Rhenium dimers reduction

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. 

The analogous coordination behavior of hydridotris(pyrazolyl)borate and tetrakis(pyrazolyl)-borate has been demonstrated by numerous reactions. Reduction of the rhenium(VII) complex [Re03 B(pz)4] with PPh3 in THF gives a reactive dimeric intermediate which reacted with monodentate and bidentate protic substrates to yield products with tridentate B(pz)4 ligands... 

Carbon dioxide reduction is thought to proceed via metallocarboxylate intermediate (s) formed by coordination of CO2 to the electron-rich Re center, although discrete steps in the process cannot be unambiguously assigned. The timing of Cl displacement from and CO2 adduction to the Re(bpy) (CO)3 unit are important mechanistic parameters. Most interpretations are based on a one-electron pathway, involving the interaction of CO2 with the product of Eq. (5) a two-electron pathway, involving interaction of CO2 with the product of Eq. (6) or a combination of these steps. Additional mechanistic considerations are the role dimeric rhenium intermediates and likely proton sources. 

For Re2(02CC Hs)4Cl2 the first reduction wave near —0.3 V is quasi-reversible. The product of this one-electron oxidation was not isolated as a solid, but ESR spectra were obtained on frozen dichloromethane solutions at 77°K at both X- and Q-band frequencies. Both naturally occurring rhenium isotopes have a nuclear spin of 5/2 with slightly different nuclear magnetic moments. For dimeric rhenium species there are three distinct isotopic isomers and each generates a unique ESR spectrum as a result of differing hyperfine interactions. The observed ESR spectrum is a superposition of these lines with the intensity... 

Formation of the rhenium(II) dimers Re2G4(PR3)4 results from the reduction of Re2Cll" with PMe3, PEt3, P(n-Pr)3, and PEt2Ph (124). Yields of greater than 50% are typical. It should be noted that similar products have also been obtained from reactions of these tertiary phosphines with the trimeric rhenium(lll)species Re3Cl9. 

In a series of papers, Holah et al. studied the donor character of TPPO, TPPS, and TPPSe towards rhodium, ruthenium, and rhenium. Treatment of TPPO with rhodium(III) chloride hydrate in ethanol causes reduction to Rh(I) and gives the dimeric complex (XXVI) in which TPPO is j -bonded to the metal. 

Rhenium i). Re3Br9 reacts with pyridine, 3-chloropyfidine, y-picoline, and benzimidazole to produce the Re" polymers [Re3BrgL3] . In contrast to this behaviour pyrazine forms an unreduced adduct, Re3Brg(pyz)3. Prolonged reaction of Re3Cl9 and P Pr3 and PEt 2 Ph in MeOH results in disruption of the trimer and reduction to metal—metal bonded dimers of the type RejBr L. " ... 

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