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Special Issue "Homogeneous Catalysis"

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A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (30 November 2010)

Special Issue Editor

Guest Editor
Prof. Dr. Piet W. N. M. Van Leeuwen (Website)

Institut Català d'Investigació Química, Avda Països Catalans, 16, 43007 Tarragona, Spain
Interests: homogeneous catalysis: carbonylation; hydroformylation; oligomerization; cross coupling reactions; molecular modelling; shape-selective catalysis; dendri­mers; mechanistic studies; catalyst immobilization; electronic/steric/bite angle ligand effects; supramolecular catalysis; microreactors; catalyst decomposition mechanisms; e-learning

Special Issue Information

Dear Colleagues,

This special issue of Molecules dedicated to Homogeneous Catalysis will have a broad focus on many aspects of homogeneous catalysis, comprising exploratory studies for new catalysts, ligands and reactions, mechanistic studies, laboratory and industrial applications concerning large-scale and small-scale markets. Homogeneous catalysis owes its development to bulk chemistry using as starting materials petrochemicals such as alkenes, carbon monoxide, methanol and oxygen. In this area both the introduction of new reactions and new catalysts continues to be of great value. In the last decades the number of new reactions and catalysts invented for organic syntheses exceeds the number of reactions for bulk chemicals by orders of magnitude. There is hardly any multistep synthesis that does not involve a palladium or ruthenium catalyzed step! This special issue will highlight all areas of current and future interest.

Prof. Dr. Piet W. N. M. van Leeuwen
Guest Editor

Keywords

  • homogeneous catalysis
  • transition metal catalysis
  • carbon-carbon bond formation
  • asymmetric catalysis
  • atom-economic catalysis

Published Papers (9 papers)

