Trovacene chemistry, 3 The mono-, di-, and tri([5]trovacenyl)boranes: a study of intermetallic communication across an sp(2)-hybridized boron atom

The paramagnetic complexes di(mesityl)([5]trovacenyl)borane (mesityl)di([5] trovacenyl)borane (6(..)), and tri([5]trovacenyl)borane (7(...)) were prepa red from [5]trovacenyllithium, (eta(5)-C7H7)V(eta(5)-C5H4Li), and (Mes)(2)B F, (Mes)BF2, and BF,, 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 communicatio n. Cyclic voltammetry points to successive vanadium-centered oxidation proc esses and boron-centered reduction, a small redox splitting delta B-1/2[(2/+), (+/0)] being observed for 6(..). According to EPR spectroscopy, perfor med in fluid solution, the exchange interaction J in the diradical 6(..) ap proaches the fast-exchange region and is attenuated significantly by quater nization at boron in [6(..)-nBu](-). Although EPR spectroscopy of the trira dical 7(...) also indicates an extensive exchange interaction the exchange parameters, derived from spectral simulation, follow the gradation 5(7(...) ) approximate to 1/3 J(6(..)). The magnetic susceptibility of 6(..) and 7(. ..) follows the same trend. As expected, compound 7(...) exhibits spin frus tration because it contains three antiferromagnetically coupled S = 1/2 sys tems that are arranged in an equilateral triangle.