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And Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes † † Kristian E

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This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. Review Cite This: Chem. Rev. 2019, 119, 2752−2875 pubs.acs.org/CR Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes † † Kristian E. Dalle, Julien Warnan, Jane J. Leung, Bertrand Reuillard, Isabell S. Karmel, and Erwin Reisner* Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom ABSTRACT: The synthesis of renewable fuels from abundant water or the greenhouse gas CO2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dots, metal oxide surfaces, and semiconductors. The molecule−material hybrid systems are organized as “dark” cathodes, colloidal photocatalysts, and photocathodes, and their figures of merit are discussed alongside system stability and catalyst integrity. The final section extends “ ” the scope of this review to prospects and challenges in targeting catalysis beyond classical H2 evolution and CO2 reduction to C1 products, by summarizing cases for higher-value products from N2 reduction, Cx>1 products from CO2 utilization, and other reductive organic transformations. CONTENTS 2.3.5. Iron 2779 2.3.6. Cobalt 2782 1. Introduction 2753 2.3.7. Nickel 2786 1.1. Motivation and Strategy 2753 fi 2.3.8. Copper 2789 1.2. Biological Templates for Arti cial Photosyn- 2.3.9. Zinc 2791 thesis 2754 2.3.10. Future Directions 2791 1.3. Structure and Activation of CO2 2755 3. Immobilization Strategies for Molecular Catalysts 2791 Downloaded via UNIV OF CAMBRIDGE on July 16, 2019 at 16:16:47 (UTC). 1.4. Mechanistic Pathways 2756 3.1. Approaches and Configurations 2792 1.5. Figures of Merit and Practical Considerations 2756 3.2. Materials 2792 2. Homogeneous Catalysis 2758 3.2.1. Electrode Materials for Electrocatalysis 2792 See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. 2.1. Aqueous Conditions for Catalysis 2758 3.2.2. Colloidal Materials for Photocatalysis 2792 2.2. Hydrogen Evolution Catalysts 2759 3.2.3. Semiconductor Electrodes for Photo- 2.2.1. Scandium, Titanium, Vanadium, and electrocatalysis 2793 Chromium 2759 3.3. Anchoring Strategies 2794 2.2.2. Manganese 2759 3.3.1. Anchoring to Carbon-Based Materials 2794 2.2.3. Iron 2760 3.3.2. Anchoring to Metal Oxide Materials 2795 2.2.4. Cobalt 2764 3.3.3. Anchoring to Nonoxide Semiconductors 2796 2.2.5. Nickel 2769 4. Immobilized Catalysts for Electrocatalysis 2797 2.2.6. Copper 2774 4.1. General Remarks 2797 2.2.7. Zinc 2775 4.2. Electrocatalytic H2 Evolution 2797 2.2.8. Heterometallic Catalysts 2775 4.2.1. Carbon Electrodes 2797 2.2.9. Future Directions 2776 4.2.2. Metal Oxide Electrodes 2801 2.3. Carbon Dioxide Reduction Catalysts 2776 2.3.1. Scandium and Titanium 2776 2.3.2. Vanadium 2776 Special Issue: First Row Metals and Catalysis 2.3.3. Chromium 2776 Received: June 21, 2018 2.3.4. Manganese 2777 Published: February 15, 2019 © 2019 American Chemical Society 2752 DOI: 10.1021/acs.chemrev.8b00392 Chem. Rev. 2019, 119, 2752−2875 Chemical Reviews Review 4.2.3. Hydrogenase-Based Electrocatalysis 2802 Notes 2842 4.3. Electrocatalytic CO2 Reduction 2803 Biographies 2842 4.3.1. Carbon Electrodes 2803 Acknowledgments 2842 4.3.2. Metal Oxide Electrodes 2807 List of Acronyms and Abbreviations 2843 4.3.3. CO2 Reductase-Based Electrocatalysis 2807 References 2844 5. Colloidal Photocatalysis 2808 5.1. General Remarks 2808 5.2. Photocatalytic H2 Evolution 2808 1. INTRODUCTION 5.2.1. Carbon-Based Colloids 2808 5.2.2. Quantum Dots 2809 1.1. Motivation and Strategy 5.2.3. Dye-Sensitized Semiconductors 2814 The worldwide reliance on fossil fuels as energy carriers and raw 5.2.4. Micelles and Vesicles 2816 materials for industrial products