L. Keith Woo

Catalytic Reactions of Carbene Precursors on Bulk Gold Metal

Bulk gold metal powder, consisting of particles (5-50 microm) much larger than nanoparticles, catalyzes the coupling of carbenes generated from diazoalkanes (R(2)C=N(2)) and 3,3-diphenylcyclopropene (DPCP) to form olefins. It also catalyzes cyclopropanation reactions of these carbene precursors with styrenes. The catalytic activity of the gold powder depends on the nature of the gold particles, as determined by TEM and SEM studies. The reactions can be understood in terms of mechanisms that involve the generation of carbene R(2)C: intermediates adsorbed on the gold surface.

Catalytic efficacy of an oxido-peroxido tungsten(VI) complex: synthesis, X-ray structure and oxidation of sulfides and olefins

An oxido-peroxido tungsten(VI) complex [WO(O2)L(CH3OH)] using salicylidene benzoyl hydrazine as a tridentate ONO donor Schiff base (H2L) has been synthesized and characterized by elemental analysis, IR, 1H NMR, molar conductance data, and single-crystal X-ray analysis. The complex was used as a catalyst for epoxidation of olefins and oxidation of sulfides. The results show that epoxides and sulfoxides were produced in high yield, turnover number, and selectivity.

Catalytic activity of MnOx/WO3 nanoparticles: synthesis, structure characterization and oxidative degradation of methylene blue

MnOx/WO3 nanoparticles were synthesized by an impregnation method and the physicochemical properties of compounds were characterized by atomic absorption spectroscopy (AAS), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalytic degradation of an organic dye, methylene blue, in the presence of nano-MnOx supported on WO3 as a catalyst and hydrogen peroxide, H2O2, as the oxidant has been studied at room temperature in water. The effects of oxidant amount, catalyst composition and an OH-radical scavenging agent on the degree of decomposition of MB dye were also studied.

Synthesis, X-ray structure, DFT studies, and catalytic activity of a vanadium(V) complex containing a tridentate Schiff base

Reactions of a solution of NH4VO3 in H2O2 and water and salicylidene benzoyl hydrazine as a tridentate Schiff base (ONO) afford a six-coordinate V(V) complex [VO(ONO)(OCH3)(CH3OH)] with a distorted octahedral configuration. The complexes [VO(ONO)(OCH3)(CH3OH)] were isolated as air-stable crystalline solids and fully characterized, including by single-crystal X-ray structure analysis. DFT calculations have been performed to understand the electronic structure of the complex. Vibrational frequencies and maximum absorption wavelengths of the complex theoretically calculated are in good agreement with experimental values. [VO(ONO)(OCH3)(CH3OH)] shows efficient oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.

Selective oxidation of sulfides and olefins by a manganese(III) complex containing an N,O-type bidentate oxazine ligand

A new manganese(III) complex [(N–O)2Mn(OAc)] was synthesized using 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (N–O) as a bidentate O, N donor. The complex has been characterized by elemental analysis, IR, UV–vis spectroscopy, and X-ray structure analysis. Oxidation of sulfides and epoxidation of olefins, respectively, to their corresponding sulfoxides and epoxides were conducted by this catalyst using urea hydrogen peroxide as oxidant at room temperature under air. The catalyst is efficient in oxidation reactions giving high yields and selectivities.

O-H insertion and tandem N-H insertion/cyclization reactions using an iron porphyrin as catalyst with diazo compounds as carbene sources

Iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols, with yields generally above 80%. Although the analogous N-H insertions are rapid at room temperature, the O-H insertion reactions are slower and required heating in refluxing methylene chloride for about 8 hours using 1.0 mol.% catalyst. Fe(TPP)Cl was also found to be effective for tandem N-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents to give piperazinones and morpholinones and related analogs such as quinoxalinones and benzoxazin-2-ones. This approach provides a new one-pot route for synthesizing these classes of heterocyclic compounds.

