Mechanism and Selectivity of Methyl and Phenyl Migrations in Hypervalent Silylated Iminoquinones

Abstract

Chlorosilanes R(X)(Y)SiCl (R = Me, Ph; X, Y = Me, Ph, Cl) have been reported to react with Pb(ONO(Q))2 (ONO(Q) = 3,5-di-tert-butyl-1,2-quinone-(3,5-di-tert-butyl-2-oxy-1-phenyl)imine) to give five-coordinate (X)(Y)Si(ON[R]O), in which the R group has migrated from silicon to nitrogen. This migration is intramolecular, as confirmed by the lack of crossover between (CH3)3SiCl and (CD3)3SiCl in their reaction with Pb(ONO(Q))2. Reaction of PhSiMeCl2 takes place with high kinetic stereoselectivity to produce isomer Ph(Cl)Si(ON[Me]O) in which the phenyl is axial in the trigonal bipyramid, which subsequently isomerizes to the thermodynamic isomer with axial chlorine. This indicates that migration takes place preferentially from the stereoisomer of the octahedral intermediate, κ(3)-Ph(CH3)(Cl)Si(ONO(Q)), in which the phenyl and methyl groups are mutually trans, indicating that the observed complete selectivity for methyl over phenyl migration is due to intrinsic differences in migratory aptitude. DFT calculations suggest that migration takes place from this isomer not because it undergoes migration faster than other possible stereoisomers, but because it is formed most rapidly, and migration occurs faster than isomerization.

New avenues for ligand-mediated processes – expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands

“…More recently the group reported a mechanistic investigation to elucidate the mechanism and explain the reactivity. 96 Cross-over experiments using (CH 3 ) 3 SiCl and (CD 3 ) 3 SiCl showed that the migration occurs in an intramolecular fashion. DFT calculations suggested that the origin for the exclusive selectivity of methyl migration is due to the faster formation of one of the possible octahedral intermediates and that migration is faster than isomerization.…”

Potassium tert-Butoxide-Catalyzed Dehydrogenative C–H Silylation of Heteroaromatics: A Combined Experimental and Computational Mechanistic Study

“…It has been well documented that the addition of strong silicophilic Lewis bases (e.g., fluoride, alkoxide) can increase the reactivity of hydro­silanes in the hydro­silylation of CO bonds . It is believed that strongly reducing hyper­coordinate silicate complexes are formed by coordination of nucleophilic anions during such processes, which typically weakens the Si–H bond and increases the hydridic character of this bond. , Studies by Corriu et al revealed that the direct reaction of (RO) 3 SiH with the corresponding KOR (R = alkyl or aryl) in THF at room temperature affords the anionic, five-coordinate hydrido­silicate [HSi­(OR) 4 ]K in good yield . Such species are found to be very effective in the reduction of carbonyl compounds, can act as an electron donor toward the dehalogenation of organic halides, or can donate one electron to a metal complex .…”

Element‐Ligand Cooperativity with p‐Block Elements

“…The migration of a methyl group from silicon to nitrogen led to the reduction of the oxidized ligand form to the amine‐bisphenolato state. Following experimental and computational work convincingly disclosed the mechanism of the reaction as an intramolecular process, somehow reminiscent of a ligand‐cooperative form of silicon–carbon bond activation . Similar reactivity was also reported for tin …”