The 1‐Phenyl‐1‐(trimethylsilyl)ethyl Cation: An NMR Spectroscopic and Computational Study of the α‐Silyl Effect in Benzyl Cations

Abstract

The 1‐phenyl‐1‐(trimethylsilyl)ethyl cation is generated as a persistent species in solution and characterized experimentally by 1H, 13C, and 29Si NMR spectroscopy. The α‐silyl effect is elucidated by comparison with other benzyl cations, such as cumyl and 1‐phenylethyl cations. Concomitant quantum chemical calculations of structures, relative thermodynamic stabilities, chemical shifts, and the harmonic oscillator model of aromaticity (HOMA) indices are congruent with the analysis of the experimental NMR spectroscopy results; therefore, we conclude that, in benzyl cations, the α‐silyl substituent is stabilizing with respect to H, but destabilizing relative to a methyl group.

Mechanistic insights on the Pd-catalyzed addition of C–X bonds across alkynes – a combined experimental and computational study

“…This result is in agreement with the known effect of silyl groups to be able to stabilize carbocations in α, 59 β 60,61 and γ 62 positions. In addition, analyzing the changes in bond lengths during the isomerization from cis - to trans -Pd( ii ) intermediate ( VIa to Va ) shows a slight elongation of the double bond and concomitant shortening of both C–Si and C–Pd bonds in the TS, suggesting a delocalization of positive charge between Pd, C and Si.…”