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

Chapter 2
1: R = tBu, X = Hdpm
2: R = Ph, X = Hdbm
Figure 2.17: Displacement reaction of 1 and 2 with Hacac.
Kinetic studies on the exchange processes were carried out by following the
reactions as a function of time and temperature by 1 H-NMR spectroscopy. The molar
ratios for [Hacac]/[Complex 1 or 2] were varied from 1:1 up to 7:1. They observed a
negligible dependence on the rate constant for ratios greater than 4:1. Accordingly a
pseudo-first-order dissociative process was proposed with the formation of a
pentacoordinated and electronically unsaturated species as the rate-limiting step.
The proposed mechanism is displayed in Scheme 2.1. The calculated values of the
pseudo-first-order rate constants, kapp, at five temperature values are displayed in
Table 2.7.
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