Direct synthesis of a geminal zwitterionic phosphonium/hydridoborate system - developing an alternative tool for generating frustrated Lewis pair hydrogen activation systems

摘要

A convenient way to a new class of geminal Mes_2PH~+/B(C_6F_5)_2H~- pairs is presented. It utilizes triflic acid addition to trans-Mes_2PCH=CHB(C_6F_5)2 followed by triflate/hydride exchange. Thermally induced ring-closure gave a phosphonium/boratacyclopropane zwitterion 8 which formed the Mes_2PH(CHMe)-B(C_6F_5)_2H P/B FLP-H_2 product 10 by subsequent treatment with triflic acid and a silane, or alternatively with dihydrogen at 90 ℃. The product 10 is an active catalyst for the hydrogenation of a variety of unsatu-rated organic substrates, including a quinoline derivative. Treatment of compound 8 with HB(C_6F_5)_2 gave a bifunctional borane 14 which selectively reduced carbon monoxide to the formyl stage.