Iron Catalysis in Organic Synthesis

Production of anilines--key intermediates for the fine chemical, agrochemical, and pharmaceutical industries--relies on precious metal catalysts that selectively hydrogenate aryl nitro groups in the presence of other easily reducible functionalities. Herein, we report convenient and stable iron oxide (Fe2O3)-based catalysts as a more earth-abundant alternative for this transformation. Pyrolysis of iron-phenanthroline complexes on carbon furnishes a unique structure in which the active Fe2O3 particles are surrounded by a nitrogen-doped carbon layer. Highly selective hydrogenation of numerous structurally diverse nitroarenes (more than 80 examples) proceeded in good to excellent yield under industrially viable conditions.

http://science.sciencemag.org/content/sci/342/6162/1073.full.pdf

Nanoscale Fe2O3-based catalysts for selective hydrogenation of nitroarenes to anilines.

Cofactor-mimetic aerobic oxidation has conceptually merged with catalysis of syngas reactions to form a wide range of Markovnikov-selective olefin radical hydrofunctionalizations. We cover the development of the field and review contributions to reaction invention, mechanism, and application to complex molecule synthesis. We also provide a mechanistic framework for understanding this compendium of radical reactions.

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Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins

The use of 3d metals in de/hydrogenation catalysis has emerged as a competitive field with respect to “traditional” precious metal catalyzed transformations. The introduction of functional pincer ligands that can store protons and/or electrons as expressed by metal–ligand cooperativity and ligand redox-activity strongly stimulated this development as a conceptual starting point for rational catalyst design. This review aims at providing a comprehensive picture of the utilization of functional pincer ligands in first-row transition metal hydrogenation and dehydrogenation catalysis and related synthetic concepts relying on these such as the hydrogen borrowing methodology. Particular emphasis is put on the implementation and relevance of cooperating and redox-active pincer ligands within the mechanistic scenarios.

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands.

The addition of a silicon-hydrogen or a boron-hydrogen bond across a carbon-carbon multiple bonds is a well-established method for the introduction of versatile silane and borane functional groups to base hydrocarbon feedstocks. Transition metal catalysis, historically with precious second- and third- row transition metals, has been used to broaden the scope of the hydrofunctionalization reaction, improve reaction rate and enhance selectivity. The anti-Markovnikov selectivity of platinum-catalyzed hydrosilylation of alkenes, for example, is an enabling synthetic technology in the multibillion-dollar silicones industry. Increased emphasis on sustainable catalytic methods and more economic processes has shifted focus to catalysis with more earth-abundant transition metals such as iron, cobalt and nickel. This review describes contemporary approaches and offers a contextual analysis of catalytic alkene hydrosilylation and hydroboration reactions using first-row transition metals. Emphasis is placed on defining advances in the field, what constitutes catalyst cost, safety, and important design features to enable precious metal-like reactivity, as well as new chemistry that is unique to first-row transition metals.

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Earth-Abundant Transition Metal Catalysts for Alkene Hydrosilylation and Hydroboration: Opportunities and Assessments.

Disclosed herein are cobalt complexes containing pyridine di-imine ligands and chelating alkenyl-modified silyl ligands, and their use as hydrosilylation and/or dehydrogenative silylation and crosslinking catalysts. The cobalt complexes also exhibit adequate air stability for handling and manipulation.

Cobalt catalysts and their use for hydrosilylation and dehydrogenative silylation

Disclosed herein is the use of manganese, iron, cobalt, or nickel complexes containing tridentate pyridine di-imine ligands as hydrosilylation catalysts. These complexes are effective for efficiently catalyzing hydrosilylation reactions, as well as offering improved selectivity and yield over existing catalyst systems.

Non-precious Metal-based Hyrdosilylation Catalysts Exhibiting Improved Selectivity

Disclosed herein are cobalt complexes containing terdentate pyridine di-imine ligands and their use as efficient and selective dehydrogenative silylation and crosslinking catalysts.

Dehydrogenative silylation and crosslinking using cobalt catalysts

Disclosed herein is the selective synthesis of mono-hydrosilylated derivatives of polyunsaturated compounds, such as trivinylcyclohexane using non-precious metal based pyridinediimine and terpyridine complex as selective hydrosilylation catalysts.

Selective non-precious metal-catalyzed mono-hydrosilylation of polyunsaturated compounds

Disclosed herein are cobalt complexes containing terdentate pyridine di-imine ligands and their use as efficient and selective dehydrogenative silylation, hydrosilylation, and crosslinking catalysts.

Susan A. Nye

Papers

Cobalt catalysts and their use for hydrosilylation and dehydrogenative silylation

Non-precious Metal-based Hyrdosilylation Catalysts Exhibiting Improved Selectivity

Dehydrogenative silylation and crosslinking using cobalt catalysts

Selective non-precious metal-catalyzed mono-hydrosilylation of polyunsaturated compounds

Dehydrogenative silylation, hydrosilylation and crosslinking using cobalt catalysts