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Influencers in Organometallic Chemistry—A Themed Issue Honoring Dr. Michel Pfeffer

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 33913

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Université de Strasbourg, CNRS, LIMA, UMR 7042, Ecole européenne de Chimie, Polymères et Matériaux, 25 rue Becquerel, 67087 Strasbourg, France
Interests: organometallics; homogeneous catalysis; 3D metal chemistry; C–H activation; hydrofunctionalization; cross-coupling; supported catalysis; structured catalytic support
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Special Issue Information

Dear Colleagues,

Dr. Michel Pfeffer was educated at the University of Strasbourg where he received his Ph.D. in 1975 under the supervision of late Prof. Jean Dehand. He then spent one year as a post-doctoral student with Prof. F. G. A. Stone at the University of Bristol (U.K.). Since 1973, he has held a CNRS position at the University of Strasbourg, where he became Research Director in 1985 and Emeritus in 2014. During these years, he has made enormous contributions to the field of metal-mediated C–H bond activation and functionalization through the formation of metallacycles, in particular, pallada- and ruthenacycles, and through subsequent reactions aimed at forming new C–C and C–Heteroatom bonds. More recently, he moved from C–H activation to medicinal chemistry through the study of the anti-cancer properties of cycloruthenated compounds.

This Special Issue of Molecules celebrates the pioneering efforts of Dr. Michel Pfeffer in the field of C–H bond functionalization and his extensive contribution to the synthesis and application of metallacycles.

Prof. Dr. Vincent Ritleng
Guest Editor

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Keywords

  • Organometallics
  • C–H activation
  • Homogeneous catalysis
  • Cyclometalated anti-cancer compounds

Published Papers (11 papers)

