Rhenium complexes electron-transfer reactions

Infrared spectroelectrochemical technique proved to be an excellent method to look at time and potential dependent changes of various types of chemical species. The employment of this technique will surely be significant on the mechanistic study of electron-transfer reactions of rhenium complexes. 

Tris(l,2-bis(dimethylphosphino)ethane)rhenium(I), [Re(DMPE)3]+ is a simple, symmetrical cation which contains three identical bidentate phosphine ligands. This complex provides a Re(II/I) redox couple with properties that are very convenient for the study of outer-sphere electron transfer reactions.1 Specifically, this couple is stable in both alkaline and acidic media and it exhibits a reversible, one-equivalent redox potential in an accessible region [ °,(II/I) = 565 mV vs. NHE]. Moreover, this complex has been used to obtain information about the biological mechanism of action of 186Re and l88Re radiopharmaceuticals.2,3... 

In view of the strong photo oxidising properties of [Re(phen)(CO)3 (imidazole)]+ (14) (Re(I)VRe(O) = ca. + 1.3 V vs NHE in CH3CN), [Re(phen)(CO)3 (H20)]+ has been reacted with azurin to give [Re(phen)(CO)3(His83)]+-AzCu+, which has been used to study photoinduced electron-transfer reactions [47]. In the absence of quenchers, excitation of the rhenium(I) complex... 

Luminescent ruthenium(II) polypyridine indole complexes such as [Ru (bpy)2(bpy-indole)]2+ (37) and their indole-free counterparts have been synthesised and characterised [77]. The ruthenium(II) indole complexes display typical MLCT (djt(Ru) tt (N N)) absorption bands, and intense and long-lived orange-red 3MLCT (djt(Ru) -> Ti (bpy-indolc)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. In contrast to the rhenium(I) indole complexes, the indole moiety does not quench the emission of the ruthenium(II) polypyridine complexes because the excited complexes are not sufficiently oxidising to initiate electron-transfer reactions. Emission titrations show that the luminescence intensities of the ruthenium(II) indole complexes are only increased by ca. 1.38- to... 

Chloride ion catalyses the reaction and has an effect on the final product which is considered to be a dinuclear Ti -Re complex. It is of interest that on preparation of rhenium(v) and reaction with Ti ", there is an instantaneous reduction to yield the same dinuclear product. The use of non-aqueous media for investigating electron-transfer reactions is increasing and a review of solvent effects of systems involving metal complexes in homogeneous and heterogeneous phases has recently been published. ... 

The reaction of the ketyl radical anion with the oxidized rhenium complex is the energy-releasing electron transfer step. This reaction cannot be carried out separately. While ketyl radical anions are stable species, the oxidized complex is not stable and must be generated as short-lived intermediat. ... 

Rhenium bipyridine comfdexes have received a great deal of attenti( because they act as photoreduction catalysts from CO2 to CO in the presence d amine with high selectivity and high efficiency [1-3]. The first step of the reaction is an electron transfer from the amine to die excited complex. However, the subsequent processes are not clear. Difficulties in die elucidation d the reaction mechanisms are ascribed to the instability of die intermediates. Furthermore, the presence of a highly non-volatile amine, e.g., triethanolamine (TEOA), makes it more difficult to isolate the intermediates. 

Examination of the chemical, electrochemical, and spectroscopic behaviour of R3EM(C0)3L (R = Ph or Me, E = Ge or Sn, M === Mn or Re, L = phen or bpy) reveals that the lowest state is one in which an electron has been transferred from the HOMO, which has sigma E—M bonding character to the LUMO which is mainly localized on The rhenium complexes emit in fluid solution at room temperature, and the luminescence may be quenched by both electron acceptors and electron donors, as in reactions (5) and (6). No net photochemistry is observed... 

The mechanism of hydride abstraction from rhenium alkyl complexes of the type [Re(Cp)(NO)(PPh3)(R)] (50) has been examined using electrochemical techniques and provides the first rate data for metal alkyl/Ph3C reactions. Both the a-hydride abstraction in equation (17) and )8-hydride abstraction in equation (18) processes are shown to involve a preequilibrium electron-transfer step shown in equation (19), followed by rate-determining hydrogen-atom transfer between... 

---