Oxidation states rhenium complexes

A series of polyoxotungstate anions which contain high valent rhenium, e.g. [Si-W10Re2O40]2 /3 /4, have been synthesized in the form of Bu"N+ salts.639 The anions contain rhenium in oxidation states VII, VI and V. Cyclic voltammograms, ESR and electronic absorption spectra have been used to characterize these complexes. 

The first rhenium dithiocarbamate complexes, [ReClaCSaCNRa)], were not reported until 1960 (1181), and even then, it was not until the 1970s that substantial inroads were made. Now, dithiocarbamates are known to stabilize rhenium in oxidation states +1 to +5, with the latter being the most common, and the chemistry is dominated by strong jt-donor ligands such as oxo and imido, and especially prevalent are nitride complexes. 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

This reaction is cataly2ed in solution by complexes of tungsten, molybdenum, or rhenium in high oxidation states, eg, Re ". Examples of active catalysts are... 

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

Binary rhenium dithiocarbamato complexes are prepared with the metal in the oxidation state -I- 3, + 4 and + 5. 

These metals form chalcogenolate complexes in several oxidation states, and from the application-oriented point of view manganese compounds have been synthesized as models for hydrodesulfurization processes and rhenium and technetium derivatives as models for radiopharmaceuticals. 

The full exploitation of the wide range of oxidation states of rhenium in radiopharmaceutical design requires not only a wide range of ligand donor types with varied n-donor and acceptor properties, but also suitable reducing agents to provide access to oxidation levels below (VII). This is because for radiopharmaceutical purposes the most conveniently man-factured form of rhenium radionuclides is perrhenate. The traditional routes to reduced rhenium complexes are not particularly amenable to use in a radiopharmaceutical context, where mild, rapid, and preferably... 

Scheme 3. Synthetic route to low oxidation state rhenium trithiacy-clononane complexes.

Molybdenum metalworking, 17 10-11 Molybdenum mill products, 17 9-10 Molybdenum-nickel alloys, 17 102 Molybdenum ore, U.S. exports of, 17 3t Molybdenum oxidation states, 17 20 Molybdenum oxides, 17 38 Molybdenum pentachloride, 17 23 Molybdenum-rhenium alloys, 17 15 Molybdenum sulfide, poisons in representative reactions, 5 258t Molybdenum-sulfur complexes, molecular, 17 37... 

In this regard a more significant determination should be obtained from a study of the polyhydride complexes [ReH7(PR3)2], in that (i) if the complex is a classical hydride the rhenium atom would be in its maximum oxidation state (+ 7) and, therefore, could not undergo further oxidation processes (ii) if the complex is a non-classical hydride, the rhenium atom would be in a lower oxidation state and, consequently, could display oxidation processes. 

Low and medium oxidation states like 0, -l-I, -fII, and -fill seem to be stabilized best by NHCs. Difficulties in preparing and isolating the desired compounds occur with higher and lower oxidation states, although extreme cases such as complexes of rhenium(VII) are known. In summary, almost every transition metal has been used to prepare NHC complexes by one of the routes described previously. 

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