Molybdenum complexes, electron-transfer reactions

Sheldon has considered the competing process of homolytic decomposition of hydroperoxides during the epoxidation of olefins with tert-h xty hydroperoxide in the presence of molybdenum complexes. It was found that homolytic decomposition of the hydroperoxide is initiated by electron transfer reactions of Mo(V) and Mo(VI) complexes with the hydroperoxide giving rise to free radical species. Reaction rates and products of hydroperoxide decomposition were dependent on the solvent and on the presence or absence of an olefin. The rates and selectivities of epoxidation were highest in polychlorinated hydrocarbons and very poor in coordinating solvents such as alcohols or ethers [387]. 

To explore the influence of coordination environment on rates and mechanisms of electron transfer reactions at molybdenum centers, we have investigated [17-20] the electrochemical behavior of several families of oxomolybdenum (VI) complexes. The compounds are illustrated in Figure 4. The first three examples are seven-coordinate complexes and exhibit pentagonal bipyramidal geometry. These compounds contain a... 

Some recent woik on the electron - transfer reactions of thioether and thiolate complexes of molybdenum is also introduced together with an approach to modification of electix es with met o-sulphur clusters - the first steps towards the assemUy of artificial metalloenzyme sites for fixing dinitrogen or other small molecules electrochemically. 

The electron - transfer reactions of organodiazenide, organohydrazide and nitride groups bound at various molybdenum dithiocaibamate sites have been studied and the reductive release of an organohydrazine shown [34 - 37] but the parent dinitrogen complexes are unknown [36,37]. 

Electron-transfer reactions in nitrogen fixation. Part 1. The electrosynthesis of dinitrogen, hydride, isocyanide, and carbonyl complexes of molybdenum intermediates, mechanisms, and energetics... 

The kinetics of several electron transfer reactions of the molybdenum cuboidal system [Mo4S4(edta)2]" ( = 2, 3, 4) with cross-reactants such as [Co(edta)]-, [Fe(edta)]-, [Co(dipic)2] , [Fe(H20)e], and [Pta ] -, have been investigated. The electron self-exchange rate constants determined for the [Mo4S4(edta)2] and [Mo4S4(edta)2] couples, by an application of the Marcus relationship, are 1.5 x 10 and 7.7 x 10 M s , respectively. The rate constants for the outer-sphere oxidation of two dimeric complexes, [MoW 0)2(p-edta-AT,lV )]2- and [W2(0)2(p-0)(p-S)(p-edta-Ar,iV )] -, by [IrCl ] in addic aqueous solution have been measured. While the oxidation of the former complex shows a simple second-order rate law, the kinetics of the oxidation of the latter complex exhibited a rate retardation in the presence of the [IrCl6] complex. 

The occurrence of structure changes as a result of electron transfer steps is well-documented [14-16]. Such a reaction has been observed for a molybdenum complex of the macrocyclic tetrathioether Meg[16]aneS4 (Meg[16]aneS4 = 3,3,7,7,11, 11,15,15-octamethyl-l,5,9,13-tetrathiacycl-ohexadecane) [17-20], which is among the... 

The first step of the mechanism leading The electrochemical study of the seven-to the formation of 8 and free nitrite coordinate complex [Mo(N2RR )(dtc)3]+ from the reaction of 7 with O2 probably 9+ (R, R = alkyl or aryl, dtc = 5 2CNMe2) involved a single electron transfer. Sub- provided an example of electrode-induced sequent radical-radical coupling of the activation of a hydrazido(2—) ligand. Corn-products, to afford a molybdenum-bound plex 9+ was shown to reduce in two nitrate, followed by N—O bond cleavage separate diffusion-controlled one-electron would eventually lead to the observed steps, with the first one reversible on the products (Sch. 8) [27]. CV timescale at room temperature and... 

The electrochemical transformation of a molybdenum nitrosyl complex [Mo(NO)(dttd)J [dttd = 1,2-bis(2-mercaptophenylthio)ethane] (30) is rather interesting (119). Ethylene is released from the backbone of the sulfur ligand upon electrochemical reduction. The resulting nitrosyl bis(dithiolene) complex reacts with O2 to give free nitrite and a Mo-oxo complex. Multielectron reduction of 30 in the presence of protons releases ethylene and the NO bond is cleaved, forming ammonia and a Mo-oxo complex (Scheme 15). The proposed reaction mechanism involves successive proton-coupled electron-transfer steps reminiscent of schemes proposed for Mo enzymes (120). 

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