Selective synthesis of iridium(iii)-derived molecular Borromean rings, [2]catenane and ring-in-ring macrocycles via coordination-driven self-assembly

Abstract

This paper reports the formation of unprecedented iridium(III)-derived topological macrocycles. Discrete molecular Borromean rings 1 and 3 in pure form are synthesized via coordination-driven self-assembly of an acceptor [(Cp*Ir)₂(OO∩OO)](OTf)₂ (Cp* = pentamethylcyclopentadienyl, OO∩OO = 6,11-dioxido-5,12-naphthacenedione) (A) with dipyridyl donors 1,4-bis(4-pyridinylethynyl)benzene (L₁) and 2,5-bis(4-pyridinylethynyl)thiophene (L₂) respectively in methanol. Self-assembly using the same acceptor under similar conditions with two other donors 9,10-bis(4-pyridinylethynyl)anthracene (L₃) and 1,4-di(4-pyridinylethynyl)buta-1,3-diyne (L₄) resulted in [2]catenane 5 and non-catenane ring-in-ring topological macrocycle 7 respectively. Rectangular macrocycles 2, 4, 6, and 8 were respectively obtained when the self-assembly of acceptor A with one of the donors L₁–L₄ was carried out under dilute conditions in nitromethane or methanol. All these new macrocycles were characterized by ¹H and ¹³C NMR, 2D NMR, ESI-MS and elemental analyses. Single crystal X-ray structures of Borromean rings 1 and 3, and ring-in-ring macrocycle 7 revealed that the length and functionality of donors enabling CH⋯π and π⋯π interactions govern the topology.