Metallacyclic Pyridylidene Structures from Reactions of Terminal Pyridylidenes with Alkenes and Acetylene

Álvarez, Eleuterio; Hernández, Yohar A.; López‐Serrano, Joaquín; Maya, Celia; Paneque, Margarita; Petronilho, Ana; Poveda, Manuel L.; Salazar, Verónica; Vattier, Florencia; Carmona, Ernesto

doi:10.1002/anie.201000608

Cited by 41 publications

(21 citation statements)

References 71 publications

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“…While 489 has not been isolated yet, its relevance has been supported by an alternative pathway and through the elimination of H 2 O from the pyridylidene complex 571 containing a metal-bound hydroxide ligand (Scheme 223). 371 Moreover, this coordinatively unsaturated species has been successfully trapped as the carbonyl species 573 upon pressurizing a solution of 482 with CO. 403,404 Complex 489 provides a metal−ligand bifunctional platform constituted of an underligated iridium center and a basic pyridyl unit. Such a configuration is reminiscent of frustrated Lewis pairs, and the close proximity of the Lewis acidic and basic site offers high versatility for the activation of strong bonds.…”

Section: Chemical Reviewsmentioning

confidence: 99%

“…Such a configuration is reminiscent of frustrated Lewis pairs, and the close proximity of the Lewis acidic and basic site offers high versatility for the activation of strong bonds. 403,404 For example, dihydrogen is heterolytically cleaved and yields the pyridylidene iridium hydride complex 572 (Scheme 223). Upon addition of CO to this complex, the carbonyl species 573 is formed, which suggests that H 2 activation is reversible, possibly via a η-H 2 intermediate.…”

Section: Chemical Reviewsmentioning

confidence: 99%

Section: Complexes With Pyridylidenes and Related Ligandsmentioning

confidence: 99%

“…Complex 489 provides a metal–ligand bifunctional platform constituted of an underligated iridium center and a basic pyridyl unit. Such a configuration is reminiscent of frustrated Lewis pairs, and the close proximity of the Lewis acidic and basic site offers high versatility for the activation of strong bonds. , …”

Section: Complexes With Pyridylidenes and Related Ligandsmentioning

confidence: 99%

“…In addition to the activation of these polar substrates, which benefit from the polarity difference of the Lewis acidic iridium center and the Lewis basic nitrogen site, also apolar substrates are effectively activated (Scheme ). , Addition of alkenes such as ethylene or propylene to the pyridylidene iridium complex 482 yields the metalacyclic complex 576 with an alkylated pyridylidene ligand. Acetylene addition produces initially the vinylidene intermediate 577 , which reacts with adventitious water to form the acyl complex 578 containing a protic pyridylidene ligand.…”

Section: Complexes With Pyridylidenes and Related Ligandsmentioning

confidence: 99%

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Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes: Synthesis, Catalysis, and Other Applications

2018

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Mesoionic carbenes are a subclass of the family of N-heterocyclic carbenes that generally feature less heteroatom stabilization of the carbenic carbon and hence impart specific donor properties and reactivity schemes when coordinated to a transition metal. Therefore, mesoionic carbenes and their complexes have attracted considerable attention both from a fundamental point of view as well as for application in catalysis and beyond. As a follow-up of an earlier Chemical Reviews overview from 2009, the organometallic chemistry of N-heterocyclic carbenes with reduced heteroatom stabilization is compiled for the 2008-2017 period, including specifically the chemistry of complexes containing 1,2,3-triazolylidenes, 4-imidazolylidenes, and related 5-membered N-heterocyclic carbenes with reduced heteratom stabilization such as (is)oxazolylidenes, pyrrazolylidenes, and thiazolylidenes, as well as pyridylidenes as 6-membered N-heterocyclic carbenes with reduced heteroatom stabilization. For each ligand subclass, metalation strategies, electronic and steric properties, and applications, in particular, in metal-mediated catalysis, are compiled. Mesoionic carbenes demonstrate particularly high activity in (water) oxidation, hydrogen transfer reactions, and cyclization reactions. Unique features of these ligands are identified such as their dipolar structure, their specific donor properties, as well as stability aspects of the ligand and the complexes, which provides opportunities for further research.

