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

A series of ruthenium hydride N-alkyl heterocyclic carbene complexes has been investigated as
catalysts for a tandem oxidation/Wittig/reduction reaction to give CC bonds from alcohols. The CH-activated carbene complex Ru(IiPr2Me2)‘(PPh3)2(CO)H (9) proves to be the most active precursor catalyzing
the reaction of PhCH2OH and Ph3PCHCN in 3 h at 70 °C. 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.