The reaction of H 2 with [RP-W(CO) 5] (R = Ph, Me) above 120 °C leads, first, to the secondary diphosphine complex (RPH-PHR)(W(CO) 5) 2 and then to the primary phosphine complex (RPH 2)(W(CO) 5). On the basis of DFT calculations, the mechanism most likely involves the addition of H 2 to the P-W bond, followed by the formation of the radical [RPH-W(CO) 5] • by homolysis of the W-H bond. In the case of [PhNHP-W(CO) 5], the hydrogenolysis takes place at the P-N bond and ultimately produces the secondary diaminophosphine complex ((PhNH) 2PH)(W(CO) 5). © 2011 American Chemical Society.