Catalysts

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15 pages, 2598 KiB

Open AccessFeature PaperArticle

MOF Encapsulation of Ru Olefin Metathesis Catalysts to Block Catalyst Decomposition

by Gerard Pareras, Davide Tiana and Albert Poater

Catalysts 2020, 10(6), 687; https://doi.org/10.3390/catal10060687 - 18 Jun 2020

Cited by 9 | Viewed by 4365

Abstract

In the present work, a catalyst variation of the second-generation Hoveyda–Grubbs catalyst, particularly the ammonium-tagged Ru-alkylidene metathesis catalyst AquaMet^TM, is under study, not simply to increase the efficiency in olefin metathesis but also the solubility in polar solvents. Moreover, this ionic [...] Read more.

In the present work, a catalyst variation of the second-generation Hoveyda–Grubbs catalyst, particularly the ammonium-tagged Ru-alkylidene metathesis catalyst AquaMet^TM, is under study, not simply to increase the efficiency in olefin metathesis but also the solubility in polar solvents. Moreover, this ionic catalyst was combined with the metal organic framework (MOF) (Cr)MIL-101-SO₃⁻(Na·15-crown-5)⁺. We started from the experimental results by Grela et al., who increased the performance when the ruthenium catalyst was confined inside the cavities of the MOF, achieving non-covalent interactions between both moieties. Here, using density functional theory (DFT) calculations, the role of the ammonium N-heterocyclic carbene (NHC) tagged and the confinement effects are checked. The kinetics are used to compare reaction profiles, whereas SambVca steric maps and NCI plots are used to characterize the role of the MOF structurally and electronically. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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12 pages, 406 KiB

Open AccessArticle

Self-Metathesis of Methyl Oleate Using Ru-NHC Complexes: A Kinetic Study

by Marc Renom Carrasco, Clémence Nikitine, Mohamed Hamou, Claude de Bellefon, Chloé Thieuleux and Valérie Meille

Catalysts 2020, 10(4), 435; https://doi.org/10.3390/catal10040435 - 17 Apr 2020

Cited by 5 | Viewed by 2792

Abstract

A kinetic study concerning the self-metathesis of methyl oleate and methyl elaidate was performed, using a variety of NHC-ruthenium pre-catalysts, bearing either mesityl groups or di-isopropyl-phenyl groups on the NHC ligand and various trans ligands with respect to the NHC unit. We showed [...] Read more.

A kinetic study concerning the self-metathesis of methyl oleate and methyl elaidate was performed, using a variety of NHC-ruthenium pre-catalysts, bearing either mesityl groups or di-isopropyl-phenyl groups on the NHC ligand and various trans ligands with respect to the NHC unit. We showed that the system can be satisfactorily described using one initiation constant per pre-catalyst and four propagation constants that, conversely, do not depend on the pre-catalyst. The difference of reactivity with oleate (Z) and elaidate (E) can be fully explained by the propagation parameters; the studied pre-catalysts initiate with the same rate starting from the Z or the E olefin. The ranking of the propagation parameters is driven by the thermodynamic equilibrium. The transformation rates of Z and E isomers is only driven by these propagation constants and nothing differentiates the initiation step. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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11 pages, 2251 KiB

Open AccessCommunication

Suzuki–Miyaura Cross-Coupling of Amides Using Well-Defined, Air- and Moisture-Stable Nickel/NHC (NHC = N-Heterocyclic Carbene) Complexes

by Jonathan Buchspies, Md. Mahbubur Rahman and Michal Szostak

Catalysts 2020, 10(4), 372; https://doi.org/10.3390/catal10040372 - 31 Mar 2020

Cited by 15 | Viewed by 5983

Abstract

In this Special Issue on N-Heterocyclic Carbenes and Their Complexes in Catalysis, we report the first example of Suzuki–Miyaura cross-coupling of amides catalyzed by well-defined, air- and moisture-stable nickel/NHC (NHC = N-heterocyclic carbene) complexes. The selective amide bond N–C(O) activation is achieved [...] Read more.

