Solvation carbonyl reduction

The most powerful reducing agent is the solvated electron with a reduction potential of-3.05 V vs. see [60], The LUMO of ethene is too high in energy to permit electron attachment to this molecule but introduction of an electron withdrawing substituent such as carbonyl or nitrile lowers the energy of the LUMO sufficiently that the rate of electron attachment becomes close to diffusion control [61]. Benzene reacts with solvated electrons more slowly than the diffusion controlled limit... 

The carbonylmetallate anions are extremely useful organometallic reagents, particularly for the syntheses of heteropolymetallic clusters.3,4,7 However, they have rarely been isolated in the solid state and their solutions are obtained either by reduction of their dimers or by reaction of NaCsHs with the parent metal carbonyls,2 and immediately used. The first method is not very economical since the dimers are usually themselves obtained from the metallate anions. The second method has been improved as detailed below to allow the easy isolation of the pure Na[M(CO)3(//s-CsH5)] (M = Cr, Mo, W) solids as DME solvates.4 The nonsolvated Na[M(CO)3(f/5-C5H5)] salts can... 

The reduction of cimicidine by sodium borohydride exactly parallels that of haplophytine. The product is a hygroscopic, solvated dihydro derivative, whose composition approximates C23H30N2O5H2O this derivative does not exhibit the carbonyl absorption at 1751 cm-1, observed in the spectrum of cimicidine, but exhibits hydroxyl absorption. The nature of this carbonyl group is unknown like haplophytine, cimicidine is inert toward carbonyl reagents. 

The reduction of the maleic anhydride adduct (303) with lithium aluminium hydride was previously reported to occur selectively to give the lactone (304). The lower selectivity now observed with sodium aluminium hydride (none at all with sodium borohydride) is interpreted as evidence for a complex (305) of the ester and anhydride carbonyl groups with a solvated lithium ion when lithium aluminium hydride is used, leading to selective reduction of the free carbonyl group.Sodium ions are considered not to form so stable a complex. 

Carbonyl derivatives and olefins are reduced by electrochemically produced solvated electrons. Camphor and 4-/-butylcyclohxanone thus form the corresponding alcohols in HMPA-ethanol the proportion of epimeric alcohols would suggest that the reduction is thermodynamically controlled [316]. Surprisingly enough, sterically hindered alkenes are reduced at a rate only slightly lower than that of cyclohexene [311]. 

The reductive fragmentation with solvated electrons (metal in liquid ammonia) of strained rings bearing carbonyl groups in a 1,4-relationship leads to dicarbonyl systems with a lower number of fused rings (Scheme 55). 

Stable dianionic derivatives of the Ti carbonyl complex [Ti(CO)6]2 have been synthesized, isolated, and characterized.1045 The [Ti(CO)6]2 ion was obtained via reductive carbonylation of Ti(CO)3(DMPE)2 or TiCl4(DME) by KCioHg in the presence of a crown ether or cryptand.1045 An octahedral environment about Ti in [K(cryptand 2.2.2)l2[Ti(CO)6] was confirmed both in solution by the observation of a septet resonance in the 49Ti NMR spectrum for the 13CO complex and cry stallographically.1046 Related complexes with weakly solvated alkali metal cations readily decomposed.1047... 

Electron Acceptance Reduction and Adduct Formation. Acceptance of electrons at specific sites on amino acids and peptides depends on their reactivities and produces different chemical consequences. Among the sites of particular importance are the terminal amino and carboxyl groups, the ring groups, the peptide carbonyl, and the sulfur bonds. Reactivities of these are reflected in the rate constants for reaction of solvated electrons with individual amino acids in aqueous solutions, as shown in Table I and as discussed by Simic (53). More detailed information, however, regarding the stepwise progression from attachment to specific radical formation has been obtained from low temperature studies. 

Recent work on the role of solvated electrons in intra-DOM reduction processes has demonstrated the importance of trapped e in reactions with species adsorbed on the DOM matrix [98-100]. Modeling of DOM mediated photoreactions indicated the importance of sorption of molecules to DOM for reaction to occur [98, 99]. This is consistent with the lifetime of e" precluding escape from the aqueous DOM matrix into bulk solution. Since many important reactions with environmental implications involve binding or adsorption to DOM - see, for example, [3,101,102] - the role of matrix effects and the caged electron could be very significant. Some workers have suggested that since e remains primarily trapped within the DOM matrix, Oj must be formed by direct electron transfer from the excited triplet state of DOM to O2 [14]. However, it is equally if not more plausible that Oj may be produced by the reduction of Oj by radicals or radical ions produced by intramolecular electron transfer reactions from irradiated DOM [25]. The participation of radicals in the production of carbonyl sulfide and carbon monoxide from irradiated DOM in South Florida coastal waters was recently demonstrated by Zika and co-workers [81-83] and potential pathways for the formation of free radicals from irradiated DOM were discussed. Clearly, the relative contribution of e q and associated transients to the photochemistry of DOM has not been unequivocally resolved in the literature. 

Since the late 1990s, new approaches to the dispersion of noble metal particles in polymer matrixes by means of chemical, photochemical and radiation-chemical reduction, the evaporation of metal atoms (including solvated ones) into different supports, etc. have been developed (see Section 8-1) [44]. Nevertheless, catalysts prepared from individual immobilized metal clusters have more definite, mostly predetermined, structures. For these purposes derivatives of Oss, It4, RU4, Rh4, Rh6, etc. clusters are most often used. Earlier studies [46] showed that the rate of ethylene hydrogenation promoted by tetrairidium or tetraruthenium carbonyl clusters bound to phosphynated polymers decreased with an increase of the number of donor... 

Metal carbonyls are commonly made by reduction of metal salts in the presenee of CO under high pressure. A variety of reducing agents have been found to be effective. In reaction (3), sodium reduction produces a solvated sodium salt of V(CO)6 this is subsequently oxidized by if to V(CO) reaction (4). 

Synthesis of oximes and amines. Copper salts solubilized in aqueous alkyl polyamines solvents have been found to promote the homogeneous reduction of nitroalkanes to oximes by CO at atmospheric pressure and 85 C in good yields and conversion(9. Catalysis is favoured by the use of copper salts of weak acids solubilized in alkylpolyamlnes solvents of pKa > 9.2. The suggested reaction path involves the formation of a solvated cuprous carbonyl complex, which by combination with the nitroalkane anion gives a copper-nitroalkane complex ... 

Ionic liquids (ILs) have attracted considerable attention as environmentally benign reaction media. By the proper variation of their anionic and cationic parts, their physical properties, such as vapour pressure, thermal stability, and solvation strength, can easily be fine-tuned [215]. Although, the ILs are widely used as environmentally benign solvents in high-pressure catalysis, there are only a few examples of their application in TH reactions of carbonyls. Berthold et al. [216] first reported the application of ILs as reaction media for TH of ketones and their a,p-unsaturated derivatives. Hermecz et al. reported the reduction of chalchone and ot,p-unsaturated carbonyl derivatives by using [ClRh(PPh3)3] and [Rh(cod)Cl]2... 

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