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Inorganics
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Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition
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Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (31 March 2025) | Viewed by 12737

Special Issue Editors

Prof. Dr. Axel Klein

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Guest Editor
Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, D-50939 Cologne, Germany
Interests: transition metal complexes (including organometallic); platinum, palladium, nickel; synthesis; electrochemistry; photophysics; spectroscopy; modelling of catalytic processes
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. S. Masoud Nabavizadeh

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Guest Editor
Rashidi Laboratory of Organometallic Chemistry, Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71467-13565, Iran
Interests: organometallic chemistry; kinetic and mechanism; photophysics
Dr. Fatemeh Niroomand Hosseini

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Guest Editor
Department of Chemistry, Shiraz Branch, Islamic Azad University, Shiraz 71993-37635, Iran
Interests: theoretical investigation of organometallic reactions

Special Issue Information

Dear Colleagues,

The interest in transition metal complexes as homogeneous catalysts is fueled from several sides. There are outstanding catalytic processes such as hydroformylation or the Wacker oxidation that produce important intermediates in our chemical supply chain on an industrial scale of millions of tons. At the same time, there are highly selective and efficient catalysts for gram-scale lab reactions with high valorization. Finally, when considering metalloenzymes in biochemical processes the list of homogeneous catalysts containing transition metals is long and the types of reactions they catalyze encompass any kind of chemical reaction we can think of.

For non-transition metal catalysis, the invariability of the octet rule for the involved light elements facilitates the description of the underlying mechanistic steps. For transition metals, the number of binding partners, spin and oxidation state; in other words, their electronic setting is variable and far less clear than an octet of electrons. Plausibility is very often the rationale of the mechanisms depicted in textbooks and publications, while consolidated knowledge is frequently scarce. However, with the highly sophisticated spectroscopic and analytical tools that we have in hand today and the dramatically developing quality of quantum chemical calculations, we are more and more able to obtain deep insight into catalytic mechanisms. In turn, this allows us to further optimize catalysts and catalytic reactions.

This Special Issue aims to bring together experimental, theoretical, and mixed experimental–theoretical approaches to reveal mechanisms in transition metal catalyzed organic, inorganic, organometallic, and biochemical transformations. It will focus on the role of the transition metal(s) in binding and activating substrates, transforming them and finally releasing them. This includes the beneficial/cooperating role of non-spectator ligands. Studies dedicated to providing insights into reaction mechanisms, including tracing or characterization of intermediates or modelling essential reaction steps, are welcome.

Prof. Dr. Axel Klein
Prof. Dr. S. Masoud Nabavizadeh
Dr. Fatemeh Niroomand Hosseini
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Inorganics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • transition metal catalysis
  • mechanistic studies
  • reactive intermediates
  • quantum chemical calculations
  • in situ spectroscopy
  • enzyme modelling
  • substrate activation
  • cooperative catalysis
  • ligand design

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Related Special Issue

Published Papers (6 papers)

