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Theoretical studies were performed on the C-S bond activation reactions of 2-/3-cyanothiophene, 2-/3-methoxythiophene, and 2-/3-methylthiophene with the [Rh(PMe3)(C5Me5)] fragment to compare with the selectivity of these reactions observed in the experimental study, with the goal of determining whether the latter represent kinetic or thermodynamic products. Density functional theory (DFT) calculations have been used to optimize the ground-state structures of the two possible insertion products and the transition state structures leading to the formation of the products arising from the above cleavage reactions to address this question. With the 2-cyano and 2-methoxy substituents, the observed formation of one product resulting from the exclusive insertion of the rhodium into the more hindered substituted C-S bond was found to be consistent with the calculated energy differences between the ground states of the two possible products (7.6 and 2.6 kcal mol-1). With 2-methylthiophene, the product resulting from the activation of the unsubstituted C-S bond is calculated to be favored by 5.8 kcal mol-1, in agreement with observed results. The ~1 :1 ratio of products with 3-cyano and 3-methyl substituted thiophenes are also found to be consistent with the small calculated energy differences (0.4 and 0.8 kcal mol-1) between the ground states of the two insertion products. Although the observed high selectivity in the formation of a single C-S bond activation product with 3-methoxythiophene appears to be underestimated in the calculations, the observed products for all substituted thiophenes correlate with the calculated thermodynamic products. In addition, the kinetic selectivities predicted based on the calculated C-S bond activation barriers are different from those observed experimentally. Consequently, these investigations demonstrate that DFT calculations can be used reliably to differentiate if an experimentally observed C-S bond activation reaction proceeds under thermodynamic or kinetic control. [ABSTRACT FROM AUTHOR]

2,3-Substituted quinolines were readily prepared from diallylanilines in good yields under mild conditions by using Co2(CO)8 as catalyst. Regioselectivity has been explored by examining a series of electron-donating and electron-withdrawing functional groups at ortho, meta, and para positions of the diallylanilines. The results show that both steric and electronic effects influence the isolated yields. Electron-withdrawing groups inhibit the reaction. Solvent effects, temperature effects, and catalyst loadings have also been investigated, Isotopic labeling experiments were devised to permit delineation of the mechanism of reaction. [ABSTRACT FROM AUTHOR]

Carbon-carbon bond activation of diphenylacetylene and several substituted derivatives has been achieved via photolysis and studied. P0-acetylene complexes with η²-coordination of the alkyne, along with the corresponding PtII CC activated photolysis products, have been synthesized and characterized, including X-ray crystal structural analysis. While the CC cleavage reaction occurs readily under photochemical conditions, thermal activation of the CC bonds or formation of PtII complexes was not observed. However, the reverse reaction, CC reductive coupling (PtII → Pt0), did occur under thermal conditions, allowing the determination of the energy barriers for CC bond formation from the different PtII complexes. For the reaction (dtbpe)Pt(-Ph)(CCPh) (2) → (dtbpe)Pt(η²-PhCCPh) (1), ΔG‡ was 32.03- (3) kcal/mol. In comparison, the energy barrier for the CC bond formation in an electron-deficient system, that is, (dtbpe)Pt(C6F5)(CCC6F5) (6) → (dtbpe)Pt(η²2-bis(pentafluorophenyl)acetylene) (5), was found to be 47.30 kcal/mol. The energy barrier for CC bond formation was able to be tuned by electronically modifying the substrate with electron-withdrawing or electron-donating groups. Upon cleavage of the CC bond in (dtbpe)Pt(η²-(p-fIuorophenyl-p-tolylacetylene) (9), both (dtbpe)Pt(p-fluorophenyl)(p-tolylacetylide) (10) and (dtbpe)Pt(p-tolyl)(p-fluorophenylacetylide) (11) were obtained. Kinetic studies of the reverse reaction confirmed that 10 was more stable toward the reductive coupling [the term "reductive coupling" is defined as the formation of (dtbpe)Pt(η²-acetylene) complex from the PtII complexj than 11 by 1.22 kcal/mol, under the assumption that the transition-state energies are the same for the two pathways. The product ratio for 10 and 11 was 55:45, showing that the electron-deficient CC bond is only slightly preferentially cleaved. [ABSTRACT FROM AUTHOR]

