Mechanistic Insights into Palladium‐Catalyzed Silylation of Aryl Iodides with Hydrosilanes through a DFT Study

Abstract

The catalytic cycles of palladium-catalyzed silylation of aryl iodides, which are initiated by oxidative addition of hydrosilane or aryl iodide through three different mechanisms characterized by intermediates R Si-Pd -H (Cycle A), Ar-Pd -I (Cycle B), and Pd (Cycle C), have been explored in detail by hybrid DFT. Calculations suggest that the chemical selectivity and reactivity of the reaction depend on the ligation state of the catalyst and specific reaction conditions, including feeding order of substrates and the presence of base. For less bulky biligated catalyst, Cycle C is energetically favored over Cycle A, through which the silylation process is slightly favored over the reduction process. Interestingly, for bulky monoligated catalyst, Cycle B is energetically more favored over generally accepted Cycle A, in which the silylation channel is slightly disfavored in comparison to that of the reduction channel. Moreover, the inclusion of base in this channel allows the silylated product become dominant. These findings offer a good explanation for the complex experimental observations. Designing a reaction process that allows the oxidative addition of palladium(0) complex to aryl iodide to occur prior to that with hydrosilane is thus suggested to improve the reactivity and chemoselectivity for the silylated product by encouraging the catalytic cycle to proceed through Cycles B (monoligated Pd catalyst) or C (biligated Pd catalyst), instead of Cycle A.

Germylation of Arenes via Pd(I) Dimer Enabled Sulfonium Salt Functionalization

“…In a few cases, reduction of the aryl tetrafluorothianthrenium salt was observed during germylation, leading to the recovery of initial arene substrate. This competing side process was also reported previously for metal-catalyzed germylation , and silylation , reactions.…”

Palladium‐Catalyzed Three‐Component Reaction of Dihydrosilanes and Vinyl Iodides in the Presence of Alcohols: Rapid Assembly of Silyl Ethers of Tertiary Silanes

“…Yamanoi had introduced bulky ( t Bu 3 P) 2 Pd as a catalyst that would usually disfavor the undesired defunctionalization pathway . This experimental finding was indeed explained by an in‐depth quantum‐chemical investigation but three different catalytic cycles are needed to rationalize the subtle effects of the phosphine ligand and the amine base . Our vinylation of dihydrosilanes is in agreement with this (Scheme , top): C(sp 2 )−Si bond formation is seen with ( t Bu 3 P) 2 Pd and hydrodeiodination is found with (Ph 3 P) 2 PdCl 2 ; the fact that the alcohol additive steers the reaction toward defunctionalization even with ( t Bu 3 P) 2 Pd shows how sensitive these cross‐couplings are toward modifications (cf.…”

Mechanistic Insights into Formation of All-Carbon Quaternary Centers via Scandium-Catalyzed C–H Alkylation of Imidazoles with 1,1-Disubstituted Alkenes

“…All calculations were performed with Gaussian 09 . The functional M06-L, suitable for applications in transition metal chemistry, has been successfully used in numerous studies on transition metal-catalyzed organic reactions. − It was combined with the dispersion correction D3 in this work to enhance computational accuracy. Structures were optimized and characterized by frequency calculations to be energy minima (zero imaginary frequencies) or transition states (only one imaginary frequency) at the M06-L-D3/6-31G­(d,p) level with the solvent (toluene) effects included using the SMD solvation model.…”