Flash Communication: Properties and Applications of a Pentavalent Bromoantimony Lewis Acid

While normally reluctant toward oxidation, SbBr₃ can be oxidized with 3,4,5,6-tetrachloro-1,2-benzoquinone (<i>o</i>-chloranil) in the presence of a Lewis base like the bromide anion or triphenylphosphine oxide (PPh₃O) to form the tetrachlorocatecholate (cat^Cl) derivatives [SbBr₄(cat^Cl)]^- ([<b>2</b>-Br]^-) and SbBr₃(cat^Cl)•OPPh₃ (<b>2</b>•OPPh₃), respectively. Structural, spectroscopic, and computational data indicate that the SbBr₃(cat^Cl) fragment is similarly, if slightly less, Lewis acidic than the previously reported SbCl₃(cat^Cl) fragment. The SbBr₃/<i>o</i>-chloranil system, as well as its previously reported counterpart SbCl₃/<i>o</i>-chloranil, were tested as Lewis acid catalysts for C-O bond metathesis and polycarbonate depolymerization. These results identified SbX₃/<i>o</i>-chloranil pairs (X = Cl, Br) as simple main-group platforms for C-O bond cleavage chemistry.