1,4-diaza-1,3-diene niobium chlorides: syntheses and X-ray crystal structures of (t-Bu-DAD)NbCl3(THF), (t-Bu-DAD)(2)NbCl, and [(t-Bu-DAD)NbCl4](H(3)Nt-Bu)

摘要

The new 1.4-diaza-1.3-diene niobium complexes (t-Bu-DAD)NbCl3(THF) (2) and (t-Bu-DAD)NbCl (3) [t-Bu-DAD=(t-Bu)N=CHCH=N(t-Bu)] have been prepared in 75-82% isolated yields by replacing of two or four chlorine atoms of NbCl, by the sterically demanding t-Bu-DAD ligand. In addition, we also describe the ionic Nb(V) complex [(t-Bu-DAD)NbCl4](H(3)Nt-Bu) (6) which was formed as a byproduct during the preparation of 2. The new compounds have been characterized in solution by NMR measurements as well as by X-ray analyses in solid state. The structural parameters within the t-Bu-DAD ligand of 6 are in agreement with a chelating enediamido dianion. On the other hand the N-C and C-C bond distances of the t-Bu-DAD ligand of 2 are rather comparable to those found in complexes having a radical-anionic t-Bu-DAD ligand. The higher steric crowding at the niobium center caused by two 1,4-diaza-1,3-diene ligands in 3 leads to a significant asymmetric distortion of the 1,3-diaza-2-niobacyclopent-4-ene rings. However, none of the 1.4-diaza-1,3-diene ligands of 2, 3 or 6 is coordinated in the sterically less demanding eta2-C,N bonding mode as found in the binuclear complex (t-Bu-DAD)(5)Nb-2 (4). (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 66]