Hydrophosphanylation of Alkynes via Magnesium Complexes: Evidence for Ligand Dependency in Structure‐Activity Relationships

Pursuing practical, straightforward, and sustainable methods for forming carbon‐phosphorus bonds is crucial in academia and industry. In this study, we showed that bis(diiminate) based magnesium complexes [L(Mg‐nBu)2] (nBu = n‐butyl) could effectively catalyse the hydrophosphanylation of alkynes resulting in monophosphanylated vinyledene‐ and 1,2‐diphosphanylated alkanes in a stepwise manner. This transformation showcases an excellent atom economy, broad functional group tolerance, and gram‐scale synthesis for organophosphorus compounds. Through controlled experiments and with the support of DFT calculations, we elucidated the reaction mechanism, identifying the active catalytic species and revealing a stepwise hydrophosphanylation process of alkynes. Although complex Mg‐1 showed its potential in this transformation, complexes Mg‐2 and Mg‐3, having ethyl and phenyl spacers, produced a lower yield of hydrophosphanylated products, indicating the role of ligand (spacer) in this catalytic reaction. Further, the activity of Mg‐1 was compared with a monomeric magnesium complex, Mg‐4, and it was found that the performance of the Mg‐4 in alkyne hydrophosphanylation is quite lower than the results obtained by using Mg‐1. This work demonstrated that a dimeric magnesium complex with a suitable spacer can enhance the catalytic activity many folds in the hydrophosphanylation of alkynes.