A polymacrocyclic oligoarylamine with a pseudobeltane motif: towards a cylindrical multispin system.

Although several types of belt-shaped compounds with novel structures have been reported over the past 30 years, they are currently receiving increasing attention in conjunction with the synthesis of the shortest possible segments of singlewalled carbon nanotubes. Nanoscaled beltlike molecules are considered to be “cycles of cycles”, and thus they have welldefined shapes with rigid cavities and can conceivably be used to construct solid-state materials with nanoporous networks. In addition, polymacrocycles with electron(or hole-) delocalized (or localized) scaffolds are fascinating for potential applications towards electron (or hole) transport and/or as magnetic materials. In this context, oligoarylamine-based macrocyclic spin systems are being pursued to take advantage of the multi-electron redox properties of oligoarylamines and the relative stability of their poly(radical cation)s. It is well known that strong Coulombic interactions between charged centers in oligoarylamine-based macrocycles hinder the generation of higher oxidation states with maximum spin multiplicity (Coulombic penalty). As we have shown recently, however, the insertion of para-phenylenediamine (PD) units into the molecular backbone can alleviate the Coulombic penalty between charged triarylaminium radical centers in oligoarylamines and lower their oxidation potentials. Tetraaza[14]m,p,m,p-cyclophane, the smallest macrocyclic oligoarylamine bearing the alternating meta–para linkage, is transformed into an almost pure spin-triplet diradical dication upon two-electron oxidation. Moreover, it has been demonstrated that the introduction of this macrocycle into a oligoarylamine backbone with one-dimensional connectivity can can convert the one-dimensional multispin system with a fragile spin-coupling pathway into a robust, aligned highspin system. Thus the polymacrocycles provided by the tetraazacyclophanes may be an indication for the further development of cylindrical multispin systems, which could culminate in nanotube-like surfaces with multi-electron redox activity. These findings led to the idea of utilizing the tetraazacyclophane unit as a component for a belt-shaped polymacrocyclic oligoarylamine. Polymacrocycle 1 (Scheme 1), which is classified as a pseudobeltane according to Vçgtle s nomenclature, 9] can be viewed as a kind of molecular belt containing six PD units connected by four 1,3,5-benzenetriyl ferromagnetic couplers, and thereby the higher oxidation states of 1 can lead to multispin systems.