PREPARATION AND CHARACTERIZATION OF ANIONIC BIS(CYCLOPENTADIENYL)NIOBIUM COMPLEXES - MOLECULAR-STRUCTURE OF [K(18-CROWN-6)][NB(ETA-C5H5)2(SNME3)2]

The reaction between [Nb(eta-C5H5)2H3] and LiBu,LiBu-1,4,7,10-tetraoxacyclododecane(12-crown-4), NaH-1,4,7,10,13-pentaoxacyclopentadecane(15-crown-5), KH-1,4,7,10,13,16-hexaoxacyclooctadecane(18-crown-6), or NaNH2 gives M[Nb(eta-C5H5)2H2] (M = Li, 1; or Na, 5) and [M(crown)][Nb(eta-C5H5)2H2] [M(crown) = Li(12-crown-4) 2, Na(15-crown-5) 3 or K(18-crown-6) 4]. The compound SnMe3Cl reacts with 1 or 4 to give [Nb(eta-C5H5)2H2(SnMe3)]. The hydrides [Nb(eta-C5H5)2H2(SnMe3)] and [Nb(eta-C5H5)2H(SnMe3)2] react with LiBu-12-crown-4, NaNH2-15-crown-5 and KH-18-crown-6 to give [M(crown)][Nb(eta-C5H5)2H(SnMe3)] [M(crown) = Li(12-crown-4), Na(15-crown-5) 7 or K(18-crown-6) 8] and [M(crown)][Nb(eta-C5H5)2(SnMe3)2] [M(crown) = Li(12-crown-4) 9, Na(15-crown-5) 10 or K(18-crown-6) 11], respectively. The X-ray crystal structure of 11 shows there to be two separate ions [Nb(eta-C5H5)2(SnMe3)2]- and [K(18-crown-6)]+ with no close interionic contacts. Structural and spectroscopic evidence is presented for the presence of Nb-H-M interactions, where M = Li, Na or K.