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The antimicrobial properties of a series of anionic bis(carbene) silver complexes Na3[Ag(NHCR)2] were investigated (2a–2g and 2c′, where NHCR is a 2,2′-(imidazol-2-ylidene)dicarboxylate-type N-heterocyclic carbene). The complexes were synthesized by the interaction of imidazolium dicarboxylate compounds with silver oxide in the presence of aqueous sodium hydroxide. Complexes 2f,g were characterized analytically and spectroscopically, and the ligand precursor 1f and complexes 2c and 2g were structurally identified by X-ray diffraction methods. The anions of 2c and 2g, [Ag(NHCR)2]3−, showed a typical linear disposition of Ccarbene-Ag-Ccarbene atoms and an uncommonly eclipsed conformation of carbene ligands. The antimicrobial properties of complexes 2a–g, which contains chiral (2b–2e and 2c′) and non-chiral derivatives (2a,f,g), were evaluated against Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, and a Gram-positive bacterium, Staphylococcus aureus. From the observed values of the minimal inhibitory concentration and minimal bactericidal concentration, complexes 2a and 2b showed the best antimicrobial activity against all strains. An interesting chirality–antimicrobial relationship was found, and eutomer 2c′ showed better activity than its enantiomer 2c against the three bacteria. Furthermore, these complexes were investigated experimentally and theoretically by 109Ag nuclear magnetic resonance, and the electronic and steric characteristics of the dianionic carbene ligands were also examined. [ABSTRACT FROM AUTHOR]

Chiral alkyl aryl sulfoxides were obtained by molybdenum-catalyzed oxidation of alkyl aryl sulfides with hydrogen peroxide as oxidant in mild conditions with high yields and moderate enantioselectivities. The asymmetry is generated by the use of imidazolium-based dicarboxylic compounds, HLR. The in-situ-generated catalyst, a mixture of aqueous [Mo(O)(O2)2(H2O)n] with HLR as chirality inductors, in the presence of [PPh4]Br, was identified as the anionic binuclear complex [PPh4]{[Mo(O)(O2)2(H2O)]2(μ-LR)}, according to spectroscopic data and Density Functional Theory (DFT) calculations. A nonclassical hydrogen bond between one C–H bond of the alkyl R group of coordinated (LR)− and one oxygen atom of the peroxido ligand was identified as the interaction responsible for the asymmetry in the process. Additionally, the step that governs the enantioselectivity was theoretically analyzed by locating the transition states of the oxido-transfer to PhMeS of model complexes [Mo(O)(O2)2(H2O)(κ1-O-LR)]− (R = H, iPr). The ∆∆G≠ is ca. 0 kcal∙mol−1 for R = H, racemic sulfoxide, meanwhile for chiral species the ∆∆G≠ of ca. 2 kcal∙mol−1 favors the formation of (R)-sulfoxide. [ABSTRACT FROM AUTHOR]

Abstract: The direct formation of a β-alcoxyalcohol from the corresponding olefin was investigated through the study of the oxidation of cyclohexene with hydrogen peroxide, as test reaction, catalysed by commercially available MoO3 in the presence of alcohols. The formation of the corresponding β-alcoxycyclohexanol was favourable in the order Me>Et> iPr> tBu, reaching approximately no yield for tBuOH. In this reaction, the lack of selectivity was due to the simultaneous formation of cyclohexane-1,2-diol by epoxide hydrolysis, a reaction that it is competitive with respect to the epoxide ring-opening reaction by the alcohol. In order to decrease the cyclohexane-1,2-diol yield, by preventing the hydrolysis reaction, several strategies were analysed and discussed. In particular, 2-methoxycyclohexanol was obtained with high yields and 99% selectivity by using as catalyst the [C4mim]4[Mo8O26] complex (C4mim=1-butyl-3-methylimidazolium). The structure of the latter octamolybdate and also that of the tetraperoxodimolybdate [Htmpy]2[{MoO(O2)2}2(μ-O)] (tmpy=2,4,6-trimethylpyridine) complex were determined by X-ray crystallography. The latter complex shows a μ2-oxygen bridging atom and two μ2-κ2–κ1-peroxo bridging ligands. This overall coordination assembly is unprecedented for binuclear molybdenum complexes. [Copyright &y& Elsevier]

Oxidoperoxido-molybdenum(vi) complexes containing acylpyrazolonate ligands were obtained by reaction of [Mo(O)(O) 2 (H 2 O) n ] with the corresponding acylpyrazolone compounds HQ R . Complexes Ph 4 P[Mo(O)(O 2 ) 2 (Q R )] (R = neopentyl, 1; perfluoroethyl, 2; hexyl, 3; phenyl, 4; naphthyl, 5; methyl, 6; cyclohexyl, 7; ethylcyclopentyl, 8) were obtained if the reaction was carried out with one equivalent of HQ R in the presence of Ph 4 PCl. Alternatively, neutral complexes [Mo(O)(O 2 )(Q R ) 2 ] (R = neopentyl, 9; hexyl, 10; cyclohexyl, 11) were formed when two equivalents of HQ R were used in the reaction. These complexes were isolated in good yields as yellow or yellow-orange crystalline solids and were spectroscopically (IR, 1 H, 13 C{ 1 H} and 31 P{ 1 H} NMR), theoretically (DFT) and structurally characterised (X-ray for 1, 2, 9 and 10). Compounds 1 and 9 were selected to investigate their catalytic behaviour in epoxidation of selected alkenes and oxidation of selected sulphides, while 10 and 11 were tested as catalyst precursors in the deoxygenation of selected epoxide substrates to alkenes, using PPh 3 as the oxygen-acceptor. Complexes Ph 4 P[Mo(O)(O 2 ) 2 (Q R )] were shown to be poor catalyst precursors in oxidation reactions, while the activity of [Mo(O)(O 2 )(Q R ) 2 ] species is good in all the studied reactions and comparable to related oxidoperoxido-molybdenum(vi) complexes. Complex [Mo(O) 2 (Q C6 ) 2 ], 12, was obtained by treatment of 10 with one equivalent of PPh 3 , demonstrating that the first step in the epoxide deoxygenation mechanism was the oxygen atom transfer toward the phosphane.