Complexes of rhenium

Again, fluoro and oxo complexes of rhenium predominate. The reaction of KF and ReFe in an inert PTFE vessel yields pink K2[ReFs], the anion of which has a square-prismatic structure hydrolysis converts it to K[ReOFs]. 

Hydrido complexes of rhenium synthesis and reactivity, D. Giusto, Inorg. Chim. Acta, Rev., 1972, 6,91-101(61). 

Another type of mixed ligand technetium or rhenium complexes in the above sense contains two or more monodentate ligands (Fig. 26b). The six-coordinated polypyridyl-thiolato complexes of rhenium(V) [ReO(terpy)(SR)2] + [186] are an example. Further representatives are a variety of mixed-ligand complexes, combining tetramethylthiourea with dimethyldithiocarbamate [TcO(tu)2-((CH3)2NCSS)]2+ [194],... 

M. Gottschaldt, D. Koth, D. Muller, I. Klette, S. Rau, H. Gorls, B. Schafer, R. P. Baum, and S. Yano, Synthesis and structure of novel sugar-substituted bipyridine complexes of rhenium and 99m-technetium, Chem. Eur. 13 (2007) 10273-10280. 

The bimetallic complex [Re(CO)3Cl]jtbpq synthesized in this work showed the typical spectroscopic and electrochemical behavior based on analogous polypyridyl complexes of rhenium(l). Re(l) dn tpbq n charge transfer transition and ligand-field n- n transitions are observed. Typical redox behavior of this system consists of Re /Re oxidation and tpbq/tpbq reduction. Such electrochemical activity, particularly in the reductive region, is found ideal for catalytic processes such as CO reduction. IR-SEC studies have shown that the reduction process occurring at -0.50... 

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. 

Re—O—Re linkage.The complexing of rhenium(iv) with thiourea (L) has been studied in HCl solutions in the presence of tin(ii) by a cation-exchange method, and equilibrium stability constants Pj—P4 for [ReOL4] -t- nCl" [ReOCl L4 -I- nh determined.The complexing of rhenium(iv) with thiocyanate ions in HCl solutions in the presence of SnClj has also been investigated and the formation of a 1 1 Re -SCN" complex confirmed. ° ... 

There are no reports of such a reaction with alkylidene complexes of rhenium such as [Re(=CCMe3)(=CHCMe3)(CH2CMe3)2] [21-23], tungsten (]W(=NAr) (=CHCMe3)(CH2CMe3)2]) [24] and other complexes of molybdenum... 

These expressions have been applied to the series isocyanide and carbonyl complexes of rhenium(I) tr ns-[ReL2(dppe)2]" (L = CNR, CO) [19, 20] and of nitrile and carbonyl compounds of iron(II) tmns-[FeL2(depe)2]2+ (L = NCR, CO) [35], and the Es and /J values of the corresponding trons- ReL(dppe)2 " and trans- FeL(depe)2 " " centers, which are given in Table 9, have been discussed earlier. 

Complexes of rhenium(bipyridine)(tricarbonyl)(picoline) units linked covalently to magnesium tetraphenylporphyrins via an amide bond between the bipyridine and one phenyl substituent of the porphyrin 19 exhibited no signs of electronic interaction between the Re(CO)3(bpy) nnits and the metalloporphyrin units in their gronnd states. However, emission spectroscopy revealed a solvent-dependent quenching of porphyrin emission upon irradiation into the long-wavelength absorption bands localized on the porphyrin. 

It was later found that some aldehyde complexes of rhenium, [Re(NO) (PPh3) 0=C(Aryl)H (Tj-C5H5)]BF4, are also present in solution as a rapidly interconverting mixture of rf isomers and the if isomer.48,49 With the exception of solvent dependence, similar dependencies of the equilibrium constants on the aryl substituents and on the temperature were observed. The solvent dependence was found to be opposite, which, however, is easily understood when taking into account that the rhenium aldehyde complexes are cationic whereas the chromium and tungsten thio- and selenoaldehyde complexes are neutral. 

Dinitrogen complexes of rhenium are relatively stable to air and moisture under ambient conditions so that they serve as convenient starting materials for a number of Re(I), Re(II), and Refill) complexes. The basis of their reactivity is the lability of the N2 ligand in either the Re(I) or Re(II) oxidation states. 

The complexes of rhenium have not been studied as extensively as those of manganese, Among the known complex ions are Re(NH3)g3+,... 

Fig. 5. A /r3-C02 bridged tetranuclear complex of rhenium, [(CO)5Re(C02)Re(CO)4]2. Reproduced with permission from Ref. 16. Copyright 1982 VerlagChemie GmbH. 

In addition to the bimetallic complexes of rhenium and alkaline metals formed as byproducts in the exchange reactions of rhenium halids with alkali alkoxides (such as, for example, LiReO(OPr )5 xLiCl(THF)2 [519]) there has been recently prepared a number ofbimetallic complexes ofrhenium and molybdenum, rhenium and tungsten, and rhenium and niobium [904, 1451]. The latter are formed either due to the formation of a metal-metal bond, arising due to combination of a free electron pair on rhenium (V) and a vacant orbital of molybdenum (VI) atom or via insertion of molybdenum or tungsten atoms into the molecular structure characteristic of rhenium (V and VI) oxoalkox-ides. The formation of the compounds with variable composition becomes possible in the latter case. 

Gillespie, A.M. and White, D.P. (2001) Understanding the steric control of stereoselective olefin binding in cyclopentadienyl complexes of rhenium an application of de novo ligand design. Organometallics, 20, 5149. 

Complexes of rhenium(I) tricarbonyl chloride with pyridyl ligands are often luminophores and hence in anion sensing have principally been used as reporter groups. In many cases this Re(I) fragment is compatible with the same bipyridyl receptor ligands that have been used in [Ru(bpy)3]2+ examples. 

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