Cyclotrisilenylium ion: the persilaaromatic compound.

Area of Science:

• Organosilicon Chemistry
• Main Group Chemistry
• Aromaticity Studies

Background:

• Cyclopropenylium ions are unique aromatic systems with a three-membered ring and 2 pi electrons.
• Stable silicon analogs of carbocations are challenging to synthesize and characterize due to silicon's electropositivity and steric demands.

Purpose of the Study:

• To synthesize and characterize the first isolable silicon congener of the cyclopropenylium ion.
• To investigate the structural and electronic properties of the novel cyclotrisilenylium ion.

Main Methods:

• Synthesis of a sterically hindered cyclotrisilene precursor.
• Reaction with a triphenylmethylium tetraarylborate salt to form the cyclotrisilenylium ion.
• Isolation and characterization of the tetraarylborate salt using X-ray crystallography and spectroscopic techniques.

Main Results:

• The highly crowded 3,3-bis(di-tert-butylmethylsilyl)-1,2-bis(tri-tert-butylsilyl)cyclotrisilene was synthesized.
• The (di-tert-butylmethylsilyl)bis(tri-tert-butylsilyl)cyclotrisilenylium ion was successfully isolated as a tetraarylborate salt.
• X-ray crystallographic analysis revealed an almost equilateral three-membered ring with Si-Si bond lengths of 2.216(3) A.
• Spectroscopic data and crystal structure confirmed the compound as a free silyl cation and a 2 pi electron aromatic species.

Conclusions:

• The first isolable silicon analog of the cyclopropenylium ion has been synthesized and characterized.
• The cyclotrisilenylium ion exhibits aromaticity, demonstrating charge delocalization over the three-membered silicon ring.
• This work expands the understanding of aromaticity in silicon-containing compounds.