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Section: Chemical Reviewsmentioning

confidence: 99%

Section: Chemical Reviewsmentioning

confidence: 99%

Section: Complexes With Pyridylidenes and Related Ligandsmentioning

confidence: 99%

Section: Complexes With Pyridylidenes and Related Ligandsmentioning

confidence: 99%

Section: Complexes With Pyridylidenes and Related Ligandsmentioning

confidence: 99%

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Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes: Synthesis, Catalysis, and Other Applications

2018

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A Labile and Catalytically Active Imidazol‐2‐yl Fragment System

et al. 2010

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N-heterocyclic carbenes (NHCs) [1] and their complexes [2] are excellent catalysts for a broad array of organic transformations, where the NHC ligands impart useful electronic and steric properties to metal centers. [3] In these systems, with commonly used ancilliary NHC ligands that are substituted at nitrogen atom(s) by alkyl, aryl, or other groups, [2,3] all catalytic transformations take place at the metal center, which is stabilized and/or activated by the NHC ligand. However, transformations that may possibly involve both the metal center and at one ring nitrogen of the NHC ligand are much less common, [4, 5c,e-g] and are limited to protic NHC complexes [4][5][6] or their conjugated bases. Thus, the NÀH function of a protic NHC complex (A or D; Scheme 1) could behave as Brønsted acid, whereas the basic nitrogen atom in the imidazol-2-yl complex (B or C) may behave as a Brønsted base. Moreover, reactivity of A with a base could lead to B, a transient species with both a vacant metal coordination site and a basic nitrogen atom, which could bind (C) and activate a substrate (C to D). These reactivity patterns might also be compatible with protic NHC complexes derived from other NHC ligands.Herein, we report a versatile organometallic system in which the combined reactivity of the imidazol-2-ylidene or imidazol-2-yl fragments and the metal center lead to ligand exchange processes that involve A and B, hydrogen activation (B!C!D), and ultimately, catalytic behavior (D + ketone! E!B + alcohol). Key differences between results herein from previous work [4] include: 1) greatly enhanced rates of reaction (for example, ligand exchange within minutes instead of days); 2) the ability to tune ligand exchange rates over several orders of magnitude; and perhaps most importantly 3) catalytic behavior, which was not at all apparent before. Moreover, we show that 15 N chemical shift information on natural-abundance samples gives valuable information on the environment of the imidazol-2-yl or imidazolylidene ligand.Reaction of 1 [4] with [CpRuCl(cod)] (Cp = cyclopentadienyl, cod = 1,5-cyclooctadiene) in THF at 100 8C led to phosphorus coordination and complete tautomerization of the imidazole to carbene 2, which shows a low-field 1 H NMR signal (d = 10.28 ppm, NH) and a doublet in the 13 C{ 1 H} NMR (d = 184.1 ppm, 2 J CP = 22.5 Hz, C2) that are consistent with structure 2 (Scheme 2). Scheme 1. Imidazol-2-yl and imidazol-2-ylidene fragment systems. The square indicates a vacant site.Scheme 2. Synthesis and reactivity of imidazol-2-yl and imidazol-2ylidene complexes (in [D 8 ]THF at room temperature unless otherwise specified). Yields are of isolated products unless otherwise specified. LDA = lithium diisopropylamide.[*] Dr.

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Katalytische Oxidation von Wasser durch einen Iridiumkomplex mit einem starken Carben‐Donorliganden

et al. 2010

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Metallacyclic Pyridylidene Structures from Reactions of Terminal Pyridylidenes with Alkenes and Acetylene

Cited by 41 publications

References 71 publications

Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes: Synthesis, Catalysis, and Other Applications

Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes: Synthesis, Catalysis, and Other Applications

A Labile and Catalytically Active Imidazol‐2‐yl Fragment System

Katalytische Oxidation von Wasser durch einen Iridiumkomplex mit einem starken Carben‐Donorliganden

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