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Research

13 pages, 2826 KiB  
Article
Theoretical Investigations of Para-Methoxystyrene/Styrene Polymerization Catalyzed by Cationic Methyl- and Dibenzobarrelene-Based α-Diimine Palladium Complexes
by Ling Zhu, Yi Luo, Xin Wen, Wenzhen Zhang and Guangli Zhou
Inorganics 2024, 12(12), 315; https://doi.org/10.3390/inorganics12120315 - 5 Dec 2024
Cited by 1 | Viewed by 818
Abstract
The polymerization mechanism of para-methoxystyrene catalyzed by cationic α-diimine palladium complexes with various ancillary ligands was rigorously examined using density functional theory. In the classical methyl-based α-diimine palladium complex [{(2,6-iPr2C6H3)-N=C(Me)-C(Me)=N-2,6-iPr [...] Read more.
The polymerization mechanism of para-methoxystyrene catalyzed by cationic α-diimine palladium complexes with various ancillary ligands was rigorously examined using density functional theory. In the classical methyl-based α-diimine palladium complex [{(2,6-iPr2C6H3)-N=C(Me)-C(Me)=N-2,6-iPr2C6H3)}PdMe]+ (A+), the 2,1-insertion of para-methoxystyrene is favored over the 1,2-insertion, both thermodynamically and kinetically, during the chain initiation step. The resulting thermodynamically favored η3-π-benzyl intermediates face a substantial energy barrier, yielding only trace amounts of polymer, as experimentally verified. In contrast, the dibenzobarrelene-based α-diimine palladium complex [{(2,6-iPr2C6H3)-N=C(R)-C(R)=N-2,6-iPr2C6H3)}PdMe]+ (R = dibenzobarrelene, B+) shows similar energy barriers for both 2,1- and 1,2-insertions. Continuous 2,1/2,1 or 2,1/1,2 insertions are impeded by excessive energy barriers. However, theoretical calculations reveal that the 1,2-insertion product can seamlessly transition into the chain propagation stage, producing a polymer with high 1,2-regioselectivity. The observed activity of complexes A+ or B+ towards para-methoxystyrene polymerization stems from the energy barrier differences between the 1,2- and 2,1-insertions, influenced by the steric hindrance from the ancillary ligands. Further investigation into the effects of steric hindrance on the chain initiation stage involved computational modeling of analogous complexes with increased steric bulk. These studies established a direct correlation between the energy barrier difference ∆∆G (1,2–2,1) and the van der Waals volume of the ancillary ligand. Larger van der Waals volumes correspond to reduced energy barrier differences, thus enhancing the regioselectivity for para-methoxystyrene polymerization. Moreover, the experimental inertness of complex B+ towards styrene polymerization is attributed to the formation of stable kinetic and thermodynamic 2,1-insertion intermediates, which obstruct further styrene monomer insertion due to an extremely high reactive energy barrier. These findings contribute to a deeper understanding of the mechanistic aspects and offer insights for designing new transition metal catalysts for the polymerization of para-alkoxystyrenes. Full article
(This article belongs to the Special Issue Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition)
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22 pages, 4367 KiB  
Article
A Comparison of β–Phenyl Elimination in Nickel and Palladium Alkyl Complexes: A Potentially Relevant Process in the Mizoroki–Heck Reaction
by Jorge A. López, Diego A. Cabo, Pilar Palma and Juan Cámpora
Inorganics 2024, 12(3), 89; https://doi.org/10.3390/inorganics12030089 - 14 Mar 2024
Cited by 2 | Viewed by 1824
Abstract
There is currently much interest in avoiding precious metals in catalysis. The development of nickel catalysts to replace palladium in the Mizoroki–Heck reaction is a relevant case in this line of research, since both elements share many chemical features. This contribution focuses on [...] Read more.
There is currently much interest in avoiding precious metals in catalysis. The development of nickel catalysts to replace palladium in the Mizoroki–Heck reaction is a relevant case in this line of research, since both elements share many chemical features. This contribution focuses on β–phenyl (β–Ph) elimination in alkyl—nickel complexes. This is the microscopic reverse of olefin insertion (or carbometallation), a fundamental step in the Heck cycle that is usually considered irreversible and selectivity-determining. However, the potential reversibility of carbometallation is generally concealed by the facile β–hydrogen (β–H) elimination that follows. Where β–hydrogen elimination is hindered, β–aryl elimination may ensue. We have previously shown that cationic 2–methyl–2–phenylpropyl (neophyl) palladium complexes supported by bidentate ligands experience β–Ph elimination, which can be seen as an example of olefin de-insertion. In this contribution, we report that β–Ph elimination can also occur in their nickel analogs, in which case fast hydrolyses of the resulting phenyl product can follow the reaction. We investigated the mechanism of these processes and compared their feasibility for nickel and palladium catalysts using DFT calculations. These results are relevant information for the design of nickel-based catalysts for the Heck reaction. Full article
