Reactivity of cyclopalladated compounds. 9. Synthesis of trinuclear compounds with a carbonylmetalate anion as a bridging unit between two palladium(II) centers. Crystal and molecular structure of cyclo-[(PdMe2NCH2C6H4)2(.mu.-Cl)(.mu.-Co(CO)4)] and cyclo-[(PdMe2NCH2C6H4)2(.mu.-Cl)[.mu.-Mo(CO)3(.eta.5-C5H5)]]