Benjamin S. Lane

Bio: Benjamin S. Lane is an academic researcher from Texas A&M University. The author has contributed to research in topics: Catalysis & Hydrogen peroxide. The author has an hindex of 6, co-authored 10 publications receiving 1300 citations.

Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Abstract: 3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

Manganese-catalyzed epoxidations of alkenes in bicarbonate solutions.

Abstract: This paper describes a method, discovered and refined by parallel screening, for the epoxidation of alkenes. It uses hydrogen peroxide as the terminal oxidant, is promoted by catalytic amounts (1.0-0.1 mol %) of manganese(2+) salts, and must be performed using at least catalytic amounts of bicarbonate buffer. Peroxymonocarbonate, HCO(4)(-), forms in the reaction, but without manganese, minimal epoxidation activity is observed in the solvents used for this research, that is, DMF and (t)BuOH. More than 30 d-block and f-block transition metal salts were screened for epoxidation activity under similar conditions, but the best catalyst found was MnSO(4). EPR studies show that Mn(2+) is initially consumed in the catalytic reaction but is regenerated toward the end of the process when presumably the hydrogen peroxide is spent. A variety of aryl-substituted, cyclic, and trialkyl-substituted alkenes were epoxidized under these conditions using 10 equiv of hydrogen peroxide, but monoalkyl-alkenes were not. To improve the substrate scope, and to increase the efficiency of hydrogen peroxide consumption, 68 diverse compounds were screened to find additives that would enhance the rate of the epoxidation reaction relative to a competing disproportionation of hydrogen peroxide. Successful additives were 6 mol % sodium acetate in the (t)BuOH system and 4 mol % salicylic acid in the DMF system. These additives enhanced the rate of the desired epoxidation reaction by 2-3 times. Reactions performed in the presence of these additives require less hydrogen peroxide and shorter reaction times, and they enhance the yields obtained from less reactive alkene substrates. Possible mechanisms for the reaction are discussed.

A cheap, catalytic, scalable, and environmentally benign method for alkene epoxidations.

