Ana B. Buades, Víctor Sanchez Arderiu, David Olid-Britos, Clara Viñas, Reijo Sillanpää, Matti Haukka, Xavier Fontrodona, Markos Paradinas, Carmen Ocal, and Francesc Teixidor*. J. Am. Chem. Soc., 2018, 140 (8), pp 2957–2970
With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M(C2B9H11)(C2B9H10)-NC5H4-C5H4N-M′(C2B9H11)(C2B9H10)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi(metallacarboranyl)viologen [3,3′-M(8-(NC5H4-C5H4N-1,2-C2B9H10)(1′,2′-C2B9H11)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount.