Formation of macrocyclic ring systems by carbonylation of trifunctional P/B/B frustrated Lewis pairs

Abstract

The trifunctional P/B/B frustrated Lewis pairs <b>11a-c</b> featuring bulky aryl groups at phosphorus [Dmesp (<b>a</b>), Tipp (<b>b</b>), Mes* (<b>c</b>)] react with H₂ by heterolytic hydrogen splitting followed by cleavage of HB(C₆F₅)₂ to give the zwitterionic six-membered heterocyclic PH phosphonium/borate products <b>14a-c</b>. Compounds <b>11a,b</b> react with carbon monoxide by means of a Lewis acid induced CO insertion/rearrangement sequence that eventually results in the formation of the macrocyclic dimers <b>17a,b</b>. The respective carbonylation reaction of the Mes*P/B/B FLP gives the macrocyclic trimer <b>18c</b>. The new products were characterized spectroscopically and by X-ray diffraction and the reaction mechanism was analyzed by DFT calculations.