NIOBIUM AND TANTALUM COMPLEXES WITH P2 AND P4 LIGANDS

The photolysis of [Cp''Ta(CO)4] 1 (Cp'' = C5H3(t)Bu2-1,3) and P4 affor ds [Cp''(CO)2Ta(eta4-P4)] 2, [{Cp''(CO)Ta}2(mu-eta2:2-P2)2] 3 and [Cp3 ''(CO)3Ta3(P2)2] 4. In a photochemical reaction 2 and [CpNb(CO)4] 5 f orm [{Cp(CO)Nb} {Cp''(CO)Ta}(mu-eta2:2-P2)2] 6 and {Cp*(CO)2Nb}{Cp*Nb }{Cp''(CO)Ta}(mu3-eta2:1:1-P2)2] 7, a compound with the novel mu3-eta2 :1:1-P2-coordination mode. The reaction of 2 and [CpCo(C2H4)2] 8 lead s to [{CpCo} {Cp''(CO)Ta}(mu-eta2:2-P2)2] 9, a heteronuclear complex with an ''early'' and a ''late'' transition metal. Complexes 2, 3, 7 a nd 9 have been further characterized by X-ray structure analyses.