-phenylbenzamide phenylhydrazone with HC(OEt)3 in the presence of NH4BF4 followed by NaOMe. Its ruthenium complexes (Ph3Tri)Cl2(PCy3)Ru:CHR (1a, R = Ph; 1b, R = CH:CMe2) were prepd. by reacting of (PCy3)2Cl2Ru:CHR with Ph3Tri(H)(OMe). Improved protocol of prepn. of (H2IMes)(PCy3)Cl2Ru:CHPh (2) from ligand-CHCl3 adduct, 1,3-dimesityl-2-(trichloromethyl)imidazolidine, is described. When the prepn. of 2 is carried out in the presence of air oxygen and moisture, only I (4, Mes = 2,4,6-Me3C6H2) could be isolated due to oxidn.-promoted C-H-bond activation and hydrolysis. Bis-imidazolylidene complexes [(H2IMes)(IMes)Cl2Ru:CHPh] (6a, IMes = 1,3-dihydro-1,3-dimesityl-2H-imidazol-2-ylidene) and [(H2IMes)2Cl2Ru:CHPh] (6b) were prepd. by pyridine for carbene substitution in [(H2IMes)Py2Cl2Ru:CHPh]. Some of the prepd. complexes are active olefin metathesis catalysts (RCM and ROMP). Although these catalysts can be prepd. adequately by the reaction of bis(phosphine) ruthenium alkylidene precursors with free NHCs, we have developed an alternative route that employs NHC-alc. or -chloroform adducts as "protected" forms of the NHC ligands. This route is advantageous because NHC adducts are easier to handle than their free carbene counterparts. Crystal structures of 4 and 6a are presented. Other side reactions encountered during the synthesis of new ruthenium alkylidene complexes include the formation of hydrido-carbonyl-chloride derivs. in the presence of primary alcs. and the deprotonation of ruthenium vinylcarbene ligands by KOBut. [on SciFinder(R)]