Synthesis, Structure, and Reactivity of Borate Ester Coordinated Organobismuth Compounds

A new class of hypervalent organobismuth compounds functionalized with coordinating pinacolborate esters of the nature ArBiCl2 (2), Ar3Bi (3), ArPh2Bi (4), Ar3BiCl2 (5), and ArPh2BiCl2 (6), where Ar = 3-fluoro-2-pinacolatoboronphenyl, have been prepared and structurally characterized. The Bi···O distance is between 2.58 and 3.47 Å in the solid state for all compounds, and reasonable bonding interactions are presumed to exist in compounds 2−4 and 6, where Bi···O < 3.0 Å. When ArPh2BiCl2 (6) is exposed to CsF in the presence of furan, the [4 + 2] cycloaddition product of 3-fluorobenzyne + furan, 8, is isolated in 58% yield. Mechanistic evidence is offered to support the claim that 6 undergoes an unprecedented fluoride-promoted fragmentation to generate 3-fluorobenzyne, pinacol, BF3, and Ph2BiF.