Evidence of a Donor–Acceptor (Ir–H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate

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• 作者：Mustapha Hamdaoui ; Marjolaine Ney ; Vivien Sarda ; Lydia Karmazin ; Corinne Bailly ; Nicolas Sieffert ; Sebastian Dohm ; Andreas Hansen ; Stefan Grimme ; Jean-Pierre Djukic
• 刊名：Organometallics
• 出版年：2016
• 出版时间：July 11, 2016
• 年：2016
• 卷：35
• 期：13
• 页码：2207-2223
• 全文大小：962K
• 年卷期：0
• ISSN：1520-6041

文摘

The ionic iridacycle [(2-phenylenepyridine-κN,κC)IrCp*(NCMe)][BArF₂₄] ([2][BArF₂₄]) displays a remarkable capability to catalyze the O-dehydrosilylation of alcohols at room temperature (0.4 × 10³ < TON < 10³, 8 × 10³ < TOF_i < 1.9 × 10⁵ h^–1 for primary alcohols) that is explained by its exothermic reaction with Et₃SiH, which affords the new cationic hydrido-Ir(III)-silylium species [3][BArF₂₄]. Isothermal calorimetric titration (ITC) indicates that the reaction of [2][BArF₂₄] with Et₃SiH requires 3 equiv of the latter and releases an enthalpy of −46 kcal/mol in chlorobenzene. Density functional theory (DFT) calculations indicate that the thermochemistry of this reaction is largely dominated by the concomitant bis-hydrosilylation of the released MeCN ligand. Attempts to produce [3][BF₄] and [3][OTf] salts resulted in the formation of a known neutral hydrido-iridium(III) complex, i.e. 4, and the release of Et₃SiF and Et₃SiOTf, respectively. In both cases formation of the cationic μ-hydrido-bridged bis-iridacyclic complexes [5][BF₄] and [5][OTf], respectively, was observed. The structure of [5][OTf] was established by X-ray diffraction analysis. Conversion of [3][BArF₂₄] into 4 upon reaction with either 4-N,N-dimethylaminopyridine or [nBu₄][OTf] indicates that the Ir center holds a +III formal oxidation state and that the Et₃Si⁺ moiety behaves as a Z-type ligand according to Green’s formalism. [3][BArF₂₄], which was trapped and structurally characterized and its electronic structure investigated by state-of-the-art DFT methods (DFT-D, EDA, ETS-NOCV, QTAIM, ELF, NCI plots and NBO), displays the features of a cohesive hydridoiridium(III)→silylium donor–acceptor complex. This study suggests that the fate of [3]⁺ in the O-dehydrosilylation of alcohols is conditioned by the nature of the associated counteranion and by the absence of Lewis base in the medium capable of irreversibly capturing the silylium species.