Kinetics, mechanism, and computational studies of rhenium-catalyzed desulfurization reactions of thiiranes (thioepoxides).

The oxorhenium(V) dimer {MeReO(edt)}2 (1; where edt = 1,2-ethanedithiolate) catalyzes S atom transfer from thiiranes to triarylphosphines and triarylarsines. Despite the fact that phosphines are more nucleophilic than arsines, phosphines are less effective because they rapidly convert the dimer catalyst to the much less reactive catalyst [MeReO(edt)(PAr3)] (2). With AsAr3, which does not yield the monomer, the rate law is given by v = k[thiirane][1], independent of the arsine concentration.

Kinetics of the reaction of chromium(VI) with tris(1,10-phenanthroline)iron(II) ions in acidic solutions. Anion and medium effects: perchlorate versus triflate.

Reinvestigation of the reaction between title reagents in aqueous acidic triflate and perchlorate media revealed an unusual difference: the reaction is strictly first-order with respect to the concentration of Fe(phen)3(2+) (phen = 1,10-phenanthroline) in the triflate medium but shows an additional, but we believe artifactual, higher-order term in the perchlorate medium. We postulate that the apparent orders with respect to [Fe(phen)3(2+)] in (H/Li)ClO4 do not indicate the actual chemical mechanism but, in whole or in part, the orders, particularly the higher-order component, reflect an interaction specific to Fe(phen)3(2+) or Fe(phen)3(3+) and ClO4(-) in solution. Data in (H/Li)O3SCF3 solutions indicate that, in the absence of added Fe(phen)3(3+), the first of the three sequential electron-transfer steps is rate controlling.

Computational study of sulfur atom-transfer reactions from thiiranes to ER3 (E = As, P; R = CH3, Ph).

Computational estimates have been made for the P=S and As=S bond strengths in triphenylphosphine sulfide and triphenylarsine sulfide, on the basis of G3 calculations for the methyl analogues and isodesmic-exchange reactions. Also, with the performance of the G3 method level for related compounds taken into consideration, the best estimates are 82 and 68 kcal/mol, respectively. While the value for triphenylarsine sulfide is within 2 kcal/mol of the single experimental estimate, that for triphenylphosphine sulfide is lower by 6 kcal/mol.

3/2-order chain kinetics involving a postulated dicationic intermediate in the isomerization of a p-isocyano to a p-cyano azaphosphatrane monocation.

Kinetic evidence suggests the possibility of a dicationic intermediate in the title reaction. Thus the linkage isomerization reaction, PNC+ = PCN+, is described by the rate law, nu = 3/2k[PNC+]3/2, which can be interpreted by a chain mechanism with the propagation reaction PNC+ + P2+ --> P2+ + PCN+. Such propagation is unusual in that the intermediate regenerates itself in this single step rather than forming a different intermediate for a second propagation step.

Kinetics of the interconversion of parahydrogen and orthohydrogen catalyzed by paramagnetic complex ions.

The rate constants of para-/orthohydrogen (p-/o-H2) nuclear spin isomerization have been measured by means of 1H NMR in deuterated solvents at 298.2 K. The indicated reaction is catalyzed by paramagnetic complex ions giving rate constants that are proportional to the concentrations of the catalysts.

Studies of C-S bond cleavage reactions of Re(V) dithiolates: synthesis, reactivity, and mechanism.

A series of rhenium(V) complexes, [(X)(ReO)(dt)(PPh(3))] and [(o-SC(6)H(4)PPh(2))(ReO)(mtp)], were prepared to explore electronic effects on the C-S cleavage reaction that occurs upon reaction with PAr(3) at ambient temperature [where X = S(C(6)H(4)-p-Z) (Z = OMe, Me, H, F, Cl), OPh, Cl, and SC(2)H(5), and dt is the chelating dithiolate ligand derived from 2-(mercaptomethyl)thiophenol, 1,2-ethanedithiol, 1,3-propanedithiol, 1,3-butanedithiol, and 2,4-pentanedithiol]. The scope and selectivity of the C-S activation were examined. The C-S bond cleavage to form metallacyclic Re(V) complexes with a ReS core occurs only for the complexes with mtp and pdt frameworks and X = SAr and SC(2)H(5).

Oxidation of vanadium(III) by hydrogen peroxide and the oxomonoperoxo vanadium(V) ion in acidic aqueous solutions: a kinetics and simulation study.

