Oxo-metal complexes

Table 11-3. Absolute 170 NMR chemical shifts [ppm] in transition metal oxo complexes.

Deng, L., Ziegler, T., 1997, Theoretical Study of the Oxidation of Alcohols to Aldehyde by d° Transition-Metal-Oxo Complexes Combined Approach Based on Density Functional Theory and die Intrinsic Reaction Coordinate Method , Organometallics, 16, 716. 

Kaupp, M., Malkina, O. L., Malkin, V. G., 1997, The Calculation of 170 Chemical Shielding in Transition Metal Oxo Complexes. I. Comparison of DFT and Ah Initio Approaches, and Mechanisms of Relativity-Induced Shielding , J. Chem. Phys., 106, 9201. 

Substitution Studies of Second- and Third-Row Transition Metal Oxo Complexes... 

SUBSTITUTION STUDIES OF SECOND- AND THIRD-ROW TRANSITION METAL OXO COMPLEXES... 

Theoretical calculations have been fundamental in solving the controversy on the mechanism for the dihydroxylation of double bonds by transition metal oxo complexes. Nowadays, this topic which was the subject of a controversy just a few years ago seems to be solved in favor of the [3+2] pathway, at least in a vast majority of the cases. Despite this spectacular success there are still a number of open issues for this particular reaction which have not been solved, and which continue to be a challenge for computational chemists. Among this, one can mention the correlation between the nature of the substrate and its reactivity with permanganate, and the mechanisms leading to the proportion of products experimentally observed when CrC Cb is applied. Hopefully, these issues will be solved in the future with the help of theoretical calculations. 

The isomerisation of allyl and propargylic alcohols involves the 1,3-shift of an oxygen atom rather than a hydrogen atom. Isomerisation of allyl alcohols can be catalysed by a variety of metal oxo complexes and in this instance the reaction does not involve metal carbon bonds as we will see. One could imagine that allylic metal species can participate in isomerisation of allylic compounds, but for the alcohols themselves this is not an easy reaction. In chapter 13 reactions of allyl acetates and the like, which are more prone to... 

Figure 14.13. Schematic dihydroxylation of alkenes by metal oxo complexes...

Hi. Cr, Mo, W. In contrast to group IV and V transition metals, the catalytic active oxidant is of another type for group VI transition metal-catalyzed epoxidations The transition-metal-oxo complexes, in which the oxygen that is transferred is bonded to the metal via a double bond, are the active oxidizing species. 

Quite recently transition metal oxo complexes with NHC ligands have been synthesized, e.g. for rhenium [71,72] and uranium [73], but no oxygen transfer using those complexes has been reported yet. 

SCHEME 45. Asymmetric oxidation of sulfides via a metal-oxo complex. 

In contrast to catalytic oxidations involving metal peroxide intermediates, catalysis by metal-oxo complexes does not in theory require the presence of a coreducing agent. Indeed, the reduction... 

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