Addition of carbenes derived from aryldiazoacetates to arenes using chloro(tetraphenylporphyrinato)iron as catalyst

Chloro(tetraphenylporphyrinato)iron, Fe(TPP)Cl, is an active catalyst for the Buchner addition of para-substituted methyl 2-phenyldiazoacetates, 1a–d, to substituted benzenes. Yields greater than 70% have been achieved at temperatures ranging from 60–100°C. Reactions of substituted methyl 2-phenyldiazoacetates with benzene gave rapidly equilibrating mixtures of norcaradienecycloheptatriene valence isomers, 2a–d/2′a–d, in yields over 70%. Treatment of chlorobenzene with methyl 2-phenyldiazoacetate produced a regio-isomeric mixture of 7-carbomethoxy-2-chloro-7-phenylnorcaradiene/7-carbomethoxy-2-chloro-7-phenylcycloheptatriene, 3a/3′a, and 7-carbomethoxy-3-chloro-7-phenylnorcaradiene/7-carbomethoxy-3-chloro-7-phenylcycloheptatriene, 4a/4′a. When p-methylanisole was treated with methyl 2-phenyldiazoacetate at 80°C, a product that largely favored a fused cyclopropane structure, 7-carbomethoxy-2-methoxy-5-methyl-7-phenylnorcaradiene, 12a, was obtained along with the benzylic C–H insertion product methyl 3-(p-methoxyphenyl)-2-phenylpropionate, 13a. Heating the norcaradiene product 12a at 110°C yielded the ring-opened diarylacetate, 14a. The diene forms of the fluxional norcaradiene-cycloheptatriene systems were trapped with benzyne to give one stereoisomer of 3,3-disubstituted benzhomobarralenes, 18a–d. The norcaradiene-cycloheptatriene valence isomers were quantitatively converted into ring-opened diaryl acetate products upon acidification in acetonitrile. Rates for the addition of methyl (p-chlorophenyl)diazoacetate to benzene were first order with respect to the diazo reagent. A concerted mechanism involing an iron carbene complex is proposed for these iron porphyrin-catalyzed Buchner reactions.

Synthesis, X-ray studies, and catalytic activity of tridentate Schiff base dioxo-molybdenum(VI)

The reaction of a solution of MoO2(acac)2 in CH3OH and salicylidene 2-picoloyl hydrazone as a tridentate ONO donor Schiff base (ONO) afford a six-coordinated Mo(VI) complex [MoO2(ONO)(CH3OH)], with a distorted octahedral configuration. [MoO2(ONO)(CH3OH)] was isolated as an air-stable crystalline solid and fully characterized by single-crystal X-ray structure analysis. [MoO2(ONO)(CH3OH)] shows reactivity in the oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air. Graphical Abstract

Syntheses and characterization of tetrakis(5-tert-butylpyrazole) Fe(II) and Mn(II) complexes. Molecular structure of Fe(Pzt-Bu)4(OTF)2

Abstract Dichlorotetrakis(5-t-butylpyrazole)iron (1), dichlorotetrakis(5-t-butylpyrazole) manganese (2), and tetrakis(5-t-butylpyrazole) iron(II) bis(trifluoromethanesulfonate) (3) were prepared and characterized. The crystal structure of 3 was determined from X-ray diffraction data. Complex 3 has a distorted octahedral structure with the two triflate ligands at mutually trans positions. Complexes 1 and 2 are mild catalysts for the selective epoxidation of styrene and norbornylene. In comparison, complex 3 is an efficient catalyst for the epoxidation of norbornylene, but promotes the oxidation of styrene predominantly to benzaldehyde.

Molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand: synthesis, X-ray studies, and catalytic activity

A new mononuclear molybdenum(VI)–oxodiperoxo complex [MoO(O2)2(phox)] with a simple bidentate ligand, 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (Hphox), has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, and 1H NMR spectroscopy. A triclinic space group P-1 was determined by X-ray crystallography from single-crystal data of this complex. The resulting complex functioned as a facile sulfide oxidation catalyst with urea hydrogen peroxide as terminal oxidant at room temperature. The catalyst showed efficient reactivity in oxidation of sulfides giving high yield and selectivity. Graphical Abstract