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Research

Jump to: Review

6 pages, 852 KiB  
Communication
Synthesis of trans-Mono(silyl)palladium(II) Bromide Complexes
by Melvyn B. Ansell, George E. Kostakis, Oscar Navarro and John Spencer
Molecules 2021, 26(9), 2460; https://doi.org/10.3390/molecules26092460 - 23 Apr 2021
Viewed by 1788
Abstract
The stoichiometric reaction of cis-[Pd(ITMe)2(SiR3)2], where (SiR3 = SiMe3 and SiMe2Ph and ITMe = 1,3,4,5-tetramethylimidazol-2-ylidene) with allyl bromide affords the corresponding allylsilanes along with complexes of the type trans-[Pd(ITMe)2(SiR [...] Read more.
The stoichiometric reaction of cis-[Pd(ITMe)2(SiR3)2], where (SiR3 = SiMe3 and SiMe2Ph and ITMe = 1,3,4,5-tetramethylimidazol-2-ylidene) with allyl bromide affords the corresponding allylsilanes along with complexes of the type trans-[Pd(ITMe)2(SiR3)(Br)]. The structure of trans-[Pd(ITMe)2(SiMe2Ph)Br] 2b has been determined in the solid state and displays a slightly distorted square-planar geometry with the two N-heterocyclic carbene ligands in a trans-configuration. Full article
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18 pages, 4199 KiB  
Article
Replacing the Z-phenyl Ring in Tamoxifen® with a para-Connected NCN Pincer-Pt-Cl Grouping by Post-Modification
by Guido D. Batema, Ties J. Korstanje, Gabriela Guillena, Gema Rodríguez, Martin Lutz, Gerard P. M. van Klink, Robert A. Gossage and Gerard van Koten
Molecules 2021, 26(7), 1888; https://doi.org/10.3390/molecules26071888 - 26 Mar 2021
Cited by 4 | Viewed by 2114
Abstract
Post-modification of a series of NCN-pincer platinum(II) complexes [PtX(NCN-R-4)] (NCN = [C6H2(CH2NMe2)2-2,6], R = C(O)H, C(O)Me and C(O)Et), X = Cl or Br) at the para-position using [...] Read more.
Post-modification of a series of NCN-pincer platinum(II) complexes [PtX(NCN-R-4)] (NCN = [C6H2(CH2NMe2)2-2,6], R = C(O)H, C(O)Me and C(O)Et), X = Cl or Br) at the para-position using the McMurry reaction was studied. The synthetic route towards two new [PtCl(NCN-R-4)] (R = C(O)Me and C(O)Et) complexes used above is likewise described. The utility and limitations of the McMurry reaction involving these pincer complexes was systematically evaluated. The predicted “homo-coupling” reaction of [PtBr(NCN-C(O)H-4)] led to the unexpected formation of 3,3′,5,5′-tetra[(dimethylamino)methyl]-4,4′-bis(platinum halide)-benzophenone (halide = Br or Cl), referred to hereafter as the bispincer-benzophenone complex 13. This material was further characterized using X-ray crystal structure determination. The applicability of the pincer complexes in the McMurry reaction is shown to open a route towards the synthesis of tamoxifen-type derivatives of which one phenyl ring of Tamoxifen® itself is replaced by an NCN arylplatinum pincer fragment. The newly synthesized derivatives can be used as potential candidates in anti-cancer drug screening protocols. Two NCN-arylpincer platinum tamoxifen type derivatives, 5 and 6, were successfully synthesized and of 5 the separation of the diastereomeric E-/Z-forms was achieved. Compound 6, which is the pivaloyl protected NCN pincer platinum hydroxy-Tamoxifen® derivative, was obtained as a mixture of E-/Z-isomers. The new derivatives were further analyzed and characterized with 1H-, 13C{1H}- and 195Pt{1H}-NMR, IR, exact mass MS and elemental analysis. Full article
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13 pages, 4205 KiB  
Article
Bis-Cyclometalated Indazole and Benzimidazole Chiral-at-Iridium Complexes: Synthesis and Asymmetric Catalysis
by Sebastian Brunen, Yvonne Grell, Philipp S. Steinlandt, Klaus Harms and Eric Meggers
Molecules 2021, 26(7), 1822; https://doi.org/10.3390/molecules26071822 - 24 Mar 2021
Cited by 8 | Viewed by 2765
Abstract
A new class of bis-cyclometalated iridium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole bidentate ligands or two inert cyclometalated 5-tert-butyl-1-methyl-2-phenylbenzimidazoles is introduced. The coordination sphere is complemented by two labile acetonitriles, and a hexafluorophosphate ion serves as a [...] Read more.
A new class of bis-cyclometalated iridium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole bidentate ligands or two inert cyclometalated 5-tert-butyl-1-methyl-2-phenylbenzimidazoles is introduced. The coordination sphere is complemented by two labile acetonitriles, and a hexafluorophosphate ion serves as a counterion for the monocationic complexes. Single enantiomers of the chiral-at-iridium complexes (>99% er) are obtained through a chiral-auxiliary-mediated approach using a monofluorinated salicyloxazoline and are investigated as catalysts in the enantioselective conjugate addition of indole to an α,β-unsaturated 2-acyl imidazole and an asymmetric Nazarov cyclization. Full article
