The first example of manganese catalyzed semihydrogenation of internal alkynes to (Z)-alkenes using ammonia borane as a hydrogen donor is reported. The reaction is catalyzed by a pincer complex of the earth abundant manganese(II) salt in the absence of any additives, base or super hydride. The ammonia borane smoothly reduces the manganese pre-catalyst [Mn(II)-PNP][Cl]2 to the catalytically active species [Mn(I)-PNP]-hydride in the triplet spin state. This manganese hydride is highly stabilized by complexation with the alkyne substrate. Computational DFT analysis studies of the reaction mechanism rationalizes the origin of stereoselectivity towards formation of (Z)-alkenes.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: L.M.A. and L.C., acknowledge King Abdullah University of Science and Technology (KAUST) for support. Gratitude is also due to the KAUST Supercomputing Laboratory using the supercomputer Shaheen II for providing the computational resources.