Use Of Homogeneous Catalysis Research Articles

Wood-Sourced Polymers as Support for Catalysis by Group 10 Transition Metals

Despite providing interesting solutions to reduce the number of synthetic steps, to decrease energy consumption or to generate less waste, therefore contributing to a more sustainable way of producing important chemicals, the expansion of the use of homogeneous catalysis in industrial processes is hampered by several drawbacks. One of the most important is the difficulty to recycle the noble metals generating potential high costs and pollution of the synthesized products by metal traces detrimental to their applications. Supporting the metals on abundant and cheap biosourced polymers has recently appeared as an almost ideal solution: They are much easier to recover from the reaction medium and usually maintain high catalytic activity. The present bibliographical review focuses on the development of catalysts based on group 10 transition metals (nickel, palladium, platinum) supported on biopolymers obtained from wood, such as cellulose, hemicellulose, lignin, and their derivatives. The applications of these catalysts in organic synthesis or depollution are also addressed in this review with examples of C-C couplings, oxidation, or hydrogenation reactions.

Reactivity Studies of Phosphinines: The Selenation of Diphenyl-Phosphine Substituents and Formation of a Chelating Bis(Phosphinine) Palladium(II) Complex

Phosphinines and donor-substituted phosphinines are of recent interest due to their use in homogeneous catalysis. In this article, a Pd(II) bis(phosphinine) complex was characterised and phosphorus–selenium coupling constants were used to assess the donor properties of the diphenylphosphine substituents of phosphinine ligands to promote their further use in catalysis. The selenation of 2,5-bis(diphenylphosphino)-3,6-dimethylphosphinine (5) and 2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (6) gave the corresponding phosphine selenides 8 and 9, respectively, leaving the phosphinine ring intact. Multinuclear NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction confirmed the oxidation of all the diphenylphosphine substituents with 1JP-Se coupling constants determined to be similar to SePPh3, indicating that the phosphinine rings were electronically similar to phenyl substituents. Solutions of 6 were found to react with oxygen slowly to produce the phosphine oxide 10 along with other by-products. The reaction of [bis{3-methyl-6-(trimethylsilyl)phosphinine-2-yl}dimethylsilane] (4) with [PdCl2(COD)] gave the chelating dichloropalladium(II) complex, as determined by multinuclear NMR spectroscopy, mass spectrometry and an elemental analysis. The molecular structure of the intermediate 2 in the formation of 4,6-di(tert-butyl)-1,3,2-diazaphosphinine (3) was also determined, which confirmed the structure of the diazaphosphacycle P(Cl){N=C(tBu)CH=C(tBu)-N(H)}.

Iridium Azocarboxamide Complexes: Variable Coordination Modes, C–H Activation, Transfer Hydrogenation Catalysis, and Mechanistic Insights

Azocarboxamides, a special class of azo ligands, display intriguing electronic properties due to their versatile binding modes and coordination flexibility. These properties may have significant implications for their use in homogeneous catalysis. In the present report, half-sandwich Ir–Cp* complexes of two different azocarboxamide ligands are presented. Different coordination motifs of the ligand were realized using base and chloride abstracting ligand to give N∧N-, N∧O-, and N∧C-chelated monomeric iridium complexes. For the azocarboxamide ligand having methoxy substituted at the phenyl ring, a mixture of N∧C-chelated mononuclear (Ir-5) and N∧N,N∧C-chelated dinuclear complexes (Ir-4) were obtained by activating the C–H bond of the aryl ring. No such C–H activation was observed for the ligand without the methoxy substituent. The molecular identity of the complexes was confirmed by spectroscopic analyses, while X-ray diffraction analyses further confirmed three-legged piano-stool structure of the complexes along with the above binding modes. All complexes were found to exhibit remarkable activity as precatalysts for the transfer hydrogenation of carbonyl groups in the presence of a base, even at low catalyst loading. Optimization of reaction conditions divulged superior catalytic activity of Ir-3 and Ir-4 complexes in transfer hydrogenation over the other catalysts. Investigation of the influence of binding modes on the catalytic activity along with wide range substrates, tolerance to functional groups, and mechanistic insights into the reaction pathway are also presented. These are the first examples of C–H activation in azocarboxamide ligands.

