Abstract: Phosphaalkenes such as 1 and 2 [(2, 6-dimethylphenyl)(diphenylmethylene) phosphine] are quite reactive in many respects but are rather sluggish in their reaction with oxygen and sulfur. Primary intermediates in the reactions of 2 are its oxide, the phosphene 6 (or the sulfur analogue 18, respectively), and the phosphinidene oxide 10 (or its sulfur analogue 19), which together with (thi0) benzophenone is formed by oxidative cleavage of ...