Reversible formylborane/SO2 coupling at a frustrated Lewis pair framework.

Carbon monoxide is reduced by HB(C6F5)2 at the Mes2PCH2CH2B(C6F5)2 P/B FLP template to give the respective FLP stabilized (η2-formyl)borane product 2. This adds sulfur dioxide by insertion of a SO bond into the three-membered ring to give the P/B FLP coordinated SO2 adduct 9.