Unexpected, Latent Radical Reaction of Methane Propagated by Trifluoromethyl Radicals

Unexpected, Latent Radical Reaction of Methane Propagated by Trifluoromethyl Radicals
Nima Zargari,† Pierre Winter,‡ Yong Liang,§ Joo Ho Lee,† Andrew Cooksy,*,‡ K. N. Houk,*,§ and Kyung Woon Jung*,†
†Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California, 837 Bloom Walk, Los Angeles, California 90089, United States
‡Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego California 92182, United States
§Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States

J. Org. Chem. 2016, 81, 9820-9825.
http://pubs.acs.org/doi/pdf/10.1021/acs.joc.6b01903

Abstract:
 

Thorough mechanistic studies and DFT calculations revealed a background radical pathway latent in metal-catalyzed oxidation reactions of methane at low temperatures. Use of hydrogen peroxide with TFAA generated a trifluoromethyl radical (•CF3), which in turn reacted with methane gas to selectively yield acetic acid. It was found that the methyl carbon of the product was derived from methane, while the carbonyl carbon was derived from TFAA. Computational studies also support these findings, revealing the reaction cycle to be energetically favorable. 

TOC:  

Carbon–Carbon Bond-Forming Reductive Elimination from Isolated Nickel(III) Complexes

James R. Bour†, Nicole M. Camasso†, Elizabeth A. Meucci†, Jeff W. Kampf†, Allan J. Canty¥, and Melanie S. Sanford*†

http://pubs.acs.org/doi/abs/10.1021/jacs.6b10350

Abstract

This manuscript describes the design, synthesis, characterization, and reactivity studies of organometallic NiIII complexes of general structure TpNiIII(R)(R1) (Tp = tris(pyrazolyl)borate). With appropriate selection of the R and R1 ligands, the complexes are stable at room temperature and can be characterized by cyclic voltammetry, EPR spectroscopy, and X-ray crystallography. Upon heating, many of these NiIII compounds undergo C(sp2)–C(sp2) or C(sp3)–C(sp2) bond-forming reactions that are challenging at lower oxidation states of nickel.

Bimetallic C−C Bond-Forming Reductive Elimination from Nickel

Abstract

Ni-catalyzed cross-coupling reactions have found important applications in organic synthesis. The fundamental characterization of the key steps in cross-coupling reactions, including C–C bond-forming reductive elimination, represents a significant challenge. Bimolecular pathways were invoked in early proposals, but the experimental evidence was limited. We present the preparation of well-defined (pyridine-pyrrolyl)Ni monomethyl and monophenyl complexes that allow the direct observation of bimolecular reductive elimination to generate ethane and biphenyl, respectively. The sp3–sp3 and sp2–sp2 couplings proceed via two distinct pathways. Oxidants promote the fast formation of Ni(III) from (pyridine-pyrrolyl)Ni-methyl, which dimerizes to afford a bimetallic Ni(III) intermediate. Our data are most consistent with the subsequent methyl coupling from the bimetallic Ni(III) to generate ethane as the rate-determining step. In contrast, the formation of biphenyl is facilitated by the coordination of a bidentate donor ligand.

http://pubs.acs.org/doi/abs/10.1021/jacs.6b00016

Selective oxidative dehydrogenation of propane to propene using boron nitride catalysts

Selective oxidative dehydrogenation of propane to propene using boron nitride catalysts 
 

J. T. Grant,1 C. A. Carrero,1 F. Goeltl,1 J. Venegas,2 P. Mueller,1 S. P. Burt,2 S. E. Specht,1 W. P. McDermott,1 A. Chieregato,1 I. Hermans1,2*
1University of Wisconsin—Madison, Department of Chemistry, 1101 University Avenue, Madison, WI 53706, USA. 2University of Wisconsin—Madison, Department of Chemical and Biological Engineering, 1415 Engineering Drive, Madison, WI 53706, USA.
*Corresponding author. E-mail: hermans@chem.wisc.edu

 

http://science.sciencemag.org/content/early/2016/11/30/science.aaf7885.full

Abstract

The exothermic oxidative dehydrogenation of propane reaction to generate propene has the potential to be a game-changing technology in the chemical industry. However, even after decades of research, selectivity to propene remains too low to be commercially attractive because of overoxidation of propene to thermodynamically favored CO2. Here, we report that hexagonal boron nitride (h-BN) and boron nitride nanotubes (BNNTs) exhibit unique and hitherto unanticipated catalytic properties resulting in great selectivity to olefins. As an example, at 14% propane conversion, we obtain selectivity of 79% propene and 12% ethene, another desired alkene. Based on catalytic experiments, spectroscopic insights and ab initio modeling, we put forward a mechanistic hypothesis in which oxygen-terminated armchair BN edges are proposed to be the catalytic active sites.

