Exploring Electrophilic Hydrophosphination via Metal Phosphenium Intermediates.

Two Mo(0) phosphenium complexes containing ancillary secondary phosphine ligands have been investigated with respect to their ability to participate in electrophilic addition at unsaturated substrates and subsequent P-H hydride transfer to "quench" the resulting carbocations. These studies provide stoichiometric "proof of concept" for a proposed new metal-catalyzed electrophilic hydrophosphination mechanism. The more strongly Lewis acidic phosphenium complex, [Mo(CO)(PRH)(PR)] (R=Ph, Tol), cleanly hydrophosphinates 1,1-diphenylethylene, benzophenone, and ethylene, while other substrates react rapidly to give products resulting from competing electrophilic processes.