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C-H Activation Reactions of Ruthenium N-Heterocyclic Carbene Complexes: Application in a Catalytic Tandem Reaction Involving C-C Bond Formation from Alcohols


Reference:

Burling, S., Paine, B. M., Nama, D., Brown, V. S., Mahon, M. F., Prior, T. J., Pregosin, P. S., Whittlesey, M. K. and Williams, J. M. J., 2007. C-H Activation Reactions of Ruthenium N-Heterocyclic Carbene Complexes: Application in a Catalytic Tandem Reaction Involving C-C Bond Formation from Alcohols. Journal of the American Chemical Society, 129 (7), pp. 1987-1995.

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Abstract

The mono NHC complexes Ru(NHC)(PPh3)2(CO)H2 (NHC = IMe4 (1,3,4,5-tetramethylimidazol-2-ylidene, 3); IEt2Me2 (1,3-diethyl-4,5-dimethylimidazol-2-ylidene, 4); ICy (1,3-dicyclohexyl-imidazol-2-ylidene, 5); IiPr2 (1,3-bis(isopropyl)-imidazol-2-ylidene, 6); IPr2 (1,3-bis(propyl)-imidazol-2-ylidene, 7)) were readily prepd. upon heating Ru(PPh3)3(CO)H2 with between 2 and 6 equiv of the appropriate NHC precursor. Reaction of 1,3-bis(isopropyl)-4,5-dimethylimidazol-2-ylidene (IiPr2Me2) with Ru(NHC)(PPh3)2(CO)H2 gave C-H-activated carbene complex Ru(CH2(Me)CIiPrMe2)(PPh3)2(CO)H (9). The Ru hydride N-alkyl heterocyclic carbene complexes were studied as catalysts for a tandem oxidn. Wittig redn. reaction to give C-C bonds from alcs. The C-H-activated carbene complex 9 proves to be the most active precursor catalyzing the reaction of PhCH2OH and Ph3P:CHCN in 3 h at 70 Deg. These results provide (a) a rare case in which N-alkyl carbenes afford higher catalytic activity than their N-aryl counterparts and (b) a novel example of the importance of NHC C-H activation in a catalytic cycle. The mol. structures of 6, 7 and 9 were detd. by x-ray crystallog.

Details

Item Type Articles
CreatorsBurling, S., Paine, B. M., Nama, D., Brown, V. S., Mahon, M. F., Prior, T. J., Pregosin, P. S., Whittlesey, M. K. and Williams, J. M. J.
DepartmentsFaculty of Science > Chemistry
RefereedYes
StatusPublished
ID Code4622

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