Broadly Accessible and Highly Active Hydrophosphination Catalysis With Simple Calcium Compounds in DMSO Solution.

Abstract

Highly earth-abundant and simple calcium precatalysts are reported that address the long-standing challenge of broad scope in hydrophosphination catalysis. With more than 120 examples of hydrophosphination reactions, calcium catalysts are the broadest in scope, including traditional styrene substrates and activated alkenes (Michael acceptors), conjugated dienes, heterocumulenes, alkynes, unactivated alkenes, and even naturally occurring alkenes. Reactions are optimized to maximum conversion, and few examples have less than 90% conversion, making these the most active catalysts to date. Two features contribute to this exceptional scope and activity. The first feature is solvent. Reactions run in DMSO experience a step up in relative rate compared to those in lower-dielectric solvents. Second, more challenging substrates are readily accessed under photocatalytic conditions, a feature already established for calcium precatalysts. The simple precatalyst, Ca(HMDS)₂(THF)₂ (HMDS  =  ^-N(SiMe₃)₂, 1), works for all reactions described, and mechanistic evidence points to a nucleophilic attack for amenable substrates. This work highlights critical advances in hydrophosphination (solvent effects, s-block catalysts, and photocatalysis) to yield an abundant metal (calcium) in green solvent with low energy input to achieve hydrophosphination of the widest scope of substrates under operationally simple conditions.