In this Special Issue on N-Heterocyclic Carbenes and Their Complexes in Catalysis, we report the first example of Suzuki–Miyaura cross-coupling of amides catalyzed by well-defined, air- and moisture-stable nickel/NHC (NHC = N-heterocyclic carbene) complexes. The selective amide bond N–C(O) activation is achieved by half-sandwich, cyclopentadienyl [CpNi(NHC)Cl] complexes. The following order of reactivity of NHC ligands has been found: IPr > IMes > IPaul ≈ IPr*. Both the neutral and the cationic complexes are efficient catalysts for the Suzuki–Miyaura cross-coupling of amides. Kinetic studies demonstrate that the reactions are complete in < 1 h at 80 °C. Complete selectivity for the cleavage of exocyclic N-acyl bond has been observed under the experimental conditions. Given the utility of nickel catalysis in activating unreactive bonds, we believe that well-defined and bench-stable [CpNi(NHC)Cl] complexes will find broad application in amide bond and related cross-couplings of bench-stable acyl-electrophiles. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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11 pages, 3154 KiB

Open AccessArticle

The Natural Product Lepidiline A as an N-Heterocyclic Carbene Ligand Precursor in Complexes of the Type [Ir(cod)(NHC)PPh₃)]X: Synthesis, Characterisation, and Application in Hydrogen Isotope Exchange Catalysis

by Alison R. Cochrane, Alan R. Kennedy, William J. Kerr, David M. Lindsay, Marc Reid and Tell Tuttle

Catalysts 2020, 10(2), 161; https://doi.org/10.3390/catal10020161 - 1 Feb 2020

Cited by 6 | Viewed by 4003

Abstract

A range of iridium(I) complexes of the type [Ir(cod)(NHC)PPh₃)]X are reported, where the N-heterocyclic carbene (NHC) is derived from the naturally-occurring imidaozlium salt, Lepidiline A (1,3-dibenzyl-4,5-dimethylimidazolium chloride). A range of complexes were prepared, with a number of NHC ligands and [...] Read more.

A range of iridium(I) complexes of the type [Ir(cod)(NHC)PPh₃)]X are reported, where the N-heterocyclic carbene (NHC) is derived from the naturally-occurring imidaozlium salt, Lepidiline A (1,3-dibenzyl-4,5-dimethylimidazolium chloride). A range of complexes were prepared, with a number of NHC ligands and counter-ions, and various steric and electronic parameters of these complexes were evaluated. The activity of the [Ir(cod)(NHC)PPh₃)]X complexes in hydrogen isotope exchange reactions was then studied, and compared to established iridium(I) complexes. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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24 pages, 2212 KiB

Open AccessArticle

A DFT Study on the Redox Active Behavior of Carbene and Pyridine Ligands in the Oxidative and Reductive Quenching Cycles of Ruthenium Photoredox Catalysts

by Edinson Medina and Balazs Pinter

Catalysts 2020, 10(1), 80; https://doi.org/10.3390/catal10010080 - 6 Jan 2020

Cited by 7 | Viewed by 5964

Abstract

In this study, a detailed look at the electronic structure changes induced by photon absorption and of the succeeding redox events of the oxidative and reductive quenching cycles of ruthenium–carbene and ruthenium–pyridine photoredox catalysts is provided through an arsenal of density functional theory-based [...] Read more.

In this study, a detailed look at the electronic structure changes induced by photon absorption and of the succeeding redox events of the oxidative and reductive quenching cycles of ruthenium–carbene and ruthenium–pyridine photoredox catalysts is provided through an arsenal of density functional theory-based techniques including electron density difference Δρ(r) maps, spin-density distributions, and the non-covalent interaction analysis. We introduced an efficient computational protocol to obtain accurate equilibrium structures and ground-state reduction potentials for these types of complexes, substantiated via a direct comparison to empirical X-ray structures and cyclic voltammetry measurements, respectively. Moreover, we demonstrated the utility of a hitherto unexplored approach to compute excited-state redox potentials based on the Gibbs free energy of the triplet metal-to-ligand charge transfer state (³MLCT). The analyzed Δρ(r) maps revealed the characteristic features of, for example, metal- and ligand-centered reductions and oxidations in both ground and excited states and MLCT processes, disclosing the active participation of carbene ligands in the redox events of homoleptic systems. Beyond analyzing ligand–ligand non-covalent interactions and redox-active behaviors of carbene and pyridine ligands side by side, the effect of such groups on the kinetics of ³MLCT to ³MC transition was scrutinized. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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21 pages, 9152 KiB

