Abnormally Bound N‐Heterocyclic Carbene Complexes of Ruthenium: CH Activation of Both C4 and C5 Positions in the Same Ligand

Ellul, Charles E.; Mahon, Mary F.; Saker, Olly; Whittlesey, Michael K.

doi:10.1002/ange.200701930

Cited by 29 publications

(17 citation statements)

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“…Anionic 1,2-dicarbenes, which are isoelectronic and share the topology of classical pyrazolates I, are much more desirable albeit rare entities. Whittlesey and co-workers described the unprecedented formation of a complex featuring bisA C H T U N G T R E N N U N G (abnormal)NHC IV, in which the anionic azolate ring is bridging two Ru atoms of a trinuclear Ru cluster; [11] this approach has so far been limited to Group VIII clusters. Herein, we describe the coordination chemistry of anionic 1,2,3-triazole-4,5-diylidene (V), which allows the facile preparation of 1,2-bimetallic complexes (Scheme 1).…”

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“…An X-ray diffraction study demonstrated that 2 is a dimetallic complex and adopts the same boat conformation as the analogous pyrazolate complex Figure 1). [14,15] The Pd À C allyl bond lengths [2.005(11)-2.061 (11) ] are significantly longer than that in pyrazolate allylpalladium complexes [2.10-2.13 ], [14b-d] indicating the stronger electron-donating capabilities of the anionic dicarbene.…”

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confidence: 99%

“…When 4 was treated with dimeric allylpalladium chloride at room temperature for two days, 2 was formed in 60 % yield (Scheme 5). (16); Cu1AÀCl1A 2.1081(10); C1ÀC2 1.387 (2); C1-Cu1A-Cl1A 176.18 (5); C2-C1-Cu1A 128.27 (11). (13); C3-Pd1-C1 90.7(5); C4-Pd2-C2 89.4(4); C2-C1-Pd1 128.3(9); C1-C2-Pd2 127.8(9); C4-C3-Pd1 127.2(9); C3-C4-Pd2 128.9(8).…”

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Anionic 1,2,3‐Triazole‐4,5‐diylidene: A 1,2‐Dihapto Ligand for the Construction of Bimetallic Complexes

Yan

Bouffard

Guisado‐Barrios

et al. 2012

Chemistry A European J

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Anionic 1,2,3‐Triazole‐4,5‐diylidene: A 1,2‐Dihapto Ligand for the Construction of Bimetallic Complexes

Yan

Bouffard

Guisado‐Barrios

et al. 2012

Chemistry A European J

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“…Recent studies by our group [17] and also by those of Whittlesey [16] and Cole [18] have revealed that some imidazolederived NHCs can be incorporated into triruthenium carbonyl clusters, when the NHCs are not used in excess, [16c, 18] to give isolable derivatives of the type [Ru 3 (CO) 11 (NHC)]. These clusters are prone to undergo intramolecular C(sp 2 )ÀH, [16a,b] C(sp 3 )ÀH, [17a,c-e] and/or C(sp 2 )ÀN [17d] bond-activation processes, but only the double CÀH activation of a methyl group in [Ru 3 (CO) 11 (Me 2 Im)] (Me 2 Im = 1,3-dimethylimidazol-2-ylidene) has been mechanistically studied.…”

Section: In Memory Of Lorenzo Pueyomentioning

confidence: 81%

A Simple Preparation of Pyridine‐Derived N‐Heterocyclic Carbenes and Their Transformation into Bridging Ligands by Orthometalation

