Platinum catalysts are reported for the direct, low-temperature, oxidative conversion of methane to a methanol derivative at greater than 70 percent one-pass yield based on methane. The catalysts are ...platinum complexes derived from the bidiazine ligand family that are stable, active, and selective for the oxidation of a carbon-hydrogen bond of methane to produce methyl esters. Mechanistic studies show that platinum(II) is the most active oxidation state of platinum for reaction with methane, and are consistent with reaction proceeding through carbon-hydrogen bond activation of methane to generate a platinum-methyl intermediate that is oxidized to generate the methyl ester product.
The novel, anti-Markovnikov, arylation of olefins with benzene to produce straight-chain alkylbenzenes with higher selectivity than branched alkylbenzenes is catalyzed by Ir(μ-acac-O,O′,C
3)(acac-
...O,O′)(acac-C
3)
2 (acac=acetylacetonato),
1 J. Am. Chem. Soc. 122 (2000) 7414. The reaction of benzene with propylene gave
n-propylbenzene and cumene in 61 and 39% selectivities, respectively. The reaction of benzene and styrene afforded 1,2-diphenylethane in 98% selectivity. Considering the anti-Markovnikov regioselectivity and lack of inhibition by water, we propose that the reaction does not proceed via a Friedel–Crafts, carbocation, mechanism. Complex
1, amongst the various transition metal complexes examined, is the most efficient for catalyzing the anti-Markovnikov olefin arylation. The crystal structure of complex
1 was solved and is consistent with a binuclear Ir(III) structure with three different types of coordinated acac ligands as reported by earlier solution IR and NMR analyses. Ir(μ-acac-O,O′,C
3)(acac-O,O′)Cl
2,
2, was prepared by the reaction of complex
1 with benzoyl chloride, and the crystal structure was also reported.
Various rhodium complexes were examined for oxidative arylation of ethylene with benzene to directly produce styrene. Using Rh(ppy)2(OAc) (1) (ppyH=2-phenylpyridine), the reaction of benzene with ...ethylene gives styrene and vinyl acetate in 77 and 23% selectivities, respectively, in contrast to the selectivities using Pd(OAc)2, which are 47% styrene and 53% vinyl acetate. The observation that complex 1 is an active catalyst for both styrene formation and H–D exchange between CH3CO2D and C6H6 suggests that styrene formation involves a Rh-mediated, benzene CH bond activation process. The crystal structures of complex 1 and Rh(ppy)2(acac–O,O′) (2) (acac=acetylacetonato) are also reported. Rh(acac)(CO)2 also works as catalyst for styrene formation by addition of acacH and O2 without any oxidizing agent, such as Cu salt. In this system, vinyl acetate is not formed at all in spite of the presence of acetic acid.
The effect of pressure on the recombination kinetics of small ligands binding to sperm whale myoglobin, protoheme dimethyl ester, and monochelated protoheme was studied with use of laser flash ...photolysis. The results are discussed in terms of the previously proposed three- and four-state reaction schemes for model hemes and myoglobin, respectively.
Picosecond kinetic studies of complexes of protoheme (PH), protoheme dimethyl ester (PHDME), and chelated protoheme (MCPH) are reported. The photolysis of carbon monoxide (CO) from complexes BHmCO ...where B is 1-methylimidazole, 1,2-dimethylimidazole, methanol, and 2-propanol all displayed no observable CO return picosecond time scales in common nonviscous solvents.
Steric effects on geminate recombinations Traylor, Teddy G; Taube, Douglas J; Jongeward, Karen A ...
Journal of the American Chemical Society,
09/1990, Letnik:
112, Številka:
19
Journal Article
Recenzirano
Steric effects on the binding of isonitrile ligands to iron(II) porphyrins were investigated by picosecond flash photolysis. Two different types of steric effects were distinguished and ...characterized: (1) steric restrictions to porphyrin planarity and (2) blocking of the pathway for ligand approach. Heme planarity was restricted by coordinating 1,2-dimethylimidazole trans to the ligand binding site being investigated. Blocking of the binding site was explored by using adamantane heme 6,6-cyclophane, in which the adamantane moiety forms a cap over the binding site. Results of picosecond kinetic measurements demonstrate that the first effect, heme nonplanarity or trans strain, influences the bond-making step, whereas the second effect, ligand blocking, involves a conformational preequilibrium prior to bond making. Relevance of these findings for contact pair recombination, in general, and for heme protein ligation, in particular, are discussed.
