Carbon dioxide reduction by an Al-O-P frustrated Lewis pair

The reaction of tBu(2)P(O)H with Bis(2)AlH (Bis = CH(SiMe3)(2)) afforded the adduct tBu(2)P(H)-O-Al(H)Bis(2) (3). It slowly releases H-2 to form the first oxygen-bridged geminal Al/P frustrated Lewis pair tBu(2)P-O-AlBis(2). It is capable of reversibly binding molecular hydrogen to afford 3, shown by NMR and H/D scrambling experiments, and forms a 1,2-adduct with CO2. Importantly, the H-2 adduct 3 reduces CO2 in a stoichiometric reaction leading to the formic acid adduct tBu(2)P(H)-O-Al(CO2H)Bis(2). The formation of the different species was explored by density functional theory calculations which provide support for the experimental results. All products were characterized by NMR spectroscopy as well as X-ray diffraction experiments and elemental analyses.