Thiosemicarbazone Complexes of Transition Metals as Catalysts for Cross-Coupling Reactions

Catalysis of cross-coupling reactions under phosphane-free conditions represents an important ongoing challenge. Although transition metal complexes based on the thiosemicarbazone unit have been known for a very long time, their use in homogeneous catalysis has been studied only relatively recently. In particular, reports of cross-coupling catalytic reactions with such complexes have appeared only in the last 15 years. This review provides a survey of the research in this area and a discussion of the prospects for future developments.

Peroxymonosulfate promoted wet air oxidation of a real wastewater from a biodiesel production plant

Wastewater from a real biodiesel plant located in the province of Badajoz (Spain) has been treated by means of the Wet air oxidation (WAO) process. The effluent was slightly acidic (pH = 5.77) with a high content of chemical oxygen demand (COD) (43.1 g L−1) mainly of organic nature (CTOC = 10.5 g L−1). The low biodegradability of this effluent (relation biological-chemical oxygen demand BOD/COD = 8.6 × 10−3), suggests the suitability to be treated by WAO oxidation. The main WAO operational variables (oxygen pressure, temperature and pH), the use of homogeneous catalysis (Cu2+), or the addition of oxidant promoters (H2O2 or peroxymonosulfate (PMS)) were explored. From the results obtained, oxygen pressure exerted a positive effect while temperature was a crucial variable in the oxidation of the most recalcitrant organics. Although alkaline pH led to an improved behavior in terms of COD and TOC removals, the lack of aromatic compounds elimination (absorbance at 254 nm) suggests the preference to oxidize non-aromatic compounds. Addition of radical promoters resulted in a positive effect. Peroxymonopersufate was more efficient than H2O2 in the promoted experimental series. Under the optimum oxidation conditions used in this study, removals of 55% in COD, 45% in TOC and 86% in aromatic compounds were experienced.

Homogeneous catalysis for the production of low-volume, high-value chemicals from biomass

The transition from petroleum to biorenewable sources of carbon to meet our energy and chemical feedstock needs is difficult, in part because these sources are so different, with petroleum being under-functionalized and biomass being over-functionalized relative to commercial chemicals. However, target lists such as the US Department of Energy’s Top 10 have converged efforts to develop the technologies needed to manufacture the most important feedstocks accessible from biorenewables. Less well defined but equally important to the economic viability of an integrated biorefinery are low-volume, high-value product streams, which would help offset the capital costs of a biorefinery. In this Review, we attempt to bring together some of the advances that could fill these niche areas, with a focus on the conversion of cellulosics into chemicals using homogeneous catalysis. The products range from high-value jet fuels to monomers for high-performance polymers and materials to pharmaceutical intermediates and cover a broad range of structural complexities. A move away from fossil fuels as an energy source will also require a move to new sources for important chemical feedstocks. This Review considers the use of homogeneous catalysis to convert cellulosics into low-volume, high-value chemicals that are currently derived from crude oil.

Secondary Phosphine Oxide–Gold(I) Complexes and Their First Application in Catalysis

A series of new secondary phosphine oxide (SPO)–gold(I) complexes have been synthesized and characterized by X-ray crystallography. Complexes exhibited dimeric structures interconnected by O–H···Cl hydrogen bonds. Their first use in homogeneous catalysis is reported and suggests a broad field of application in prototypical enyne cycloisomerization and hydroxy- and methoxycyclization reactions.

A personal view on homogeneous catalysis and its perspectives for the use of renewables

AbstractThis personal account is based on a talk at the conference “Fats and Oils as Renewable Feedstock for the Chemical Industry” in Emden, Germany. It describes selected perspectives and challenges applying catalysis for the refinement of renewables. Because the author himself has not been active in the past using biomass‐based starting materials, special focus is given on the use of homogeneous catalysis as a tool for a more sustainable chemistry in industry and academia. Recent developments of catalysts in our research group are used to illustrate the current status and challenges of homogeneous catalysis in this area.

Synthesis and reactivity of new strained cyclic allene and alkyne precursors

Abstract The synthesis of ortho-(trimethylsilyl)vinyl triflates is described. Fluoride-induced decomposition of these triflates leads to the generation of strained cycloallenes and cycloalkynes under mild reaction conditions. The generation rate of these highly reactive intermediates can be modulated by modifying the solubility of the fluoride source. The slow generation of cyclic allenes and alkynes is a prerequisite for their use in homogeneous catalysis.

