Transition metals, NMR

Buhl, M., 1997, Density Functional Calculations of Transition Metal NMR Chemical Shifts Dramatic Effects of Hartree-Fock Exchange , Chem. Phys. Lett., 267, 251. 

Transition metal NMR studies of organometallic and inorganic coordination compounds... 

Transition metal NMR spectroscopy is not only a valuable source of structural information, but metal chemical shifts may also permit predictions of the reactivity and possibly even catalytic activity of a complex.51 The key to such analyses is frequently the observation of correlations of metal chemical shifts... 

Correlations between Transition-Metal NMR Chemical Shifts and Reactivities... 

Modem methods based on density-functional theory (DFT) can describe relative activation barriers of organometallic reactions, i.e. relative reactivities, as well as the transition-metal NMR chemical shifts of the reactant complexes involved. It is thus possible to reproduce or rationalize observed correlations between these properties or to predict new ones. NMR/reactivity correlations that could be reproduced theoretically ("intrinsic correlations") are summarized. Newly predicted NMR/ reactivity correlations are discussed for the ethylene polymerization with V(=0-X)R3 or V(=Y)R3 catalysts. When X or Y are varied (X = A1H3, Li+, SbF5, H+ Y = NH, O, S, Se), both... 

In the preceding chapter it has been shown that the DFT methods currently available can be used to reproduce relative trends in both reactivities and transition-metal NMR chemical shifts. Thus, NMR/reactivity correlations can be modeled theoretically, at least when relative reactivities are reflected in relative energies on the potential energy surfaces (activation barriers, BDEs). It should in principle also be possible to predict new such correlations. This is done in the following, with the emphasis on olefin polymerization with vanadium-based catalysts. 

The application of DFT methods to the computation of transition-metal NMR has been reviewed in the past [1-4]. A short overview was recently prepared by Buhl [5], NMR calculations on heavier transition-metal complexes have further been discussed in reviews devoted to relativistic NMR methodology [6-9], Thus, the present overview does not attempt to give a full coverage of the available literature, but to present a number of illustrative examples, the present status of such computations and their accuracy and limitations, along with a description of the underlying methodology. Because of the high importance of relativistic effects on NMR parameters, which is clearly represented in the available literature on DFT NMR computations of transition-metal complexes, the reader will find that a substantial portion of this paper is devoted to this topic. 

Supercriticial fluids look set to continue to their invasion of the territory of traditional organic solvents in all areas of chemistry. Perhaps the most interesting area for exploration for the organometallic NMR spectroscopist is the use of SCFs for homogeneous catalysis. The presence of a single phase simplifies operation and may lead to enhanced reaction rates, while low viscosity aids observation of quadrupolar nuclei, which includes many of the transition metals. NMR studies in situ could allow observation of reaction intermediates and new insights into the mechanisms of these important reactions. 

Different methods of computation have been performed for comprehensive investigations on the thermal effects and vibrational corrections to transition metal NMR chemical shifts. Studies related to TiClxMe4 x (v = 0-3) are included.240... 

W. von Phillipsborn (1999) Chemical Society Reviews, vol. 28, p. 95 - Probing organometallic structure and reactivity by transition metal NMR spectroscopy . 

The Mo nucleus is preferred to the Mo nucleus even though they are of similar spin (/ = S/2) and resonate at very similar frequencies (6.51 versus 6.65 MHz) because the former has a significantly higher natural abundance (15.72% vs 9.46%), smaller quadrupole moment (0.12 x 10 m vs 1.1 X 10 m ) and a greater sensitivity (relative to C, 2.92 vs 1.87). Consequently, much has been published in the area of Mo NMR in the last 10 years since the last comprehensive review, by Minelli er al. Other general reviews for Group 6 metal NMR in particular and transition metal NMR in general have also been published. " This review is primarily concerned with Mo NMR data from the 10-year period, 1985-1995, for all seven common oxidation states of molybdenum, Mo(0)-Mo(VI). Some notes on the developments in the areas of Cr, and solid-state NMR over the same time period are included. 

The major portion of transition metal NMR data available is for complexes of the d electronic configuration. This is very true for Mo NMR because Mo(0) has a very rich and widespread chemistry relative to the other common oxidation states of molybdenum. ... 

Pregosin, P. S.Transition Metal NMR Spectroscopy 1991, Elsevier Amsterdam. 

Buhl, M. Correlation between Transition-Metal NMR Chemical Shifts and Reactivities , in Modeling NMR Chemical Shifts, Gaining Insights into Structure and Environment (ACS Symposium Series, 732) Facelli, J. C., Ed., ACS Washington DC, 1999, pp 240-250. 

Transition metal complexes, 0 chemical shifts, 255-58 Transition metal NMR, 445-56 Transition probability, 71 Transverse relaxation see Relaxaton, spin-spin 2, 3, 5 -Tri-O-benzoyluridine, 235-36 Tritium... 

B. Gierczyk, Application of Transition Metals NMR in Supramolecular Chemistiy, in From Molecules to Functiomd Architecture Supramolecular Interactions, ed. V. I. Rybachenko, East Publisher House, Donetsk, Ukraine, 2012, p. 269. 

Rehder D (1986) Applications of transition metal NMR spectroscopy in coordination chemistry. Chimia 6 186-199. 

Transition metal NMR has been surveyed by Kidd and Goodfellow, Kidd (nuclear shielding),Rinaldi, Levy, and Choppin (selected topics only), and Wehrli (quadrupolar nuclei). Monographs have appeared on V NMR primarily concerned with solution and solid state measurements, the chromium triad, and on the first transition series nuclei (Sc to Zn). Some generalizations on nuclear shielding in carbonyl complexes of V, Mn, and Nb have been reported. A comprehensive account on the complete block of the rf-metals has recently appeared. ... 

---