Transfer semihydrogenation of alkynes catalyzed by a zero-valent palladium N-heterocyclic carbene complex

(Chemical Equation Presented) Beyond Lindlar and without hydrogen: Transfer hydrogenation of internal alkynes catalyzed by a palladium(0) catalyst containing an N-heterocyclic carbene ligand gives Z alkenes without over-reduction to alkanes (see scheme). Contrary to most transfer hydrogenations, ketones are not reduced. As such, this is the first catalyst that shows excellent stereo- and chemo-selectivity for the semihydrogenation of alkynes without the need for hydrogen gas. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.