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N-Heterocyclic carbenes in catalytic organic synthesis, vol.

This short review summarizes the recent progress in organofluorinations catalyzed by N-heterocyclic carbene (NHC)-transition metal ion complexes. NHC-metal ion complexes are increasingly used in a variety of organic transformations, and they have opened up new opportunities, especially in the synthesis of organofluorine compounds. New advances in olefin metathesis, trifluoromethylations, Heck and Suzuki coupling, selective hydrodefluorination, and enantioselective synthesis of organofluorine compounds have been achieved through catalysis by NHC and their metal ion complexes. In this review, synthetic methods for various NHC-metal ion complexes and their applications in the synthesis of organofluorine compounds are comprehensively outlined.

T1 - N-Heterocyclic carbenes in organofluorine chemistry

References:
1) Polymer-Supported, Carbon Dioxide-Protected N-Heterocyclic Carbenes: Synthesis and Application in Organo- and Organometallic Catalysis, G. M. Pawar, M. R. Buchmeiser, Adv. Synth. Catal., 352 (5) 917-928 (2010)
2) Ring-Opening Metathesis Polymerization-Derived, Polymer-Bound Cu-Catalysts for Click-Chemistry and Hydrosilylation Reactions Under Micellar Conditions, G. Pawar, B., Bantu, J. Weckesser, S. Blechert, K. Wurst, M. R. Buchmeiser, Dalton Trans., 9043-9051 (2009)
3) Alternating Ring-Opening Metathesis Copolymerization by Grubbs-Type Initiators Based On Unsymmetrical N-Heterocyclic Carbenes, M. Lichtenheldt, D. Wang, K. Vehlow, I. Reinhardt, C. Kühnel, U. Decker, S. Blechert, M. R. Buchmeiser, Chem. Eur. J., 15, 9451-9457 (2009)
4) Ru-Alkylidene Metathesis Catalysts Based on 1,3-Dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidenes: Synthesis, Structure, and Activity, P. S. Kumar, K. Wurst, M. R. Buchmeiser, Organometallics, 28, 1785-1790 (2009)
5) Polymer-Supported Well-Defined Metathesis Catalysts, M. R. Buchmeiser, Chem. Rev., 109 (2), 303-321 (2009)
6) CO2- and SnII-Adducts of N-Heterocyclic Carbenes as Delayed Action Catalysts For Polyurethane Synthesis, B. Bantu, G. M. Pawar, U. Decker, Klaus Wurst, A. M. Schmidt, M. R. Buchmeiser, Chem. Eur. J., 15, 3103-3109 (2009)
7) Alternating Copolymerizations Using a Grubbs-Type Initiator Based on an Unsymmetrical, Chiral N-Heterocyclic Carbene, K. Velow, D. Wang, S. Blechert, M. R. Buchmeiser, Angew. Chem., 120, 2655-2658 (2008); Angew. Chem. Int. Ed., 47, 2615-2618 (2008)

N-heterocyclic carbenes in catalytic organic synthesis

T1 - Research on the design, synthesis, and catalytic activity of chiral N-heterocyclic carbene ligand-metal complexes

We are investigating N,S- and N,O-heterocyclic carbenes and their complexes as alternatives to the commonly known N,N-heterocyclic analogues. Since sulfur is less and oxygen more electronegative than nitrogen, we expect a different donor-ability of N,S-and N,O-heterocyclic carbenes, which may lead to interesting complex properties. In collaboration with the group of Prof. Hahn in Munster, Germany, we have prepared benzothiazolin-2-ylidene complexes of Ir(I) and studied the donor strength of N,S-heterocyclic carbenes.

Triazolylidene silver complexes are precursors of highly active catalysts for oxazoline formation via aldol condensation. The catalytic performance mirrors that of gold carbene species that are activated with Ag+, suggesting a retro-transfer of the carbene from Au to Ag.

The advantages of N-heterocyclic carbene’s as ..

Triazolylidene silver complexes are precursors of highly active catalysts for oxazoline formation via aldol condensation. The catalytic performance mirrors that of gold carbene species that are activated with Ag+, suggesting a retro-transfer of the carbene from Au to Ag.

