Isabel W. C. E. Arends

New developments in catalytic alcohol oxidations for fine chemicals synthesis

New developments in liquid phase catalytic oxidations of alcohols with O2 and H2O2 as the primary oxidant are reviewed. Both homogeneous and heterogeneous catalysts are discussed and compared and emphasis is placed on methods having broad utility for the synthesis of fine chemicals. Mechanistic features of the various systems are also discussed, e.g., oxometal vs. peroxometal pathways in oxidations with H2O2 and oxometal vs. hydridometal pathways with O2 as the oxidant.

Activities and stabilities of heterogeneous catalysts in selective liquid phase oxidations: recent developments

Abstract Different strategies for the heterogenization of redox-active elements in solid matrices are reviewed. These include framework-substituted molecular sieves, amorphous mixed oxides by grafting or sol–gel methods, grafting or tethering to the inner walls of mesoporous molecular sieves, encapsulation by ship-in-a-bottle or other techniques and ion exchange in layered double hydroxides. The different approaches are illustrated by reference to recent developments involving a variety of metal catalysts — titanium, chromium, cobalt, manganese, iron, ruthenium, tungsten, molybdenum, vanadium and tantalum — in oxidations with O 2 , H 2 O 2 and RO 2 H as primary oxidants. Emphasis is placed on an evaluation of the stability of the various catalysts under reaction conditions, a conditio sine qua non for practical utility. Protocols for establishing heterogeneity are discussed. An analysis of experimental results leads to the conclusion that many of the systems described in the literature, particularly those involving oxometal species, are unstable towards leaching or the appropriate rigorous tests for heterogeneity have not been performed.

Enzyme-mediated oxidations for the chemist

Biocatalysis is an enabling technology adding to organic oxidation chemistry. Especially the high selectivity of enzymatic oxidation coevally operating under mild conditions and not necessitating problematic solvents makes it a very valuable tool for (green) chemistry. The present state of the art in the use of enzymes and microorganisms for catalytic oxidation and oxyfunctionalization chemistry is reviewed.

Are Natural Deep Eutectic Solvents the Missing Link in Understanding Cellular Metabolism and Physiology

Over the past decade, metabolomics has developed into a major tool for studying the metabolism of organisms and cells, and through this approach much has been learned about metabolic networks and the reactions of organisms to various external conditions ([Lay et al., 2006][1]). Most of this work

Enzymatic reductions for the chemist

When challenged by a difficult reduction reaction, a chemist should always also consider biocatalysis in synthesis planning. The inherent selectivity of enzymes has been known for many decades now and the practical applicability of biocatalysis has undergone dramatic improvements rendering it a true alternative to established chemocatalysis. In this contribution recent developments in the field of enzymatic reduction using whole cells and isolated enzymes are reviewed.

Catalytic Conversions in Water. Part 21: Mechanistic Investigations on the Palladium‐Catalysed Aerobic Oxidation of Alcohols in Water†

Water-soluble complexes of palladium(II) with phenanthroline-derivatives are stable, recyclable catalysts for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic liquid-liquid system. The active catalyst is a dihydroxy-bridged palladium dimer. Kinetics of the reaction, ligand and anion effects are discussed.

Biocatalytic Redox Reactions for Organic Synthesis: Nonconventional Regeneration Methods

Redox enzymes have tremendous potential as catalysts for preparative organic chemistry. Their usually high selectivity, paired with their catalytic efficiency under mild reaction conditions, makes them potentially very valuable tools for synthesis. The number of interesting monooxygenases, dehydrogenases, reductases, oxidases, and peroxidases is steadily increasing and the tailoring of a given biocatalyst is more and more becoming standard technology. However, their cofactor dependency still represents a major impediment en route to true preparative applicability. Currently, three different approaches to deal with this ‘cofactor challenge’ are being pursued: using whole cells, biomimetic approaches comprising enzymatic cofactor regenerations systems, and ‘unconventional’ nonenzymatic regeneration. The latter technique offers the promise of enabling simple, easily applicable, and robust reaction schemes, for example, by circumventing the ‘cofactor challenge’ and introducing redox power directly to the enzyme’s active sites.

Liquid phase oxidation at metal ions and complexes in constrained environments

Abstract Various approaches towards the rational design of novel catalysts based on the concept of confinement (site-isolation) of redox active metal centres in molecular sieves are reviewed. These comprise (a) substitution of T elements (Si, Al and P) in the framework of silicates, zeolites, AlPOs and SAPOs, (b) encapsulation of metal complexes in intrazeolite space (ship-in-a-bottle catalysts) and (c) grafting or tethering of metal complexes to the internal surface of the molecular sieves. Related materials - redox pillared clays, clay intercalated metal complexes, redox aerogels and metal complexes incorporated in aerogels - are also reviewed. The advantages and limitations of the various materials with regard to activity and selectivity as catalysts for liquid phase oxidations with O2, H2O2 and RO2H and stability towards leaching, are discussed.

Cu(II)-nitroxyl radicals as catalytic galactose oxidase mimics

Results from Hammett correlation studies and primary kinetic isotope effects for the CuCl-TEMPO catalysed aerobic benzyl alcohol oxidations are inconsistent with an oxoammonium based mechanism. We postulate a copper-mediated dehydrogenation mechanism, in which TEMPO regenerates the active Cu(II)-species. This mechanism is analogous to that observed for Galactose Oxidase and mimics thereof.

Recent developments in selective catalytic epoxidations with H2O2

In this review the state-of-the-art of catalytic processes known today for selective epoxidations using aqueous H2O2 as the oxidant is presented. Recent achievements from our laboratories on the development of catalysts for epoxidations with H2O2 are given as well. For all systems their viability for application in green catalytic processes is evaluated, based on selectivity of the reaction, turnover frequency, substrate scope and solvent needed.