presents several challenges for 5.2.5. Hydrogenase-Based Systems 2817 the coming decades. Reserves are finite, and their combustion 5.3. Photocatalytic CO2 Reduction 2818 for power generation and use by the petrochemical industry has 5.3.1. Carbon-Based Colloids 2818 1−3 substantially contributed to rising atmospheric CO2 levels, 5.3.2. Quantum Dots 2818 which has recently been emphasized by the 2015 United 5.3.3. Dye-Sensitized Semiconductors 2819 Nations Climate Change Conference in Paris.4 Worldwide 5.3.4. CO2 Reductase-Based Systems 2820 energy demand is steadily increasing, and fossil fuels made up 5.4. Conclusion and Outlook 2820 more than 80% of global energy consumption in 2017.5,6 6. Dye-Sensitized Photocathodes 2821 Alternatives such as wind, hydro, and solar power are rapidly 6.1. General Remarks 2821 growing sources of sustainable electricity, but their intermit- 6.2. Component Requirements and Character- tency makes energy storage a contemporary challenge. Renew- istics 2821 able electricity also does not provide combustible fuels for use in 6.2.1. p-Type Semiconductor: a NiO Story 2821 the transport sector, in particular aviation and heavy freight over 6.2.2. Photosensitizer and Electrocatalyst 2821 long-distances, nor feedstock chemicals for making plastics, 6.3. Photoelectrochemical H2 Evolution 2822 rubbers, fertilizers, and pharmaceuticals. New approaches are 6.3.1. Coimmobilization 2822 therefore needed to provide sustainable resources for fuels and 6.3.2. Layer-by-Layer Coassembly 2825 commodity production. 6.3.3. Photosensitizer-Catalyst Dyads 2826 CO2 is the thermodynamically stable end product of 6.4. Photoelectrochemical CO2 Reduction 2827 numerous chemical and biological oxidation reactions,2,7 and 6.5. Conclusion and Outlook 2827 the reverse processes that form chemicals from CO2 thus require 7. Narrow-Bandgap Semiconductor Photocathodes 2828 energy input.7,8 The Sun continuously supplies approximately 7.1. General Remarks 2828 100 000−120 000 TW to Earth, more than 5000 times the 7.2. Component Requirements and Character- current global primary energy consumption of 18 TW, making it − istics 2828 the most sustainable energy source available to humanity.5,9 11 7.2.1. Narrow-Bandgap p-Type Semiconduc- Nature harnesses this energy through photosynthesis, using tors 2828 fi sunlight to drive xation of atmospheric CO2 under mild 7.2.2. Molecular Catalyst 2829 conditions on an estimated scale of 100−120 gigatonnes per 7.2.3. Indium Phosphide 2830 annum.12,13 This biological process provides a strategy for 7.2.4. Gallium Phosphide 2831 employing light to capture CO2 and convert it into a chemical 7.2.5. Gallium Indium Phosphide 2832 energy vector, thereby closing the carbon cycle and simulta- 7.2.6. Silicon 2832 neously alleviating global warming.2 Mimicry of the natural 7.2.7. Organic Bulk Heterojunction Semicon- pathways through artificial photosynthetic design can provide us ductors 2833 with a route to solar fuels (Figure 1). 7.2.8. Hydrogenase-Based Systems 2834 ’Solar fuels’ describes any concentrated chemical energy 7.3. CO2 Reduction 2834 carrier with long-term storage capacity that contains chemical 7.4. Conclusion and Outlook 2834 bonds in which solar energy has been stored.14,15 This review 8. Beyond H2 and C1 Chemistry 2834 primarily focuses on pathways to these fuels that have been 8.1. Reduction of CO2 to Hydrocarbon Fuels 2835 among the most intensely researched in the last decades: those 8.2. Reductive Organic Transformations 2835 employing molecular catalysts with the ability to use sunlight 8.2.1. Reduction of Alkenes 2835 directly (photoresponsive systems) or indirectly (by photo- 8.2.2. Reductive Dehalogenation 2836 sensitizer-coupling) to generate H2 and products from CO2 