Chiral NCN Pincer Rhodium(III) Complexes with Bis(imidazolinyl)phenyl Ligands: Synthesis and Enantioselective Catalytic Alkynylation of Trifluoropyruvates with Terminal Alkynes

A series of new chiral C2-symmetrical NCN pincer rhodium(III) complexes with bis(imidazolinyl)phenyl ligands have been conveniently synthesized from easily available materials. The complexes were subsequently applied in the enantioselective addition of terminal alkynes to trifluoropyruvates. With catalyst loading of 1.53.0mol%, the alkynylation of ethyl or methyl trifluoropyruvate with a variety of electronically and structurally diverse terminal alkynes gave the optically active trifluoromethyl-substituted tertiary propargylic alcohols with enantioselectivities of up to >99% ee and high yields. Although good to excellent enantioselectivities (8598% ee) could be achieved only for some of the aliphatic terminal alkynes under the optimized conditions, the enantioselectivities were consistently excellent (94% to >99% ee) in the case of aromatic as well as heteroaromatic alkynes and enynes.