pentacarbonyltungsten complex and dimethyl acetylenedicarboxylate can be used as a precursor for the methylphosphaketene tungsten complex under UV irradiation at room temperature. Under these conditions, the phosphaketenecomplex easily loses CO to give the methylphosphinidene complex. Highly reactive alcohols and primary alkylamines trap both the phosphaketene and the phosphinidene complexes. Less reactive