Open AccessArticle

Strong Solvent Effects on Catalytic Transfer Hydrogenation of Ketones with [Ir(cod)(NHC)(PR₃)] Catalysts in 2-Propanol-Water Mixtures

by Krisztina Orosz, Gábor Papp, Ágnes Kathó, Ferenc Joó and Henrietta Horváth

Catalysts 2020, 10(1), 17; https://doi.org/10.3390/catal10010017 - 21 Dec 2019

Cited by 13 | Viewed by 4555

Abstract

The synthesis and characterization of the new Ir(I)-complexes [IrCl(cod)(Bnmim)], [Ir(cod)(emim)(PPh₃)]Cl and [Ir(cod)(Bnmim)(mtppms)] are reported. The zwitterionic complexes [Ir(cod)(NHC)(mtppms)] and Na₂[Ir(cod)(NHC)(mtppts)] (NHC = emim, bmim or Bnmim; mtppms-Na and mtppts-Na₃ = sodium salts [...] Read more.

The synthesis and characterization of the new Ir(I)-complexes [IrCl(cod)(Bnmim)], [Ir(cod)(emim)(PPh₃)]Cl and [Ir(cod)(Bnmim)(mtppms)] are reported. The zwitterionic complexes [Ir(cod)(NHC)(mtppms)] and Na₂[Ir(cod)(NHC)(mtppts)] (NHC = emim, bmim or Bnmim; mtppms-Na and mtppts-Na₃ = sodium salts of mono- and trisulfonated triphenylphosphine, respectively) were found to be effective precatalysts for transfer hydrogenation of aromatic and aliphatic ketones in basic 2-propanol-water mixtures with initial turnover frequencies up to 510 h⁻¹ at 80 °C, and their catalytic performances were compared to those of [IrCl(cod)(NHC)] complexes (NHC = emim, bmim, Bnmim, IMes) and [Ir(cod)(emim)(PPh₃)]Cl. Three of the catalysts were characterized by single-crystal X-ray diffraction. The reaction rates of the transfer hydrogenation of acetophenone and benzophenone showed strong dependence on the water concentration of the solvent, indicating preferential solvation of the catalytically active metal complexes. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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12 pages, 1938 KiB

Open AccessCommunication

Highly Efficient N-Heterocyclic Carbene/Ruthenium Catalytic Systems for the Acceptorless Dehydrogenation of Alcohols to Carboxylic Acids: Effects of Ancillary and Additional Ligands

by Wan-Qiang Wang, Hua Cheng, Ye Yuan, Yu-Qing He, Hua-Jing Wang, Zhi-Qin Wang, Wei Sang, Cheng Chen and Francis Verpoort

Catalysts 2020, 10(1), 10; https://doi.org/10.3390/catal10010010 - 19 Dec 2019

Cited by 20 | Viewed by 4140

Abstract

The transition-metal-catalyzed alcohol dehydrogenation to carboxylic acids has been identified as an atom-economical and attractive process. Among various catalytic systems, Ru-based systems have been the most accessed and investigated ones. With our growing interest in the discovery of new Ru catalysts comprising N [...] Read more.

The transition-metal-catalyzed alcohol dehydrogenation to carboxylic acids has been identified as an atom-economical and attractive process. Among various catalytic systems, Ru-based systems have been the most accessed and investigated ones. With our growing interest in the discovery of new Ru catalysts comprising N-heterocyclic carbene (NHC) ligands for the dehydrogenative reactions of alcohols, we designed and prepared five NHC/Ru complexes ([Ru]-1–[Ru]-5) bearing different ancillary NHC ligands. Moreover, the effects of ancillary and additional ligands on the alcohol dehydrogenation with KOH were thoroughly explored, followed by the screening of other parameters. Accordingly, a highly active catalytic system, which is composed of [Ru]-5 combined with an additional NHC precursor L5, was discovered, affording a variety of acid products in a highly efficient manner. Gratifyingly, an extremely low Ru loading (125 ppm) and the maximum TOF value until now (4800) were obtained. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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14 pages, 3027 KiB

Open AccessArticle

Hydroalkoxylation of Terminal and Internal Alkynes Catalyzed by Dinuclear Gold(I) Complexes with Bridging Di(N-Heterocyclic Carbene) Ligands

by Elena Marcheggiani, Cristina Tubaro, Andrea Biffis, Claudia Graiff and Marco Baron

Catalysts 2020, 10(1), 1; https://doi.org/10.3390/catal10010001 - 18 Dec 2019

Cited by 9 | Viewed by 4300

Abstract

A series of six dinuclear gold(I) complexes with bridging bidentate N-heterocycic carbene ligands (NHCs) of general formula Au₂Br₂L^X (L = diNHC, X = 1–6) have been studied as catalysts in the intermolecular hydroalkoxylation of terminal and internal alkynes. [...] Read more.

