Supramolecular assembly and transfer hydrogenation catalysis with ruthenium(II) complexes of 2,6-di(1H-pyrazol-3-yl)pyridine derivatives

Two new tridentate ligands 2,6-bis(5-ethyl-1H-pyrazol-3-yl)pyridine and 2,6-bis(5-benzamido-1H-pyrazol-3-yl)pyridine, have been synthesized. These ligands have been used in a new series of six complexes of formula "RuCl2(PPh3)2(LR)·nH2O" (n = 1 or 2) where LR is 2,6-bis(5-R-1H-pyrazol-3-yl)pyridine (R = Me, Et, tBu, NH2, NHC{O}tBu and NHC{O}Ph). Crystal structures of [RuCl(PPh3)2(LMe)]Cl·MeOH and [Ru(OH2)(PPh3)2(LtBu)]Cl2·4CDCl3 contain six-coordinate complex centers with trans-phosphine ligands, and show that the chloride ions can occupy the first or second coordination spheres of the complexes. The latter structure demonstrates that the chloride ions in this type of compound can be labile under ambient conditions, which is an essential pre-requisite for catalytic activity. Anion metathesis yielded [Ru(OH2)(PPh3)2(LtBu)][PF6]2, which was also crystallographically characterized. All the complexes (except air-sensitive [RuCl2(PPh3)2(LNH2)]) were screened for activity towards transfer hydrogenation of acetophenone in refluxing 2-propanol. The chloride salt catalysts are active but show a significant induction period, which may imply decomposition of the complexes during the reaction. However the activity of the PF6 - salt is much higher, which shows that competition between chloride and substrate for the metal center is a significant factor in catalysis by these compounds

New N,N and N,N,N Ligands and Their Application in Catalytic Reactions

The scientific intention of this work was to synthesize and characterize new bidentate, tridentate and multidentate ligands and to apply them in heterogenous catalysis. For each type of the ligands, new methods of synthesis were developed. Starting from 1,1'-(pyridine-2,6-diyl)diethanone and dimethylpyridine-2,6-dicarboxylate different bispyrazolpyridines were synthesized and novel ruthenium complexes of the type (L)(NNN)RuCl2 could be obtained. The complexes with L = triphenylphosphine turned out to be highly efficient catalyst precursors for the transfer hydrogenation of aromatic ketones. Introduction of a butyl group in the 5-positions of the pyrazoles leads to a pronounced increase of catalytic activity. To find a method for the synthesis of bispyrimidinepyridines, different reactants and condition were applied and it was found that these tridentate ligands can be obtained by mixing and grinding the tetraketone with guanidinium carbonate and silica, which plays the role of a catalyst in this ring closing reaction. The bidentate 2-amino-4-(2-pyridinyl)pyrimidines were synthesized from different substrates according to the desired substituent on the pyrimidine ring. Reacting these bidentate ligands with the ruthenium(II) precursor [(η6-cymene)Ru(Cl)(μ 2-Cl)]2 gave cationic ruthenium(II) complexes of the type [(η6-cymene)Ru(Cl)(adpm)]Cl (adpm = chelating 2-amino-4-(2-yridinyl)pyrimidine ligand). Stirring the freshly prepared complexes with either NaBPh4, NaBF4 or KPF6, the chloride anion was exchanged against other coordinating anions (BF4-, PF6-, BPh4-).Some of these ruthenium complexes have shown very special activities in the transfer hydrogenation of ketones by reacting them in the absence of the base. This led to detailed investigations on the mechanism of this reaction. According to the activities and with the help of ESI-MS experiments and DFT calculations, a mechanism was proposed for the transfer hydrogenation of acetophenone in the absence of the base. It shows that in the absence of the base, a C-H bond activation at the pyrimidine ring should occur to activate the catalyst. The palladium complexes of bidentate N,N ligands were examined in coupling reactions. As expected, they did not show very special activities. Multidentate ligands, having pyrimidine groups as relatively soft donors for late transition metals and simultaneously possessing a binding position for a hard Lewis-acid, could be obtained using the new synthesized bidentate and tridentate ligands