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Research

Jump to: Review

Open AccessArticle New Chiral P-N Ligands for the Regio- and Stereoselective Pd-Catalyzed Dimerization of Styrene
Molecules 2011, 16(2), 1804-1824; doi:10.3390/molecules16021804
Received: 27 December 2010 / Revised: 17 February 2011 / Accepted: 18 February 2011 / Published: 22 February 2011
Cited by 9 | PDF Full-text (336 KB) | Supplementary Files
Abstract
Two new chiral, enantiomerically pure, hybrid P-N ligands, namely (2R,5S)-2-phenyl-3-(2-pyridyl)-1,3-diaza-2-phosphanicyclo[3,3,0]octan-4-one (1) and (2R,5S)-2-phenyl-3-(2-pyridyl)-1,3-diaza-2-phosphanicyclo[3,3,0]octane (2), have been synthesized starting from L-proline. The two ligands differ in the presence or not of [...] Read more.
Two new chiral, enantiomerically pure, hybrid P-N ligands, namely (2R,5S)-2-phenyl-3-(2-pyridyl)-1,3-diaza-2-phosphanicyclo[3,3,0]octan-4-one (1) and (2R,5S)-2-phenyl-3-(2-pyridyl)-1,3-diaza-2-phosphanicyclo[3,3,0]octane (2), have been synthesized starting from L-proline. The two ligands differ in the presence or not of a carbonyl group in the diazaphosphane ring. Their coordination chemistry towards Pd(II) was studied by reacting them with [Pd(CH3)Cl(cod)]. A different behaviour was observed: ligand 2 shows the expected bidentate chelating behaviour leading to the mononuclear Pd-complex, while ligand 1 acts as a terdentate ligand giving a dinuclear species. The corresponding cationic derivatives were obtained from the palladium neutral complexes, both as mono- and dinuclear derivatives, and tested as precatalysts for styrene dimerization, yielding E-1,3-diphenyl-1-butene regio- and stereoselectively as the sole product. A detailed analysis of the catalytic behaviour is reported. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
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Open AccessArticle The Influence of Comonomer on Ethylene/α-Olefin Copolymers Prepared Using [Bis(N-(3-tert butylsalicylidene)anilinato)] Titanium (IV) Dichloride Complex
Molecules 2011, 16(2), 1655-1666; doi:10.3390/molecules16021655
Received: 25 November 2010 / Revised: 11 February 2011 / Accepted: 14 February 2011 / Published: 15 February 2011
Cited by 2 | PDF Full-text (552 KB)
Abstract
We describe the synthesis of [bis(N-(3-tert-butylsalicylidene)anilinato)] titanium (IV) dichloride (Ti-FI complex) and examine the effects of comonomer (feed concentration and type) on its catalytic performance and properties of the resulting polymers. Ethylene/1-hexene and ethylene/1-octene copolymers were prepared through [...] Read more.
We describe the synthesis of [bis(N-(3-tert-butylsalicylidene)anilinato)] titanium (IV) dichloride (Ti-FI complex) and examine the effects of comonomer (feed concentration and type) on its catalytic performance and properties of the resulting polymers. Ethylene/1-hexene and ethylene/1-octene copolymers were prepared through copolymerization using Ti-FI catalyst, activated by MAO cocatalyst at 323 K and 50 psi ethylene pressure at various initial comonomer concentrations. The obtained copolymers were characterized by DSC, GPC and 13C-NMR. The results indicate that Ti-FI complex performs as a high potential catalyst, as evidenced by high activity and high molecular weight and uniform molecular weight distribution of its products. Nevertheless, the bulky structure of FI catalyst seems to hinder the insertion of α-olefin comonomer, contributing to the pretty low comonomer incorporation into the polymer chain. The catalytic activity was enhanced with the comonomer feed concentration, but the molecular weight and melting temperature decreased. By comparison both sets of catalytic systems, namely ethylene/1-hexene and ethylene/1-octene copolymerization, the first one afforded better activity by reason of easier insertion of short chain comonomer. Although 1-hexene copolymers also exhibited higher molecular weight than 1-octene, no significant difference in both melting temperature and crystallinity can be noticed between these comonomers. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
Open AccessArticle Homopolymerization of Ethylene, 1-Hexene, Styrene and Copolymerization of Styrene With 1,3-Cyclohexadiene Using (h5-Tetramethylcyclopentadienyl)dimethylsilyl(N-Ar’)amido-TiCl2/MAO (Ar’=6-(2-(Diethylboryl)phenyl)pyrid-2-yl, Biphen-3-yl)