Over a million turnovers for a molecular WOC

http://onlinelibrary.wiley.com/doi/10.1002/anie.201609167/abstract

A Million Turnover Molecular Anode for Catalytic Water Oxidation

• 
  

• First published: 7 November 2016Full publication history
• DOI: 10.1002/anie.201609167View/save citation
• Cited by: 0 articles

• 
  
• 

Abstract

Molecular ruthenium-based water oxidation catalyst precursors of general formula [Ru(tda)(Lⁱ)₂] (tda²⁻ is [2,2′:6′,2′′-terpyridine]-6,6′′-dicarboxylato; L¹=4-(pyren-1-yl)-N-(pyridin-4-ylmethyl)butanamide, 1 b; L²=4-(pyren-1-yl)pyridine), 1 c), have been prepared and thoroughly characterized. Both complexes contain a pyrene group allowing ready and efficiently anchoring via π interactions on multi-walled carbon nanotubes (MWCNT). These hybrid solid state materials are exceptionally stable molecular water-oxidation anodes capable of carrying out more than a million turnover numbers (TNs) at pH 7 with an E_app=1.45 V vs. NHE without any sign of degradation. XAS spectroscopy analysis before, during, and after catalysis together with electrochemical techniques allow their unprecedented oxidative ruggedness to be monitored and verified.

Multinuclear copper complexes for mild alkane oxidation

Communication

http://onlinelibrary.wiley.com/doi/10.1002/anie.200500585/abstract

 

Multinuclear Copper Triethanolamine Complexes as Selective Catalysts for the Peroxidative Oxidation of Alkanes under Mild Conditions^†

Authors

• 
  

  1. 
     

• 
  

  1. 
     

• 
  

  1. 
     

• 
  

  1. 
     

• 
  

  1. 
     

• 
  

  • 
    

  1. 
     

• First published: 8 June 2005Full publication history
• DOI: 10.1002/anie.200500585View/save citation
• Cited by: 147 articles
• 
  

• ^†
  This work has been partially supported by the Fundação para a Ciência e a Tecnologia and its POCTI programme (FEDER funded) (project POCTI/QUI/43415/2001), Portugal, and by a Human Resources and Mobility Marie-Curie Research Training Network (AQUACHEM project, CMTN-CT-2003-503864).

Abstract

Rich activity from a few coppers: Di-, tri-, tetra-, and polynuclear copper triethanolamine complexes are easily prepared and are selective and efficient catalysts for alkane peroxidative oxidation under mild conditions (see picture).

C–H Activation on Co,O Sites: Isolated Surface Sites versus Molecular Analogs

http://pubs.acs.org/doi/abs/10.1021/jacs.6b08705
Deven P. Estes,† Georges Siddiqi,† Florian Allouche,† Kirill V. Kovtunov,§,∥ Olga V. Safonova,‡ Alexander L. Trigub,⊥ Igor V. Koptyug,§,∥ and Christophe Coperet ́ *,†

http://pubs.acs.org/doi/abs/10.1021/jacs.6b08705

Abstract

The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. Transition-metal ions (V, Cr, Fe, Co, etc.) isolated on silica surfaces are known to catalyze such processes. The mechanisms of these processes are currently unknown but are thought to involve C–H activation as the rate-determining step. Here, we synthesize well-defined Co(II) ions on a silica surface using a metal siloxide precursor followed by thermal treatment under vacuum at 500 °C. We show that these isolated Co(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes. We then investigate the mechanisms of these processes using kinetics, kinetic isotope effects, isotopic labeling experiments, parahydrogen induced polarization (PHIP) NMR, and comparison with a molecular analog. The data are consistent with all of these reactions occurring by a common mechanism, involving heterolytic C–H or H–H activation via a 1,2 addition across a Co–O bond.