Ruthenium Catalyzed Hydroboration of Terminal Alkynes to Z-Vinylboronates

The nonclassical ruthenium hydride pincer complex Ru(PNP)(H)(2)(H(2)) 1 (PNP = 1,3-bis(di-tert-butyl-phosphinomethyl)pyridine) catalyzes the anti-Markovnikov addition of pinacolborane to terminal alkynes yielding Z-vinylboronates at mild conditions. The complex Ru(PNP)(H)(2)(HBpin) 2 (HBpin = pinacolborane), which was identified at the end of the reaction and prepared independently, is proposed as the direct precursor to the catalytic cycle involving rearrangement of coordinated alkyne to Z-vinylidene as a key step for the apparent trans-hydroboration.