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

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

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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^†

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

Low-Temperature Transformation of Methane to Methanol on Pd1O4 Single Sites Anchored on the Internal Surface of Microporous Silicate

http://onlinelibrary.wiley.com/doi/10.1002/anie.201604708/abstract

Abstract

Direct conversion of methane to chemical feedstocks such as methanol under mild conditions is a challenging but ideal solution for utilization of methane. Pd1O4 single-sites anchored on the internal surface of micropores of a microporous silicate exhibit high selectivity and activity in transforming CH4 to CH3OH at 50–95 °C in aqueous phase through partial oxidation of CH4 with H2O2. The selectivity for methanol production remains at 86.4 %, while the activity for methanol production at 95 °C is about 2.78 molecules per Pd1O4 site per second when 2.0 wt % CuO is used as a co-catalyst with the Pd1O4@ZSM-5. Thermodynamic calculations suggest that the reaction toward methanol production is highly favorable compared to formation of a byproduct, methyl peroxide.