Premium
Persistent Bissilylated Arenium Ions
Author(s) -
Meyer Rita,
Werner Karla,
Müller Thomas
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020301)8:5<1163::aid-chem1163>3.0.co;2-m
Subject(s) - chemistry , moiety , aryl , acetonitrile , ion , carbanion , silylation , photochemistry , nucleophile , medicinal chemistry , stereochemistry , organic chemistry , catalysis , alkyl
A series of bissilylated arenium ions 1 with different substitution patterns on the aryl ring have been synthesized by hydride abstraction from 2‐aryl‐substituted 2,6‐dimethyl‐2,6‐disilaheptanes ( 2 ) via transient silylium ions. The arenium ions have been identified by their characteristic NMR chemical shifts, ( δ 29 Si=19.1–25.6, δ 13 C ipso =89.0–102.4, δ 13 C ortho =160.9–182.0, tlsb=‐1%> δ 13 C meta =132.5–146.9, δ 13 C para =150.2–169.9) supported by quantum mechanical calculations of structures, energies, and magnetic properties at the B3LYP/6‐311G(d,p)//B3LYP/6‐31G(d) + ΔZPVE level of theory. The calculations clearly reveal the charge dispersing and stabilizing effect of the silyl substituents in arenium ions 1 . The bissilylated benzenium ion 1 a is more stable than the parent benzenium ion (C 6 H 7 + ) by 37.6 kcal mol −1 . The synthesized arenium ions 1 are stable in solution at room temperature for periods ranging from a few hours to days. This unusual stability is attributed to: 1) the thermodynamic stabilization of the arenium ion by two β ‐silyl substituents and 2) the essentially non‐nucleophilic reaction conditions (the use of the weakly coordinating [B(C 6 F 5 ) 4 ] − anion and aromatic hydrocarbons as solvents). Addition of stronger nucleophiles than aromatic hydrocarbons (for example, acetonitrile) results in desilylation of the arenium ion 1 and recovery of the 2‐aryl‐2,6‐disilaheptane moiety.