8.2.3. Reduction of Carbonyl Derivatives 2836 reduction. Photocatalytic processes that produce these products 8.2.4. NADH-Mediated Reduction Reactions 2837 are collectively described as artificial photosynthesis,16 as they 8.3. Reduction of Molecular Nitrogen 2838 take inspiration from the first step of natural photosynthesis 8.3.1. N2 Fixation by Nitrogenases 2838 where water is photocatalytically split into dioxygen and 8.3.2. Reduction of N2 Using Transition Metal “hydrogen”.9 “Hydrogen” refers here to the combination of Complexes 2839 protons and low potential electrons extracted from H2O, which 9. Conclusion 2841 in Nature are then used along with CO2 to form organic Author Information 2842 compounds. These chemicals are the basis of our global energy Corresponding Author 2842 economy, providing us with “fuels” to sustain life, whether sugars ORCID 2842 for metabolism or fossil fuels for generating electricity and Author Contributions 2842 powering transportation. Combining the “hydrogen” bound in 2753 DOI: 10.1021/acs.chemrev.8b00392 Chem. Rev. 2019, 119, 2752−2875 Chemical Reviews Review Figure 1. Schematic representation of (a) natural and (b) artificial photosynthesis. these fuels with O2 releases energy, reversing the process and nickel(II) complexes rapidly undergo ligand exchange, the 9 thereby liberating H2O and CO2 (Figure 1). In this regard, corresponding ruthenium/osmium(II) and palladium/ 27 photocatalytic production of H2 through water splitting can be platinum(II) complexes tend to be kinetically inert.
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  • Gold Coordination During Homogeneous Alkyne and Allene Cyclisation Catalysis: Coordination to Substrates, to Ancillary Ligands and in Intermediates

    Gold Coordination During Homogeneous Alkyne and Allene Cyclisation Catalysis: Coordination to Substrates, to Ancillary Ligands and in Intermediates

    Page 1 of 13 Review Article Gold coordination during homogeneous alkyne and allene cyclisation catalysis: Coordination to substrates, to ancillary ligands and in intermediates Authors: The ever-increasing role of homogeneous gold catalysis in organic synthesis and the consequent Helgard G. Raubenheimer1 Hubert Schmidbaur2 need to be able to rationally control the rate and outcome of such reactions has emphasised the importance of each successive metal–carbon coordination step. Concentrating on alkyne Affiliations: and allene cyclisation and upon reaction mechanisms postulated on the basis of empirical and 1 Department of Chemistry theoretical results, we have examined the coordination of gold fragments to triple bonds, the and Polymer Science, University of Stellenbosch, modification of gold(I) precatalysts to effect specific reaction pathways or enantioselectivity South Africa and the isolation of coordinated intermediates or model compounds thereof. Some of the recent advances that have been made in various laboratories are described in this compact 2 Department Chemie, review. Technische Universität München, Munich, Germany Introduction Correspondence to: Helgard Raubenheimer The observation by W.C. Zeise in 1827 that ethylene forms a complex with a low-valent platinum salt was the key discovery that not only led to the development of one of the most important email: branches of organometallic chemistry, but also had an enormous economic impact through its [email protected] relevance to catalysis of organic transformations. Although less well known to the public, and Postal address: even to many of the scientific community, the catalysis of reactions of unsaturated hydrocarbons, Private Bag X1, Matieland in particular of acetylene, by mercury salts was practised widely after the 1890s and was of great 7602, South Africa industrial significance.