A solution and solid state study of niobium complexes University of ...

Chapter 2
In 1991 Lee et al. 83 published a paper where they used 93 Nb- and 1 H NMR
spectroscopy to investigate the different substitution products of [NbCl5-x(OMe)x] that
forms in the stepwise substitution of NbCl5 by MeOH in non co-ordinating solvents.
Their results confirmed Schönherr’s et al. 84 results that only [NbCl2(OMe)3] is formed
on adding an excess MeOH to NbCl5 in non-polar solvents.
To validate their results they isolated and characterized [NbCl4(OMe)],
[NbCl2(OMe)3] and [Nb(OMe)5] as reference samples. They did not isolate
[NbCl3(OMe)2] as it readily disproportionates to form [NbCl2(OMe)3] and
[NbCl4(OMe)]. This is due to the lower solubility of [NbCl4(OMe)] and the stability of
[NbCl2(OMe)3]. The coordination of NbCl5 with MeOH in different aromatic solvents
was followed by 93 Nb NMR and compared to the relative reference peaks. The
results are presented in Table 2.6.
Table 2.6: Assignment of 93 Nb NMR signals to NbCl5-x(OMe)x species. 84
Solvent x = 0 x = 1 x = 3 x = 4 x = 5
Benzene 2.6 -497 -810 -1010 -1160
Toluene 2 -495 -810 - -1150
Methanol -0.5 -480 -820 -1015 -1155
Ethanol - -470 -830 -1020 -1180
Isopropanol - -470 -830 -1025 -1135
Acetonitrile - -495 / -560 -850 - -1160
2.8 Kinetic Studies of Niobium Complexes
Antiñolo et al. 85 published a paper in 2000 in which they studied the reaction of
niobium alkoxo complexes with different β-diketones. The β-diketones of choice was
tBuCOCH2COtBu (Hdpm), PhCOCH2COPh (Hdbm) and acacH. They followed the
kinetics of the displacement reaction of [NbCl2(OEt)2(dpm)] (complex 1) and
[NbCl2(OEt)2(dbm)] (complex 2) with acacH to give [NbCl2(OEt)2(acac)] as seen in
Figure 2.17.
83 G. R. Lee, J. A. Crayston, Dalton Trans., 3073, 1991.
84 M. Schönherr, L. Kolditz, Z. Chem., 10, 72, 1970.
85 A. Antiñolo, F. Carrillo-Hermosilla, J. Fernández-Baeza, S. Garcia-Yuste, A. Otera, E. Palomares, A. M.
Rodriguez, L. F. Sánchez-Barba, J. Organomet. Chem., 603, 194, 2000.
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