New N,N and N,N,N Ligands and Their Application in Catalytic Reactions

The scientific intention of this work was to synthesize and characterize new bidentate, tridentate and multidentate ligands and to apply them in heterogenous catalysis. For each type of the ligands, new methods of synthesis were developed. Starting from 1,1'-(pyridine-2,6-diyl)diethanone and dimethylpyridine-2,6-dicarboxylate different bispyrazolpyridines were synthesized and novel ruthenium complexes of the type (L)(NNN)RuCl2 could be obtained. The complexes with L = triphenylphosphine turned out to be highly efficient catalyst precursors for the transfer hydrogenation of aromatic ketones. Introduction of a butyl group in the 5-positions of the pyrazoles leads to a pronounced increase of catalytic activity. To find a method for the synthesis of bispyrimidinepyridines, different reactants and condition were applied and it was found that these tridentate ligands can be obtained by mixing and grinding the tetraketone with guanidinium carbonate and silica, which plays the role of a catalyst in this ring closing reaction. The bidentate 2-amino-4-(2-pyridinyl)pyrimidines were synthesized from different substrates according to the desired substituent on the pyrimidine ring. Reacting these bidentate ligands with the ruthenium(II) precursor [(η6-cymene)Ru(Cl)(μ 2-Cl)]2 gave cationic ruthenium(II) complexes of the type [(η6-cymene)Ru(Cl)(adpm)]Cl (adpm = chelating 2-amino-4-(2-yridinyl)pyrimidine ligand). Stirring the freshly prepared complexes with either NaBPh4, NaBF4 or KPF6, the chloride anion was exchanged against other coordinating anions (BF4-, PF6-, BPh4-).Some of these ruthenium complexes have shown very special activities in the transfer hydrogenation of ketones by reacting them in the absence of the base. This led to detailed investigations on the mechanism of this reaction. According to the activities and with the help of ESI-MS experiments and DFT calculations, a mechanism was proposed for the transfer hydrogenation of acetophenone in the absence of the base. It shows that in the absence of the base, a C-H bond activation at the pyrimidine ring should occur to activate the catalyst. The palladium complexes of bidentate N,N ligands were examined in coupling reactions. As expected, they did not show very special activities. Multidentate ligands, having pyrimidine groups as relatively soft donors for late transition metals and simultaneously possessing a binding position for a hard Lewis-acid, could be obtained using the new synthesized bidentate and tridentate ligands

Organische, nicht lineare optische Chromophore

Gegenstand der vorliegenden Erfindung sind Verbindungen enthaltend eine terminale Gruppe D enthaltend mindestens eine funktionelle Elektronendonorgruppe d; eine terminale Gruppe A enthaltend mindestens eine funktionelle Elektronenakzeptorgruppe a und eine Brückeneinheit B, die D mit A verbindet, enthaltend ein Gerüst aus konjugierten Doppelbindungen für einen Ladungstransfer von D nach A dadurch gekennzeichnet, dass die Verbindung eine Heteroatom-enthaltende Methyliden (= Methin) -Gruppe -CH=HetA enthält, mit HetA ausgewählt aus der Gruppe bestehend aus N, P. Ferner betrifft die Erfindung die Synthese und die Verwendung dieser Verbindungen

Roll-over cyclometalation: A versatile tool to enhance the catalytic activity of transition metal complexes