Molecules 2011, 16(1), 567-582; doi:10.3390/molecules16010567
Received: 1 December 2010 / Revised: 9 January 2011 / Accepted: 13 January 2011 / Published: 14 January 2011
Cited by 7 | PDF Full-text (519 KB)
Abstract
The propensity of a half-sandwich (η5-tetramethylcyclopentadienyl) dimethylsilylamido TiIV-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is [...] Read more.
The propensity of a half-sandwich (η5-tetramethylcyclopentadienyl) dimethylsilylamido TiIV-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is described. The reactivity of Ti-8 was investigated in comparison to a 6-(2-(diethylboryl)phenyl)pyrid-2-yl-free analogue (Ti-3). Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
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Open AccessArticle Observation of Different Catalytic Activity of Various 1-Olefins during Ethylene/1-Olefin Copolymerization with Homogeneous Metallocene Catalysts
Molecules 2011, 16(1), 373-383; doi:10.3390/molecules16010373
Received: 18 November 2010 / Revised: 28 December 2010 / Accepted: 5 January 2011 / Published: 7 January 2011
Cited by 9 | PDF Full-text (548 KB)
Abstract
This research aimed to investigate the copolymerization of ethylene and various 1-olefins. The comonomer lengths were varied from 1-hexene (1-C6) up to 1-octadecene (1-C18) in order to study the effect of comonomer chain length on the activity and [...] Read more.
This research aimed to investigate the copolymerization of ethylene and various 1-olefins. The comonomer lengths were varied from 1-hexene (1-C6) up to 1-octadecene (1-C18) in order to study the effect of comonomer chain length on the activity and properties of the polymer in the metallocene/MAO catalyst system. The results indicated that two distinct cases can be described for the effect of 1-olefin chain length on the activity. Considering the short chain length comonomers, such as 1-hexene, 1-octene and 1-decene, it is obvious that the polymerization activity decreased when the length of comonomer was higher, which is probably due to increased steric hindrance at the catalytic center hindering the insertion of ethylene monomer to the active sites, hence, the polymerization rate decreased. On the contrary, for the longer chain 1-olefins, namely 1-dodecene, 1-tetradecene and 1-octadecene, an increase in the comonomer chain length resulted in better activity due to the opening of the gap aperture between Cp(centroid)-M-Cp-(centroid), which forced the coordination site to open more. This effect facilitated the polymerization of the ethylene monomer at the catalytic sites, and thus, the activity increased. The copolymers obtained were further characterized using thermal analysis, X-ray diffraction spectroscopy and 13C-NMR techniques. It could be seen that the melting temperature and comonomer distribution were not affected by the 1-olefin chain length. The polymer crystallinity decreased slightly with increasing comonomer chain length. Moreover, all the synthesized polymers were typical LLDPE having random comonomer distribution. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
Open AccessArticle Magnetically Recoverable Magnetite/Gold Catalyst Stabilized by Poly(N-vinyl-2-pyrrolidone) for Aerobic Oxidation of Alcohols
Molecules 2011, 16(1), 149-161; doi:10.3390/molecules16010149
Received: 1 December 2010 / Revised: 16 December 2010 / Accepted: 28 December 2010 / Published: 29 December 2010
Cited by 11 | PDF Full-text (376 KB)
Abstract
Fe3O4:PVP/Au nanocomposite synthesized via a two-step procedure was tested as a quasi-homogenous alcohol oxidation catalyst. It was found that the nanocomposite was able to carry out aerobic oxidation of alcohols in water at room temperature. Studies show rapid [...] Read more.
Fe3O4:PVP/Au nanocomposite synthesized via a two-step procedure was tested as a quasi-homogenous alcohol oxidation catalyst. It was found that the nanocomposite was able to carry out aerobic oxidation of alcohols in water at room temperature. Studies show rapid magnetic recoverability and reusability characteristics. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)