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19 pages, 3760 KiB  
Article
Fluorescent Orthopalladated Complexes of 4-Aryliden-5(4H)-oxazolones from the Kaede Protein: Synthesis and Characterization
by Eduardo Laga, David Dalmau, Sofía Arregui, Olga Crespo, Ana I. Jimenez, Alexandra Pop, Cristian Silvestru and Esteban P. Urriolabeitia
Molecules 2021, 26(5), 1238; https://doi.org/10.3390/molecules26051238 - 25 Feb 2021
Cited by 7 | Viewed by 2484
Abstract
The goal of the work reported here was to amplify the fluorescent properties of 4-aryliden-5(4H)-oxazolones by suppression of the hula-twist non-radiative deactivation pathway. This aim was achieved by simultaneous bonding of a Pd center to the N atom of the heterocycle [...] Read more.
The goal of the work reported here was to amplify the fluorescent properties of 4-aryliden-5(4H)-oxazolones by suppression of the hula-twist non-radiative deactivation pathway. This aim was achieved by simultaneous bonding of a Pd center to the N atom of the heterocycle and the ortho carbon of the arylidene ring. Two different 4-((Z)-arylidene)-2-((E)-styryl)-5(4H)-oxazolones, the structures of which are closely related to the chromophore of the Kaede protein and substituted at the 2- and 4-positions of the arylidene ring (1a OMe; 1b F), were used as starting materials. Oxazolones 1a and 1b were reacted with Pd(OAc)2 to give the corresponding dinuclear orthometalated palladium derivates 2a and 2b by regioselective C–H activation of the ortho-position of the arylidene ring. Reaction of 2a (2b) with LiCl promoted the metathesis of the bridging carboxylate by chloride ligands to afford dinuclear 3a (3b). Mononuclear complexes containing the orthopalladated oxazolone and a variety of ancillary ligands (acetylacetonate (4a, 4b), hydroxyquinolinate (5a), aminoquinoline (6a), bipyridine (7a), phenanthroline (8a)) were prepared from 3a or 3b through metathesis of anionic ligands or substitution of neutral weakly bonded ligands. All species were fully characterized and the X-ray determination of the molecular structure of 7a was carried out. This structure has strongly distorted ligands due to intramolecular interactions. Fluorescence measurements showed an increase in the quantum yield (QY) by up to one order of magnitude on comparing the free oxazolone (QY < 1%) with the palladated oxazolone (QY = 12% for 6a). This fact shows that the coordination of the oxazolone to the palladium efficiently suppresses the hula-twist deactivation pathway. Full article
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12 pages, 2319 KiB  
Article
New Bifunctional Bis(azairidacycle) with Axial Chirality via Double Cyclometalation of 2,2′-Bis(aminomethyl)-1,1′-binaphthyl
by Yasuhiro Sato, Yuichi Kawata, Shungo Yasui, Yoshihito Kayaki and Takao Ikariya
Molecules 2021, 26(4), 1165; https://doi.org/10.3390/molecules26041165 - 22 Feb 2021
Cited by 3 | Viewed by 2546
Abstract
As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C–N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2′-bis(aminomethyl)-1,1′-binaphthyl (1) from 1,1-bi-2-naphthol (BINOL) was accomplished by a [...] Read more.
As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C–N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2′-bis(aminomethyl)-1,1′-binaphthyl (1) from 1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed cyanation and subsequent reduction with Raney-Ni and KBH4. The reaction of (S)-1 with an equimolar amount of [IrCl2Cp*]2 (Cp* = η5–C5(CH3)5) in the presence of sodium acetate in acetonitrile at 80 °C gave a diastereomeric mixture of new dinuclear dichloridodiiridium complexes (5) through the double C–H bond cleavage, as confirmed by 1H NMR spectroscopy. A loss of the central chirality on the Ir centers of 5 was demonstrated by treatment with KOC(CH3)3 to generate the corresponding 16e amidoiridium complex 6. The following hydrogen transfer from 2-propanol to 6 provided diastereomers of hydrido(amine)iridium retaining the bis(azairidacycle) architecture. The dinuclear chlorido(amine)iridium 5 can serve as a catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with a substrate to a catalyst ratio of 200 in the presence of KOC(CH3)3 in 2-propanol, leading to (S)-1-phenylethanol with up to an enantiomeric excess (ee) of 67%. Full article
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Review

