Program Results

Introduction to the event

Technological and energy demands necessitate the development of clean energy technologies, energy-efficient electronics, and high-performance catalysts. These innovations must prioritize cost-effectiveness while avoiding reliance on scarce or toxic elements. Organic π-conjugated structures serve as foundational components for key technologies including organic transistors, organic light-emitting diodes, organic photovoltaics, and (photo)organocatalytic systems.

The Farrell laboratory investigates the frontiers of organic π-systems through the development of innovative synthetic methodologies that access unprecedented π-conjugated architectures. Unlike conventional two-dimensional hexagonal carbon frameworks, these novel π-structures incorporate strategic heteroatom substitutions and diverse ring topologies. The research program focuses on understanding and optimizing the optical and electronic properties of these compounds to engineer high-performance functional materials.

In a recent publication, the Farrell laboratory has reported a new metal-free alkyne annulation reaction that enables π-extension of boron-doped polycyclic aromatic hydrocarbons (Figure 1, Chem. Sci. 2024, 15, 16210-16215. DOI: 10.1039/D4SC03781B). This methodology provides an efficient synthetic route to highly sought-after low-LUMO energy π-systems with significant potential for n-type semiconductor applications. The concept was demonstrated through the synthesis of a series of functionalized, structurally constrained 6a,15adiborabenzo[tuv]naphtho[2,1-b]picenes. The observed regioselectivity, combined with DFT calculations, supported an unusual annulation mechanism proceeding via intramolecular electrophilic aromatic substitution of a zwitterionic intermediate. The resulting annulated products display ambient stability, exceptionally deep LUMO energy levels, intense visible-range absorptions, and unhindered π-systems that adopt distinct solid-state packing arrangements dependent upon the nature of their substituents.

Further research on boron- and nitrogen-doped polycyclic aromatic hydrocarbons focused on investigating isonitrile-boron trihalide adducts and their subsequent rearrangement reactions (Figure 2, Dalton Trans. 2025, 54, 7189-7193. DOI: 10.1039/D5DT00210A). Through examination of the reactivity of 2-biphenylisocyanide-BX3 adducts (where X = I, Br, Cl), unexpected C-C bond-forming borylative cyclizations were observed through functionalization of a biphenyl C-H bond to produce phenanthridinium 6-borate zwitterions. The reaction of 2-biphenylisocyanide-BCl3 also produced a helical 2,2'bisphenanthridinechelated dichloroboronium salt product, indicating the metal-free formation of three C-C bonds. This discovery holds particular significance because CC bond formation is a fundamental transformation in organic synthesis. Reactions that activate unreactive C-H bonds, and those that simultaneously form both C-C and C-B bonds, are particularly valuable for synthetic applications.

Finally, in an effort to further understand fundamental steps in the electrophilic borylation reaction critical to many B-doped PAH syntheses, studies were undertaken of three new 2-(naphthalen-1-yl)vinyl Nheterocyclic carbene (NHC)-boranes [Can. J. Chem. 2025, in press. DOI:10.1139/cjc-2025-0061]. Surprisingly, acid-mediated electrophilic borylation/cyclization reactions of these compounds were concomitant with double bond reductions. Mechanistic investigations suggest that the observed alkene saturation arises from a rearrangement process involving electrophilic borylation intermediates, shedding new light on electrophilic borylation mechanisms.

Figure 1. Metal-free alkyne annulation enabling π-extension of borondoped polycyclic aromatic hydrocarbons [Chem. Sci. 2024, 15, 16210-16215. DOI: 10.1039/D4SC03781B].

Figure 2. The Farrell laboratory’s work on cyclization reactions highlighted on the front cover of Dalton Transactions [Dalton Trans.2025, 54, 7189-7193. DOI: 10.1039/D5DT00210A].