(This article belongs to the Special Issue Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition)
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11 pages, 2215 KiB  
Article
Structural and Spectroscopic Characterization of Co(II) Bis(Benzenedichlorodithiolate): An Intermediate in Hydrogen Evolution Catalysis
by Virginia A. Larson, Jeff W. Kampf and Nicolai Lehnert
Inorganics 2024, 12(3), 75; https://doi.org/10.3390/inorganics12030075 - 29 Feb 2024
Cited by 1 | Viewed by 1886
Abstract
Co bis(benzenedithiolate) type complexes have captivated chemists for decades for their interesting geometric and electronic structures and more recently, for their impressive ability to mediate the hydrogen evolution reaction (HER) both photo- and electrocatalytically. However, these complexes have nearly exclusively been characterized in [...] Read more.
Co bis(benzenedithiolate) type complexes have captivated chemists for decades for their interesting geometric and electronic structures and more recently, for their impressive ability to mediate the hydrogen evolution reaction (HER) both photo- and electrocatalytically. However, these complexes have nearly exclusively been characterized in their air-stable Co(III) oxidation states. In this work, Co(II) bis(benzenedichlorodithiolate) was prepared by chemical and electrochemical one-electron reduction. This reduced Co(II) complex was characterized by X-ray crystallography and in-depth spectroscopic studies—including UV-Vis, magnetic circular dichroism, and electron paramagnetic resonance spectroscopy. [Co(II)(Cl2bdt)2]2− is thereby shown to be a square planar complex, with a primarily metal-centered reduction, and an St = 1/2 spin state. This study informs our understanding of the first step in the HER catalytic cycle of Co bis(benzenedithiolate) type complexes and paves the way for future mechanistic studies on this catalyst family. Full article
(This article belongs to the Special Issue Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition)
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13 pages, 3051 KiB  
Article
The Fast Formation of a Highly Active Homogeneous Catalytic System upon the Soft Leaching of Pd Species from a Heterogeneous Pd/C Precursor
by Alexey S. Galushko, Valentina V. Ilyushenkova, Julia V. Burykina, Ruslan R. Shaydullin, Evgeniy O. Pentsak and Valentine P. Ananikov
Inorganics 2023, 11(6), 260; https://doi.org/10.3390/inorganics11060260 - 19 Jun 2023
Cited by 6 | Viewed by 2201
Abstract
Understanding the interface between soluble metal complexes and supported metal particles is important in order to reveal reaction mechanisms in a new generation of highly active homogeneous transition metal catalysts. In this study, we show that, in the case of palladium forming on [...] Read more.
Understanding the interface between soluble metal complexes and supported metal particles is important in order to reveal reaction mechanisms in a new generation of highly active homogeneous transition metal catalysts. In this study, we show that, in the case of palladium forming on a carbon (Pd/C) catalyst from a soluble Pd(0) complex Pd2dba3, the nature of deposited particles on a carbon surface turns out to be much richer than previously assumed, even if a very simple experimental procedure is utilized without the use of additional reagents and procedures. In the process of obtaining a heterogeneous Pd/C catalyst, highly active “hidden” metal centers are formed on the carbon surface, which are leached out by the solvent and demonstrate diverse reactivity in the solution phase. The results indicate that heterogeneous catalysts may naturally contain trace amounts of molecular monometallic centers of a different nature by easily transforming them to the homogeneous catalytic system. In line with a modern concept, a heterogenized homogeneous catalyst precursor was found to leach first, leaving metal nanoparticles mostly intact on the surface. In this study, we point out that the previously neglected soft leaching process contributes to high catalyst activity. The results we obtained demand for leaching to be reconsidered as a flexible tool for catalyst construction and for the rational design of highly active and selective homogeneous catalytic systems, starting from easily available heterogeneous catalyst precursors. Full article