Abstract: Benign Method for Alkene Epoxidations Benjamin S. Lane and Kevin Burgess* Department of Chemistry, Texas A & M UniVersity PO Box 30012, College Station, Texas 77842-3012 ReceiVed NoVember 17, 2000 This paper reports a simple method wherein manganese (2+) salts, for example, MnSO4, catalyze epoxidation of alkenes using 30% aqueous hydrogen peroxide as the terminal oxidant. The reactions are performed by dissolving the substrate and catalyst in DMF or tert-butyl alcohol and then slowly adding a mixture of 30% hydrogen peroxide and aqueous 0.2 M sodium hydrogen carbonate buffer. This method has several desirable attributes with respect to cost, simplicity, and environmental factors. This project emerged from a control experiment performed while screening new, chiral, 1,4,7-triazacyclononane (TACN) complexes as potential asymmetric epoxidation catalysts. High throughput screens in a simple plate apparatus1 indicated simple manganese (2+) salts, without any organic ligand, mediated the epoxidation but only in hydrogen carbonate buffer. There was no epoxidation in buffers based on triethanolamine, 3-[Nmorpholino]propanesulfonic acid (MOPS), phosphate, or borate. Alkenes are epoxidized by hydrogen peroxide/NaHCO3 in H2O (for water soluble alkenes) or in acetonitrile/water mixtures.2,3 We suspected that the transformations in the presence of manganese (2+) salts were fundamentally different because the reaction times reported for the metal-free system3 were significantly longer than those required in the current study. Moreover, the rates of epoxidation in the metal-free system were known to be significantly slower when tert-butyl alcohol was used as the solvent rather than acetonitrile; however, the former solvent was effective in the manganese-containing system. A set of experiments was performed to test for differences between the metal-free and manganese-containing systems. Figure 1 shows a direct comparison of epoxidation of 4-vinylbenzoic acid under exploratory, unrefined conditions (i.e., hydrogen peroxide added all at once at the beginning of the reaction; tertbutyl alcohol solvent). These data showed that the extent of conversion of alkene to epoxide was comparable when 0.1 and 1.0 mol % of manganese sulfate were used. It is less for 0.01 mol % Mn2+, but still much greater than the background conversion that occurred when no metal salt was used. Epoxidation of trans-1,2-diphenylethene was chosen as a model to optimize the conditions. This lypophilic substrate was selected so that solubility issues could be addressed using a relatively difficult case. When the substrate, 10 equiv of 30% hydrogen peroxide, and 1 mol % MnSO4, were mixed in 0.2 M NaHCO3 (pH 8.0) and DMF (1.0:1.4) and the reaction was stirred for 24 h, the yield of the epoxide was only 20%. Precipitation was observed in this experiment, indicating solubility problems. Consequently, slow addition of the aqueous components was investigated to minimize the precipitation, and the yield of product increased. Conversely, increasing the buffer concentration above 0.2 M would be expected to accentuate the insolubility problem, and indeed lower yields were obtained when higher buffer concentrations were used. Finally, a set of conditions were developed wherein a mixture of the buffer and 10 equiv of the peroxide were gradually added over 16 h to a solution of the substrate and catalyst in DMF. These reactions gave 1,2-diphenylethene oxide in 92% isolated yield. Table 1 summarizes the data obtained using various alkenes. 1-Decene was unreactive under these conditions (GC; entry 1). Entries 2, 3, and 16 illustrate that disubstituted aliphatic alkenes were reactive, and an excellent yield of cyclohexene oxide was obtained. Oxidation of the tetrahydroanthraquinone (entry 3) gave a significant amount of the corresponding quinone as a major byproduct. No Baeyer-Villager oxidation was observed for this material or in a control experiment using benzophenone as a substrate (no reaction occurred, data not shown). Entries 4-8 illustrate epoxidations of trisubstituted alkenes. R-Pinene reacted without cyclobutane rupture (entry 4), and citronellal was epoxidized without oxidation of the aldehyde functionality (entry 5; NMR). Similarly, the alcohol functionality of 3-methyl-2-buten1-ol was preserved in the epoxidation process, and no Payne rearrangement product was observed either (entry 6). Entry 7 tested for the generation of radical character adjacent the cyclopropane in the epoxidation, but no cyclopropane opening was observed. Epoxidation of linalool (entry 8) demonstrated that trisubstituted aliphatic alkenes can be selectively epoxidized in the presence of terminal alkenes. This experiment also implies that the allylic hydroxyl does not activate the terminal alkene via a directing effect. Entries 9-12 illustrate that epoxidations of arylsubstituted alkenes proceed smoothly; qualitatively, the rates of these reactions were observed to be appreciably faster than for aliphatic alkenes. The only complication was that a significant amount of trans-3-phenylpropenal was formed in entry 11. Epoxidation of the acid shown in entry 12 was not accompanied by decarboxylation or double bond migration. Some reactions with less catalyst were then attempted since it was evident that aryl alkenes were more reactive than aliphatic ones. Only 0.1 mol % of manganese sulfate was used for the reactions depicted in entries 13-15, and these epoxidations proceeded smoothly. Entries 14 and 15 illustrate that even extremely acidsensitive epoxides can be formed, and the products are stable under the reaction conditions. The last entry in the table was performed on a 1 mol scale; a detailed procedure for preparation and isolation of 84.5 g of cyclooctene oxide is provided here.4 The featured catalytic epoxidation method has numerous attributes. Manganese (2+) salts are cheap, readily available, and relatively nontoxic, and only small amounts (1.0-0.1 mol %) are required. Hydrogen peroxide and sodium hydrogen carbonate are widely used in large-scale production of other chemicals. No halide is involved in the transformation. Slow addition reduces the effective concentration of peroxide and the corresponding risk of explosion. The reaction is run at room temperature in solvents (1) Porte, A. M.; Reibenspies, J.; Burgess, K. J. Am. Chem. Soc. 1998, 120, 9180-9187. (2) Frank, W. C. Tetrahedron Asymmetry 1998, 9, 3745-3749. (3) Yao, H.; Richardson, D. E. J. Am. Chem. Soc. 2000, 122, 3220-3221. Figure 1. Opimization of the number of the hydrogen peroxide/catalyst stoichiometry. Yield determined by HPLC versus an internal standard. Error bars represent the standard deviation of two trials 2933 J. Am. Chem. Soc. 2001, 123, 2933-2934

Direct Palladium-Catalyzed C-2 and C-3 Arylation of Indoles: A Mechanistic Rationale for Regioselectivity [J. Am. Chem. Soc. 2005, 127, 8050−8057].

