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The field of transition metal catalysis has experienced incredible growth during the past decade. The reasons for this are obvious when one considers the world's energy problems and the need for new and less energy demanding syntheses of important chemicals. Heterogeneous catalysis has played a major industrial role; however, such reactions are generally not selective and are exceedingly difficult to study. Homogeneous catalysis suffers from on-site engineering difficulties; however, such reactions usually provide the desired selectivity. For example, Monsanto's synthesis of optically-active amino acids employs a chiral homogeneous rhodium diphosphine catalyst. Industrial uses of homogeneous catalyst systems are increasing. It is not by accident that many homogeneous catalysts contain tertiary phosphine ligands. These ligands possess the correct steric and electronic properties that are necessary for catalytic reactivity and selectivity. This point will be emphasized throughout the book. Thus the stage is set for a comprehensive be treatment of the many ways in which phosphine catalyst systems can designed, synthesized, and studied.
In the last decade there have been numerous advances in the area of rhodium-catalyzed hydroformylation, such as highly selective catalysts of industrial importance, new insights into mechanisms of the reaction, very selective asymmetric catalysts, in situ characterization and application to organic synthesis. The views on hydroformylation which still prevail in the current textbooks have become obsolete in several respects. Therefore, it was felt timely to collect these advances in a book. The book contains a series of chapters discussing several rhodium systems arranged according to ligand type, including asymmetric ligands, a chapter on applications in organic chemistry, a chapter on modern processes and separations, and a chapter on catalyst preparation and laboratory techniques. This book concentrates on highlights, rather than a concise review mentioning all articles in just one line. The book aims at an audience of advanced students, experts in the field, and scientists from related fields. The didactic approach also makes it useful as a guide for an advanced course.
A useful guide to the fundamentals and applications of deep eutectic solvents Deep Eutectic Solvents contains a comprehensive review of the use of deep eutectic solvents (DESs) as an environmentally benign alternative reaction media for chemical transformations and processes. The contributors cover a range of topics including synthesis, structure, properties, toxicity and biodegradability of DESs. The book also explores myriad applications in various disciplines, such as organic synthesis and (bio)catalysis, electrochemistry, extraction, analytical chemistry, polymerizations, (nano)materials preparation, biomass processing, and gas adsorption. The book is aimed at organic chemists, catalytic chemists, pharmaceutical chemists, biochemists, electrochemists, and others involved in the design of eco-friendly reactions and processes. This important book: -Explores the promise of DESs as an environmentally benign alternative to hazardous organic solvents -Covers the synthesis, structure, properties (incl. toxicity) as well as a wide range of applications -Offers a springboard for stimulating critical discussion and encouraging further advances in the field Deep Eutectic Solvents is an interdisciplinary resource for researchers in academia and industry interested in the many uses of DESs as an environmentally benign alternative reaction media.
Homogeneous hydrogenation is one of the most thoroughly studied fields of homogeneous catalysis. The results of these studies have proved to be most important for an understanding of the underlying principles of the activation of small molecules by transition metal complexes. During the past three decades homogeneous hydrogenation has found widespread application in organic chemistry, including the production of important pharmaceuticals, especially where a sophisticated degree of selectivity is required. This volume presents a general account of the main principles and applications of homogeneous hydrogenation by transition metal complexes. Special attention is devoted to the mechanisms by which these processes occur, and the role of the recently discovered complexes of molecular hydrogen is described. Sources of hydrogen, other than H2, are also considered (transfer hydrogenation). The latest achievements in highly stereoselective hydrogenations have made possible many new applications in organic synthesis. These applications are documented by giving details of the reduction of important unsaturated substrates (alkenes, alkynes, aldehydes and ketones, nitrocompounds, etc.). Hydrogenation in biphasic and phase transfer catalyzed systems is also described. Finally, a discussion of the biochemical routes of H2 activation highlights the similarities and differences in performing hydrogenation in both natural and synthetic systems. For researchers working in the fields of homogeneous catalysis, especially in areas such as pharmaceuticals, plastics and fine chemicals.
