B–H Bond Cleavage via Metal–Ligand Cooperation by Dearomatized Ruthenium Pincer Complexes

Anaby, Aviel; Butschke, Burkhard; Ben‐David, Yehoshoa; Shimon, Linda J. W.; Leitus, Gregory; Feller, Moran; Milstein, David

doi:10.1021/om500311a

Cited by 49 publications

(48 citation statements)

References 105 publications

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“…Upon reaction of the dearomatized ruthenium pincer complex 27 (scheme 12) with pinacolor catechol borane, facile B-H bond cleavage occurred [31]. Unexpectedly, in this case, dehydrogenative addition of the B-H bond across the metal centre and the unsaturated ligand arm took place, with liberation of dihydrogen, resulting in formation of the dearomatized complex 28 in which the boryl group resides on the benzylic arm of the pincer complex.…”

Section: Boron-hydrogen Activationmentioning

confidence: 99%

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Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Milstein

2015

Phil. Trans. R. Soc. A.

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107

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Metal–ligand cooperation (MLC) plays an important role in bond activation processes, enabling many chemical and biological catalytic reactions. A recent new mode of activation of chemical bonds involves ligand aromatization–dearomatization processes in pyridine-based pincer complexes in which chemical bonds are broken reversibly across the metal centre and the pincer-ligand arm, leading to new bond-making and -breaking processes, and new catalysis. In this short review, such processes are briefly exemplified in the activation of C–H, H–H, O–H, N–H and B–H bonds, and mechanistic insight is provided. This new bond activation mode has led to the development of various catalytic reactions, mainly based on alcohols and amines, and to a stepwise approach to thermal H 2 and light-induced O 2 liberation from water.

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Section: Boron-hydrogen Activationmentioning

confidence: 99%

“…This is then followed by H 2 elimination to yield the complex 28. Further insight regarding the dehydrogenative pathway was provided by a DFT study [31]. Based on this B-H activation mode, Ru-catalysed dehydrogenative coupling of boranes with arenes to form aryl boranes was demonstrated [31].…”

Section: Boron-hydrogen Activationmentioning

confidence: 99%

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Milstein

2015

Phil. Trans. R. Soc. A.

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107

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“…33 These reactions involve the X-H (X=H, C, O, N, and B) activations, [34][35][36][37][38][39][40][41] dehydrogenative coupling reactions, [42][43][44][45][46][47][48] and hydrogenation reactions. [49][50][51][52][53][54][55][56] In addition, a theoretical study about the ruthenium acridine complex was also reported.…”

Section: Computational Mechanistic Studiesmentioning

confidence: 99%

“…40 Cleavage of the B-H bond of boranes by the dearomatized ruthenium pincer complexes also involves metal-ligand cooperation. 41 The reaction favors the product where the Lewis acidic boron atom adds to the benzylic arm of the ligand and hydride adds to the ruthenium atom.…”

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confidence: 99%

Computational Mechanistic Studies on Reactions of Transition Metal Complexes with Noninnocent Pincer Ligands: Aromatization–Dearomatization or Not

Hall

2015

ACS Catal.

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The development of green chemistry has attracted the chemists' attentions in recent years. Among them, Milstein and coworkers have discovered a new mode of metal-ligand cooperation in complexes, where an aromatization-dearomatization process of the pyridine or acridine-based PNP and PNN "pincer" ligands appears to be a key element. These complexes were reported to lead to unusual X-H (X=H, C, O, N, and B) activation reactions and to environmentally benign catalysis involving dehydrogenative coupling reactions and hydrogenation reactions, representing an important development in green chemistry. This review provides a summary of theoretical studies on the mechanisms of the reactions mediated by transition metal complexes with noninnocent pincer ligands synthesized by Milstein and coworkers. The aromatization-dearomatization process of the pyridine or acridine-based PNP and PNN "pincer" ligands were found to play important roles in some reactions, while other reactions do not involve the aromatization-dearomatization process. For some reactions, several research groups proposed different mechanisms to explain the same reaction. Thus, to compare these mechanisms, we recalculate their rate-determining steps by using the functionals that are calibrated to produce results close to those from coupled cluster calculations. Moreover, the understanding of the reaction mechanisms can help researchers to improve the current reactions and design new reactions.

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“…Pyridine is aromatised because the inner ring C-C bond lengths are comparable to those observed in 1 at around 1.38 Å. 28 DFT calculations pointed towards an intermediate with aromatic pyridine and borane at the benzylic position, resembling the isolated complex 5. Interestingly, two π-π interactions are present in this structure between fluorinated rings and the central pyridine and one phenyl group (Fig.…”

Section: Reactivity Of 3 and 4 Featuring L* Ligandmentioning

confidence: 86%

Palladium(ii) complexes featuring a mixed phosphine–pyridine–iminophosphorane pincer ligand: synthesis and reactivity

Cheisson

Auffrant

2016

Dalton Trans.

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An original mixed ligand (labelled L) of formula PPh2-CH2-Pyr-CH2-N[double bond, length as m-dash]PPh3, combining a pyridine core with phosphine and iminophosphorane, was synthesised. Its coordination with palladium(II) centers was studied. With [Pd(COD)Cl2], a cationic complex [LPdCl](Cl) 1, where L is coordinated in the pincer mode, was obtained. Chloride abstraction with silver salt in the presence of pyridine generated the dicationic complex [LPd(py)](BF4)2 (2). When reacting with a base such as potassium hexamethyldisilazane (KHMDS), 1 gave the neutral complex 3 [L*PdCl], wherein the benzylic position alpha to phosphine was selectively deprotonated, which induced dearomatisation of the pyridine ring. A similar complex [L*Pd(CH3)] (4) was obtained upon a reaction of [Pd(CH3)2(TMEDA)] and Lvia the departure of methane. Neutral complexes with the deprotonated ligand such as 3 yielded in the presence of deuterated methanol the corresponding deuterated complex, showing that the protonation is reversible with this ligand. Finally, upon attempting to dealkylate complex 4 using B(C6F5)3, an unexpected zwitterionic borated complex 5, resulting from the formation of a C-B bond in the benzylic position with restoration of the aromatic character of the pyridine, was isolated. Interestingly, when the metal was introduced after the ligand interacted with the borane reagent, another palladium complex formed, namely, [LPdMe][MeB(C6F5)3], originating from methyl abstraction.

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B–H Bond Cleavage via Metal–Ligand Cooperation by Dearomatized Ruthenium Pincer Complexes

Cited by 49 publications

References 105 publications

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Computational Mechanistic Studies on Reactions of Transition Metal Complexes with Noninnocent Pincer Ligands: Aromatization–Dearomatization or Not

Palladium(ii) complexes featuring a mixed phosphine–pyridine–iminophosphorane pincer ligand: synthesis and reactivity

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