Iridium(III) Silylene Complexes PDF Download

Author: Binh Dang Ho
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Languages : en
Pages : 0

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Book Description
The scope of this thesis spans the most recent advances in the investigation of chemical bonds of iridium-silicon complexes, in which a metal-bound silyl group behaves as a Z ligand that maintains a dative bond with the metal centre. This contrasts greatly with the case where this group behaves like an X ligand, that is where this silyl group binds to Ir through a covalent bond. Finally, and most interestingly are silylene ligands that in principle should establish a double bond with the Ir centre. The idea of evaluating and tuning the electrophilic character of the silyl moiety and adjuncts its “silylicity” was probed by experimental and theoretical means. To conduct that scheme, a broad range of metal-silane adducts and other metal-silyl complexes were investigated by the computation of metal-silyl interaction energies to outline the established tools that rationalize the bonding relationship that exists between the metal center and a SiR3 moiety. Also, this research revealed a clear separation between cases in which the Z character of the silyl moiety is the best description, and cases that belong to “classical” situations in which the X character dominates. Moreover, we postulated that for metal-silane adducts that possess a low intrinsic silylicity, a high “silylicity” can be triggered by ligand replacement or by changing in the charge of the complex.While working on this topic, we discovered that in the presence of tetrahydrofuran (THF), [(Ir-H)→SiRH2]+ adducts readily convert by H2 gas elimination at sub-ambient temperature into new THF-stabilized metallacyclic Ir(III)-"silylene" complexes. The emergence of metal silylene complexes via sequential H-Si activations followed by the spontaneous release of H2 featured in this thesis is unique. The primary goal of this thesis finally was to fully characterize those elusive complexes by NMR spectroscopy analyses and X-ray diffraction analysis. Furthermore, theoretical investigations (static DFT-D reaction-energy profiling, ETS-NOCV) and NMR kinetic studies were utilized to demonstrate the role of THF which facilitated H2 elimination. Coupled with silylene metal complex chemistry mentioned above, cationic iridacycle 1b is of interesting catalytic reactivity toward nitro arenes, which can perform the nitro reduction in arenes to give aniline type products.In crafting a new development of this chemistry, it is safe to hypothesize that cationic hydrido-Ir(III)-silylium species, whose catalytic reactivity is of significant correlation with the extend of polarization of the molecule can enhance in the key intermediates the molecule polarization, and therefore increase its catalytic reactivity. Such polarization that occurs already in the Ir-silane adduct stems from the electropositivity of Si centre. Keeping the main ligand backbone constant, introduction of a fluoro substituent can improve the polarization of the same molecule and by way of consequence increase its catalytic reactivity.As expected, F-1a also displays remarkable catalytic reactivity toward a benchmark test reaction that can be followed by piezometry, i.e. the O-dehydrosilylation of alcohols at room temperature with Et3SiH. A hydrido-Ir(III)-silylium intermediate crystal was trapped as well following on a reaction with Et2SiH. In conclusion, based on the discovery of hydrido-Ir(III)-silylium intermediates associated with a comprehensive study of their reactivity and catalytic performance, this thesis has taken steps to advance knowledge of Ir-silicon complexes by synthesis and the full structural characterization of notoriously elusive metal silylene complexes. Also, sophisticated computational methods have been employed to shed light on the mechanism of conversion of Ir-silane adducts into silylenes of which a great number were trapped by reactive recrystallization and subsequently characterized by X-ray diffraction analysis.