I have obtained my undergraduate education from the University of Bern from 1991 to 1996 and subsequently moved to the Netherlands for graduate studies under the supervison of Gerard van Koten at Utrecht University. In a truly fantastic research environment I completed my PhD thesis in 2000 on the development of new sensors, switches, and catalysts derived from late transition metal pincer complexes. The thesis was later awarded the Bakker price from the Royal Dutch Society of Chemistry. I then joined the group of Robert H. Crabtree at Yale as postdoctoral fellow, working on carbene ligands for bond activation, which was a hugely influential period in terms of chemistry and beyond. In mid 2002, I relocated back to Europe and was employed by Ciba SC (Basel, Switzerland) as a postdoctoral researcher working on nanoparticles for coating effects in an industrial environment. In 2003, I returned to academia and launched my independent research as an Alfred Werner Assistant Professor at the University of Fribourg (Switzerland). During that time, I have also been a visiting professor with Sally Brooker at Otago University (New Zealand), and I received an ERC Starting Grant. In 2009, I join the faculty at University College Dublin as full professor. The Dublin time stood out for the many great colleagues I met, the modern infrastructure, and above all the enthusiastic and dedicated research team that our group has become. Our research achievements have been recognized during that period by a Humboldt research award (Bessel Fellowship), by a distinction from the Catalysis Society of South Africa (CATSA eminent visitor), and by an ERC Consolidator Grant. In 2014, I accepted a call from my alma mater and since summer 2015 , I am back in Switzerland as Professor of Inorganic Chemistry. I am fortunate enough that the entire research team joined me in relocating to Bern, where we have brand new labs that suit us perfectly. Throughout these years and to date, I have been privileged and proud to have been part of a fantastic research team, and to have been supported (and challenged) by most inspiring collaborators around the globe.

Outside my chemistry life, I enjoy family life, spending time in the mountains, all types of sports activities, and traveling to meet colleagues and friends.

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N-Heterocyclic Carbenes in Catalytic Organic Synthesis

AB - New chiral C2 symmetric N-heterocyclic carbene (NHC) ligands with a binaphthyl backbone have been synthesized. X-ray crystallographic analysis of the new NHC-AuCl complex revealed that the phenyl groups of the binaphthyl backbone sterically regulated the direction of the nitrogen substituents of the imidazolylidene which would induce enantioselectivity in reactions. The new cationic NHC-Au(I) complexes efficiently catalyzed the cyclization of a 1,6-ene-yne and the intermediate of the cyclization was trapped by MeOH to afford the final product in high yields with up to 44% ee.

N-heterocyclic Carbenes - Chemistry LibreTexts

N2 - New chiral C2 symmetric N-heterocyclic carbene (NHC) ligands with a binaphthyl backbone have been synthesized. X-ray crystallographic analysis of the new NHC-AuCl complex revealed that the phenyl groups of the binaphthyl backbone sterically regulated the direction of the nitrogen substituents of the imidazolylidene which would induce enantioselectivity in reactions. The new cationic NHC-Au(I) complexes efficiently catalyzed the cyclization of a 1,6-ene-yne and the intermediate of the cyclization was trapped by MeOH to afford the final product in high yields with up to 44% ee.

Science of Synthesis: N-Heterocyclic Carbenes in …

New chiral C2 symmetric N-heterocyclic carbene (NHC) ligands with a binaphthyl backbone have been synthesized. X-ray crystallographic analysis of the new NHC-AuCl complex revealed that the phenyl groups of the binaphthyl backbone sterically regulated the direction of the nitrogen substituents of the imidazolylidene which would induce enantioselectivity in reactions. The new cationic NHC-Au(I) complexes efficiently catalyzed the cyclization of a 1,6-ene-yne and the intermediate of the cyclization was trapped by MeOH to afford the final product in high yields with up to 44% ee.

N-Heterocyclic Carbenes (RSC Publishing)

We are fascinated by the diversity of effects that ligands can have to instigate new properties in transition metal complexes and we are therefore strongly interested in designing and developing new ligands that impart specific properties to the metal center. One of these ligands are triazolylidenes, a mesoionic carbene that we discovered in 2008. This ligand offers various opportunities for catalysis, including strong electron donor properties, a high synthetic flexibility that allows for a wide variety of functional and chelating groups to be incorporated, and a high polarity, which imparts solubility in water and other polar media. We have obtained evidence in a variety of catalytic reactions like nickel-catalysed hydrosilylation, ruthenium-catalyzed alcohol dehydrogenation, or iridium-catalyzed water oxidation, that the triazolylidene ligand scaffold is controlling the reactivity of the coordinated metal center. Because of the synthetic versatility and the easy accessibility of the ligand, tailoring of the ligand properties is straightforward and we have disclosed improved catalytic activity by ligand tuning. More recently, we have discovered a straightforward approach to functionalize the ligand on the complex as opposed to the more traditional approach of preparing a functional ligand and only then install the metal center. This approach gives rapid access to a large diversity of functionalized ligands in a very last step, and to ligand scaffolds that are not accessible by traditional routes.

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