Rhenium complexes multiple bonds

Ritter, S. Thesis, Synthesis, Characterisation, Structures and Reactivity of Complexes with Rhenium-Nitrogen Multiple Bonds. Urriversity of Tubingen, 1995. 

In the case of technetum, this is the most practically used element among non-/ radioactive ones for medical and technical purposes [283], so the permanent interest in its coordination chemistry (in particular, the structural aspect of its compounds [547] and kinetics of substitution reactions [548]) is not surprising [549]. The theoretical interest in Tc is provoked, in particular, by the fact that this is a rhenium analogue. This element (Re) forms multiple metal-metal bond complexes and has been studied intensively in order to achieve a better understanding of the physical and chemical properties of multiple bonds between metal atoms [533],... 

Rhenium occupies a very important place in the development of the chemistry of complexes containing metal metal double, triple and quadruple bonds. This chemistry involves coordination complexes that contain pairs or trinuclear clusters of rhenium atoms and has been surveyed in a recent monograph entitled Multiple Bonds Between Metal Atoms .5 This source, which covers the literature up to early 1981, has also been invaluable in preparing the present review and can be consulted for a more complete and detailed coverage of these classes of complexes. 

Re multiple bond character. This result raises the important question as to whether some of the rhenium(IV) complexes that are believed to contain a linear Re—O—Re unit (Section 43.6.1.7) might not in reality have structures related to this oxalate derivative. The suggestion that the Re,v complex with 5,6-diphenyl-2,3-dihydro(asym)triazine-3-thione (HL), that has been used for the spectrophotometric determination of rhenium, might be Re2(ju-0)2L4, containing bidentate (N and S) coordination from L, is not without precedent. This complex is prepared by the usual SnCl2 reduction of [Re04] in HC1 in the presence of HL.306... 

Eisch, John J., Boron-Carbon Multiple Bonds Fleig, Patrick F., see Wojtczak, William A. Gable, Kevin P Rhenium and Technetium Oxo Complexes in the Study of 39 355... 

W. A. Herrmann, J. D. G. Correia, G. R. J. Artus, R. W. Fischer, C. C. Romao, Multiple bonds between main group elements and transition metals, 155. (Hexamethylphosphoramide) methyl (oxo) bis(Ti -peroxo)rhenium(Vll), the first example of an anhydrous rhenium peroxo complex Crystal structure and catalytic properties, J. Organomet. Chem. 520 (1996) 139. 

The most prevalent complexes of this oxidation state are those which contain the [ReO] ", [Re02] and [RejOj] moieties, a reflection of the increasing stability of the rhenium-oxygen bond as the oxidation state increases. The tendency of Re to form multiple bonds (as in [Re=0] and [0=Re=0] ) is also seen in its behavior toward nitrogen, viz. the stabilization of the [Re=N] (nitrido) and [Re=NR] + (nitrene) moieties. With few exceptions, complexes of Re have been found to be essentially diamagnetic, i.e. to contain a spin-paired configuration. Because of the dominance of the [ReO] +, [Re02] and [RejOj] units in the chemistry of Re, such complexes will be considered first in the chemistry of this oxidation state. 

Reaction of 3 with Ph3C+PF6" resulted in the formation of methylidene complex [(n-C5H5)Re(N0)(PPh3)(CH2)]+ PF6 (8) in 88-100% spectroscopic yields, as shown in Figure 11. Although 8 decomposes in solution slowly at -10 °C and rapidly at 25 °C (She decomposition is second order in 8), it can be isolated as an off-white powder (pure by H NMR) when the reaction is worked up at -23 °C. The methylidene H and 13C NMR chemical shifts are similar to those observed previously for carbene complexes [28]. However, the multiplicity of the H NMR spectrum indicates the two methylidene protons to be non-equivalent (Figure 11). Since no coalescence is.observed below the decomposition point of 8, a lower limit of AG >15 kcal/mol can be set for the rotational barrier about the rhenium-methylidene bond. 

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