Synthesis and characterization of {[(COD)Rh(bis-(2R,3R)-2,5-diethylphospholanobenzene)] +BARF −} for use in homogeneous catalysis in supercritical carbon dioxide

Reaction of [(COD) 2Cl 2Rh] (COD: cyclo-octadiene) with sodium tetrakis((3,5-trifluoromethyl)phenyl)borate (NaBARF) in the presence of an excess of COD yields [(COD) 2Rh] +BARF −. The COD ligands are readily displaced by the bidentate ligand 1,2-bis((2R,5R)-2,5-diethylphosphalono)benzene (Et-DuPHOS) to form [(COD)Rh(Et-DuPHOS)]BARF, the structure of which has been determined by X-ray crystallography. BARF was selected as the counterion in order to achieve solubility in supercritical carbon dioxide for use in asymmetric hydrogenation and hydroformylation reactions. Density-functional theory calculations were used to study the intermediates in asymmetric hydroformylation of styrene. The energies of the two-enantiomer models differ by 11.3 kcal mol −1.

Probing new classes of π-acceptor ligands for rhodium catalyzed hydroformylation of styrene

Three hitherto unexplored classes of strong π-acceptor ligands for use in homogeneous catalysis—phospha-π-aromatic compounds (class A), pyrrolyl phosphines (class B) and phosphenium cations (class C)—have been evaluatated for rhodium catalyzed hydroformylation of styrene. When testing monodentate ligands, the ortho/ ortho′-disubstituted phosphabenzene derivative 1b provided a rhodium-catalyst endowed with the highest catalytic activity. Based upon these results a first series of bidentate phosphabenzene ligands have been tailored employing the concept of an electronic differentiation of the two binding sites. An oxazoline/phosphabenzene system 8 which is capable of forming an eight-membered chelation ring gave the best results. Thus, a quantitative conversion of styrene at ambient temperature afforded the desired 2-phenylpropanal in high regioselectivity (25:1).

Ortho-bis(amino)arylnickel(II) halide complexes containing perfluoroalkyl chains as model catalyst precursors for use in fluorous biphase systems

A novel synthetic procedure is presented to modify 1,3-bis[(dimethylamino)methyl]benzene to accommodate perfluoro alkyl chains. These ligands are then converted into nickel- and platinum-chloride organometallic derivatives, which can serve as model compounds for use in homogeneous catalysis. A nickel complex is shown to be an active catalyst for the 1 : 1 addition of CCl 4 to methylmethacrylate (Kharasch addition reaction) in dichloromethane but lacks sufficient solubility for use under fluorous biphase conditions. The structure in the solid state of this fluorous Ni species, which is a rare example of a structurally characterised perfluoro organometallic compound, was elucidated by single crystal X-ray diffraction.

Platinum carbonyls and their use in homogeneous catalysis

Platinum carbonyls and their use in homogeneous catalysis

Commercial Applications of Reactions Catalyzed by Soluble Complexes of Cobalt and Rhodium

Abstract The past quarter century has witnessed an enormous transformation in the use of soluble transition metal complexes as catalysts in the chemical process industries. Until the mid-1950s, industrial use of homogeneous catalysis was largely confined to reactions of acetylene [1]. As indicated in Fig. 1, a large family of acetylene-based reactions was used to produce polymer intermediates such as vinyl acetate, vinyl chloride, acrylonitrile, chloroprene, and 1,4-butanediol. The processes were simple but they were relatively expensive because they were based on an expensive raw material. The large energy content of the acetylene molecule (ΔF°=50.84 kcal/mol) made it both hazardous to handle and expensive even in times when energy was cheaper.

有機合成に用いられる金属化合物の合成と性質 Ｒｕ，Ｏｓ Ｒｕｔｈｅｎｉｕｍ ａｎｄ ｏｓｍｉｕｍ ｃｏｍｐｏｕｎｄｓ （ルテニウムおよびオスミウム化合物）

This article deals chiefly with low-valent ruthenium- and osmium-phosphine complexes and presents a brief review of their available methods of synthesis with preparative examples. Also described are the recent examples of their use in homogeneous catalysis.