Niobium complexes with terdentate diphosphino- and diamino-amido ligands. Crystal sturcture of [{NbCl3[N(CH2CH2PMe2)2]}2]·C 6H5Me

Abstract

The reaction of [NbCl₄(thf)₂](thf = tetrahydrofuran) with bis (tertiary phosphinoethyl) amides Li-[N(CH₂CH₂PR₂)₂](R = Me or Prⁱ) resulted in the formation of new niobium dialkylamides. The specific complexes generated depend on the stoichiometry of the reaction and the bulk of the tertiary phosphine substituents. Thus, with the bulky diisopropylphosphino function, monomeric paramagnetic mono- and bis-ligand complexes are obtained, [NbCl₃{N(CH₂CH₂PPrⁱ₂)₂}] and [NbCl₂{N(CH₂CH₂PPrⁱ₂)₂}₂]. However with the less sterically encumbered dimethylphosphino function only the diamagnetic dinuclear complex, [{NbCl₃[N(CH₂CH₂PMe₂)₂]}₂], can be isolated; its stucture shows equivalent bridging terdentate amide ligands with two bridging chlorides for each dimeric unit resulting in eight-co-ordinate niobium atoms. In contrast, the bis(2-diethylaminoethyl) amide Li[N(CH₂CH₂NEt₂)₂], an analogue of the smaller phosphine, again only gave rise to paramagnetic monomeric derivatives.