Reduction rhenium complex

The need to achieve high yield in one-pot synthesis, coupled to the relative kinetic inertness of rhenium complex (e.g. compared to technetium) and the mild conditions required has led to the development of useful versatile rhenium(V) intermediates that can be quickly prepared in quantitative yield, and are metastable, i.e. kinetically labile enough to react rapidly with the final chelator, again in high yield. The most widely used ligands suitable for this purpose are polydentate hydroxycarboxylic acids such as glucoheptonate [116a], citrate (47), tartrate (48), and 2-hydroxyisobutyric acid (49) [159]. Examples are discussed elsewhere in this chapter. They are typically used in the presence of Sn(II) to reduce Re(VII) to Re(V), at moderately elevated temperature (50-100 °C) at pH 2-3 (acid pH promotes reduction of perrhenate, presumably by facilitat-... 

Scheme 144 Catalytic cycle of cathodic carbon dioxide reduction with rhenium complexes to carbon monoxide.

Rhenium(VII) trioxo-complexes with derivatives of the Klaui ligand (19) are stable in air and organic solvents, but slowly decompose in aqueous solutions yielding perrhenic [Re03(cpCo PO(OR)2 3)] can be prepared from Re20v, perrhenate, or by oxidation of the corresponding Re tricarbonyl complex. Reduction with phosphines in the presence of HBr... 

ReCl3(PPh3)(benzil)] reacts with bipy and related ligands or terpy to form a number of rhe-nium(III) and rhenium(II) compounds which are useful precursors for the synthesis of lower-valent rhenium complexes. " Thus, reduction of [Re(bipy)3][PF6]2 with zinc amalgam results in the rhenium(I) compound [Re(bipy)3][PF6] in excellent yields. The corresponding terpyridyl bis-chelate [Re(terpy)2][PF6] has been prepared in a similar manner. " The electrochemistry of the products provides a convenient measure of the chemical reactivity associated with the redox processes. Thus, the one-electron oxidation of [Re(bipy)3]" is reversible at -0.33 V, whereas the Re"/Re" redox couple is irreversible and occurs at relatively low potentials (-1-0.61 V) which is consistent with the instability of [Re(bipy)3] + in solution. However, in the presence of a small coordinating molecule such as CNBu, oxidation to the rhenium(III) state is readily available by the formation of seven-coordinate complexes of the composition [Re(bipy)3(L)]. " ... 

Low-valent rhenium complexes are effective in the catalytic reduction of carbon dioxide. The conversion can be accomplished photolytically or electrochemically and is of interest with regard to fuel production and greenhouse gas remediation [9]. Electrocatalytic reduction of CO2 to CO is initiated by the reduction of fac-Re(bpy)(CO)3Cl or a related complex and can be accomplished in homogeneous solution [54, 55] or on a polymer-modified electrode surface [56]. Catalytic current... 

Recently, the interest in Re (I) complexes has been increased due to their potential utility for the activation and reduction of C02 into CO and C032 in a purpose of construction of artificial photosynthetic systems [11-13]. Rhenium Complexes such as ReX(CO)3(bpy) (X=C1, Br) and Re(CO)2(bpy)[P(OEt)3]2 have been used as photocatalysts for C02 reduction to CO in solvent mixture of triethanolamine/dimethylformamide [12,13]. Most of the research on photochemical activation and reduction of C02 using Re(I) complexes have focused on the homogeneous solution systems. There are few reports concerned about the encapsulation of rhenium complexes into molecular sieves and their photochemical application to the photochemical reduction of C02. 

Raman spectroscopy metal in water complexes, 309 Rare earth complexes acetylacetone synthesis, 377 guanidinium, 282 hydroxamic acids, 506 Redox properties bipyridyl metal complexes, 90 Reductive coupling nitrile metal complexes, 265 Resorcinol, 2,4-dinitro-metal complexes, 273 Rhenium complexes acetylacetone, 376 synthesis, 375, 378... 

The rhenium complexes described in Section 11.2 have also been studied as electron mediators for C02 reduction at metal electrodes. Hawecker et al. used the complex Re(bpy)(CO)3Cl in DMF/water (9 1) at glassy carbon electrodes at a potential of-1.44V (versus SCE) to produce CO with 98% faradaic efficiency [15, 87]. Likewise, Sullivan et al. reported the production of CO with similar efficiency at a platinum electrode at -1.5 V (versus SCE) by using the complex fac-Re(bpy) (CO)3Cl [88]. Ruthenium complexes that have been used in photochemical... 

Selective carbon dioxide reduction to CO has been accomplished in a non-aqueous medium that includes tricarbonyl (2,2 -bipyridinium) rhenium , /ac-Re(bpy) (CO)3X (X=Cl, Br) as light-active component and homogeneous catalyst for C02 reduction [183-185]. In dimethylformamide solutions that include TEOA as sacrificial electron donor, photosensitized reduction of C02 to CO proceeds with a quantum efficiency of

Mechanistic investigations have revealed that reductive ET quenching of the rhenium complex (Eq. (54)) yields the catalytic intermediate active in deoxygenation of C02. It has been suggested that carbon... 

In addition to described heterogeneous systems a homogeneous photocatalytic C02 reduction was tested using heteroleptic rhenium complexes [99, 100] and supramolecular ruthenium and rhenium bi- and tetranuclear complexes their excited states were quenched by 1-benzyl-1,4-dihydronicotinamide (BNAH) and C02 was reduced by the electron donor intermediate species [101]. 

The last section describes rmique and high photocatal5rtic activities of the rheniiun(I) diimine carbonyl complexes, especially for CO2 reduction. The photocatalyses of mononuclear rhenium complexes, multicomponent systems, supramolecular systems with a Ru(II) complex as a photosensitizer, and a rhenium complex with periodic mesoporous organosilica as a light-harvesting system. 

A strong correlation between the first reduction potential and the photocatalytic ability of rhenium complexes has been reported (65). For example, complexes with Ey2 > — 1.4 V versus Ag/AgNOa show only low photocatalytic ability for CO2... 

---