SYNTHESIS, ELECTROCHEMISTRY AND REACTIVITY OF FORMATO-NIOBOCENE AND ACETATO-NIOBOCENE COMPLEXES

The complex [Nb(eta(5)-C(5)H(4)SiMe(3))(2)H-3] 1 reacted with CO2 to g ive the formato complex [Nb(eta(5)-C(5)H(4)SiMe(3))(2){OC(O)H-O,O'}] 2 , which can alternatively be prepared from a two-electron reduction of [Nb(eta(5)-C(5)M(4)SiMe(3))(2)Cl-2] 3 in the presence of formic acid. the reaction of 2 with different pi-acids or heterocumulene molecules resulted in opening of the bidentate formate ligand giving rise to th e monodentate formato-containing complexes [Nb(eta 5-C(5)H(4)SiMe(3))( 2){OC(O)H-O}L], L = CS2 4, CO 5 or 2,6-Me(2)C(6)H(3)NC 6. On the other hand; [Nb(eta(5)-C(5)H(4)SiMe(3))(2){OC(O)Me-O,O'}] 8 was prepared fr om either the reaction of [Nb(eta(5)-C(5)H(4)SiMe(3))(2)Cl] 7 with 1 e quivalent of TI(O(2)CMe) or from a two-electron reduction of 3 in the presence of acetic acid. The complex [Nb(eta(5)-C(5)H(4)SiMe(3))(2)(Me COCHCOMe-O,O')] 9 can also be isolated from the reaction of 7 with 1 e quivalent of Tl(acac) (acac = acetylacetonate). Complex 8 reacted with oxygen to give [Nb(eta(5)-C(5)H(4)SiMe(3))(2)O{OC(O)Me-O}] 10, and wi th pi-acids or heterocumulenes to give products with a monodentate OC( O)Me ligand, namely [Nb(eta(5)-C(5)H(4)SiMe(3))(2){OC(O)Me-O}L], L = C S2 11, SCNPh 12, PhNCCPhEt 13, MeO(2)CC=CCO(2)Me 14, Bu(t)NC 15 or CO 16. The structures of all complexes have been established by spectrosc opic methods.