Alkane CH functionalization and oxidation with molecular oxygen

 Paper highlights 3 strategies for partial oxidation of hydrocarbons using specific examples

 

Alkane C–H Functionalization and Oxidation with Molecular Oxygen

Dominik Munz and Thomas Strassner^*

Physikalische Organische Chemie, Technische Universität Dresden, 01069 Dresden, Germany

Inorg. Chem., 2015, 54 (11), pp 5043–5052

DOI: 10.1021/ic502515x

Publication Date (Web): March 30, 2015

Synopsis

General strategies for the partial oxidation of methane and lower alkanes by molecular oxygen are discussed on the basis of three examples. These are the functionalization of methane and propane by palladium bis(N-heterocyclic carbene) complexes in combination with vanadium cocatalysts, the functionalization of methane catalyzed by cobalt salts, and the stoichiometric reaction of methane with group XVII compounds.

Abstract

The application of environmentally benign, cheap, and economically viable oxidation procedures is a key challenge of homogeneous, oxidative alkane functionalization. The typically harsh reaction conditions and the propensity of dioxygen for radical reactivity call for extraordinary robust catalysts. Mainly three strategies have been applied. These are (1) the combination of a catalyst responsible for C–H activation with a cocatalyst responsible for dioxygen activation, (2) transition-metal catalysts, which react with both hydrocarbons and molecular oxygen, and (3) the introduction of very robust main-group element catalysts for C–H functionalization chemistry. Herein, these three approaches will be assessed and exemplified by the reactivity of chelated palladium (N-heterocyclic carbene) catalysts in combination with a vanadium cocatalyst, the methane functionalization by cobalt catalysts, and the reaction of group XVII compounds with alkanes.

Catalytic Mechanism and Efficiency of Methane Oxidation by Hg(II) in Sulfuric Acid and Comparison to Radical Initiated Conditions

Catalytic Mechanism and Efficiency of Methane Oxidation by Hg(II) in Sulfuric Acid and Comparison to Radical Initiated Conditions

Jack T. Fuller, III, Steven Butler, Deepa Devarajan, Austin Jacobs, Brian G. Hashiguchi, Michael M. Konnick, William A. Goddard, III, Jason Gonzales, Roy A. Periana, and Daniel H. Ess

ACS Catal. 2016, 6, 4312-4322
http://pubs.acs.org/doi/pdf/10.1021/acscatal.6b00226

TOC: 


Abstract: 

Methane conversion to methyl bisulfate by HgII(SO4) in sulfuric acid is an example of fast and selective alkane oxidation catalysis. Dichotomous mechanisms involving C−H activation and electron transfer have been proposed based on experiments. Radical oxidation pathways have also been proposed for some reaction conditions. HgII is also of significant interest because as a d10 transition metal it is similar to d10 main-group metals that also oxidize alkanes. Density- functional calculations are presented that use both implicit and a mixture of implicit/explicit solvent models for the complete HgII catalytic cycle of methane oxidation to methyl bisulfate. These calculations are consistent with experiment and reveal that methane is functionalized to methyl bisulfate by a C−H activation and reductive metal alkyl functionalization mechanism. This reaction pathway is lower in energy than both electron transfer and proton-coupled electron transfer pathways. After methane C−H functionalization, catalysis is completed by conversion of the proposed resting state, [HgI(HSO4)]2, into Hg0 followed by Hg0 to HgII oxidation induced by SO3 from dehydration of sulfuric acid. This catalytic cycle is efficient because in sulfuric acid the HgII/Hg0 potential results in a moderate free energy barrier for oxidation (∼40 kcal/mol) and HgII is electrophilic enough to induce barriers of <40 kcal/mol for C−H activation and reductive metal alkyl functionalization. Comparison of HgII to TlIII shows that while C−H activation and reductive metal alkyl functionalization have reasonable barriers for TlIII, the oxidation of TlI to TlIII has a significantly larger barrier than Hg0 to HgII oxidation and therefore TlIII is not catalytic in sulfuric acid. Comparison of HgII to CdII and ZnII reveals that while M0 to MII oxidation and C−H activation are feasible for these first-row and second-row transition metals, reductive metal alkyl functionalization barriers are very large and catalysis is not feasible. Calculations are also presented that outline the mechanism and energy landscape for radical-initiated (K2S2O8) methane oxidation to methanesulfonic acid in sulfuric acid. 

Potassium teter-butoxide Strikes Again!

