Chirooptical 2,2′-Dimethoxybiphenyl Crystals Generated From Suzuki–Miyaura Coupling Reaction Catalyzed by Pd-Loaded Chiral Silica

Abstract

In this work, we report a one-pot approach that combines crystal ripening with the Suzuki–Miyaura coupling reaction. We investigated the reaction between 2-methoxyphenyl bromide and 2-methoxyphenylboronic acid, catalyzed by a series of Pd-loaded chiral optical (_D- or _L-) and racemic (_DL-) silica/polyethyleneimine (PEI) systems, which produced crystalline 2,2′-dimethoxybiphenyl (DMB). The silica used as a catalyst was prepared using our previously established method, in which chirality was imparted to the silica through catalytic templates composed of polyethyleneimine (PEI) and tartaric acid. Both enantiopure (_D- or _L-; 100% ee) and racemic (_DL-; 0% ee) tartaric acid-mediated silica, after tartaric acid removal and palladium (Pd) loading, exhibited similar catalytic activities, leading to the quantitative precipitation of 2,2′-dimethoxybiphenyl in a water/ethanol (1:1 by volume) medium. Interestingly, the 2,2′-dimethoxybiphenyl crystals formed and ripened in the presence of Pd-loaded chiral _D- and _L-silica/PEI exhibited octahedral morphology and displayed remarkable chiroptical activity with a mirror-image relationship. This represents a novel example of using chiral Pd-loaded silica to synthesize axially chiral biphenyl in crystalline form.