Rh-coordinated histidyl bolaamphiphile assembly: a catalyst for the isomerization of cis-stilbene and cis-alkene

Abstract

In this study, we present a colloidal assembly of histidyl bolaamphiphiles whose imidazoles coordinate with rhodium ions (HisC7[Rh]) to exhibit catalytic isomerization activity for cis-stilbene and cis-alkene molecules. The histidyl bolaamphiphiles self-assemble to form a soft scaffold that functions analogously to an apoenzyme. This scaffold exposes multiple histidyl imidazoles and carboxylates on its surface, to which rhodium ions bind, generating catalytically active sites. The Rh coordination with the biochemical functional groups was verified through comprehensive vibrational spectroscopy and calorimetry. The colloidal HisC7[Rh] demonstrated a significant catalytic effect on the isomerization of cis- to trans-stilbene under mild H₂ conditions, resulting in 69% yield of trans-stilbene. In contrast, when Rh(cod)₂BF₄ was employed as a control catalyst, only the hydrogenated products of bibenzyl were obtained. These findings underscore the crucial role of histidyl motifs in exhibiting unique catalytic isomerization activity through the coordination with Rh. The catalytic activity of HisC7[Rh] is governed by several factors, such as rhodium content, solvent composition, temperature, and H₂ pressure. Moreover, HisC7[Rh] displayed moderate isomerization activity towards not only stilbene but also unsaturated fatty acid isomers, highlighting its expansive potential as an isomerization catalyst.