Selective hydrogenation of the CC-triple bond in PhCCPh by tris(triphenylphosphine)cobalt activated NaBH₄; deuterium tracing experiments

Sodium borohydride does not on its own react with diphenylacetylene, but becomes an active hydrogenation agent in the presence of (Ph₃P)₃CoCl. Unlike systems involving other catalysts, e.g. cobalt halides in ethanol, this is a selective reagent for hydrogenation in which an alkyne is selectively hydrogenated to cis and trans alkenes. The role of NaBH₄ in this hydrogenation and isomerization has been studied by deuterium labelling. A brief comparison is made with other active catalysts in this system like (Ph₃P)₃CoBH₄.