Reactions at a dimolybdenum(V) sulfur bridge. Formation of disulfide (S22-), monosubstituted organic disulfide (RSS-) and tetrasulfide (S42-) bridges

Abstract

Compounds of the general form [MO~(NA~)~(S~P(OC~H~)~)~S(O~CR)]~(S~) (Ar = C6Hs, p-C&CH,; R = alkyl, aryl) were prepared by the reaction of [MO(NA~)(S,P(OC~H~)~)S]~ with H 2 0 2 in the presence of a carboxylic acid. The compounds contain a disulfide linkage bridging in inter-and intradimer fashion, formed by the oxidation of two Mo2S?+ cores to give SMo2SSMo2S, formally equivalent to SMo2S' thiyl radical coupling. Mixed dimer-organic disulfides were prepared by the reaction of [Mo2-(NC6H4CH~)2(S2P(OC2H~)2)2S2(02ccH3)]with sulfenyl chlorides, R'SCI (R' = alkyl, aryl). The products, [Mo2-(NC6H4CH3)2(S2P(OC2Hs)2)2s(02ccH3)(ssR')], contain an unusual R'SS-linkage to the two Mo(V) sites within the dimer, representable by SMo,SSR', wherein the monosubstituted organic disulfide ion bridges by its @-sulfur. A bridge tetrasulfide, [MO,(NC~H~CH~)~(S~P(OC~H~)~)~S(~~CCH~)]~(S~), was prepared by the reaction of [ M O , ( N C~H~C H , ) , ( S~P (~C~H~)~)~S~-(02CCH3)]-with S2CI2 and contains the SMo2SSSSMo2S unit, in which the tetrasulfide bridges also in inter-and intradimer fashion via its terminal sulfur atoms. Most of the compounds show stereoisomers related by bridge sulfur inversion. Reactions with triphenylphosphine gave either desulfurization or reduction.

Formation of stable aryldisulphide ions in dimethylacetamide from the reaction of sulphur with thiolate ions

“…The following two paragraphs will discuss the oxidation of all the thiolates studied into aryldisulphide ions [equation (l)] and then into RS,R [equation (7)].…”

“…Thus, when sulphur is added at & < y < d to a solution of phenyl or p-tolyl disulphide ions (lc or 2c), the absorption bands of S;-(617 nm) and of the complex C* (480 nm) increase with y. At each addition of s8, the solution first becomes blue because of the rapid oxidation (7) then slowly turns pale yellow because of the formation of C* (9). Only when y becomes higher than 3/8 could sulphur be detected on the voltammetric curves and the absorption maximum at 480 nm shifts towards 500 nm with the partial formation of S i -according to (3).…”

“…Nevertheless, the complexity of the spectra as a result of the simultaneous equilibria ( 7), (9), and (3) precludes determination of a constant to characterise the level of oxidation (7).…”

“…(b) The disulphide ions arising from thiolates the structure of which explains the weaker S-nucleophilic power (6b)-(9b), will be slightly (6c)-(8c) or not at all further oxidised into RS,R. Both forward and backward shifts of equilibrium (7) have been studied: 2 RS; + $ S8+RS2R + 2 S;- (7) ( i ) addition of sulphur beyond the ratio y = 1/8 and determination of the constant…”

“…We have previously shown2' that they are the reaction products of methyl iodide with S;-/Sisolutions because of the equilibria between the radical anions and their dimers, Sg and S i -/Sip all nucleophilic reagents. These ions are present in the reaction medium because of the weak oxidation according to (7).…”