The photo- and thermal chem. of the heterobimetallic fulvalene (Fv) complex Fv[W(CO)3Me][Rh(CO)2] (1) was investigated, and compds. Fv(CO)2MeWRh(CO)[m-CO] (2), Fv(CO)3WRh(CO)Me (3), and Fv(CO)3WRh(CO)C(O)Me (4) were characterized. Reaction mechanisms were studied by labeling expts. using 13CO and by analogy to the Mo-Rh system. The complexes Fv(CO)3MoRh(CO)C(O)Me (7) and Fv(CO)3MoRh(CO)Me (8) were characterized. Reaction of 3 and 4 with PMe3 gave the zwitterionic species Fv[W(CO)3][Rh(PMe3)2Me] (16) and Fv[W(CO)3][Rh(PMe3)2C(O)Me] (17), resp. An excess of PMe3 led to the mononuclear compds. FvRh(PMe3)2Me (18) and FvRh(PMe3)2C(O)Me (19). The latter was reacted with Mo(CO)3(EtCN)3 to give zwitterionic Fv[Mo(CO)3][Rh(PMe3)2C(O)Me] (20). The x-ray structures of the acyl complexes 4 and 17 were detd.