A variety of diallylanilines are shown to undergo cobalt-carbonyl catalyzed rearrangement to quinolines. Diallylanilines are also used as allyl transfer reagents to convert benzaldimines into quinolines. Substitution in the 2- and 3-positions of the quinoline is featured in all transformations. [ABSTRACT FROM AUTHOR]

Describes the mechanism of hydrodefluorination reactions of zirconium hydroxide with polyfluorinated olefins. Repulsion between lone pairs on fluorine and pi-electrons; Occurrence of insertion/beta-fluoride elimination mechanism; Allylic C-F bonds of the olefins; Presence of primary and secondary alkylzirconium olefin insertion intermediates.

Describes the conformation behavior and coordination chemistry of orthocyclophane with platinum group metals. Synthesis of ionic heteroleptic complexes; Influence of electronic properties of metal ion on conformational changes; Role of conformational chemistry on molecular recognition.

Presents a study which examined the reactivity of a nickel hydride complex toward carbon-sulfur bond activation in thiophenic molecules. Preparation of the nickel hydride dimer; Reactions with thiopene and benzothiopene; Preparation of sulfur-bridged dinuclear complexes; Mechanism of desulfurization of dibenzothiopene; Conclusions.

Presents information on a study on the synthesis and characterization of (tris(3,5-dimethylpyrazolyl)borato)rhodium alkyl and vinyl chloride complexes. Research methodology; Results of this study; Statistical data gathered.

Proposes a mechanism of carbon-fluorine bond activation by (C5Me5)Rh(PMe3)H2. Examination of the relative reactivity of (C5Me5)Rh(PMe3) with different fluoroaromatics; Observance of high selectivity; Mechanism of C-F cleavage in polyfluorinated aromatic substrates.

Examines regiochemical selectivity in the carbon-sulfur bond cleavage of 2-methylbenzothiophene. Insertion of rhodium into the sulfur-carbon bond adjacent to the methyl substituent 2k; Conversion of the 2k to the isomer; Kinetic product crystallized as a racemic twin in the orthorhombic space group.

Investigates the hydrodesulfurization of thiophene to butadiene and butane by a homogeneous iridium complex. Cleavage of a thiophene carbon-sulfur bond; Reaction of the butadiene complexes with carbon monoxide; Crystallization of the dicarbonyl complex in monoclinic space group; Reaction of the butadiene complex with hydrogen.

Discusses results of the reaction between indene and a cyclopentadienyl complex. Yielding of mixture of two organometallic complexes; Characterization and reactivity; Mechanism for formation; Bonds; Specific crystallizations of resultant complexes.

Studies the kinetic and thermodynamic selectivity of carbon-hydrogen (C-H) bonds. Irradiation of the carbodiimide complex in alkane and arene solvents; Formation of the C-H oxidative addition product; Activation of methane; Thermodynamic conditions of the reactions of benzylic and aromatic C-H bonds; Rates of reductive elimination.

An introduction to the journal is presented in which the associate editor discusses an article on the use of a N-Heterocyclic carbene (NHC) in organocatalysis by Rovis, the initiators of NHC that allows polymerization of lactides to cyclic polylactides by Waymouth, and the gold(I) NHC cation which catalyzes hydration of alkynes to ketones by Nolan.

Examines the evidence for the existence of a late-metal terminal sulfido complex. Binding modes of a sulfur atom to a supported nickel; Desulfurization of organosulfur substrates using homogenous nickel complexes; Loss of benzene and formation of the terminal oxo complex; Preparation of a nickel complex incorporating chelating phosphines.

Studies the effects of catalytic hydrogenolysis of an aryl-aryl carbon-carbon bond with a rhodium complex. Review of reports on metal-aryl bonds; Analysis of the thermal conversion of the complexes in the presence of an excess of deuterated biphenylene; Description of the cleavage of the well-hidden carbon-carbon bond of biphenylene.