[5]Trovacenyl Boronic Acid, (η⁷-C₇H₇)V[η⁵-C₅H₄B(OH)₂], and Its Anhydride Tri([5]trovacenyl)boroxine, 1,3,5-[(η⁷-C₇H₇)V(η⁵-C₅H₄)]₃B₃O₃^,1

Abstract

The paramagnetic boronic acid (η7-C7H7)V[η5-C5H4B(OH)2] (3•) has been prepared and characterized structurally, emphasis being placed on hydrogen bonding motives present in the crystal. EPR spectroscopy reveals that association of 3• is absent in fluid solution. Tri([5]trovacenyl)boroxine, 4•••, the cyclic anhydride of 3•, engages in antiferromagnetic exchange; magnetic susceptometry provides the value J(4•••) = −1.04 cm-1. Accordingly, the EPR spectrum of 4••• in fluid solution points to 22 51V hyperfine components separated by one-third of the coupling constant of mononuclear trovacene derivatives. Redox splittings δE1/2 between consecutive oxidation steps of 4••• are not resolved, i.e., δE1/2 ≤ 60 mV.