Mono- and bis-η-cyclopentadienyl derivatives of niobium and tantalum: improved synthetic routes via trialkyl(cyclopentadienyl)tin reagents

Abstract

The compounds [SnBuⁿ₃(σ-C₅H₄R)](R = H or Me) have been used to prepare the species [MCl₄(C₅H₄R)](M = Nb or Ta, R = H or Me), [TaX₂(η-C₅H₅)₂](X = Cl or Br), and [NbCl₂(η-C₅H₄Me)₂] in very high yields. Using these compounds as starting materials the following products have been prepared [NbCl₄(η-C₅H₄Me)L][L = MeCN, PhCN, P(OMe)₃, or Ph₂PCH₂CH₂PPh₂(dppe)], [Ta(η-C₅H₅)₂H₃], and [Ta(η-C₅H₅)₂Y₂] where Y₂=(SMe)₂ or PhCH₂Cl. Partial hydrolysis of [NbCl₄(η-C₅H₄Me)] gives the compound [{NbCl₃(η-C₅H₄Me)(OH₂)}₂O]. Reduction of [NbCl₄(η-C₅H₅)] with [{AlEtCl₂}₂] in the presence of dppe gives [NbCl₃(η-C₅H₅)(dppe)]·PhMe. This reduces with sodium amalgam in the presence of carbon monoxide giving [Nb(η-C₅H₅)(dppe)(CO)₂] which protonates in acid giving [Nb(η-C₅H₅)(dppe)(CO)₂H][PF₆]. The compounds [Pt{Ta(η-C₅H₅)₂(SMe)₂}₂][PF₆]₂ and [NbBr₃(η-C₅H₅)(dppe)]·PhMe are also described.