Roll-over cyclometalation is a special case of cyclometalation. While in classical cyclometalation, C,H-activation (deprotonation or oxidative addition) has to occur at the ligand to result in a metallacycle, in roll-over cyclometalation the ligand in principle has the chance to undergo chelating coordination without cleavage of a C-H bond (e.g. ?2-N,N?- vs. ?2-C,N-coordination at 2,2?-bipyridines). Nature thus can decide for which route shall be followed. In this review, the basic parameters for bringing a system into roll-over cyclometalation are discussed, followed by an overview on compounds that have been published in this field during the last years. The major emphasis of this review however is on applications of roll-over cyclometalation in catalysis, a rather new field in coordination and organometallic chemistry. 2018 Elsevier B.V.Our studies on roll-over cyclometalation are supported by the German research foundation DFG within the transregional collaborative research center SFB/TRR 88 Cooperative effects in homo and heterometallic complexes (3MET) and by the state research center OPTIMAS. We furthermore gratefully acknowledge the research college MAGNENZ and the state research unit NanoKat for financial support. M. L. thanks the Konrad-Adenauer-Stiftung and A.F. thanks the Cusanuswerk for a PhD grant. Dr. Kifah S. M. Salih studied chemistry at the Al-Mustansiriyah University (Baghdad, Iraq, B.Sc. 1998) and at the University of Jordan (Amman, Jordan, M.Sc. 2004), where he finished with a master thesis on Synthesis of Some New Coumarin Derivatives. After two years working as a researcher in the group of Prof. Dr. Mohammad S. Mubarak (Univ. of Jordan), he in 2006 joined the group of Prof. Dr. Lukas J. Goo?en at the Technische Universit?t Kaiserslautern for a PhD thesis supported by a DAAD scholarship. Kifah S. M. Salih finished his PhD in 2010 with a thesis on Environmentally Benign Synthesis of Enamides via Waste-Free Catalytic Addition of Amides to Terminal Alkynes. During this time, he received the award of the Karl-Ziegler-Stiftung. He then took the opportunity to work for three years as a postdoc in the group of Prof. Dr. Werner R. Thiel (TU Kaiserslautern), where he mainly focused on the synthesis of mangetic nanoparticles an their application in catalysis. From 2014 Kifah S. M. Salih was visiting lecturer at the Sultan Qaboos University (Muscat, Oman) and in 2015 he became lecturer at the Department of Chemistry and Earth Sciences of Qatar University (Doha, Qatar). Prof. Dr. Werner R. Thiel studied chemistry at the Technische Universitt Mnchen (Germany), where he received his diploma in 1987 with a thesis on Synthesis and Characterization of High Valent (? 5 -Pentamethylcyclopentadienyl)chromium Complexes carried out in the group of Prof. Dr. Wolfgang A. Herrmann. In 1990, he received his PhD with a thesis on Synthesis, Derivatization and Characterization of Chelate Complexes of 2,2?-Bipyridine: Reactivity and Structural Aspects (TU M nchen, W. A. Herrmann). Supported by a Feodor Lynen-Grant of the Alexander von Humboldt-Stiftung , Werner R. Thiel worked for one year in the group of Prof. Dr. Didier Astruc at the Universit de Bordeaux I (Bordeaux, France). After coming back to TU Mnchen in 1991 he started with own projects which were summarized in a habilitation in 1997. In 2000 he became associate professor for inorganic chemistry at the Technische Universit?t Chemnitz (Germany) and in 2004 full professor at the Technische Universit?t Kaiserslautern (Germany). Werner R. Thiel is author of about 180 publications with a focus on transition metal catalyzed reactions and their mechanisms and on the use of porous inorganic supports in catalysis

Exploring the Gas-Phase Activation and Reactivity of a Ruthenium Transfer Hydrogenation Catalyst by Experiment and Theory in Concert

This study elucidates structures, activation barriers, and the gas-phase reactivity of cationic ruthenium transfer hydrogenation catalysts of the structural type [(η⁶-cym)­RuX­(pympyr)]⁺. In these complexes, the central ruthenium­(+II) ion is coordinated to an η⁶-bound <i>p</i>-cymene (η⁶-cym), a bidentate 2-R-4-(2-pyridinyl)­pyrimidine ligand (pympyr) with R = NH₂ or N­(CH₃)₂, and an anion X = I^–, Br^–, Cl^–, or CF₃SO₃^–. We present infrared multiple-photon dissociation (IR-MPD) spectra of precursors (before HCl loss) and of activated complexes (after HCl loss), which elucidates C–H activation as the key step in the activation mechanism. A resonant two-color IR-MPD scheme serves to record several otherwise “dark” bands and enhances the validity of spectral assignments. We show that collision-induced dissociation (CID)-derived activation energies of the [(η⁶-cym)­RuX­(pympyr)]⁺ (R = N­(CH₃)₂) complexes depend crucially on the anion X. The obtained activation energies for the HX loss correlate well with quantum chemical activation barriers and are in line with the HSAB concept. We further elucidate the reaction of the activated complexes with D₂ under single-collision conditions. Quantum mechanical simulations substantiate that the resulting species represent analogues for hydrido intermediates formed after abstraction of H⁺ and H^– from isopropanol, as postulated for the catalytic cycle of transfer hydrogenation by us before