Dimethylsulfoxide, complexes

The coordination number of Ni rarely exceeds 6 and its principal stereochemistries are octahedral and square planar (4-coordinalc) with rather fewer examples of trigonal bipyramidal (5), square pyramidal (5), and tetrahedral (4). Octahedral complexes of Ni arc obtained (often from aqueous solution by replacement of coordinated water) especially with neutral N-donor ligands such as NH3, en, bipy and phen, but also with NCS, N02 and the 0-donor dimethylsulfoxide. dmso (Me2SO). 

However, we have to criticize more specifically the paper by Lown et al. (1984), who characterized alkanediazonium ions, as well as (E)- and (Z)-alkanediazoate ions, by 15N NMR spectroscopy. They also report NMR data on the (E)- and (Z)-benzenediazohydroxides as reference compounds, describing the way they obtained these compounds in only three lines. Obviously the authors are not familiar with the work on the complex system of acid-base equilibria which led 30 years earlier to the conclusion that the maximum equilibrium concentration of benzenediazohydroxide is less than 1 % of the stoichiometric concentration in water (see Ch. 5). The method of Lown et al. consists in adding 10% (v/v) water to a mixture of benzenediazonium chloride and KOH in dimethylsulfoxide. In the opinion of the present author it is unlikely that this procedure yields the (Z)- and CE>benzenediazohydroxides. Such a claim needs more detailed experimental evidence. 

The chemistry of elemental sulfur and sulfur-rich molecules including polysulfides in liquid ammonia [82] and in primary as well as secondary amines [83] is complex because of the possible formation of sulfur-nitrogen compounds. Therefore, polysulfide solutions in these solvents will not be discussed here. Inert solvents which have often been used are dimethylfor-mamide (DMF) [84-86], tetrahydrofuran (THF) [87], dimethylsulfoxide (DMSO) [87], and hexamethylphosphoric triamide (HMPA) [86, 88]. 

Fernandez, E.J., Laguna, A., Lopez-de-Luzuriaga, J.M., Montiel, M Olmos, M.E. and Perez, J. (2005) Dimethylsulfoxide gold-thaDium complexes. Effects of the metal-metal interactions on the luminescence. Inorganica Chimica Acta, 358(14), 4293 300. 

More recently, this method has been extended to preparation of a variety of disulfonium dications from both acyclic and cyclic bis-sulfides, including very labile dications not observed when other methods were used.78 Thus, simple acyclic S-S dications were prepared by an intermolecular reaction of a monosulfide, a monosulfoxide and triflic anhydride.79 In the first step, reaction of triflic anhydride with dimethylsulfoxide generates a highly electrophilic80 complex 50 (dimethyl sulfide ditriflate).81 The latter reacts with dimethyl sulfide to give labile tetramethyldisulfonium dication 51 identified by NMR spectroscopy.79 In a similar manner, bis-(tetramethylene)disulfonium dication 52 is obtained from tetrahydrothiophene and its S-oxide (Scheme 17). 

Iron complexes or microsomal nonheme iron are undoubtedly obligatory components in the microsomal oxidation of many organic compounds mediated by hydroxyl radicals. In 1980, Cohen and Cederbaum [27] suggested that rat liver microsomes oxidized ethanol, methional, 2-keto-4-thiomethylbutyric acid, and dimethylsulfoxide via hydrogen atom abstraction by hydroxyl radicals. Then, Ingelman-Sundberg and Ekstrom [28] assumed that the hydroxylation of aniline by reconstituted microsomal cytochrome P-450 system is mediated by hydroxyl radicals formed in the superoxide-driven Fenton reaction. Similar conclusion has been made for the explanation of inhibitory effects of pyrazole and 4-methylpyrazole on the microsomal oxidation of ethanol and DMSO [29],... 

Iodides of soft metal ions such as mercury (II) are essentially un-ionized in dimethylsulfoxide 54). This feature is due both to the strength of the Hg-I bond and the weakness of the Hg-DMSO bond which appears to occur through the sulfur atom of the DMSO molecule, as is known for the palladium (II) complex 5S). 

These researchers found that the nucleophilicity of the complex depended on the electronic nature of the porphyrin. While a [(TPFPP)Fe (02)] (TPFPP equals the dianion of me5 o-tetrakis(pentafluorophenyl)porphyrin) complex did not epoxidize alkenes, adding dimethylsulfoxide (DMSO) as an axial ligand restored the complexes nucleophilicity and ability to epoxidize alkenes. The authors ascribed this restored capability to push the side-on peroxo into a more open, end-on, nucleophilic conformation. Watanabe and co-workers... 

High-spin, five-coordinate complexes are known of type [MnLXJPFg (X = F, Cl, Br, or I and L = 2,9-dimethyl-3,10-diphenyl-1,4,8,11-tetraazacyclotetra-l,3,8,10-tetraene). Electrochemical investigation of these complexes revealed that they are surprisingly resistant to oxidation in dimethylsulfoxide." ... 

Polyurethanes 96 containing 1 have been prepared by several research groups, and complex polyurethanes with an elastomeric character and good mechanical properties were described in a few patents. These polymers were obtained from 1 and diisocyanates in the presence of suitable catalysts, e.g., Braun and Bergmann used triethylamine in dimethylsulfoxide [104]. 

Divalent metal ions, reversible binding, 38 153 Dixenon cation, 46 68 Dizinc enzymes, 40 351-354 DMA, see Dicarbomethoxy acetylene DMAD complexes, see Dicarboxymethoxy dithiolene complexes DMAE, see Dimethylarsinoylethanol DMF, reduction potentials, 33 57 DMSO, see Dimethylsulfoxide DNA... 

Photoreduction of cobalt(III) complexes in nonaqueous solvent systems has been little studied because of the limited solubility of cobalt(III) complexes and their tendency to photooxidize the solvent. Irradiation with 365-mjj. light of cis- or trans-Co(en)2C 2 + and Co(en)2Cl(DMSO)2+ in dimethylsulfoxide (DMSO) leads rapidly to production of a green tetrahedral cobalt(II) product apparently with concurrent solvent oxidation.53,71 Irradiation with 365-mjx light of the molecular Co(acac)3 in benzene rapidly gives a red precipitate which may be the cobalt(II) acetylacetonate.53... 

The second critical test of this conjugate base mechanism is based on the fact that this five-coordinated intermediate, if indeed it exists, would not always have to react with the solvent, though the solvent would be what it would react with under most circumstances. We have run this type of base hydrolysis in the presence of many anions of high concentration, and the only thing that we can find is the hydroxo complex so at least in water solution, water seems to be what this five-coordinated intermediate picks up. But in dimethylsulfoxide it certainly is possible to throw in various anions, and since dimethylsulfoxide is not as good as water in coordination, other nucleophiles may react. We do find in dimethylsulfoxide that a base, such as hydroxide ion, speeds up the rate of base hydrolysis but the product, instead of being a hydroxo compound, is the complex corresponding to whatever anion we have added, such as nitrite ion, azide ion, and thiocyanate ion. 

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