The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform
James H Espenson - One of the best experts on this subject based on the ideXlab platform.
-
related rhenium v catalysts adopt different mechanisms for oxygen atom transfer
Coordination Chemistry Reviews, 2005Co-Authors: James H EspensonAbstract:Abstract The chemical mechanisms for three related rhenium(V) catalysts of oxygen atom transfer reactions are reviewed. Two of the catalysts are compounds with a single rhenium atom, [MeReE(mtp)(PPh3)], where E is either O ( 1 ) or S ( 2 ) and mtpH 2 is 2-(mercaptomethyl)thiophenol; the third is the di-rhenium compound {MeReO(mtp)} 2 ( 3 ). In each of them, the Re atom is square-pyramidal, sitting slightly above the approximate basal plane defined by S, S, C, and P; the oxo or thio group occupies the axial position. They all catalyze oxygen atom transfer from Pyridine N -oxides to PAr 3 . The reaction rates are in the orders 3 ≫ 1 ≫ 2 ; even more striking is that the rate laws for the trio of catalysts is distinctly different. This signals the intervention of different chemical steps and intermediates.
-
nucleophilic assistance in rhenium catalyzed oxygen atom transfer
Organometallics, 2004Co-Authors: Michael J Vasbinder, James H EspensonAbstract:Oxygen atom transfer from Pyridine N-Oxides (PyO) to triphenylphosphine is catalyzed by MeReO(mtp)PPh3, 1, where mtpH2 is 2-(mercaptomethyl)thiophenol, at a rate given by v = kc[1][PyO]2/[PPh3]. When, however, other nucleophiles N are added, the rate law becomes v = kN[1][PyO][N]/[PPh3], and values of kN correlate with the nucleophilic strength of the added cocatalyst N.
-
kinetics and mechanism of rhenium catalyzed oxygen atom transfer from Pyridine n oxides to phosphines
Inorganic Chemistry, 2002Co-Authors: Ying Wang, James H EspensonAbstract:The oxygen atom transfer (OAT) reaction cited does not occur on its own in >10 h. Oxorhenium(V) compounds having the formula MeReO(dithiolate)PZ3 catalyze the reaction; the catalyst most studied was MeReO(mtp)PPh3, 1, where mtpH2 = 2-(mercaptomethyl)thiophenol. The mechanism was studied by multiple techniques. Kinetics (initial-rate and full-time-course methods) established this rate law: v = kc[1][PyO]2[PPh3]-1. Here and elsewhere PyO symbolizes the general case XC5H4NO and PicO that with X = 4-Me. For 4-picoline, kc = (1.50 ± 0.05) × 104 L mol-1 s-1 in benzene at 25.0 °C; the inverse phosphine dependence signals the need for the removal of phosphine from the coordination sphere of rhenium prior to the rate-controlling step (RCS). The actual entry of PPh3 into the cycle occurs in a fast step later in the catalytic cycle, after the RCS; its relative rate constants (k4) were evaluated with pairwise combinations of phosphines. Substituent effects were studied in three ways: for (YC6H4)3P, a Hammett correl...
Masaaki Hirobe - One of the best experts on this subject based on the ideXlab platform.
-
four recent studies in cytochrome p450 modelings a stable iron porphyrin coordinated by a thiolate ligand a robust ruthenium porphyrin Pyridine n oxide derivatives system polypeptide bound iron porphyrin application to drug metabolism studies
Journal of Molecular Catalysis A-chemical, 1996Co-Authors: Tsunehiko Higuchi, Masaaki HirobeAbstract:Abstract (1) A distinctive structural feature of P450 is the unusual thiolate coordination to heme. We have succeeded in the preparation of the first synthetic thiolato-iron porphyrin ( SR complex) which retains its structure during catalytic oxidation. Experiments using SR complex have revealed that the thiolate ligand greatly accelerates the rate of the OO bond cleavage and its heterolysis even in highly hydrophobic media. (2) Heteroaromatic N -oxides were found to be excellent oxidants in the presence of ruthenium porphyrin. 2,6-disubstituted Pyridine N -oxides plus a catalytic amount of Ru porphyrin oxidized olefins and sulfides to afford epoxides and sulfoxides, respectively, in high yields. The system in the presence of hydrogen halide effectively oxidized unactivated alkanes and arenes to give alcohols (or ketones) and p -quinones in high yields with high selectivity and an extremely high catalyst turnover number (up to 1.2 × 10 5 ). (3) A polypeptide-bound porphyrinatoiron complex was prepared. The polymer complex exhibited greater P450-like activity than non-bound Fe(TPP)Cl in the oxidation of olefin and aniline derivatives. (4) P450 mimics were applied to drug metabolism studies. These model systems were effective for one-step preparation of unstable metabolic intermediates, ‘candidate metabolites’, and for the discovery of novel modes of metabolism.
