Giant Cycloparaphenylene-Scaffolded Porphyrins as Photocatalysts

Abstract

The efficient synthesis of cycloparaphenylenes (CPPs) with the designated functional groups still remains challenging. Meanwhile, the applications of functional CPPs have received increasing attention. In this paper, we first present a staged macrocyclization and TMS-I exchange strategy for the precise synthesis of [12]CPP-8I, while a direct three-fold macrocyclization of a diiodo-terphenyl precursor yields [9]CPP-6I in 39% yield. These results not only provide reliable routes to iodinated CPPs, but also reveal the influence of ring size on their chemical reactivity. Second, we further synthesized the giant porphyrin-CPP conjugates [12]CPP-8tBu₃TPP and [9]CPP-6tBu₃TPP from the respective iodinated precursors via Suzuki coupling with the porphyrin boronic ester. The unique 3D structure of the CPP scaffold can weaken intermolecular π-π stacking and favor the intermolecular loose packing of porphyrin units, ushering in generating ¹O₂ and O₂ ^·- with high efficiency under light irradiation in DMF. Third, the giant porphyrin-CPP conjugates, in particular [9]CPP-6tBu₃TPP, were demonstrated to be efficient photocatalysts for the photochemical reaction between tertiary aniline and maleimide with high yield and wide substrate scope, significantly outperforming porphyrins and other benchmark catalysts reported previously. Furthermore, the utility of [9]CPP-6tBu₃TPP as the photocatalyst for developing photoinduced polymerization was explored.

Keywords: Cycloparaphenylenes; Macrocyclization; Photocatalyst; Porphyrin; Reactive oxygen species.