The reaction between vanadium(III) and hydrogen peroxide in aqueous acidic solutions was investigated. The rate law shows first-order dependences on both vanadium(III) and hydrogen peroxide concentrations, with a rate constant, defined in terms of -d[H(2)O(2)]/dt, of 2.06 +/- 0.

Rhenium(V) complexes with thiolato and dithiolato ligands: synthesis, structures, and monomerization reactions.

The new compound {(PhS)(2)ReO(mu-SPh)}(2), 1, was synthesized from Re(2)O(7) and PhSH and then used as the synthon for a number of hitherto unknown oxorhenium(V) compounds. Reactions between dithiols and 1 (2:1 ratio) afford {PhSReO(dt)}(2), where the dithiols, dtH(2), are 1,2-ethanedithiol (edtH(2)), 1,3-propanedithiol (pdtH(2)), 1,3-butanedithiol (pdtMeH(2)), 1,2-benzenedithiol (bdtH(2)), 2-(mercaptomethyl)thiophenol (mtpH(2)), and 2-mercaptoethyl sulfide (mesH(2)). Similar reactions carried out with a 3:1 ratio of dtH(2) to 1 afford [(ReO)(2)(dt)(3)], dt = edt, pdt.

New oxorhenium(V) compound for catalyzed oxygen atom transfer from picoline N-oxide to triarylphosphines.

The synthesis and characterization of a new oxorhenium(V) compound is reported; it is [MeReO(edt)(bpym)], 8, where edt = 1,2-ethanedithiolate and bpym = 2,2'-bipyrimidine. Compound 8 was characterized by NMR spectroscopy and single-crystal X-ray analysis. It exists as a six-coordinate Re(V) compound comparable to the previously known [MeReO(edt)(bpy)] and [MeReO(mtp)(bpy)].

Oxidation of triarylphosphines and aryl methyl sulfides with hydrogen peroxide catalyzed by dioxovanadium(V) ion.

Although neither vanadium(V) ions nor hydrogen peroxide efficiently oxidize the title substrates, they do so in combination, with vanadium(V) as the catalyst in acidic aqueous acetonitrile. The kinetic data show that, of the two peroxovanadium species present, OV(O2)+ and OV(O2)2-, only the latter reacts at a detectable rate. This unanticipated result can be attributed to the weaker O-O and V-O bonds in the diperoxo complex.

Catalysis by methyltrioxorhenium(VII): reduction of hydronium ions by europium(II) and reduction of perchlorate ions by europium(II) and chromium(II).

The title reactions occur stepwise, the first and fastest being MeReO3 + Eu2+ --> Re(VI) + Eu3+ (k298 = 2.7 x 10(4) L mol(-1) s(-1)), followed by rapid reduction of Re(VI) by Eu2+ to MeReO2. The latter species is reduced by a third Eu2+ to Re(IV), a metastable species characterized by an intense charge transfer band, epsilon410 = 910 L mol(-1) cm(-1) at pH 1; the rate constant for its formation is 61.

Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid.

Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.

Ligand displacement and oxidation reactions of methyl(oxo)rhenium(V) complexes.

Compounds that contain the anion [MeReO(edt)(SPh)](-) (3-) were synthesized with the countercations 2-picolinium (PicH+3-) and 2,6-lutidinium (LutH+3-), where edt is 1,2-ethanedithiolate. Both PicH+3- and MeReO(edt)(tetramethylthiourea) (4) were crystallographically characterized. The rhenium atom in each of these compounds exists in a five-coordinate distorted square pyramid.

A non-radical chain mechanism for oxygen atom transfer with a thiorhenium(V) catalyst.

The compound MeRe(S)(mtp)(PPh3), 2, where mtpH2 is 2-(mercaptomethyl)thiophenol, was used to catalyze the reaction between pyridine N-oxides, PyO, and triphenylphosphine. The rate law is -d[PyO]/dt=kc'[2].[PyO](1/2), with kc' at 25.

Kinetic study of the phthalimide N-oxyl radical in acetic acid. Hydrogen abstraction from substituted toluenes, benzaldehydes, and benzyl alcohols.