Keith Fagnou - One of the best experts on this subject based on the ideXlab platform.
-
a solution to the 2 pyridyl organometallic cross coupling problem regioselective catalytic direct arylation of Pyridine n oxides
Journal of the American Chemical Society, 2005Co-Authors: Louischarles Campeau, And Sophie Rousseaux, Keith FagnouAbstract:Direct arylation reactions of Pyridine N-Oxides occur in excellent yield with complete selectivity for the 2-position with a wide range of aryl bromides. This reactivity permits the use of inexpensive, commercially available, and bench-stable Pyridine N-Oxides as replacements for problematic 2-metallaPyridines in palladium-catalyzed cross-coupling reactions.
Michael J Vasbinder - One of the best experts on this subject based on the ideXlab platform.
-
nucleophilic assistance in rhenium catalyzed oxygen atom transfer
Organometallics, 2004Co-Authors: Michael J Vasbinder, James H EspensonAbstract:Oxygen atom transfer from Pyridine N-Oxides (PyO) to triphenylphosphine is catalyzed by MeReO(mtp)PPh3, 1, where mtpH2 is 2-(mercaptomethyl)thiophenol, at a rate given by v = kc[1][PyO]2/[PPh3]. When, however, other nucleophiles N are added, the rate law becomes v = kN[1][PyO][N]/[PPh3], and values of kN correlate with the nucleophilic strength of the added cocatalyst N.
Tsunehiko Higuchi - One of the best experts on this subject based on the ideXlab platform.
-
four recent studies in cytochrome p450 modelings a stable iron porphyrin coordinated by a thiolate ligand a robust ruthenium porphyrin Pyridine n oxide derivatives system polypeptide bound iron porphyrin application to drug metabolism studies
Journal of Molecular Catalysis A-chemical, 1996Co-Authors: Tsunehiko Higuchi, Masaaki HirobeAbstract:Abstract (1) A distinctive structural feature of P450 is the unusual thiolate coordination to heme. We have succeeded in the preparation of the first synthetic thiolato-iron porphyrin ( SR complex) which retains its structure during catalytic oxidation. Experiments using SR complex have revealed that the thiolate ligand greatly accelerates the rate of the OO bond cleavage and its heterolysis even in highly hydrophobic media. (2) Heteroaromatic N -oxides were found to be excellent oxidants in the presence of ruthenium porphyrin. 2,6-disubstituted Pyridine N -oxides plus a catalytic amount of Ru porphyrin oxidized olefins and sulfides to afford epoxides and sulfoxides, respectively, in high yields. The system in the presence of hydrogen halide effectively oxidized unactivated alkanes and arenes to give alcohols (or ketones) and p -quinones in high yields with high selectivity and an extremely high catalyst turnover number (up to 1.2 × 10 5 ). (3) A polypeptide-bound porphyrinatoiron complex was prepared. The polymer complex exhibited greater P450-like activity than non-bound Fe(TPP)Cl in the oxidation of olefin and aniline derivatives. (4) P450 mimics were applied to drug metabolism studies. These model systems were effective for one-step preparation of unstable metabolic intermediates, ‘candidate metabolites’, and for the discovery of novel modes of metabolism.
