Chiral-at-Ruthenium Catalyst with Sterically Demanding Furo[3,2-b]pyridine Ligands

A sterically demanding derivative of a previously introduced chiral-at-metal ruthenium(II) catalyst scaffold is introduced. It is composed of two bidentate furo[3,2-b]pyridyl functionalized N-heterocyclic carbene ligands. Their cis-coordination generates helical chirality and a stereogenic ruthenium center. Two additional labile acetonitriles compose the catalytic site which is highly shielded by two 2-(tert-butyl)furo[3,2-b]pyridine moieties. The synthesis of the non-racemic ruthenium catalyst and its catalytic properties for the enantioselective alkynylation of 2,2,2-trifluoroacetophenone and pentafluorobenzaldehyde are reported and compared with sterically less demanding derivatives.