et al. 2008

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A plethora of transition-metal complexes containing Nheterocyclic carbene (NHC) ligands have been prepared over the past decade, [1] particularly because many of them are among the most active catalysts for important organic reactions, such as olefin metathesis and various C À C bondforming processes. [2] The great majority of the NHC ligands of these complexes are two-nitrogen, five-membered, heterocyclic carbenes.Metal complexes containing one-nitrogen, six-membered, heterocyclic carbene ligands are far less common. [3][4][5][6][7][8][9][10][11][12] Cationic nickel(II) or palladium(II) complexes that have been prepared in the laboratories of Raubenheimer, Herrmann, or Frenking by oxidative addition (or oxidative substitution) of the CÀX (X = halogen) bond of N-alkyl (or N-aryl) halopyridinium (or haloquinolinium, haloacridinium, etc.) salts to appropriate metal(0) precursors. [3] This synthetic method is restricted to metal complexes that can undergo easy oxidative addition reactions. It can provide not only complexes with normal pyrid-2-ylidene-type ligands, in which the metal is bound to a C atom away from the N atom of the heterocyclic ligand (A in Scheme 1, for example), but also complexes with remote pyrid-4-ylidene-type ligands, in which the metal is bound to a C atom para to the N atom (B in Scheme 1, for example). These complexes are also active as catalysts for C À C coupling reactions. [3,5] Some pyridine-derived NHC ligands have also been prepared by oxidative addition of pyridinium CÀH bonds, [6] N-alkylation of coordinated pyridyl ligands, [7] and deprotonation of isoquinolinium cations. [8] Recent studies by the groups of Bergman, [9] Carmona, [10] Esteruelas, [11] and Li [12] have shown that some pyridines can undergo metal-induced rearrangements to form NHC ligands. These reactions, which are restricted to a few metal systems, generally involve tautomerization processes (such as that shown in Scheme 2 for 2-substituted pyridines).Herein, we report that simple pyrid-2-ylidenes can also be prepared by deprotonation of N-substituted pyridinium cations (Scheme 3) and that they can be trapped in solution by metal complexes, such as [Ru 3 (CO) 12 ]. Interestingly, the great basicity of this type of NHC [3,6] and the polynuclear character of the ruthenium cluster trigger the room-temperature transformation of the initial k 1 -C 2 -pyrid-2-ylidene ligands into unprecedented face-capping m 3 -k 2 -C 2 ,C 3 -pyrid-3yl-2-ylidene ligands by orthometalation. The mechanism of this process, modeled by density functional (DFT) calculations, is also reported.Scheme 2. Metal-induced tautomerization of substituted pyridines.Scheme 3. Deprotonation of N-methylpyridinium to give N-methylpyrid-2-ylidene. The carbene (C) and ylidic (D and E) resonance structures of this NHC are also shown. Scheme 1. Syntheses of complexes containing "normal" (A) and "remote" (B) pyridylidene ligands derived from halopyridinium cations.

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“…Complex 3, which is very poorly soluble, is of interest as it can be described as the first example of an NHC moiety bound simultaneously to two transition-metal ions in both the normal (C2) and the abnormal (C4 or C5) positions. [9,[22][23][24] Additional experiments were carried out to gain some insight into the mechanism leading to the formation of 3. Presumably, 2 a is in equilibrium with an intermediate such as A (Scheme 1, top; note that A may alternatively be formulated with an h 3 -allyl group and an ionic chloride), which positions the allyl fragment and the imidazole backbone CÀH in close proximity suitable for a slow process of CÀH insertion or-more likely-formation of a four-membered metallacycle transition state that leads to elimination of propene.…”

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Non‐Innocence of N‐Heterocyclic Carbene Ligands: Intermolecular CH Activation in Allyl Palladium NHC Complexes

Scheele

Dechert

Meyer

2008

Chemistry A European J

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Abnormally Bound N‐Heterocyclic Carbene Complexes of Ruthenium: CH Activation of Both C4 and C5 Positions in the Same Ligand

Cited by 29 publications

References 28 publications

Anionic 1,2,3‐Triazole‐4,5‐diylidene: A 1,2‐Dihapto Ligand for the Construction of Bimetallic Complexes

Anionic 1,2,3‐Triazole‐4,5‐diylidene: A 1,2‐Dihapto Ligand for the Construction of Bimetallic Complexes

A Simple Preparation of Pyridine‐Derived N‐Heterocyclic Carbenes and Their Transformation into Bridging Ligands by Orthometalation

Non‐Innocence of N‐Heterocyclic Carbene Ligands: Intermolecular CH Activation in Allyl Palladium NHC Complexes

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