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.