Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal-Ligand Cooperativity Enables Selective Alkyne Hydrogenation.

A new series of bifunctional Ru complexes with pendent Lewis acidic boranes were prepared by late-stage modification of an active hydrogen-transfer catalyst. The appended boranes modulate the reactivity of a metal hydride as well as catalytic hydrogenations. After installing acidic auxiliary groups, the complexes become multifunctional and catalyze the cis-selective hydrogenation of alkynes with higher rates, conversions, and selectivities compared with the unmodified catalyst.