Synthesis and Structure of Mono-, Di-, and Trinuclear Fluorotriarylbismuthonium Cations.

A series of cationic fluorotriarylbismuthonium salts bearing differently substituted aryl groups (Ar = 9,9-Me2-9H-xanthene, Ph, Mes, and 3,5-tBu-C6H3) have been synthesized and characterized. While the presence of simple phenyl substituents around the Bi center results in a polymeric structure with three Bi centers in the repeating monomer, substituents at the ortho- and meta-positions lead to cationic mono- and dinuclear fluorobismuthonium complexes, respectively. Preparation of all compounds is accomplished by fluoride abstraction from the parent triaryl Bi(V) difluorides using NaBArF (BArF - = B[C6H3-3,5-(CF3)2]4 -). Structural parameters were obtained via single crystal X-ray diffraction (XRD), and their behavior in solution was studied by NMR spectroscopy. Trinuclear and binuclear complexes are held together through one bridging fluoride (µ-F) between two Bi(V) centers. In contrast, the presence of Me groups in both ortho-positions of the aryl ring provides the adequate steric encumbrance to isolate a unique mononuclear nonstabilized fluorotriarylbismuthonium cation. This compound features a distorted tetrahedral geometry and is remarkably stable at room temperature both in solution (toluene, benzene and THF) and in the solid state.