Rearrangement of Pyridine to Its 2-Carbene Tautomer Mediated by Iridium

Álvarez, Eleuterio; Conejero, Salvador; Lara, Patricia; López, Jörge A.; Paneque, Margarita; Petronilho, Ana; Poveda, Manuel L.; Rı́o, Diego del; Serrano, Oracio; Carmona, Ernesto

doi:10.1021/ja075685i

Cited by 82 publications

(31 citation statements)

References 23 publications

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“…In conclusion, this work confirms that the tautomerization of 2-substituted pyridines by Tp Me 2 Ir III fragments [11] is a general reaction that is extendable to polypyridine ligands such as 2,2'-bipyridine and 1,10-phenanthroline. A new coordination mode of these important and ubiquitous ligands as monohapto N-heterocyclic carbenes (or alternatively as ylidic structures) has been discovered.…”

Section: Methodssupporting

confidence: 81%

“…The IR spectrum of compound 3 shows a broad band centered at ñ = 3265 cm À1 due to the n(NÀH) stretching absorption, while a deshielded resonance at d = 14.60 ppm can be observed in the 1 H NMR spectrum for this functionality. A comparison with data for related compounds [11] suggests the existence of an intramolecular hydrogen bond between the NH unit of the coordinated ring and the N atom of the other ring (see below). The Ir-bound carbene carbon atom resonates at d = 180.2 ppm in the 13 …”

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confidence: 98%

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Monodentate, N‐Heterocyclic Carbene‐Type Coordination of 2,2′‐Bipyridine and 1,10‐Phenanthroline to Iridium

et al. 2008

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Section: Methodssupporting

confidence: 81%

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confidence: 98%

Monodentate, N‐Heterocyclic Carbene‐Type Coordination of 2,2′‐Bipyridine and 1,10‐Phenanthroline to Iridium

et al. 2008

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“…This proposal is in accordance with the observation that 1-OH 2 reacts with propene (Scheme 1) and butadiene (Scheme 2) under very similar reaction conditions, as well as with previous studies from our group based on related [Tp´Ir(R)(R´)L] complexes with labile ligands L, like N 2 . 8 DFT calculations (wB97xD 9 /6-31+G(d,p) and lanl2dz) were also carried out using the simplified system shown in Chart 2 (butadiene + iridacycle 2 without fused benzene, parent Tp and unsubstituted butadiene).…”

Section: Scheme 4 Formation Of the Da Adduct 8 By The Reaction Of Thmentioning

confidence: 99%

A Diels–Alder Reaction Triggered by a [4 + 3] Metallacycloaddition

et al. 2015

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The TpMe2 Ir(III) complex 1-OH 2 (Tp Me2 = hydrotris(3,5-dimethylpyrazolyl)borate) that, in addition to a labile molecule of water, contains an iridium-bonded alkenyl moiety -C(R)=C(R)− (R = CO 2 Me) as part of a benzo annulated five-membered iridacycle, reacts readily with the conjugated dienes butadiene and 2,3-dimethylbutadiene to afford the corresponding Diels-Alder products. Experimental and DFT studies are in accordance with an initial [4 + 3] cyclometallation reaction between the diene and the fivecoordinated 16-electron organometallic fragment 1 (generated from 1-OH 2 by facile water dissociation). The reaction can be extended to a related TpIr(III) complex (Tp = hydrotris(pyrazolyl)borate) that feature also a labile ligand (e.g. 2-THF).The Diels-Alder (DA) [4 + 2] cycloaddition, first reported in 1928, 1 is arguably one of the cornerstones of Organic Chemistry. The existence of different variants has allowed its application to a myriad of synthetic processes and has inspired, from the early days of its discovery, numerous experimental and theoretical studies.2 Even if from a mechanistic point of view the [4 + 2] cycloaddition seems to be a simple reaction, an important breakthrough was the recognition of the accelerating effect caused by Lewis acids in hetero-DA reactions, as a consequence of their interaction with the heteroatom. Interestingly a recent study in this Journal has revealed a remarkable acceleration caused by a Li + cation enclosed in a fullerene cage, on the reaction of the latter species with cyclohexadiene. 3In this contribution, we wish to report on the striking reactivity of butadiene and 2,3-dimethylbutadiene toward an iridium-alkenyl terminus, [Ir−C(CO 2 Me)=C(CO 2 Me)−], that is part of two different, five-membered Ir(III) metallacyclic complexes, namely , 1-OH 2 and , 2-THF (Tp Me2 = hydrotris(3,5-dimethylpyrazolyl)borate; Tp = hidrotris(pyrazolyl)borate, Chart 1; R = CO 2 Me). The outcomes of these reactions are DA products, but at variance with classical DA [4 + 2] cycloadditions, the success of our approach depends critically upon the facile generation of a vacant coordination site adjacent to the Ir-alkenyl linkage. As demonstrated by the experimental and DFT studies herein discussed, this allows for a [4 + 3] low-energy metallacycloaddition path 4 that greatly facilitates the formation of the DA adducts. Chart 1. Tp-type ligands used in this study.This reactivity clearly differs from other reactions experienced by compound 1-OH 2 . Thus, recent work from our group 5 dealt with the study of its reactivity toward α-olefins, R´CH=CH 2 and for instance propene (R´= Me) reacted with 1-OH 2 to form (Scheme 1) the hydride-β-iridanaphthalene derivative 3, as a consequence of an iridium promoted propene-to-propylidene isomerization, 6 followed by chemo-and stereo-selective carbene migratory insertion into the Ir−C aryl bond and α-H elimination. Scheme 1. Formation of the β-iridanaphthalene 3 from the reaction of the aquo adduct 1-OH 2 and propeneIn contrast with this resul...

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“…Depending on the ring substitution pattern, both 2-and 4-pyridylidene complexes have been prepared by such a rearrangement. [30][31][32][33][34] In contrast, C-H activation of N-alkylated pyridinium precursors that could allow for C2-or C4-coordination, exclusively leads to metallation at the 4-position. [35][36][37][38][39] This observation has been attributed to the steric bulk of the N-alkyl group.…”

Section: Introductionmentioning

confidence: 99%

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

et al. 2010

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Rearrangement of Pyridine to Its 2-Carbene Tautomer Mediated by Iridium

Abstract: Contents:-General.-Synthesis and spectroscopic and analytical data for new compounds.-Table S.1. Crystal data and structure refinement for compound 3.

Cited by 82 publications

References 23 publications

Monodentate, N‐Heterocyclic Carbene‐Type Coordination of 2,2′‐Bipyridine and 1,10‐Phenanthroline to Iridium

Monodentate, N‐Heterocyclic Carbene‐Type Coordination of 2,2′‐Bipyridine and 1,10‐Phenanthroline to Iridium

A Diels–Alder Reaction Triggered by a [4 + 3] Metallacycloaddition

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

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