[Ru(NHC)(P-P)(CO)HF] (NHC=N-heterocyclic carbene; P-P=xantphos, dppf) complexes: Efforts to prepare new hydrodefluorination catalysts

The ruthenium N-heterocyclic carbene (NHC) hydride fluoride complexes Ru(NHC)(P-P)(CO)HF (NHC=ICy (3), IEt2Me2 (5), P-P=xantphos; NHC=ICy (7), P-P=dppf) have been prepared by treatment of the corresponding dihydride complexes [Ru(NHC)(P-P)(CO)H2] (NHC=ICy (2), IEt2Me2 (4) P-P=xantphos; NHC=ICy (6), P-P=dppf) with Et3N3HF. In all cases, the hydride fluoride complexes exist in solution as two conformers or isomers. Although 3, 5 and 7 could be converted back to 2, 4 and 6, respectively, by heating with Et3SiH, efforts to generate a catalytic cycle for the hydrodefluorination of aromatic fluorocarbons by subsequent reaction of Ru(NHC)(P-P)(CO)H2 with C6F6 were prevented by the much more favourable cyclometallation of the carbene ligand.