(This article belongs to the Special Issue Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition)
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14 pages, 4253 KiB  
Article
The Role of Non-Covalent Interactions in the Reactions between Palladium Hydrido Complex with Amidoarylphosphine Pincer Ligand and Brønsted Acids
by Vladislava A. Kirkina, Vasilisa A. Kulikova, Evgenii I. Gutsul, Zufar N. Gafurov, Ilias F. Sakhapov, Dmitry G. Yakhvarov, Yulia V. Nelyubina, Oleg A. Filippov, Elena S. Shubina and Natalia V. Belkova
Inorganics 2023, 11(5), 212; https://doi.org/10.3390/inorganics11050212 - 15 May 2023
Cited by 6 | Viewed by 2013
Abstract
The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols and formic acid) was studied in benzene or toluene as well as in neat alcohols by IR and [...] Read more.
The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols and formic acid) was studied in benzene or toluene as well as in neat alcohols by IR and NMR spectroscopies. The structures of hydrogen-bonded complexes were also optimized at the DFT/ωB97-XD/def2-TZVP level. The nitrogen atom of the amidophosphine pincer ligand readily accepts proton not only from strong Brønsted acids but from relatively weak fluorinated alcohols. That suggests that binding to palladium(II) increases the diarylamine basicity, making it a strong base. Nevertheless, H+ can be taken from [(PN(H)P)PdH]+ (2) by pyridine or hexamethylphosphoramide (HMPA). These observations confirm the need for a shuttle base to form [(PN(H)P)PdH]+ (2) as the result of the heterolytic splitting of H2 by [(PNP)Pd]+. At that, a stoichiometric amount of formic acid protonates a hydride ligand yielding an unstable η2-H2 complex that rapidly converts into formate (PNP)Pd(OCHO), which loses CO2 to restore (PNP)PdH, whereas the relatively high acid excess hampers this reaction through competitive protonation at nitrogen atom. Full article
(This article belongs to the Special Issue Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition)
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19 pages, 2502 KiB  
Article
C–H Metalation of Terpyridine Stereoisomers with Ni(II), Pd(II), and Pt(II)
by Leo Payen, Lukas Kletsch, Tobias Lapić, Mathias Wickleder and Axel Klein
Inorganics 2023, 11(4), 174; https://doi.org/10.3390/inorganics11040174 - 21 Apr 2023
Cited by 6 | Viewed by 2907
Abstract
Ni(II), Pd(II), and Pt(II) complexes [M(Y-terpy)X] (X = Cl or Br) containing the tridentate N^C^N-cyclometalating 2,3′:5′,2″and 2,2′:4′,2″ stereoisomers of the well-known tridentate N^N^N ligand 2,2′:6′,2″-terpyridine (terpy) were synthesised in moderate to good yields through C–H activation. For the Pt complexes, the phenyl ethynide [...] Read more.
Ni(II), Pd(II), and Pt(II) complexes [M(Y-terpy)X] (X = Cl or Br) containing the tridentate N^C^N-cyclometalating 2,3′:5′,2″and 2,2′:4′,2″ stereoisomers of the well-known tridentate N^N^N ligand 2,2′:6′,2″-terpyridine (terpy) were synthesised in moderate to good yields through C–H activation. For the Pt complexes, the phenyl ethynide derivatives [Pt(Y-terpy)(C≡CPh)] were also obtained under Sonogashira conditions. In contrast to this, C^N^N cyclometalated complexes using the 2,2′:6′,3″- and 2,2′:6′4″-terpy isomers were not obtained. Comparison of the N^C^N complexes of the cyclometalated 2,3′:5′,2″- and 2,2′:4′,2″-terpy ligands with complexes [M(dpb)Cl] of the prototypical N^C^N cyclometalating ligand dpb− (Hdpb = 2,6-diphenyl-pyridine) showed higher potentials for the terpy complexes for the ligand-centred reductions in line with the superior π-accepting properties of the terpy ligands compared with dpb. Metal-centred oxidations were facilitated by the dpb ligand carrying a central σ-donating phenyl group instead of a metalated pyridine moiety. The same trends were found for the long-wavelength absorptions and the derived electrochemical and optical band gaps. The lower σ-donating capacities of the cyclometalated terpy derivatives is also confirmed by a reduced trans influence in the structure of [Ni(2,3′:5′,2″-terpy)Br0.14/OAc0.86]. Attempts to re-crystallise some poorly soluble Pd(II) and Pt(II) complexes of this series under solvothermal conditions (HOAc) gave two structures with N-protonated cyclometalated pyridine moieties, [Pt(2,3′:5′,2″-terpyH)Cl].Cl and [Pd(2,3′:5′,2″-terpyH)Cl2]. Full article
(This article belongs to the Special Issue Revealing Reaction Mechanisms in Homogeneous Transition Metal Catalysis, 2nd Edition)
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