New Phosphinidene Transfer Reagents

Chemists have discovered a simple procedure to make unprotected phosphanorbornadienes, a class of strained phosphorus compounds that has eluded isolation until now (J. Am. Chem. Soc., DOI: 10.1021/ja306902j). The achievement by Alexandra Velian and Christopher C. Cummins of Massachusetts Institute of Technology opens the way to using the phosphanorbornadiene group as a substituent in chemical synthesis. In prior efforts to synthesize phosphanorbornadienes, researchers assumed the molecules’ instability would require protecting the reactive lone pair of electrons on the unsaturated phosphorus atom by coordinating a metal or by forming a phosphine oxide. Velian and Cummins found that wasn’t necessary. They treated bulkily substituted phosphorus dichlorides (RPCl₂) with the reducing agent magnesium anthracene to make unprotected dibenzophosphanorbornadienes (shown). These new compounds may serve as precursors to or transfer reagents for an array of unsaturated phosphorus intermediates known as phosphinidenes, which are phosphorus analogs of carbenes, Cummins says. “Mastering the chemistry of phosphinidenes offers the possibility of easily grafting phosphorus groups onto unsaturated polymeric materials and unsaturated drugs,” notes François Mathey, a phosphorus chemist at Nanyang Technological University, in Singapore.