NIOBIUM COMPLEXES WITH TERDENTATE DIPHOSPHINO-AMIDO AND DIAMINO-AMIDOLIGANDS - CRYSTAL-STRUCTURE OF L3[N(CH(2)CH(2)PME(2))(2)])2]CENTER-DOT-C(6)H(5)ME

The reaction of [NbCl4(thf)(2)] (thf = tetrahydrofuran) with bis(terti ary phosphinoethyl)amides Li-[N(CH(2)CH(2)PR(2))(2)] (R = Me or Pr) re sulted in the formation of new niobium dialkylamides. The specific com plexes generated depend on the stoichiometry of the reaction and the b ulk of the tertiary phosphine substituents. Thus, with the bulky diiso propylphosphino function, monomeric paramagnetic mono- and bis-ligand complexes are obtained, [NbCl3{N(CH2CH2PPr2)(2)}] and [NbCl2{N(CH2CH2P -Pr-2)(2)}(2)]. However with the less sterically encumbered dimethylph osphino function only the diamagnetic dinuclear complex, [{NbCl3[N(CH( 2)CH(2)PMe(2))(2)}(2)], can be isolated; its crystal structure shows e quivalent bridging terdentate amide ligands with two bridging chloride s for each dimeric unit resulting in eight-co-ordinate niobium atoms. In contrast, the bis(2-diethylaminoethyl)amide Li[N(CH(2)CH(2)NEt(2))( 2)], analogue of the smaller phosphine, again only gave rise to parama gnetic monomeric derivatives.