The phthalimide N-oxyl (PINO) radical was generated by the oxidation of N-hydroxyphthalimide (NHPI) with Pb(OAc)4 in acetic acid. The molar absorptivity of PINO* is 1.36 x 10(3) L mol(-1) cm(-1) at lambda(max) 382 nm.

Kinetics and mechanism of oxygen atom transfer from methyl phenyl sulfoxide to triarylphosphines catalyzed by an oxorhenium(V) dimer.

An oxorhenium(V) dimer, [PMeReO(mtp)](2), D, where mtpH(2) is 2-(mercaptomethyl)thiophenol, catalyzes oxygen atom transfer reaction from methyl phenyl sulfoxide to triarylphosphines. Kinetic studies in benzene-d(6) at 23 degrees C indicate that the reaction takes place through the formation of an adduct between D and sulfoxide. The equilibrium constants, K(DL), for adduct formation were determined by spectrophotometric titration, and the values of K(DL) for MeS(O)C(6)H(4)-4-R were obtained as 14.

Photoaccelerated oxidation of chlorinated phenols.

Exposure to visible light increases the rate of oxidation of chlorinated phenols by hydrogen peroxide in aqueous solution in either the presence or the absence of iron-based catalysts, which may be explained by the aqueous photoreactions of chloroquinone intermediates.

Syntheses and oxidation of methyloxorhenium(V) complexes with tridentate ligands.

Four new methyloxorhenium(V) compounds were synthesized with these tridentate chelating ligands: 2-mercaptoethyl sulfide (abbreviated HSSSH), 2-mercaptoethyl ether (HSOSH), thioldiglycolic acid (HOSOH), and 2-(salicylideneamino)benzoic acid (HONOH). Their reactions with MeReO(3) under suitable conditions led to these products: MeReO(SSS), 1, MeReO(SOS), 2, MeReO(OSO)(PAr(3)), 3, and MeReO(ONO)(PPh(3)), 4. These compounds were characterized spectroscopically and crystallographically.

Methyloxorhenium(V) complexes with two bidentate ligands: syntheses and reactivity studies.

Four new methyloxorhenium(V) complexes were synthesized: MeReO(PA)(2) (1), MeReO(HQ)(2) (2), MeReO(MQ)(2) (3), and MeReO(diphenylphosphinobenzoate)(2) (4) (in which PAH = 2-picolinic acid, HQH = 8-hydroxyquinoline, and MQH = 8-mercaptoquinoline). Although only one geometric structure has been identified crystallographically for 1, 2, and 3, two isomers of 3 and 4 in solution were detected by NMR spectroscopy. These compounds catalyze the sulfoxidation of thioethers by pyridine N-oxides and sulfoxides.

Kinetic and mechanistic studies of sulfur transfer from imidomethylrhenium sulfides.

The bis(2,6-diisopropylphenylimido)methylrhenium(VII) sulfide dimer, [CH(3)Re(NAr)(2)](2)(mu-S)(2) (1), reacts with a 1:1 amount of a phosphine or an alkyl isocyanide to yield a dimeric rhenium(VI) species, [CH(3)Re(NAr)(2)](2)(mu-S) (2), which has been structurally characterized. The two rhenium atoms in 2 are within bonding distance, 280 pm, more than 90 pm shorter than in 1. With excess L, 1 reacts to give a monomeric rhenium(V) complex, CH(3)Re(NAr)(2)L(2) (3A, L = PZ(3), Z = alkyl, aryl; 3B, L = isocyanide).

Kinetics and mechanism of oxygen atom abstraction from a dioxo-rhenium(VII) complex.

The kinetics of reaction between triarylphosphanes and two newly prepared dioxorhenium(VII) compounds has been evaluated. The compounds are MeRe(VII)(O)(2)("O,S") in which "O,S" represents an alkoxo, thiolato chelating ligand. With MeReO(3), ligands derived from 1-mercaptoethanol and 1-mercapto-2-propanol form MeRe(O)(2)(met), 2, and MeRe(O)(2)(m2p), 3.

Synthesis and characterization of dimetallic oxorhenium(V) and dioxorhenium(VII) compounds, and a study of stoichiometric and catalytic reactions.

Chelating dithiolate ligands--e.g., mtp from 2-(mercaptomethyl)thiophenol, edt from 1,2-ethanedithiol, and pdt from 1,3-propanedithiol--stabilize high-valent oxorhenium(V) against hydrolytic and oxidative decomposition.