Hydrophosphination of Styrene and Polymerization of Vinylpyridine: A Computational Investigation of Calcium-Catalyzed Reactions and the Role of Fluxional Noncovalent Interactions

A computational investigation of the intermolecular hydrophosphination of styrene and 2-vinylpyridine, catalyzed by the heteroleptic β-diketiminato-stabilized calcium complex [(PhNC(Me)CHC(Me)NPh)CaPPh2], is presented. Alkene insertion does not proceed via the traditional route as proposed by experimental and theoretical research related to intermolecular hydroamination catalyzed by alkaline earth or lanthanide complexes. In contrast, for the hydrophosphination mechanism, insertion proceeds via outer sphere, conjugative addition where there is no direct interaction of Ca with the vinyl functionality. Following the initial rate-determining alkene insertion, two distinct mechanisms emerge, protonolysis or polymerization. Polymerization of styrene is energetically less favorable than protonolysis, whereas the reverse is determined for 2-vinylpyridine, thereby providing strong evidence of outcomes observed experimentally. The vinylarene ring is important as it allows for preferential coordination of the unsat...