2,2′-Bipyridyl-Embedded Cycloparaphenylenes as a General Strategy To Investigate Nanohoop-Based Coordination Complexes

Because
of their unique cyclic architectures, tunable electronic
properties, and supramolecular chemistries, cycloparaphenylenes (CPPs)
have the potential to act as a new class of ligands for coordination
cages, metal–organic frameworks, and small-molecule transition-metal
complexes. However, currently there is no general strategy to coordinate
the cyclic framework to a variety of metal centers. We report here
a general and scalable synthetic strategy to embed 2,2′-bipyridine
units into the backbone of CPPs. We use this approach to synthesize
a 2,2′-bipyridine-embedded [8]­CPP, which we show can successfully
coordinate to both Pd­(II) and Ru­(II) metal centers. The resulting
coordination complexes, a Pd­(II)–nanohoop dimer and a bis­(bipyridyl)­ruthenium­(II)-functionalized
nanohoop, show unique solid-state and photophysical properties. This
work provides a proof of concept for a general strategy to use nanohoops
and their derivatives as a new class of ligands.

环对苯撑（cycloparaphenylene, CPPs）凭借其独特的环状架构、可调谐的电子特性以及超分子化学特性，有望成为一类可应用于配位笼、金属有机框架以及小分子过渡金属配合物的新型配体。然而目前尚无通用策略可将该环状骨架与多种金属中心进行配位。本文报道了一种通用且可规模化的合成策略，可将2,2'-联吡啶（2,2′-bipyridine）单元嵌入CPPs的主链中。我们利用该方法合成了嵌入2,2'-联吡啶的[8]CPP，并证实其可成功与Pd(II)和Ru(II)金属中心配位。所得配位配合物包括Pd(II)-纳米环（nanohoop）二聚体以及双(联吡啶)钌(II)功能化纳米环，二者均展现出独特的固态与光物理特性。本工作为将纳米环及其衍生物作为一类新型配体的通用策略提供了概念验证。