and Fuels Changzhi Li,† Xiaochen Zhao,† Aiqin Wang,† George W. Huber,†,‡ and Tao Zhang*,† †State Key Laborotary of Catalysis, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ‡Department of Chemical and Biological Engineering, University of WisconsinMadison, Madison, Wisconsin 53706, United States

Catalytic Transformation of Lignin for the Production of Chemicals and Fuels

3.1. C-M and X-H as Nucleophiles 1806 3.2. C-H and X-M as Nucleophiles 1809 3.2.1. C-Halogen Bond Formations 1809 3.2.2. C-O Bond Formations 1812 3.3. C-H and X-H as Nucleophiles 1812 3.3.1. C-O Bond Formations 1812 3.3.2. C-N Bond Formations 1815 4. Oxidative X-X Bond Formations between Two Nucleophiles 1819 5. Conclusions 1819 Author Information 1819 Biographies 1819 Acknowledgment 1820 References 1820

Bond Formations between Two Nucleophiles: Transition Metal Catalyzed Oxidative Cross-Coupling Reactions

Catalytic transformation of ubiquitous C–H bonds into valuable C–N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C–H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications

C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.

3d Transition Metals for C-H Activation.

Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple "upstream" (i.e., lignin bioengineering, lignin isolation and "early-stage catalytic conversion of lignin") and "downstream" (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a "beginning-to-end" analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis.

Atmospheric oxygen was used for the first time as an oxidant in metal-catalyzed homocoupling of Grignard reagents. These manganese- or iron-catalyzed reactions are efficient, cheap, and eco-friendly. They are applicable to the large-scale synthesis of symmetrical conjugated compounds.

http://www.cs.gordon.edu/~ijl/che340/project/Manganese-%20or%20Iron-Catalyzed%20Homocoupling%20of%20Grignard%20Reagents%20Using%20Atmospheric%20Oxygen%20as%20an%20Oxidant.pdf

Manganese- or iron-catalyzed homocoupling of grignard reagents using atmospheric oxygen as an oxidant.

Mechanochemical degradation of lignin and wood by solvent-free grinding in a reactive medium

Ruthenium–triphos complexes exhibited unprecedented catalytic activity and selectivity in the redox-neutral CC bond cleavage of the β-O-4 lignin linkage of 1,3-dilignol model compounds. A mechanistic pathway involving a dehydrogenation-initiated retro-aldol reaction for the CC bond cleavage was proposed in line with experimental data and DFT calculations.

Ruthenium‐Catalyzed C ? C Bond Cleavage in Lignin Model Substrates

Chemistry of organomanganese(II) compounds.

Alkyl–alkynyl cross-coupling can be achieved through one of two pathways. The first one consists in alkylating a metal acetylide with a primary alkyl iodide or bromide. Sodium, potassium, or lithium acetylides have been extensively used, but the reaction suffers from some limitations. As an example, the substitution reaction does not tolerate the presence of reactive functional groups such as esters or nitriles. On the other hand, b-branched primary, secondary, or tertiary alkyl halides mainly undergo an elimination reaction and do not lead to the substitution product, or in only poor yields. The coupling of tertiary alkyl halides with alkynylalanes was reported. However, the method is not general, and only one of the three alkynyl groups is transferred. The alkyl–alkynyl cross-coupling can also be performed according to a second pathway, which involves reacting an alkylmetal with an alkynyl halide. The first attempts were carried out by reacting iodoor bromoalkynes with Grignard reagents in the presence of cobalt salts, or organocopper derivatives. However, poor to moderate yields are generally obtained. Later, a few trialkylaluminium reagents were coupled successfully with alkynyl bromides under nickel catalysis, however only one alkyl group was transferred in moderate to good yields. An interesting general method was described by Yeh and Knochel in 1989, in which functionalized organocuprate reagents, AlkFg–Cu(CN)ZnI (Fg = functional group), react with simple bromoor iodoalkynes to afford functionalized alkynes in good yields. However, the reaction conditions (12–16 h at 65 8C), and the use of a stoichiometric amount of copper are not very convenient for large-scale preparations. The aryl–alkynyl coupling is generally performed by using the well-known Sonogashira reaction between aromatic halides and terminal alkynes in the presence of both copper and palladium salts. In contrast, the coupling of an arylmetal with an alkynyl halide has been almost ignored until now. In 1972, Oliver and Walton studied the reaction of arylcopper reagents with iodo-trimethylsilylacetylene, but the reaction has not been extended to other substrates. In fact, it should be noted that as a rule, no general procedure is currently available to couple aryl or alkyl Grignard reagents with alkynyl halides. Herein we report the first efficient copper-catalyzed alkynylation of alkyl and aryl Grignard reagents. Weedon and co-workers reported that the coppercatalyzed coupling of alkyl Grignard reagents with alkynyl halides only gives poor yields of the substitution product. As mentioned by Normant and co-workers, the halogen/ magnesium exchange generally takes place predominantly. Recently, in the light of our experience in copper-catalyzed cross-coupling reactions with Grignard reagents, we decided to reinvestigate this reaction and we discovered that, in fact, satisfactory yields can be obtained by slowly introducing the Grignard reagent to the reaction mixture. As an example, in the presence of 3 mol % CuCl2 in THF at 0 8C, the addition of nBuMgCl (12 mmol) to heptynyl bromide (10 mmol) over a 45 minute period gave 73 % of 5-undecyne (Table 1, entry 1). To improve this result, we have tested the

Julien Buendia

Papers

Manganese- or iron-catalyzed homocoupling of grignard reagents using atmospheric oxygen as an oxidant.

Mechanochemical degradation of lignin and wood by solvent-free grinding in a reactive medium

Ruthenium‐Catalyzed C ? C Bond Cleavage in Lignin Model Substrates

Chemistry of organomanganese(II) compounds.

Copper-Catalyzed Cross-Coupling of Alkyl and Aryl Grignard Reagents with Alkynyl Halides