Reactions of carbenes and photoexcited ketones with phosphorus compounds

The photoinduced reactions of aromatic carbonyl compounds and diaryldiazomethanes with phosphorus derivatives were investigated by EPR and laser flash photolysis techniques. Triplet ketones reacted with tetraethyl pyrophosphite via a mechanism akin to a homolytic dieplacement ( SH~p)ro cess at an almost diffusion controlled rate (km = (7.96 * 0.04) X l@ M-' for benzophenone). Triplet benzophenone reacted very rapidly with tetraphenyldiphosphine (km = 2 x lo8 M-' s-' ), Tetraethyl pyrophosphite also underwent homolytic attack by triplet diphenylcarbene (km = (7.4 * 0.7) X los M-' s-') to give a diradical intermediate (or transition state) which, by @-fragmentationg, ave Ph&OP(O)(OEt),. Product studies supported the proposed mechanism. In contrast with diphenylcarbene, fluorenylidene appeared to react via a nonradical mechanism.