Acid-free nickel catalyst for stereo- and regioselective hydrophosphorylation of alkynes: Synthetic procedure and combined experimental and theoretical mechanistic study

The nickel catalyst prepared in situ from nickel bis(acetylacetonate) [Ni(acac) 2 ] precursor and bis(diphenylphosphino)ethane (DPPE) ligand has shown excellent performance in the hydrophosphorylation of alkynes. Markovnikov-type regioselective addition to terminal alkynes and stereoselective addition to internal alkynes were carried out with high selectivity without an acidic co-catalyst (in contrast to the palladium/acid catalytic system). Various H-phosphonates and alkynes reacted smoothly in the developed catalytic system with up to 99% yield. The mechanisms of catalyst activation and C-P bond formation were revealed by experimental (NMR, ESI-MS, X-ray) and theoretical (density functional calculations) studies. Two different pathways of the alkyne insertion in the coordination sphere of the metal are reported for the first time.