ELECTROCHEMICAL SYNTHESIS AND REACTIVITY OF CARBONATO-NIOBOCENE COMPLEXES

The addition of the CO32- dianion to the electrogenerated species Nb(e ta(5)-C(5)H(5)RR')(2)Cl (2: R = H, R' = SiMe(3); 2': R = R' = SiMe(3)) gives in ca. 50% yields the anionic carbonate niobium(III) complex [N b(eta(5)-C(5)H(3)RR')(2)(O (C) over bar(O)O-O,O')](-) (3: R = H, R' = SiMe(3); 3': R = R' = SiMe(3)) which are oxidized electrochemically to the corresponding paramagnetic niobium(IV) complex [Nb(eta(5)-C(5)H(3 )RR')(2)(OC(O)O-O,O')] (5: R = H, R' = SiMe(3); 5': R = R' = SiMe(3)). These paramagnetic derivatives have been characterized by ESR and IR spectroscopy. Mechanistic aspects concerning the formation of 3 and 3' are discussed. 3 can also be obtained from two-electron reduction of Nb(eta(5)-C(5)H(4)SiMe(3))(2)(O)Cl, 4, in the presence of carbon dioxi de. The addition of the formate anion HCO2- to 3 gives the formato com plex Nb(eta(5)-C(5)H(4)SiMe(3))(2)(OC(O)H-O,O') 6.