E- and Z‑Selective Transfer Semihydrogenation of Alkynes Catalyzed by Standard Ruthenium Olefin Metathesis Catalysts

Selective transfer semihydrogenation of alkynes to yield alkenes was achieved with commercial first and second generation Hoveyda–Grubbs catalysts and formic acid as a hydrogen donor. This catalytic system is distinguished by its selectivity and compatibility with many functional groups (halogens, cyano, nitro, sulfide, alkenes). The metathetic activity of the ruthenium catalysts may be utilized in tandem sequences of olefin metathesis plus alkyne reduction.