The Golden Age of Transfer Hydrogenation

Ruthenium-Catalyzed Reactions for Organic Synthesis.

Selective catalytic hydrogenation has wide applications in both petrochemical and fine chemical industries, however, it remains challenging when two or multiple functional groups coexist in the substrate. To tackle this challenge, the "active site isolation" strategy has been proved effective, and various approaches to the site isolation have been developed. In this review, we have summarized these approaches, including adsorption/grafting of N/S-containing organic molecules on the metal surface, partial covering of active metal surface by metal oxides either via doping or through strong metal-support interaction, confinement of active metal nanoparticles in micro- or mesopores of the supports, formation of bimetallic alloys or intermetallics or core@shell structures with a relatively inert metal (IB and IIB) or nonmetal element (B, C, S, etc.), and construction of single-atom catalysts on reducible oxides or inert metals. Both advantages and disadvantages of each approach toward the site isolation have been discussed for three types of chemoselective hydrogenation reactions, including alkynes/dienes to monoenes, α,β-unsaturated aldehydes/ketones to the unsaturated alcohols, and substituted nitroarenes to the corresponding anilines. The key factors affecting the catalytic activity/selectivity, in particular, the geometric and electronic structure of the active sites, are discussed with the aim to extract fundamental principles for the development of efficient and selective catalysts in hydrogenation as well as other transformations.

Selective Hydrogenation over Supported Metal Catalysts: From Nanoparticles to Single Atoms

Reducing oxygen content in biomass-derived feedstocks via hydrodeoxygenation (HDO) is a key step in their upgrading to fuels and valuable chemicals. Organic molecules, e.g., alcohols and formic acid, can donate hydrogen to reduce the substrate in a process called catalytic transfer hydrogenation (CTH). Although it is practiced far less frequently than molecular-hydrogen-based HDO processes, CTH has been proven to be an efficient and selective strategy in biomass upgrading in the last two decades. In this paper, we present a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation. Hydrogenation and cleavage of C═O and C–O bonds, respectively, are the two main categories of reactions discussed, owing to their importance in the HDO of biomass-derived feedstocks. On acid–base catalysts, Lewis acid–base pair sites, rather than a single acid or base site, mediate hydrogenation of carbonyl groups with alcohols...

Heterogeneous Catalytic Transfer Hydrogenation as an Effective Pathway in Biomass Upgrading

Lignin accounts for approximately 25–35 % of the organic matrix of wood and lignocellulosic biomass in itself is the most abundant renewable material on the planet. It has long been recognized as a potential feedstock for producing chemicals, fuels, and materials. Despite this excellent availabilty of lignin it is a low value compound and has so far mainly been used as energy source in combustion applications. Less than 5 % are being processed for other purposes. This article discusses the potential for an increased use of lignin as a renewable raw material, possible conversion routes towards monomeric phenolic compounds, and applications for these products. A brief overview about present state-of-the-art is given and a high-yielding, one-step approach of producing alkylated phenolic compounds from lignin is presented.

Phenols from Lignin

1. Olefins 2. Acetylenes 3. Carbonyl Compounds 4. Nitriles 5. Imines, Hydroxylamines, Hydrazones 6. Azo Compounds 7. Nitro Compounds B. Hydrogenolysis 1 , Nitriles 2. Halides 3. Allylic and Benzylic Functional Groups 4. Amines C. Structural Selectivity D. Special Synthetic Applications IV. Mechanism V . Summary and Prospects V I , References 567 568 568 569 569 570 570 570 570 570 570 571 571 571 571 571 571 571 571 571 573 574 575 576 580 580

Terry J. Nestrick

Papers

Catalytic Transfer Hydrogenation

Synthesis of trans, trans-.alpha.-farnesene

Catalytic transfer reduction: scope and utility

Convenient O-alkylation of phenols