A series of six dinuclear gold(I) complexes with bridging bidentate N-heterocycic carbene ligands (NHCs) of general formula Au₂Br₂L^X (L = diNHC, X = 1–6) have been studied as catalysts in the intermolecular hydroalkoxylation of terminal and internal alkynes. The best catalytic results have been obtained by using Au₂Br₂L⁴, characterized by 2,6-diisopropylphenyl wingtip substituents and a methylene bridging group between the two NHC donors. Complex Au₂Br₂L⁴ has been structurally characterized for the first time in this work, showing the presence of intramolecular aurophiclic interaction in the solid state. In the adopted reaction conditions Au₂Br₂L⁴ is able to convert challenging substrates such as diphenylacetylene. Comparative catalytic tests by using the mononuclear gold(I) complexes AuIL⁷ and IPrAuCl have been performed in order to determine the possible presence of cooperative effects in the catalytic process. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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12 pages, 3169 KiB

Open AccessArticle

N-Heterocyclic Carbene-Supported Aryl- and Alk- oxides of Beryllium and Magnesium

by Jacob E. Walley, Yuen-Onn Wong, Lucas A. Freeman, Diane A. Dickie and Robert J. Gilliard, Jr.

Catalysts 2019, 9(11), 934; https://doi.org/10.3390/catal9110934 - 8 Nov 2019

Cited by 23 | Viewed by 4429

Abstract

Recently, we have witnessed significant progress with regard to the synthesis of molecular alkaline earth metal reagents and catalysts. To provide new precursors for light alkaline earth metal chemistry, molecular aryloxide and alkoxide complexes of beryllium and magnesium are reported. The reaction of [...] Read more.

Recently, we have witnessed significant progress with regard to the synthesis of molecular alkaline earth metal reagents and catalysts. To provide new precursors for light alkaline earth metal chemistry, molecular aryloxide and alkoxide complexes of beryllium and magnesium are reported. The reaction of beryllium chloride dietherate with two equivalents of 1,3-diisopropyl-4,5-dimethylimidizol-2-ylidine (sIPr) results in the formation of a bis(N-heterocyclic carbene) (NHC) beryllium dichloride complex, (sIPr)₂BeCl₂ (1). Compound 1 reacts with lithium diisopropylphenoxide (LiODipp) or sodium ethoxide (NaOEt) to form the terminal aryloxide (sIPr)Be(ODipp)₂ (2) and alkoxide dimer [(sIPr)Be(OEt)Cl]₂ (3), respectively. Compounds 2 and 3 represent the first beryllium alkoxide and aryloxide species supported by NHCs. Structurally related dimers of magnesium, [(sIPr)Mg(OEt)Brl]₂ (4) and [(sIPr)Mg(OEt)Me]₂ (5), were also prepared. Compounds 1-5 were characterized by single crystal X-ray diffraction studies, ¹H, ¹³C, and ⁹Be NMR spectroscopy where applicable. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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Review

Jump to: Research

23 pages, 6186 KiB

Open AccessReview

Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition

by Xiang-Ting Tang, Fan Yang, Ting-Ting Zhang, Yi-Fan Liu, Si-Yu Liu, Tong-Fu Su, Dong-Can Lv and Wen-Bo Shen

Catalysts 2020, 10(3), 350; https://doi.org/10.3390/catal10030350 - 20 Mar 2020

Cited by 35 | Viewed by 6012

Abstract

Recent rapid development in homogeneous gold catalysis affords an alternative and particularly thriving strategy for the generation of gold carbenes through gold-catalyzed oxidation/amination/cycloaddition of alkynes, while it avoids the employment of hazardous and potentially explosive diazo compounds as starting materials for carbene generation. [...] Read more.

