Trovacene Chemistry, 3~[not=] The Mono-, Di-, and Tri([5]trovacenyl)boranes: A Study of Intermetallic Communication Across an sp~2-Hybridized Boron Atom

摘要

The paramagnetic complexes di(mesityl)([5]trovacenyl)borane (5~.), (mesityl)di([5]trovacenyl)borane (6~(..)), and tri([5]trovacenyl)borane (7~(...)) were prepared from [5]trovacenyllithium, (#eta#~5-C_7H_7)V(#eta#~5-C_5H_4Li), and (Mes)_2 BF, (Mes)BF_2, and BF_3, respectively. The propeller-shaped species 5~., 6~(..), and 7~(...) were subjected to X-ray diffraction with the aim of possibly correlating the twist angles with intramolecular intermetallic communication. Cyclic voltammetry points to successive vanadium-centered oxidation processes and boron-centered reduction, a small redox splitting #delta#E_(1/2)[(2+/+), (+/0)] being observed for 6~(..). According to EPR spectroscopy, performed in fluid solution, the exchange interaction J in the diradical 6~(..) approaches the fast-exchange region and is attenuated significantly by quaternization at boron in [6~(..)-nBu]~-. Although EPR spectroscopy of the triradical 7~(...) also indicates an extensive exchange interaction, the exchange parameters, derived from spectral simulation, follow the gradation J(7~(...)) approx= 1/3 J(6~..)). The magnetic susceptibility of 6~(..) and 7~(...)) follows the same trend. As expected, compound 7~(...) exhibits spin frustration because it contains three antiferromagnetically coupled S = 1/2 systems that are arranged in an equilateral triangly.