Exploring the Limits of π‐Acid Catalysis Using Strongly Electrophilic Main Group Metal Complexes: The Case of Zinc and Aluminium

Tian, Jiaxin; Chen, Yan; Vayer, Marie; Djurovic, Alexandre; Guillot, Régis; Guermazi, Refka; Dagorne, Samuel; Bour, Christophe; Gandon, Vincent

doi:10.1002/chem.202001376

Cited by 20 publications

(12 citation statements)

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“…Five-/four-coordinate Al(III) cations were also recently exploited as catalysts for the cyanosilylation of carbonyl substrates and the Tishchenko reaction [6]. Strong Lewis acids of the type AlR 2 + and AlBr 2 + also catalyze CO 2 hydrosilylation and carbonyl-olefin metathesis, respectively, further illustrating the potential of low-coordinate Al cations in catalysis [7,8]. Three-coordinate Al cations of the type (NacNac)Al-R + (R = H, alkyl) were recently shown to be highly efficient catalysts in alkene hydrosilylation [9].…”

Section: Introductionmentioning

confidence: 99%

NHC-stabilized Al(III) and Ga(III) cationic alkyls: Synthesis, structure and use in hydrosilylation catalysis

2021

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Cationic Al(III) and Ga(III) species supported by N-heterocyclic carbene (NHC) ligands, (IDipp)AlMe 2 (PhBr)] + ([1] + , IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2ylidene) and (IDipp)GaMe 2 ] + ([2] + ), were prepared and structurally characterized as B(C 6 F 5 ) 4 salts via ionization of the corresponding neutral precursors (IDipp)MMe 3 (M = Al, Ga) with [Ph 3 C][B(C 6 F 5 ) 4 ] in PhBr at room temperature. Both [1][B(C 6 F 5 ) 4 ] and [2][B(C 6 F 5 ) 4 ] salt were isolated in high yield and their solid state structures established through X-ray crystallographic studies. Cations [1] + and [2] + , which are rare examples of structurally characterized tris-organyl Al(III) and Ga(III) cations, stand as potent Lewis acids as experimentally estimated through the Gutmann-Beckett method. These cations were further exploited in hydrosilylation catalysis of alkynes, benzaldehyde and CO 2 using HSiEt 3 as an hydrosilane source. Hydrosilylation of 1-hexyne, 4-phenylbutyne and phenylacetylene led to the formation of the corresponding Z-selective products 3-5, respectively, while benzaldehyde was converted to PhCH 2 OSiEt 3 (6). Cations [1] + and [2] + also slowly catalyze CO 2 hydrosilylation with the selective formation of the methanol-equivalent MeOSiEt 3 .

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Section: Introductionmentioning

confidence: 99%

NHC-stabilized Al(III) and Ga(III) cationic alkyls: Synthesis, structure and use in hydrosilylation catalysis

2021

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“…In the case of the NHC-M complexes, those involving zinc (i.e., M = Zn) are of increasing practical importance [ 35 , 36 , 38 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 ], due in part to the easy availability and relatively low cost of precursors of such complexes. Practical applications of NHC-Zn complexes in organometallic catalysis have recently been extensively described [ 34 , 35 , 36 , 38 ].…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of N-Heterocyclic-Carbene–ZnX2 (X = H, Me, Et) Complexes

Jabłoński

2021

Materials

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This article discusses the properties of as many as 30 carbene–ZnX2 (X = H, Me, Et) complexes featuring a zinc bond C⋯Zn. The group of carbenes is represented by imidazol-2-ylidene and its nine derivatives (labeled as IR), in which both hydrogen atoms of N-H bonds have been substituted by R groups with various spatial hindrances, from the smallest Me, iPr, tBu through Ph, Tol, and Xyl to the bulkiest Mes, Dipp, and Ad. The main goal is to study the relationship between type and size of R and X and both the strength of C⋯Zn and the torsional angle of the ZnX2 plane with respect to the plane of the imidazol-2-ylidene ring. Despite the considerable diversity of R and X, the range of dC⋯Zn is quite narrow: 2.12–2.20 Å. On the contrary, D0 is characterized by a fairly wide range of 18.5–27.4 kcal/mol. For the smallest carbenes, the ZnX2 molecule is either in the plane of the carbene or is only slightly twisted with respect to it. The twist angle becomes larger and more varied with the bulkier R. However, the value of this angle is not easy to predict because it results not only from the presence of steric effects but also from the possible presence of various interatomic interactions, such as dihydrogen bonds, tetrel bonds, agostic bonds, and hydrogen bonds. It has been shown that at least some of these interactions may have a non-negligible influence on the structure of the IR–ZnX2 complex. This fact should be taken into account in addition to the commonly discussed R⋯X steric repulsion.

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“…21 Thus, soft Lewis acids are supposed to transform 22a into an indene's derivative, while harder acids lead to alternative bicyclic products. 22 According to the test, alumina can be counterintuitively classified as a soft π-acid since the major product was found to be the indene's derivative 22. 23 Noteworthy, our method could not induce some other common cycloizomerizations of 1,6-enynes (Table S3).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Alumina-Mediated π-Activation of Alkynes

et al. 2021

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The ability to induce powerful atom-economic transformation of alkynes is the key feature of carbophilic π-Lewis acids such as gold-and platinum-based catalysts. The unique catalytic activity of these compounds in electrophilic activations of alkynes is explained through relativistic effects, enabling efficient orbital overlapping with π-systems. For this reason, it is believed that noble metals are indispensable components in the catalysis of such reactions. In this study, we report that thermally activated γ-Al 2 O 3 activates enynes, diynes, and arene-ynes in a manner enabling reactions that were typically assigned to the softest π-Lewis acids, while some were known to be triggered exclusively by gold catalysts. We demonstrate the scope of these transformations and suggest a qualitative explanation of this phenomenon based on the Dewar−Chatt−Duncanson model confirmed by density functional theory calculations.

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Exploring the Limits of π‐Acid Catalysis Using Strongly Electrophilic Main Group Metal Complexes: The Case of Zinc and Aluminium

Cited by 20 publications

References 74 publications

NHC-stabilized Al(III) and Ga(III) cationic alkyls: Synthesis, structure and use in hydrosilylation catalysis

NHC-stabilized Al(III) and Ga(III) cationic alkyls: Synthesis, structure and use in hydrosilylation catalysis

Theoretical Study of N-Heterocyclic-Carbene–ZnX2 (X = H, Me, Et) Complexes

Alumina-Mediated π-Activation of Alkynes

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