Hexakis(3,6‐di‐tert‐butyl‐4‐oxo‐2,5‐cyclohexadien‐1‐ylidene)cyclohexane: Closed‐Shell [6]Radialene or Open‐Shell Hexa‐Radicaloid?

Abstract

A star-shaped hexaquinocyclohexane molecule 4 c is reported, which turns out to be a closed-shell extended [6]radialene with a twisted-boat conformation according to X-ray crystallographic analysis. It was formed by an unusually slow decay of its in situ generated open-shell valence isomer, the hexa-radicaloid 4 o, with a half-life time of about 156 min at room temperature. Reaction progress kinetic analysis revealed a large energy barrier of about 95.5±4.3 kJ mol at room temperature from the hexa-radical form 4 o to the contorted [6]radialene form 4 c, because the transformation needs to overcome large steric repulsion between the neighboring phenoxyl units. Compound 4 c can be chemically reduced to radical anion and dianion, and the dianion is actually a diradical dianion, with a calculated diradical character of 71.9 %. This study demonstrates the unique chemical bonding nature of contorted quinoidal π-conjugated molecules and a very unusual valence isomerization process.

A BODIPY-Bridged Bisphenoxyl Diradicaloid: Solvent-Dependent Diradical Character and Physical Properties

“…Compound 2 was synthesized according to Scheme 1. Suzuki coupling between 3,5-dichloro-BODIPY ( 3 ) [23] and (3,5-di- tert -butyl-4-((trimethyl-silyl)oxy)phenyl)boronic acid ( 4 ) [24] gave the diphenol precursor ( 5 ) in 56% yield after simultaneous deprotection of trimethylsilyl groups under basic conditions. Treatment of 5 with PbO 2 in dry dichloromethane (DCM) afforded the target compound 2 in a nearly quantitative yield.…”