Acid-Catalyzed Dehydrocoupling of Phosphines.

A new strategy for transition-metal-free, Bro̷nsted acid-catalyzed dehydrocoupling of P-H bonds in organophosphorus compounds is described. Using para-benzoquinones as hydrogen acceptors, this method enables room-temperature coupling of primary and secondary phosphines to form P-P-bonded products. Ortho-phosphinophenol (PP) and ortho-diphosphinobenzene (DPB) are efficiently converted to the heterocyclic dimers [C6H4P(O)]2 (DBODP) and [C6H4P(PH)]2 (DBTP), respectively, in the presence of catalytic quantities of strong Bro̷nsted acids (or AlCl3) and 2,5-di-tert-butyl-1,4-benzoquinone (tBuBQ). DBODP and its ditungsten pentacarbonyl adduct were structurally characterized. The scope of the process extends to representative primary and secondary phosphines, and combined experimental/computational analyses support a mechanism in which acid activation of the quinone promotes hydride abstraction from phosphorus to generate a phosphinophosphenium intermediate that undergoes P-P bond formation and closes the catalytic cycle. This mild, acceptor-mediated platform complements established transition-metal and main-group approaches to P-P bond construction.