Jump to: Research

18 pages, 5928 KiB  
Review
Bypassing the Resistance Mechanisms of the Tumor Ecosystem by Targeting the Endoplasmic Reticulum Stress Pathway Using Ruthenium- and Osmium-Based Organometallic Compounds: An Exciting Long-Term Collaboration with Dr. Michel Pfeffer
by Christian Gaiddon, Isabelle Gross, Xiangjun Meng, Marjorie Sidhoum, Georg Mellitzer, Benoit Romain, Jean-Batiste Delhorme, Aïna Venkatasamy, Alain C. Jung and Michel Pfeffer
Molecules 2021, 26(17), 5386; https://doi.org/10.3390/molecules26175386 - 4 Sep 2021
Cited by 8 | Viewed by 2766
Abstract
Metal complexes have been used to treat cancer since the discovery of cisplatin and its interaction with DNA in the 1960’s. Facing the resistance mechanisms against platinum salts and their side effects, safer therapeutic approaches have been sought through other metals, including ruthenium. [...] Read more.
Metal complexes have been used to treat cancer since the discovery of cisplatin and its interaction with DNA in the 1960’s. Facing the resistance mechanisms against platinum salts and their side effects, safer therapeutic approaches have been sought through other metals, including ruthenium. In the early 2000s, Michel Pfeffer and his collaborators started to investigate the biological activity of organo-ruthenium/osmium complexes, demonstrating their ability to interfere with the activity of purified redox enzymes. Then, they discovered that these organo-ruthenium/osmium complexes could act independently of DNA damage and bypass the requirement for the tumor suppressor gene TP53 to induce the endoplasmic reticulum (ER) stress pathway, which is an original cell death pathway. They showed that other types of ruthenium complexes—as well complexes with other metals (osmium, iron, platinum)—can induce this pathway as well. They also demonstrated that ruthenium complexes accumulate in the ER after entering the cell using passive and active mechanisms. These particular physico-chemical properties of the organometallic complexes designed by Dr. Pfeffer contribute to their ability to reduce tumor growth and angiogenesis. Taken together, the pioneering work of Dr. Michel Pfeffer over his career provides us with a legacy that we have yet to fully embrace. Full article
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45 pages, 14955 KiB  
Review
Ruthenacycles and Iridacycles as Transfer Hydrogenation Catalysts
by Vincent Ritleng and Johannes G. de Vries
Molecules 2021, 26(13), 4076; https://doi.org/10.3390/molecules26134076 - 3 Jul 2021
Cited by 23 | Viewed by 3403
Abstract
In this review, we describe the synthesis and use in hydrogen transfer reactions of ruthenacycles and iridacycles. The review limits itself to metallacycles where a ligand is bound in bidentate fashion to either ruthenium or iridium via a carbon–metal sigma bond, as well [...] Read more.
In this review, we describe the synthesis and use in hydrogen transfer reactions of ruthenacycles and iridacycles. The review limits itself to metallacycles where a ligand is bound in bidentate fashion to either ruthenium or iridium via a carbon–metal sigma bond, as well as a dative bond from a heteroatom or an N-heterocyclic carbene. Pincer complexes fall outside the scope. Described are applications in (asymmetric) transfer hydrogenation of aldehydes, ketones, and imines, as well as reductive aminations. Oxidation reactions, i.e., classical Oppenauer oxidation, which is the reverse of transfer hydrogenation, as well as dehydrogenations and oxidations with oxygen, are described. Racemizations of alcohols and secondary amines are also catalyzed by ruthenacycles and iridacycles. Full article
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16 pages, 5297 KiB  
Review
Benzodiazepines: Drugs with Chemical Skeletons Suitable for the Preparation of Metallacycles with Potential Pharmacological Activity
by Artur V. da Silva, Simoni M. P. Meneghetti and Mario R. Meneghetti
Molecules 2021, 26(9), 2796; https://doi.org/10.3390/molecules26092796 - 10 May 2021
Cited by 8 | Viewed by 3639
Abstract
The synthesis of organometallic compounds with potential pharmacological activity has attracted the attention of many research groups, aiming to take advantage of aspects that the presence of the metal-carbon bond can bring to the design of new pharmaceutical drugs. In this context, we [...] Read more.
