The thermolysis of the phosphinidene complex [Cp*P{W(CO)5}2] (1) in toluene in the presence of tBuCCMe leads to the four-membered ring complexes [[{2-C(Me)C(tBu)}Cp*(CO)W(3-P){W(CO)3}]{4:1:1-P{W(CO)5}WCp*(CO)C(Me)C(tBu)}] (4) as the major product and [[W{Cp*(CO)2}W(CO)2WCp*(CO){1:1-C(Me)C(tBu)}](,3:2:1-P2{W(CO)5}] (5). The reaction of 1 with PhCCPh leads to [[W(CO)2{2-C(Ph)C(Ph)}][(4:1-P{W(CO)5}W{Cp*(CO)2}C(Ph)C(Ph)]] (6). The products 4 and 6 can be regarded as the formal cycloaddition products of the phosphido complex intermediate [Cp*(CO)2WPW(CO)5] (B), formed by Cp* migration within the phosphinidene complex 1. Furthermore, the reaction of 1 with PhCCPh gives the minor product [[{2:1-C(Ph)C(Ph)}2{W(CO)4}2]{,1:1-P{C(Me){C(Me)}3C(Me)}{C(Ph)}{C(Ph)}] (7) as a result of a 1,3-dipolaric cycloaddition of the alkyne into a phosphaallylic subunit of the Cp*P moiety of 1. Compounds 4-7 have been characterized by means of their spectroscopic data as well as by single-crystal X-ray structure analysis.