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.

Merging Visible Light Photoredox Catalysis with Metal Catalyzed C–H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants

http://pubs.acs.org/doi/abs/10.1021/acs.accounts.6b00275
David C. Fabry† and Magnus Rueping*‡
† Institute of Organic Chemistry, RWTH-Aachen University, Landoltweg 1, 52072 Aachen, Germany
‡ King Abdullah University of Science and Technology (KAUST), KAUST Catalysis Center (KCC), Thuwal, 23955-6900Saudi Arabia
Acc. Chem. Res., 2016, 49 (9), pp 1969–1979
DOI: 10.1021/acs.accounts.6b00275
Publication Date (Web): August 24, 2016


Abstract 

The development of efficient catalytic systems for direct aromatic C–H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C–C and C–heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C–H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, “greener” approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable.


In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C–H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal catalyst via a coupled electron transfer (ET) process.


Here we describe our first successful endeavors to address the above challenges by combining visible light photoredox catalysis with different ruthenium, rhodium, or palladium catalyzed C–H activations. Since only small amounts of the oxidant are generated and are immediately consumed in these transformations, side reactions of substrates or products can be avoided. Thus, usually oxidant-sensible substrates can be used, which makes these methods highly suitable for complex molecular structure syntheses. Moreover, mechanistic studies shed light on new reaction pathways, intermediates, and in situ generated species. The successful development of our dual catalysis concept, consisting of combined visible light photoredox catalysis and metal catalyzed C–H functionalization, provides many new opportunities for further explorations in the field of C–H functionalization.

Fundamentals of beta-alkyl elimination

New paper from former post-doc, Matt O'Reilly.

http://pubs.acs.org/doi/abs/10.1021/acs.chemrev.6b00054

β-Alkyl Elimination: Fundamental Principles and Some Applications

Matthew E. O’Reilly, Saikat Dutta, and Adam S. Veige^*

Department of Chemistry, Center for Catalysis, University of Florida, Gainesville, Florida 32611, United States

Chem. Rev., 2016, 116 (14), pp 8105–8145

DOI: 10.1021/acs.chemrev.6b00054

Publication Date (Web): July 1, 2016

Abstract

This review describes organometallic compounds and materials that are capable of mediating a rarely encountered but fundamentally important reaction: β-alkyl elimination at the metal–C_α–C_β–R moiety, in which an alkyl group attached to the C_β atom is transferred to the metal or to a coordinated substrate. The objectives of this review are to provide a cohesive fundamental understanding of β-alkyl-elimination reactions and to highlight its applications in olefin polymerization, alkane hydrogenolysis, depolymerization of branched polymers, ring-opening polymerization of cycloalkanes, and other useful organic reactions. To provide a coherent understanding of the β-alkyl elimination reaction, special attention is given to conditions and strategies used to facilitate β-alkyl-elimination/transfer events in metal-catalyzed olefin polymerization, which provide the well-studied examples.