Patrick G. Campbell

Recent Advances in Azaborine Chemistry

The chemistry of organoboron compounds has been primarily dominated by their use as powerful reagents in synthetic organic chemistry. Recently, the incorporation of boron as part of a functional target structure has emerged as a useful way to generate diversity in organic compounds. A commonly applied strategy is the replacement of a CC unit with its isoelectronic BN unit. In particular, the BN/CC isosterism of the ubiquitous arene motif has undergone a renaissance in the past decade. The parent molecule of the 1,2-dihydro-1,2-azaborine family has now been isolated. New mono- and polycyclic B,N heterocycles have been synthesized for potential use in biomedical and materials science applications. This review is a tribute to Dewars first synthesis of a monocyclic 1,2-dihydro-1,2-azaborine 50 years ago and discusses recent advances in the synthesis and characterization of heterocycles that contain carbon, boron, and nitrogen.

A Single-Component Liquid-Phase Hydrogen Storage Material

The current state-of-the-art for hydrogen storage is compressed H(2) at 700 bar. The development of a liquid-phase hydrogen storage material has the potential to take advantage of the existing liquid-based distribution infrastructure. We describe a liquid-phase hydrogen storage material that is a liquid under ambient conditions (i.e., at 20 °C and 1 atm pressure), air- and moisture-stable, and recyclable; releases H(2) controllably and cleanly at temperatures below or at the proton exchange membrane fuel cell waste-heat temperature of 80 °C; utilizes catalysts that are cheap and abundant for H(2) desorption; features reasonable gravimetric and volumetric storage capacity; and does not undergo a phase change upon H(2) desorption.

Hydrogen Storage by Boron−Nitrogen Heterocycles: A Simple Route for Spent Fuel Regeneration

We describe a new hydrogen storage platform based on well-defined BN heterocyle materials. Specifically, we demonstrate that regeneration of the spent fuel back to the charged fuel can be accomplished using molecular H(2) and H(-)/H(+) sources. Crystallographic characterization of intermediates along the regeneration pathway confirms our structural assignments and reveals unique bonding changes associated with increasing hydrogen content on boron and nitrogen. Synthetic access to the fully charged BN cyclohexane fuels will now enable investigations of these materials in hydrogen desorption studies.

Resonance stabilization energy of 1,2-azaborines: a quantitative experimental study by reaction calorimetry.

Aromatic and single-olefin six-membered BN heterocycles were synthesized, and the heats of hydrogenation were measured calorimetrically. A comparison of the hydrogenation enthalpies of these compounds revealed that 1,2-azaborines have a resonance stabilization energy of 16.6 ± 1.3 kcal/mol, in good agreement with calculated values.

B-Methyl Amine Borane Derivatives: Synthesis, Characterization, and Hydrogen Release

We describe the synthesis of MeH2N–BH2Me (3) and H3N–BH2Me (4) as potential hydrogen storage materials with 6.8 wt-% and 8.9 wt-% capacity, respectively. Compounds 3 and 4 readily release 2 equivalents of H2 at 80°C in the presence of a CoCl2 catalyst to furnish the corresponding trimerized borazine derivatives. Regeneration of 3 from its spent fuel material can be accomplished using a simple two-step process: activation with formic acid followed by reduction with LiAlH4.