Intramolecular N→B Coordination as a Stabilizing Scaffold for π-Conjugated Radical Anions with Tunable Redox Potentials

5 years ago

Intramolecular N→B Coordination as a Stabilizing Scaffold for π-Conjugated Radical Anions with Tunable Redox Potentials

Benjamin Rudolf, Antonio J. Pierik, Frank Pammer, Dominique F. Bechtel, Yu Sun, Markus Grandl

In this work we report on a preparative strategy that allows the facile tuning of the electron affinities of π-conjugated organic n-type materials via intramolecular N→B coordination: 2-fold hydroboration of a pyrazine-derived substrate with 9H-borabicyclo[3.3.1]nonane (9H-BBN) and Piers’ borane ((C₆F₅)₂BH) furnishes the intramolecularly N→B-coordinated compounds PzBBN and PzBPF in high yield. For each borane racemic mixtures of the respective chiral derivatives and achiral meso compounds have been isolated, and their electrochemical, optical, and structural properties have been investigated and complemented by DFT calculations. The boranes exhibit high electron affinities with electrochemical LUMO energy levels of −3.69 and −4.30 eV, respectively. The corresponding radical anions PzBBN^•– and PzBPF^•– can be reversibly generated and are stable in solution at ambient temperature. Analysis of the radical species by EPR spectroscopy and single-crystal analysis of [PzBPF]^•–[CoCp₂]⁺ allowed further corroboration of the π-delocalized nature of these radicals.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.6b00916

DOI: 10.1021/acs.organomet.6b00916