A transition metal handyman

Organic electronic materials offer promising avenues towards environmentally friendly and low-weight light emitting diodes, transistors and photovoltaic cells. In this context, cyclophenylene hydrocarbons, which are macrocycles constructed from simple benzene units directly covalently linked together, constitute ideal candidates for organo-electronic applications. Possessing efficient charge transport properties and high thermal stabilities cyclophenylene hydrocarbons have received considerable attention, furthermore the incorporation of heteroatoms is of particular interest to construct materials with tuneable electrochemical performances. However, the lack of effective large-scale synthesis methods for these macrocycles makes their uses in practical applications challenging, such that if these materials are to be used, they require a synthetic handyman.

Hiroyuki Isobe’s group at the University of Tokyo, Japan, has long been studying synthetic methodologies for preparing various classes of macrocyclic hydrocarbons. The group successfully employed a one-pot macrocyclisation method to synthesise a series of cyclo-meta-phenylene macrocycles ([n]CMP) by treating a selected precursor, m-dibromobenzene, with an organo-nickel compound in a particular solvent mixture.¹ They could isolate each macrocycle from [5]CMP to [9]CMP by sequential recrystallisation in different solvents, and obtained [5]CMP and [6]CMP products in a gram scale.