Recent rapid development in homogeneous gold catalysis affords an alternative and particularly thriving strategy for the generation of gold carbenes through gold-catalyzed oxidation/amination/cycloaddition of alkynes, while it avoids the employment of hazardous and potentially explosive diazo compounds as starting materials for carbene generation. In addition to facile and secure operation, gold carbenes generated in this strategy display good chemoselectivity distinct from other metal carbenes produced from the related diazo approach. N-heterocyclic carbene (NHC) gold is a special metal complex that can be used as ancillary ligands, which provides enhanced stability and can also act as an efficient chiral directing group. In this review, we will present an overview of these recent advances in alkyne oxidation/amination/cycloaddition by highlighting their specificity and applicability, aiming to facilitate progress in this very exciting area of research. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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30 pages, 7416 KiB

Open AccessReview

Photophysics and Photochemistry of Iron Carbene Complexes for Solar Energy Conversion and Photocatalysis

by Linnea Lindh, Pavel Chábera, Nils W. Rosemann, Jens Uhlig, Kenneth Wärnmark, Arkady Yartsev, Villy Sundström and Petter Persson

Catalysts 2020, 10(3), 315; https://doi.org/10.3390/catal10030315 - 10 Mar 2020

Cited by 56 | Viewed by 7842

Abstract

Earth-abundant first row transition metal complexes are important for the development of large-scale photocatalytic and solar energy conversion applications. Coordination compounds based on iron are especially interesting, as iron is the most common transition metal element in the Earth’s crust. Unfortunately, iron-polypyridyl and [...] Read more.

Earth-abundant first row transition metal complexes are important for the development of large-scale photocatalytic and solar energy conversion applications. Coordination compounds based on iron are especially interesting, as iron is the most common transition metal element in the Earth’s crust. Unfortunately, iron-polypyridyl and related traditional iron-based complexes generally suffer from poor excited state properties, including short excited-state lifetimes, that make them unsuitable for most light-driven applications. Iron carbene complexes have emerged in the last decade as a new class of coordination compounds with significantly improved photophysical and photochemical properties, that make them attractive candidates for a range of light-driven applications. Specific aspects of the photophysics and photochemistry of these iron carbenes discussed here include long-lived excited state lifetimes of charge transfer excited states, capabilities to act as photosensitizers in solar energy conversion applications like dye-sensitized solar cells, as well as recent demonstrations of promising progress towards driving photoredox and photocatalytic processes. Complementary advances towards photofunctional systems with both Fe(II) complexes featuring metal-to-ligand charge transfer excited states, and Fe(III) complexes displaying ligand-to-metal charge transfer excited states are discussed. Finally, we outline emerging opportunities to utilize the improved photochemical properties of iron carbenes and related complexes for photovoltaic, photoelectrochemical and photocatalytic applications. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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31 pages, 3591 KiB

Open AccessReview

Design and Synthesis of Photoactive Iron N-Heterocyclic Carbene Complexes

by Simon Kaufhold and Kenneth Wärnmark

Catalysts 2020, 10(1), 132; https://doi.org/10.3390/catal10010132 - 17 Jan 2020

Cited by 42 | Viewed by 7988

Abstract

The use of iron in photoactive metal complexes has been investigated for decades. In this respect, the charge transfer (CT) states are of particular interest, since they are usually responsible for the photofunctionality of such compounds. However, only recently breakthroughs have been made [...] Read more.

The use of iron in photoactive metal complexes has been investigated for decades. In this respect, the charge transfer (CT) states are of particular interest, since they are usually responsible for the photofunctionality of such compounds. However, only recently breakthroughs have been made in extending CT excited state lifetimes that are notoriously short-lived in classical polypyridine iron coordination compounds. This success is in large parts owed to the use of strongly σ-donating N-heterocyclic carbene (NHC) ligands that help manipulating the photophysical and photochemical properties of iron complexes. In this review we aim to map out the basic design principles for the generation of photofunctional iron NHC complexes, summarize the progress made so far and recapitulate on the synthetic methods used. Further, we want to highlight the challenges still existing and give inspiration for future generations of photoactive iron complexes. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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40 pages, 9563 KiB

Open AccessFeature PaperReview

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

by Michał Michalak and Wioletta Kośnik

Catalysts 2019, 9(11), 890; https://doi.org/10.3390/catal9110890 - 25 Oct 2019

Cited by 28 | Viewed by 5842

Abstract

N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity [...] Read more.

N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity for the activation of carbon-carbon multiple bonds, allowing many useful transformations of alkynes, allenes, and alkenes, inaccessible by other metal complexes. The present review summarizes synthetic efforts towards the preparation of chiral N-heterocyclic gold(I) complexes exhibiting C₂ and C₁ symmetry, as well as their applications in enantioselective catalysis. Finally, the emerging area of rare gold(III) complexes and their preliminary usage in asymmetric catalysis is also presented. Full article

(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)

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