ABSTRACT
A novel dimeric rhenium(IV) complex, [Re2(SCH2CH2S)4], and a monomeric methyloxorhenium(V) complex, [CH3ReO(SCH2CH2S)PPh3], were synthesized from methyloxorhenium(V) complexes and characterized crystallographically. The structure of [Re2(SCH2CH2S)4], the formation reaction of which showed surprising demethylation conceivably through the homolytic cleaveage of the rhenium-carbon bond, features distorted trigonal prismatic coordination of sulfurs around the metal center and a rhenium-rhenium triple bond. A revised structure, [Tc2(SCH2CH2S)4], is proposed for a related technetium complex, originally identified as [Tc2(SCH2CH2S)2(SCH=CHS)2] (Tisato et al. Inorg. Chem. 1993, 32, 2042). Additionally, a new compound, CH3Re(O)(SPh)2PPh3, was prepared.
ABSTRACT
The kinetics and mechanism of the reactions of the dimeric and monomeric methyloxo(dithiolato)rhenium(V) complexes [(o-SC6H4CH2S)Re(O)CH3]2 and [(o-SC6H4CH2S)PyRe(O)CH3] (Py = pyridine) with XO, sulfoxides, and pyridine N-oxides are studied. In these reactions, an oxygen atom from XO is transferred to rhenium, from which it later removed. A reaction scheme is proposed to interpret the kinetic data. This scheme features the formation of a monomeric (sulfoxide)- or (pyridine N-oxide)(dithiolato)methyloxorhenium(V) complex followed by its bimolecular oxidation in a rate-controlling step. Several sulfoxides (methyl, methyl phenyl, and substituted diphenyl) all react at similar rates. Activation parameters are determined for dimethyl sulfoxide and di-4-tolyl sulfoxide from temperature-dependent studies. The reactions with pyridine N-oxides show autocatalysis in which the catalyst is confirmed to be pyridine formed in the reactions.
ABSTRACT
The sulfur-bridged dimeric dithiolato rhenium(V) chelate [CH3(O)Re(eta 2,mu-o-SCH2C6H4S)]2 (D), derived from 2-mercaptothiophenol, was monomerized to give [CH3(O)Re(eta 2-o-SCH2C6H4S)]L (M-L) in benzene upon reaction with various neutral and anionic monodentate ligands (L) such as pyridine and its substituted derivatives, triarylphosphines, dimethyl sulfoxide, 4-picoline-N-oxide, and halide ions. The kinetic observations can readily be interpreted for all ligands by a unified mechanism in which the initial fast formation of a 1:1 (DL) and 1:2 (DL2) adduct is followed by the slow monomerization of each species so formed. The use of different ligands gave insight into different steps of the same multistep mechanism. The kinetics of ligand exchange between free L and the monomeric complexes was also studied; an associative pathway has been proposed to interpret the results. The crystal structures of two new monomeric ML complexes (with L = 4-acetylpyridine and 1,3-diethylthiourea) are reported.
ABSTRACT
The kinetics and mechanism of the iron(III)-phosphate ion reaction were studied at large iron(III) excess using the stopped-flow method at 10.0 degrees C in 1.0 M NaClO4. In the first few hundred milliseconds of the reaction, the formation of a novel tetranuclear complex was confirmed. The following composition is proposed for the new species: Fe4(PO4)(OH)2(H2O)16(7+). According to detailed kinetic studies, the formation of this species is first order with respect to Fe2(OH)2(H2O)8(4+) and H2PO4- and presumably proceeds via a dinuclear intermediate species. At longer reaction times slow dissociation of the tetranuclear complex controls the formation of the thermodynamically favored Fe(PO4)(H2O)5 complex. The overall reaction was interpreted in terms of the following reactions: Fe2(OH)2(H2O)8(4+) [symbol: see text] 2Fe3+ mn; Fe2(OH)2(H2O)8(4+) + P(V) [symbol: see text] Fe2PV; Fe2PV + Fe2(OH)2(H2O)8(4+) [symbol: see text] Fe4PV; Fe3+ mn + P(V) [symbol: see text] Fe(PO4)(H2O)5. (Fe3+ mn = Fe(H2O)6(3+) + Fe(OH)(H2O)5(2+); P(V) = H3PO4 + H2PO4-; Fe2PV = Fe2(HPO4)(OH)(H2O)8(3+); Fe4PV = Fe4(PO4)(OH)2(H2O)16(7+).) The pH dependence and relevant rate and equilibrium constants are reported for the individual reaction steps.
