Polycyclic aromatic hydrocarbons in which one or more CC units have been replaced by isoelectronic BN units have attracted interest as potentially improved organic materials in various devices. This promise has been hampered by a lack of access to gram quantities of these materials. However, the exploitation of keystone reactions such as ring closing metathesis, borylative cyclization of amino styrenes and electrophilic borylation has lead to strategies for access to workable amounts of material. These strategies can be augmented by judicious postfunctionalization reactions to diversify the library of materials available. This Frontier article highlights some of the recent successes and shows that the long promised applications of BN-doped PAHs are beginning to be explored in a meaningful way.

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The Lewis acidic fluoroarylborane B(o-HC6F4)3 (2) was prepared and its Lewis acid strength assessed in comparison to the known, related boranes B(C6F5)3 (1) and B(p-HC6F4)3 (3). Experimental methods based on spectroscopic probes and equilibrium measurements were used to show that B(C6F5)3 is the strongest Lewis acid of the three; while the Lewis acidities of 2 and 3 are comparable, the p-H-substituted isomer is slightly stronger in the tests employed. This contrasts with predictions made on the basis of computed bond formation energies, as recently reported by Durfey and Gilbert.

A method for the preparation of 3-bora-9aza-indene heterocycles based on zirconocene mediated functionalization of the ortho-CH bonds of pyridines has been developed and used to make two such compounds. Unlike other methods, the boron center in these heterocycles remains functionalized with a chloride ligand and so the compounds can be further elaborated through halide abstraction and reduction. The utility of the method was further demonstrated by applying it towards the preparation of 1,5dibora-4a,8a-diaza BN analogues of the intriguing hydrocarbon s-indacene starting from 2,5-dimethylpyrazine. Gram quantities of one such compound was prepared and fully characterized, and both experimental and computational data is presented to compare its properties to those of the parent hydrocarbon s-indacene. These data indicate that the BN substituted derivative exhibits lowered aromaticity in relation to the hydrocarbon.