Sulfur Atom Transfer Reactions Research Articles

Synthesis, characterization and X-ray crystal structure of Tp*WII{(R)-(+)-NHCH(Me)Ph}(CO)2

Reaction of Tp*WIII(CO)2 [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate] with (R)-(+)-α-methylbenzylamine [(R)-(+)-LH2] in dichloromethane yields blue, diamagnetic Tp*WII{(R)-(+)-LH}(CO)2, which has been characterised by microanalysis, mass spectrometry, infrared, 1H NMR, 13C{1H} NMR and electronic spectroscopies, and X-ray crystallography. The six-coordinate, distorted-octahedral (skew-trapezoidal-bipyramidal) complex is composed of a W(II) center bound to mutually cis carbonyl [C–W–C = 71.1(3)°] and (R)-(+)-LH ligands and a facially tridentate Tp* ligand. The complex is unusually stable and resistant to oxygen- and sulfur-atom transfer reactions directed at the W center.

Comparative Kinetics and Mechanism of Oxygen and Sulfur Atom Transfer Reactions Mediated by Bis(dithiolene) Complexes of Molybdenum and Tungsten

Although the kinetics and mechanism of metal-mediated oxygen atom (oxo) transfer reactions have been examined in some detail, sulfur atom (sulfido) transfer reactions have not been similarly scrutinized. The reactions [M(IV)(O-p-C(6)H(4)X')(S(2)C(2)Me(2))(2)](1-) + Ph(3)AsQ --> [M(VI)Q(O-p-C(6)H(4)X')(S(2)C(2)Me(2))(2)](1-) + Ph(3)As (M = Mo, W; Q = O, S) with variable substituent X' have been investigated in acetonitrile in order to determine the relative rates of oxo versus sulfido transfer at constant structure (square pyramidal) of the atom acceptor and of atom transfer at constant structure of the atom donor and metal variability of the atom acceptor. All reactions exhibit second-order kinetics and entropies of activation (-25 to -45 eu) consistent with an associative transition state. At parity of atom acceptor, k(2)(S) (0.25-0.75 M(-1)s(-1)) > k(2)(O) (0.023-0.060 M(-1)s(-1)) with M = Mo and k(2)(S) (4.1-66.7 M(-1)s(-1)) > k(2)(O) (1.8-9.8 M(-1)s(-1)) with M = W. At constant atom donor and X', k(2)(W) > k(2)(Mo) with reactivity ratios k(2)(W)/k(2)(Mo) = 78-184 (Q = O) and 16-89 (Q = S). Rate constants refer to 298 K. At constant M and Q, rates increase in the order X' = Me less, similar OMe < H < Br < COMe < CN; increasing electron-withdrawing propensity accelerates reaction rates. The probable transition state involves significant Ph(3)AsQ...M bond-making (X' rate trend) and concomitant As-Q bond weakening (bond energy order As-O > As-S). Orders of oxo and sulfido donor ability of substrates and complexes are deduced on the basis of qualitative reactivity properties determined here and elsewhere. This work complements previous studies of the reaction systems [M(IV)(O-p-C(6)H(4)X')(S(2)C(2)Me(2))(2)](1-)/XO where the substrates are N-oxides and S-oxides and k(2)(W) > k(2)(Mo) at constant substrate also applies. The reaction order of substrates is Me(3)NO > (CH(2))(4)SO > Ph(3)AsS > Ph(3)AsO. This research provides the first quantitative information of metal-mediated sulfido transfer.

Synthesis, Structure, and Reactivity of Novel Dithiolato(oxo)rhenium(V) Complexes

Oxygen atom transfer catalyzed by transition metal complexes holds great interest owing to its chemical and biological relevance. The intriguing mechanisms of certain of these reactions catalyzed by organorhenium oxides have been revealed. As the authors became involved in certain sulfur atom transfer reactions, it became important to synthesize stable thiolato complexes derived from methyltrioxorhenium (CH{sub 3}ReO{sub 3} or MTO), in that they are related to important catalytic intermediates. A tetrathiophenylato complex, unstable above 15 C, has been reported, as have anionic dithiolato complexes of rhenium(V)-sulfides. Prompted by these reports, the authors sought to prepare new, thermally stable thiolato complexes derived from MTO. They have synthesized, analyzed, and characterized new oxorhenium(V) complexes containing a dithiolato ligand. The dinuclear version of this complex is monomerized upon reaction with triphenylphosphine. The dimer readily reacts with several O-atom donors, undergoing oxidation both at the metal and at the ligand. They are currently investigating the scope and mechanism of this reaction and further studying the reactivity of this binuclear complex.

Oxomolybdenum Chemistry: An Experiment

Oxo complexes dominate the high-valent chemistry of the early and middle transition elements and oxygen atom transfer is important in industrial and biological processes. This undergraduate experiment focuses on the reactivity of oxomolybdenum complexes. A number of complexes, with a variety of coordination numbers, geometries and nuclearities, are prepared via nucleophilic or electrophilic attack on an oxo ligand of cis-MoO2(S2CNEt2)2: they are characterized by analysis, infrared and 1H NMR spectroscopy, and mass spectrometry. Finally, an examination is made of their oxygen atom and sulfur atom transfer reactions. The complexes synthesized and examined include: cis-MoO2(S2CNEt2)2, MoO(S2CNEt,))2, Mo2O2(micro-O)(S2CNEt2)4, MoOCl2(S2CNEt2)2 and MoO(S2)(S2CNEt2)2.

Fragmentation of organic anions induced by exothermic addition reactions

AbstractThe addition reactions of a series of carbanions with CO2, COS and CS2 have been studied in a flowing afterglow apparatus. Carbon dioxide simply forms the adduct, but the more highly exothermic additions to COS and CS2 lead both to addition and addition followed by fragmentation. A number of novel fragmentation pathways have been observed for additions to diazo anions and to anions derived by proton abstraction from allenes. In addition to these reactions, highly basic anions are observed to undergo sulfur atom transfer reactions with CS2.