Abstract: We have recently developed palladium-catalyzed methods for direct arylation of indoles (and other azoles) wherein high C-2 selectivity was observed for both free (NH)-indole and (NR)-indole. To provide a rationale for the observed selectivity ("nonelectrophilic" regioselectivity), mechanistic studies were conducted, using the phenylation of 1-methylindole as a model system. The reaction order was determined for iodobenzene (zero order), indole (first order), and the catalyst (first order). These kinetic studies, together with the Hammett plot, provided a strong support for the electrophilic palladation pathway. In addition, the kinetic isotope effect (KIE(H/D)) was determined for both C-2 and C-3 positions. A surprisingly large value of 1.6 was found for the C-3 position where the substitution does not occur (secondary KIE), while a smaller value of 1.2 was found at C-2 (apparent primary KIE). On the basis of these findings, a mechanistic interpretation is presented that features an electrophilic palladation of indole, accompanied by a 1,2-migration of an intermediate palladium species. This paradigm was used to design new catalytic conditions for the C-3 arylation of indole. In case of free (NH)-indole, regioselectivity of the arylation reaction (C-2 versus C-3) was achieved by the choice of magnesium base.

Hydrogen Peroxide Synthesis: An Outlook beyond the Anthraquinone Process

Abstract: Hydrogen peroxide (H2O2) is widely used in almost all industrial areas, particularly in the chemical industry and environmental protection. The only degradation product of its use is water, and thus it has played a large role in environmentally friendly methods in the chemical industry. Hydrogen peroxide is produced on an industrial scale by the anthraquinone oxidation (AO) process. However, this process can hardly be considered a green method. It involves the sequential hydrogenation and oxidation of an alkylanthraquinone precursor dissolved in a mixture of organic solvents followed by liquid–liquid extraction to recover H2O2. The AO process is a multistep method that requires significant energy input and generates waste, which has a negative effect on its sustainability and production costs. The transport, storage, and handling of bulk H2O2 involve hazards and escalating expenses. Thus, novel, cleaner methods for the production of H2O2 are being explored. The direct synthesis of H2O2 from O2 and H2 using a variety of catalysts, and the factors influencing the formation and decomposition of H2O2 are examined in detail in this Review.

Zr-based metal-organic frameworks: design, synthesis, structure, and applications.

Abstract: Among the large family of metal–organic frameworks (MOFs), Zr-based MOFs, which exhibit rich structure types, outstanding stability, intriguing properties and functions, are foreseen as one of the most promising MOF materials for practical applications. Although this specific type of MOF is still in its early stage of development, significant progress has been made in recent years. Herein, advances in Zr-MOFs since 2008 are summarized and reviewed from three aspects: design and synthesis, structure, and applications. Four synthesis strategies implemented in building and/or modifying Zr-MOFs as well as their scale-up preparation under green and industrially feasible conditions are illustrated first. Zr-MOFs with various structural types are then classified and discussed in terms of different Zr-based secondary building units and organic ligands. Finally, applications of Zr-MOFs in catalysis, molecule adsorption and separation, drug delivery, and fluorescence sensing, and as porous carriers are highlighted. Such a review based on a specific type of MOF is expected to provide guidance for the in-depth investigation of MOFs towards practical applications.

Biologically inspired oxidation catalysis

Abstract: The development of processes for selective hydrocarbon oxidation is a goal that has long been pursued. An additional challenge is to make such processes environmentally friendly, for example by using non-toxic reagents and energy-efficient catalytic methods. Excellent examples are naturally occurring iron- or copper-containing metalloenzymes, and extensive studies have revealed the key chemical principles that underlie their efficacy as catalysts for aerobic oxidations. Important inroads have been made in applying this knowledge to the development of synthetic catalysts that model enzyme function. Such biologically inspired hydrocarbon oxidation catalysts hold great promise for wide-ranging synthetic applications.

Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Abstract: 3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

Advances in Homogeneous and Heterogeneous Catalytic Asymmetric Epoxidation

Abstract: Laboratory for Advanced Materials and New Catalysis, School of Chemistry and Materials Science, Hubei University, Wuhan 430062, China,Laboratory of Natural Gas Utilization and Applied Catalysis, Dalian Institute of Chemical Physics of Chinese Academy of Sciences, Dalian 116023,China, and Jingmen Technological College, Jingmen 448000, ChinaReceived June 30, 2004