Ligand hybrid design is becoming an increasingly important area of the synthetic activity in organometallic chemistry. The coordination chemistry of diallylphosphines and phosphine-stabilized germylenes has been studied in this thesis. In particular, phosphine-stabilized germylenes have not only been studied by its potential use as ligands for transition metals, but also as possible synthetic tools in organic chemistry. Diallylphosphine behave as bidentate ligands to stabilize cationic rhodium species of type [Rh(COD){?3(P,C,C)RP(CH2CH=CH2)2}][BF4] [R= iPr2N, tBu and Ph]. Hemilabile properties of diallylphosphine ligands have been demonstrated by ligand exchange reactions. In solution, a dynamic equilibrium of exchange between the two allylic double bonds was detected by low temperature NMR analysis. In the same way, the reversible displacement of coordinated allylic double bond by acetonitrile could be observed. Theoretical calculations have been performed to explain the experimental results for the order of reactivity on removing the acetonitrile under vacuum. Germylenes stabilized by coordination of a phosphine ligand have been synthesized and fully characterized. Reactivity studies showed that phosphine-stabilized germylenes are unreactive toward unsaturated compounds, such as: alkyne, alkene and carbonyl derivatives, but reactive toward 2,3-dimethylbutadiene. The reactivity of phosphine-stabilized germylenes toward transition metal complexes have been studied by reaction with the dimer complex [Rh2(μ-Cl2)(COD)2], demonstrating that phosphine-stabilized germylenes are useful ligands with high potential in organometallic chemistry. The first isolable germanium analogue of alkynes, known as germyne, stabilized by coordination of a phosphine ligand has been synthesized and fully characterized. Synthesized germynes rearrange at RT affording a phosphaalkene and a new stable N-heterocyclic germylene. Keywords: Hybrid ligands, hemilabile properties, coordination chemistry, diallylphosphines, phosphine-stabilized germylene, germyne.
The synthesis and characterisation of a new class of multidentate conformationally flexible phosphino-alkene ligands, called dbaPHOS (127) and monodbaPHOS (128), are described is this PhD thesis. The related phosphine sulphide ligands, namely dbaTHIOPHOS (137) and monodbaTHIOPHOS (149), have also been prepared. The coordination chemistry of the novel ligands was investigated with a variety of late-transition metals, including Cu, Rh, Pd and Pt. X-ray crystal structure determination of the complexes containing these ligands highlights the multiple coordination modes and versatility of each ligand system. The ability of the 1,4-dien-3-one backbone to adopt different conformational geometries around metal centers is of particular note. DbaPHOS (127) was found to act as a cis- and trans-chelating bisphosphine in both square planar PdII and PtII complexes. The 1,4-dien-3-one motif is hemilabile; exchange between coordinated and non-coordinated alkenes is observed in both the Pd0 complex, 167, and the related cationic CuI complex, 193. An investigation into the CuI complexes' activity in the cyclopropanation of styrene, as catalysts, showed that they are commensurate with other recently reported systems. In addition to the coordination chemistry of the novel ligand systems, some interesting findings emerged in the ligand synthesis and characterisation studies. For example, monodbaTHIOPHOS (149) undergoes an interesting solid-state [2+2] intramolecular cycloaddition transformation, giving cycloadduct, 206. Furthermore, 2-hydroperoxytetrahydrofuran was found to be an impurity in the microwave-assisted Horner-Wadsworth-Emmons reaction of 2-(diphenylthiophosphine)benzaldehyde (136) with 1,3-bis-(ethoxyphosphonato)-acetone (130) to give of dbaTHIOPHOS (137) and an unexpected THF insertion product, 138. The latter is explained by a side reaction involving the reduced compound, tetrahydrofuran-2-ol, derived from 2-hydroperoxytetrahydrofuran.