Reversible C(sp³)-Si Oxidative Addition of Unsupported Organosilanes: Effects of Silicon Substituents on Kinetics and Thermodynamics

Abstract

The intermolecular oxidative addition of unactivated C­(sp3)-Si bonds is reported for a family of organosilanes at a cationic pincer-supported iridium complex. To our knowledge, no examples of oxidative addition to give analogous unsupported (alkyl)metal silyl complexes have been previously reported. The generality of this transformation is excellent, with successful examples demonstrated for tetraorganosilanes, mono- and poly alkoxysilanes, and two siloxysilanes. Oxidative addition is found to be completely reversible, with the product of reductive elimination being subject to trapping by triethylsilane. The successful isolation of these metal silyl complexes has allowed for an in-depth kinetic analysis of C­(sp3)-Si reductive elimination, a process with strong implications in both catalytic C–H silylation and olefin hydrosilylation. The apparent order of reactivity is SiMe3 > SiMe2(CF3) > SiMe2OSiMe3 > SiMe2OSiMe2OSiMe3 > SiMe2(OMe) > SiMe2(OEt) > SiMe­(OMe)2. A DFT analysis of the oxidative addition products shows that the thermodynamic stability of the (alkyl)metal silyl complexes span a range of ca. 10 kcal·mol–1, which relate closely with the experimentally determined rates of C­(sp3)-Si reductive elimination and trapping, though a clear kinetic distinction exists between methoxy- and siloxysilyl complexes.

Breaking Conventional Site Selectivity in C–H Bond Activation: Selective sp3 versus sp2 Silylation by a Pincer-Based Pocket

“…The formation of the silyl hydride complexes, together with the observation that the TAD activity of ( i Pr P S C O P)Ir was suppressed by hydrosilane, suggest that the C(sp 3 )–H silylation reaction proceeds via the DHSi pathway, rather than the TAD/HSi pathway. This inference is further supported by systematic DFT calculations (mainly by PWPB95D3(BJ)//B3LYP-D3 methods; see the SI for the computational details). , Following the generation of the active 14-electron ( i Pr P S C O P)Ir species INT0 through the TBE hydrosilylation with Ir(III) silyl hydride complex 6 (which requires a barrier of ∼25.7 kcal/mol above 6 ; see Figure S13 in Supporting Information (SI)), the substrate 1a coordinates to the Ir(I) center of INT0 and then undergoes facile Si–H oxidative addition (no transition state found in our relaxed energy scan calculations, see Figure S16 in the Supporting Information) to form a stable 5-coordinate 16-electron Ir(III) silyl hydride intermediate INT1 (Δ G = −3.7 kcal/mol, Figure A). Afterward, δ-C(sp 3 )–H bond activation occurs to give an unstable 7-coordinate, 18-electron Ir(V) dihydride silyl intermediate INT2 (Δ G = 24.3 kcal/mol) via TS1…”

Benzimidazole-modified organosilane functionalized silica nanoparticles as a ‘turn-off’ fluorescent probe for highly selective Cu2+ ion detection: unravelling logic gate behaviour and molecular docking studies

“…Furthermore, they serve as versatile intermediates suitable for a multitude of chemical reactions. [21][22][23][24][25][26][27] Schiff bases are categorized as a subclass of imines. Schiff bases play a crucial role in synthesizing a variety of both simple and complex organic compounds by serving as intermediates.…”

Thermodynamic Analysis of the Main Reactions Involved in the Synthesis of Organosilanes

“…For example, Acker et al 12 performed a thermodynamic study of the copper-catalyzed direct synthesis of methylchlorosilanes in a reaction system but did not suggest how to optimize the reaction parameters to improve the selectivity of CH 3 SiHCl 2 , (CH 3 ) 2 SiHCl, and CH 3 SiCl 3 . Torgunrud et al 13 investigated the thermodynamics of silica depolymerization with alcohols, and Chapp et al 14 investigated the effect of silica substituents on the kinetics and thermodynamics of reversible C(sp3) silica oxidative additions to unloaded organosilanes. However, the above studies on silicon compounds still need to fully reveal the thermodynamic processes of the reactions associated with organic silicon compounds.…”