A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in "green" solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific ipso-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B-C bond cleavage and facile protonolysis of a Au-σ-phenyl intermediate.
This paper describes the synthesis of neutral nickel(II) catalysts for the polymerization of ethylene. A series of 2-(arylamino)-5-methylcyclopent-2-en-1-one (aryl = 2,6-diisopropylphenyl, 2,4,6-trimethylphenyl, 3,5-dimethylphenyl, and 4methylphenyl) proligands, derived from the condensation of aryl amines with maple lactone, were synthesized as their keto-enamine tautomers. Deprotonation with NaH gave their respective sodium imino-enolate salts, which underwent salt metathesis with Ni(II) precursors to give square planar [Ni(Ar)(κ 2 -imino-enolate)(PPh 3 )] (Ar = Ph, ortho-tolyl) complexes containing 5-membered [N,O] chelates. Precatalysts with N-Dipp (Dipp = 2,6-diisopropylphenyl) substituents were found to exhibit moderate activity in the polymerization of ethylene when using B(C 6 F 5 ) 3 or [Ni(cod) 2 ] (cod = 1,4-cyclooctadiene) as coactivators, producing polymers with a high molecular weight, as determined by GPC. The reaction was found to be highly dependent on temperature, with the catalysts most active at 80 °C. Differences in polymer structure were also found when using B(C 6 F 5 ) 3 or [Ni(cod) 2 ] as the cocatalyst, with [Ni(cod) 2 ] producing a more highly branched polymer. Reducing the steric bulk at the N substituent of the ligand led to inactive species.
Gas-phase reaction of 1,3-dithiolane-2-thione over molybdenum trioxide supported on pumice stone results in efficient conversion into 1,3-dithiolan-2-one. The solid reagent is regenerated on exposure to air and thus acts as a catalyst for the overall conversion of the thione and oxygen from the air into the ketone and sulfur dioxide. The process can be carried out under either dynamic vacuum or atmospheric pressure flow conditions and using a solid reagent prepared either by physical mixing of MoO
3
with the support or by solution impregnation, with an isolated yield of up to 67% obtained.
We report a combined experimental and computational study of the mechanism of the Cu-catalyzed arylboronic acid iododeboronation reaction. A combination of structural and DFT analyses has allowed determination of the identity of the reaction pre-catalyst and the first complete description of the catalytic cycle. Key findings include a rationale for ligand stoichiometry related to key turnover events – the ligand facilitates transmetalation via H-bonding to an organoboron boronate generated in situ and ligand loss/gain is integral to the key oxidative events. These data provide a framework for understanding ligand effects on these key mechanistic processes, which underpin several classes of Cu-mediated oxidative coupling reactions.
Gold-Catalyzed Proto-and Deuterodeboronation. -A Au(I)-catalyzed protodeboration of a variety of arylboronic acids using dimethylcarbonate as the solvent is presented. In the presence of D 2O the corresponding regioselectively deuterated products are obtained. -(BARKER, G.; WEBSTER, S.; JOHNSON, D. G.; CURLEY, R.; ANDREWS, M.; YOUNG, P. C.; MACGREGOR*, S. A.; LEE, A.-L.; J. Org. Chem. 80 (2015) 20, 9807-9816, http://dx.doi.org/10.1021/acs.joc.5b01041 ; Inst. Chem. Sci., Heriot-Watt Univ., Riccarton, Edinburgh EH14 4AS, UK; Eng.) -Mais 10-026
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