Dimethyl sulfoxide, reaction with metal complexes

The complications which result from the hydrolysis of alkali metal cyanides in aqueous media may be avoided by the use of non-aqueous solvents. The one most often employed is liquid ammonia, in which derivatives of some of the lanthanides and of titanium(III) may be obtained from the metal halides and cyanide.13 By addition of potassium as reductant, complexes of cobalt(O), nickel(O), titanium(II) and titanium(III) may be prepared and a complex of zirconium(0) has been obtained in a remarkable disproportion of zirconium(III) into zirconium(IV) and zirconium(0).14 Other solvents which have been shown to be suitable for halide-cyanide exchange reactions include ethanol, methanol, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide. With their aid, species of different stoichiometry from those isolated from aqueous media can sometimes be made [Hg(CN)3], for example, is obtained as its cesium salt form CsF, KCN and Hg(CN)2 in ethanol.15... 

Coordinated a-amino amides can be formed by the nucleophilic addition of amines to coordinated a-amino esters (see Chapter 7.4). This reaction forms the basis of attempts to use suitable metal coordination to promote peptide synthesis. Again, studies have been carried out using coordination of several metals and an interesting early example is amide formation on an amino acid imine complex of magnesium (equation 75).355 However, cobalt(III) complexes, because of their high kinetic stability, have received most serious investigation. These studies have been closely associated with those previously described for the hydrolysis of esters, amides and peptides. Whereas hydrolysis is observed when reactions are carried out in water, reactions in dimethyl-formamide or dimethyl sulfoxide result in peptide bond formation. These comparative results are illustrated in Scheme 91.356-358 The key intermediate (126) has also been reacted with dipeptide... 

Even with immobilized catalysts being developed, removal of ruthenium by-products remains an important challenge. Georg and coworkers found that addition of 50 equiv (relative to ruthenium) of dimethyl sulfoxide or triphenylphosphine oxide brought ruthenium levels in reaction mixtures down from 50 to l-2qgmg-. The ruthenium levels in purified products are similar to those reported by Grubbs, where the metal was removed as trishydroxymethylphosphine complexes, " and those from the Pb(OAc)4 oxidation of ruthenium reported by Paquette. 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

The oxidation of OH by [Fe(CN)6] in solution has been examined. Application of an electrical potential drives the reaction electrochemically, rather than merely generating a local concentration of OH at the anode, as has been suggested previously, to produce both O and [Fe(CN)6] in the vicinity of the same electrode. With high [OH ] or [Fe(CN)6] /[Fe(CN)6] ratio, the reaction proceeds spontaneously with a second-order rate constant of 2.2 x 10 M s at 25 °C. Under anaerobic conditions, iron(III) porphyrin complexes in dimethyl sulfoxide solution are reduced to the iron(II) state by addition of hydroxide ion or alkoxide ions. Excess hydroxide ion serves to generate the hydroxoiron(II) complex. The oxidation of hydroxide and phenoxide ions in acetonitrile has been characterized electrochemically " in the presence of transition metal complexes [Mn(II)L] [M = Fe,Mn,Co,Ni L = (OPPh2)4,(bipy)3] and metalloporphyrins, M(por) [M = Mn(III), Fe(III), Co(II) por = 5,10,15,20-tetraphenylpor-phinato(2-), 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphinato(2-)]. Shifts to less positive potentials for OH and PhO are suggested to be due to the stabilization of the oxy radical products (OH and PhO ) via a covalent bond. Oxidation is facilitated by an ECE mechanism when OH is in excess. 

The PMR spectra of the o - and tt -allyl complexes correspond very well with the spectra of the corresponding manganese and cobalt carbonyl complexes (9). Although the exact location of the tt -allyl group with respect to the metal is not known, the reaction with cyanide ion indicates that the TT -allyl group may be considered to be bidentate, a conclusion in full accord with the displacement of carbon monoxide in the conversion of a -to-tt-allyl cobalt and manganese carbonyls (9), and with the coordination of dimethyl-sulfoxide in the conversion of 7r-to-o -allyl palladium chloride (10). Structure(I) is tentatively proposed for the tt -allyl cyanocobaltate complex. 

Dimethyl sulfoxide, a product of an oxidation reaction on dimethyl sulfide, contains a very polar sulfoxide functional group (6 = 16.4). This highly polar functional group enables DMSO to form complexes with many metal ions, to act as a reaction medium for synthetic reactions, and to dissolve a large number of organic resins and polymers. 

Oxidation replaces the carbon-metal double bond of metal-carbene complexes with a carbon-oxygen double bond. A variety of oxidizing agents including pyridine iV-oxide (Cotton and Lukehart, 1971), dimethyl sulfoxide (C. P. Casey, R. L. Boggs, and W. R. Brunsvold, unpublished results, 1974), ceric ion (Casey et al., 1972) and oxygen (Fischer and Riedmuller, 1974) have been employed. These oxidations are normally clean, high-yield reactions... 

Facilitating the introduction of the metal carboxylates into the epoxy compositions is possible by complexing them with such volatile, coordinating, and electron-donating solvents as dimethyl formamide, dimethyl sulfoxide, dimethyl sulfolane, tetramethyl urea, dimethyl acetamide, methylcaprolactam, or methyl pyrrollidone. These solvents evaporate when applied to a surface to reactivate the salt catalysts by the formation of the occupied coordination sites, which results in the reaction of the epoxy oligomers with the carboxylic acid anhydrides [214]. 

In parallel, it was reported by Housecroft and coworkers a completely different metalloden-dritic system based on a pentaerythritol, as a core molecule, and four carboranyl-functionalized complexes of 2,2 6, 2"-terpyridine ruthenium. The reaction of pentaerythrytol with 4 -Cl-2,2 6, 2" -terpyridine in dimethyl sulfoxide (DMSO) in the presence of KOH gave a molecule that contains four tpy metal-binding sites, the crucial point for the formation of the metallodendrimer. The reaction of this with the carboranyl-functionalized Ru complex [Ru 4 -[2-(tert-butyldimethylsilyl)-l,2-carboranyl]-2,2 6, 2"-ter-pyridine Cl3], [Ru(sicarbtpy)Cl3], in ethane-l,2-diol at 120°C led to the formation of the first generation of a cationic tetranuclear metallodendrimer (Scheme 27.12), confirmed by NMR and MALDI-TOF. 

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