The synthesis of organometallic compounds with potential pharmacological activity has attracted the attention of many research groups, aiming to take advantage of aspects that the presence of the metal-carbon bond can bring to the design of new pharmaceutical drugs. In this context, we have gathered studies reported in the literature in which psychoactive benzodiazepine drugs were used as ligands in the preparation of organometallic and metal complexes and provide details on some of their biological effects. We also highlight that most commonly known benzodiazepine-based drugs display molecular features that allow the preparation of metallacycles via C-H activation. These organometallic compounds merit further attention regarding their potential biological effects, not only in terms of psychoactive drugs but also in the search for drug replacements, for example, for cancer treatments. Full article
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15 pages, 3473 KiB  
Review
Hydrosilylation Reactions Catalyzed by Rhenium
by Duo Wei, Ruqaya Buhaibeh, Yves Canac and Jean-Baptiste Sortais
Molecules 2021, 26(9), 2598; https://doi.org/10.3390/molecules26092598 - 29 Apr 2021
Cited by 10 | Viewed by 4296
Abstract
Hydrosilylation is an important process, not only in the silicon industry to produce silicon polymers, but also in fine chemistry. In this review, the development of rhenium-based catalysts for the hydrosilylation of unsaturated bonds in carbonyl-, cyano-, nitro-, carboxylic acid derivatives and alkenes [...] Read more.
Hydrosilylation is an important process, not only in the silicon industry to produce silicon polymers, but also in fine chemistry. In this review, the development of rhenium-based catalysts for the hydrosilylation of unsaturated bonds in carbonyl-, cyano-, nitro-, carboxylic acid derivatives and alkenes is summarized. Mechanisms of rhenium-catalyzed hydrosilylation are discussed. Full article
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50 pages, 20656 KiB  
Review
Cyclometalated Osmium Compounds and beyond: Synthesis, Properties, Applications
by Ricardo Cerón-Camacho, Manuel A. Roque-Ramires, Alexander D. Ryabov and Ronan Le Lagadec
Molecules 2021, 26(6), 1563; https://doi.org/10.3390/molecules26061563 - 12 Mar 2021
Cited by 11 | Viewed by 3990
Abstract
The synthesis of cyclometalated osmium complexes is usually more complicated than of other transition metals such as Ni, Pd, Pt, Rh, where cyclometalation reactions readily occur via direct activation of C–H bonds. It differs also from their ruthenium analogs. Cyclometalation for osmium usually [...] Read more.
The synthesis of cyclometalated osmium complexes is usually more complicated than of other transition metals such as Ni, Pd, Pt, Rh, where cyclometalation reactions readily occur via direct activation of C–H bonds. It differs also from their ruthenium analogs. Cyclometalation for osmium usually occurs under more severe conditions, in polar solvents, using specific precursors, stronger acids, or bases. Such requirements expand reaction mechanisms to electrophilic activation, transmetalation, and oxidative addition, often involving C–H bond activations. Osmacycles exhibit specific applications in homogeneous catalysis, photophysics, bioelectrocatalysis and are studied as anticancer agents. This review describes major synthetic pathways to osmacycles and related compounds and discusses their practical applications. Full article
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31 pages, 34052 KiB  
Review
The Exchange of Cyclometalated Ligands
by Alexander D. Ryabov
Molecules 2021, 26(1), 210; https://doi.org/10.3390/molecules26010210 - 3 Jan 2021
Cited by 4 | Viewed by 2892
Abstract
Reactions of cyclometalated compounds are numerous. This account is focused on one of such reactions, the exchange of cyclometalated ligands, a reaction between a cyclometalated compound and an incoming ligand that replaces a previously cyclometalated ligand to form a new metalacycle: + H-C*~Z [...] Read more.
Reactions of cyclometalated compounds are numerous. This account is focused on one of such reactions, the exchange of cyclometalated ligands, a reaction between a cyclometalated compound and an incoming ligand that replaces a previously cyclometalated ligand to form a new metalacycle: + H-C*~Z ⇄ + H-C~Y. Originally discovered for PdII complexes with Y/Z = N, P, S, the exchange appeared to be a mechanistically challenging, simple, and convenient routine for the synthesis of cyclopalladated complexes. Over four decades it was expanded to cyclometalated derivatives of platinum, ruthenium, manganese, rhodium, and iridium. The exchange, which is also questionably referred to as transcyclometalation, offers attractive synthetic possibilities and assists in disclosing key mechanistic pathways associated with the C–H bond activation by transition metal complexes and C–M bond cleavage. Both synthetic and mechanistic aspects of the exchange are reviewed and discussed. Full article
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