Link to Manuscript

C–H carboxylation of heteroarenes with ambient CO₂

Sabine Fenner^a and   Lutz Ackermann*^a  

Green Chem., 2016, Advance Article

The C–H carboxylation of heteroarenes was achieved under transition metal-free reaction conditions with naturally abundant CO₂ as the C1 source at relatively low temperature. The C–H carboxylation was mediated by KOt-Bu at atmospheric pressure of CO₂, and thereby provided atom- and step-economical access to various heteroaromatic carboxylic acid derivatives.

Mild metal-catalyzed C–H activation: examples and concepts

Mild metal-catalyzed C–H activation: examples and concepts

T. Gensch, M. N. Hopkinson, F. Glorius, and J. Wencel-Delord

Chem. Soc. Rev.

Abstract:

Organic reactions that involve the direct functionalization of non-activated C–H bonds represent an attractive class of transformations which maximize atom- and step-economy, and simplify chemical synthesis. Due to the high stability of C–H bonds, these processes, however, have most often required harsh reaction conditions, which has drastically limited their use as tools for the synthesis of complex organic molecules. Following the increased understanding of mechanistic aspects of C–H activation gained over recent years, great strides have been taken to design and develop new protocols that proceed efficiently under mild conditions and duly benefit from improved functional group tolerance and selectivity. In this review, we present the current state of the art in this field and detail C–H activation transformations reported since 2011 that proceed either at or below ambient temperature, in the absence of strongly acidic or basic additives or without strong oxidants. Furthermore, by identifying and discussing the major strategies that have led to these improvements, we hope that this review will serve as a useful conceptual overview and inspire the next generation of mild C–H transformations.

Silver(I)-Catalyzed Tandem Sigamatropic Rearrangement/1,3‑H Shift/ 6π Aza-electrocyclization of N‑Propargylic Hydrazones: A Mild Synthetic Route to 1,6-Dihydropyridazines

Silver(I)-Catalyzed Tandem Sigamatropic Rearrangement/1,3‑H Shift/ 6 π Aza-electrocyclization of N‑Propargylic Hydrazones: A Mild Synthetic Route to 1,6-Dihydropyridazines

Zong-Cang Ding, Lu-Chuan Ju, Ying Yang, Xiao-Ming An, Yun-Bing Zhou, Ren-Hao Li, Hai-Tao Tang, Cheng-Ke Ding, and Zhuang-Ping Zhan*

 

Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, P. R. China

J. Org. Chem. DOI: 10.1021/acs.joc.6b00428

TOC:

Abstract:

A highly efficient AgOTf catalyzed [3,3]

sigmatropic rearrangement/1,3-H shift/6π aza-electrocycliza-

tion cascade reaction of N-propargylic hydrazones has been

developed. This method provides a new mild synthetic route

to various polysubstituted 1,6-dihydropyridazines including the

3-CF3-substituted ones with high selectivity.

 

Alkyl–Aryl Coupling Catalyzed by Tandem Systems of Pincer-Ligated Iridium Complexes and Zeolites

Long V. Dinh^†, Bo Li^†, Akshai Kumar^†‡, William Schinski^§, Kathleen D. Field^†, Alexander Kuperman^§, Fuat E. Celik^*⊥, and Alan S. Goldman^*†

^† Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States

^‡ Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam India

^§ Chevron Energy Technology Company, 100 Chevron Way, Richmond, California 94802, United States

^⊥ Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States

ACS Catal., 2016, 6, pp 2836–2841

DOI: 10.1021/acscatal.6b00149

Publication Date (Web): March 28, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acscatal.6b00149

We report that pincer-ligated iridium catalysts for alkane dehydrogenation can operate in tandem with zeolite catalysts for arene–alkene coupling, to effect the overall intramolecular dehydrocoupling of alkyl–H and aryl–H bonds (i.e., the dehydrocyclization of alkyl benzene). Thus, zeolite and soluble iridium cocatalysts in refluxing pentylbenzene (205 °C) gave high yields of 1-methyl-1,2,3,4-tetrahydronaphthalene. Subsequent dehydrogenation and isomerization affords 1- and 2-methylnaphthalene and 2-methyl-1,2,3,4-tetrahydronaphthalene. Total yields of cyclized product as high as 5.4 M (94%) have been obtained, corresponding to 6800 turnovers per mol Ir. Turnover numbers for the tandem-catalyzed dehydrocyclization are much greater than those obtained for simple dehydrogenation by Ir catalysts (to give olefins) in the absence of zeolite.