Synthesis, electrochemistry and reactivity of formato– and acetato–niobocene complexes

Abstract

The complex [Nb(η⁵-C₅H₄SiMe₃)₂H₃]1 reacted with CO₂ to give the formato complex [Nb(η⁵-C₅H₄SiMe₃)₂{OC(O)H-O,O′}]2, which can alternatively be prepared from a two-electron reduction of [Nb(η⁵-C₅H₄SiMe₃)₂Cl₂]3 in the presence of formic acid. The reaction of 2 with different π-acids or heterocumulene molecules resulted in opening of the bidentate formate ligand giving rise to the monodentate formato-containing complexes [Nb(η⁵-C₅H₄SiMe₃)₂{OC(O)H-O}L], L = CS₂4, CO 5 or 2,6-Me₂C₆H₃NC 6. On the other hand, [Nb(η⁵-C₅H₄SiMe₃)₂{OC(O)Me-O,O′}]8 was prepared from either the reaction of [Nb(η⁵-C₅H₄SiMe₃)₂Cl]7 with 1 equivalent of Tl(O₂CMe) or from a two-electron reduction of 3 in the presence of acetic acid. The complex [Nb(η⁵-C₅H₄SiMe₃)₂(MeCOCHCOMe-O,O′)]9 can also be isolated from the reaction of 7 with 1 equivalent of Tl(acac)(acac = acetylacetonate). Complex 8 reacted with oxygen to give [Nb(η⁵-C₅H₄SiMe₃)₂O{OC(O)Me-O}]10, and with π-acids or heterocumulenes to give products with a monodentate OC(O)Me ligand, namely [Nb(η⁵-C₅H₄SiMe₃)₂{OC(O)Me-O}L], L = CS₂11, SCNPh 12, PhNCCPhEt 13, MeO₂CCCCO₂Me 14, Bu^tNC 15 or CO 16. The structures of all complexes have been established by spectroscopic methods.