Review

Jump to: Research

Open AccessReview Palladium Catalyzed Allylic C-H Alkylation: A Mechanistic Perspective
Molecules 2011, 16(1), 951-969; doi:10.3390/molecules16010951
Received: 30 November 2010 / Revised: 13 January 2011 / Accepted: 18 January 2011 / Published: 21 January 2011
Cited by 30 | PDF Full-text (622 KB)
Abstract
The atom-efficiency of one of the most widely used catalytic reactions for forging C-C bonds, the Tsuji-Trost reaction, is limited by the need of preoxidized reagents. This limitation can be overcome by utilization of the recently discovered palladium-catalyzed C-H activation, the allylic [...] Read more.
The atom-efficiency of one of the most widely used catalytic reactions for forging C-C bonds, the Tsuji-Trost reaction, is limited by the need of preoxidized reagents. This limitation can be overcome by utilization of the recently discovered palladium-catalyzed C-H activation, the allylic C-H alkylation reaction which is the topic of the current review. Particular emphasis is put on current mechanistic proposals for the three reaction types comprising the overall transformation: C-H activation, nucleophillic addition, and re-oxidation of the active catalyst. Recent advances in C-H bond activation are highlighted with emphasis on those leading to C-C bond formation, but where it was deemed necessary for the general understanding of the process closely related C-H oxidations and aminations are also included. It is found that C-H cleavage is most likely achieved by ligand participation which could involve an acetate ion coordinated to Pd. Several of the reported systems rely on benzoquinone for re-oxidation of the active catalyst. The scope for nucleophilic addition in allylic C-H alkylation is currently limited, due to demands on pKa of the nucleophile. This limitation could be due to the pH dependence of the benzoquinone/hydroquinone redox couple. Alternative methods for re-oxidation that does not rely on benzoquinone could be able to alleviate this limitation. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
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Open AccessReview Recent Advances in the Application of Chiral Phosphine Ligands in Pd-Catalysed Asymmetric Allylic Alkylation
Molecules 2011, 16(1), 970-1010; doi:10.3390/molecules16010970
Received: 20 December 2010 / Revised: 18 January 2011 / Accepted: 19 January 2011 / Published: 21 January 2011
Cited by 38 | PDF Full-text (1797 KB)
Abstract
One of the most powerful approaches for the formation of simple and complex chiral molecules is the metal-catalysed asymmetric allylic alkylation. This reaction has been broadly studied with a great variety of substrates and nucleophiles under different reaction conditions and it has [...] Read more.
One of the most powerful approaches for the formation of simple and complex chiral molecules is the metal-catalysed asymmetric allylic alkylation. This reaction has been broadly studied with a great variety of substrates and nucleophiles under different reaction conditions and it has promoted the synthesis of new chiral ligands to be evaluated as asymmetric inductors. Although the mechanism as well as the active species equilibria are known, the performance of the catalytic system depends on the fine tuning of factors such as type of substrate, nucleophile nature, reaction medium, catalytic precursor and type of ligand used. Particularly interesting are chiral phosphines which have proved to be effective asymmetric inductors in several such reactions. The present review covers the application of phosphine-donor ligands in Pd-catalysed asymmetric allylic alkylation in the last decade. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
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Open AccessReview Transition Metal Catalyzed Synthesis of Aryl Sulfides
Molecules 2011, 16(1), 590-608; doi:10.3390/molecules16010590
Received: 17 December 2010 / Revised: 10 January 2011 / Accepted: 14 January 2011 / Published: 17 January 2011
Cited by 95 | PDF Full-text (238 KB)
Abstract
The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought [...] Read more.
The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought to plague catalyst activity in the presence of transition metals. Indeed, strong coordination of thiolates and thioethers to transition metals can often hinder catalytic activity; however, various catalysts are able to withstand catalyst deactivation and form aryl carbon-sulfur bonds in high-yielding transformations. This review discusses the metal-catalyzed arylation of thiols and the use of disulfides as metal-thiolate precursors for the formation of C-S bonds. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)
Open AccessReview Theoretical Studies of Homogeneous Catalysts Mimicking Nitrogenase
Molecules 2011, 16(1), 442-465; doi:10.3390/molecules16010442
Received: 1 December 2010 / Revised: 27 December 2010 / Accepted: 5 January 2011 / Published: 10 January 2011
Cited by 11 | PDF Full-text (949 KB)
Abstract
The conversion of molecular nitrogen to ammonia is a key biological and chemical process and represents one of the most challenging topics in chemistry and biology. In Nature the Mo-containing nitrogenase enzymes perform nitrogen ‘fixation’ via an iron molybdenum cofactor (FeMo-co) under [...] Read more.
The conversion of molecular nitrogen to ammonia is a key biological and chemical process and represents one of the most challenging topics in chemistry and biology. In Nature the Mo-containing nitrogenase enzymes perform nitrogen ‘fixation’ via an iron molybdenum cofactor (FeMo-co) under ambient conditions. In contrast, industrially, the Haber-Bosch process reduces molecular nitrogen and hydrogen to ammonia with a heterogeneous iron catalyst under drastic conditions of temperature and pressure. This process accounts for the production of millions of tons of nitrogen compounds used for agricultural and industrial purposes, but the high temperature and pressure required result in a large energy loss, leading to several economic and environmental issues. During the last 40 years many attempts have been made to synthesize simple homogeneous catalysts that can activate dinitrogen under the same mild conditions of the nitrogenase enzymes. Several compounds, almost all containing transition metals, have been shown to bind and activate N2 to various degrees. However, to date Mo(N2)(HIPTN)3N with (HIPTN)3N= hexaisopropyl-terphenyl-triamidoamine is the only compound performing this process catalytically. In this review we describe how Density Functional Theory calculations have been of help in elucidating the reaction mechanisms of the inorganic compounds that activate or fix N2. These studies provided important insights that rationalize and complement the experimental findings about the reaction mechanisms of known catalysts, predicting the reactivity of new potential catalysts and helping in tailoring new efficient catalytic compounds. Full article
(This article belongs to the Special Issue Homogeneous Catalysis)

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