[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 Et3N·3HF. 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.

Treatment of [Ru(NHC)(P–P)(CO)H2] (NHC = N-heterocyclic carbene; P–P = xantphos, dppf) with Et3N·3HF affords the corresponding hydride fluoride species [Ru(NHC)(P–P)(CO)HF]. Studies on the interconversion of these two sets of compounds in a cycle for the catalytic hydrodefluorination of aromatic fluorocarbons have been undertaken.Figure optionsDownload as PowerPoint slideResearch highlights
► New ruthenium N-heterocyclic carbene hydride fluoride complexes exist as mixtures of isomers at low temperature.
► These species can be converted to the corresponding dihydride complexes upon treatment with alkysilanes.
► Efforts to establish a catalytic cycle for hydrodefluorination of aromatic fluorocarbons are thwarted by facile intramolecular C–H activation of the NHC ligands.