Silica Nanopowder Supported Frustrated Lewis Pairs for CO Capture and Conversion to Formic Acid.

Treatment of hydroxylated silica nanopowders and allyl-functionalized silica nanopowders with 3-(diphenylborano)- or 3-bis(pentafluorophenylborano)propyltrimethoxysilane or 2-(diphenylphosphino)- or 2-(dicyclohexylphosphino)ethyltriethoxysilane generates silica nanopowder supported Lewis acids and silica nanopowder supported Lewis bases . These surfaces were characterized by C, B, and P cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR), X-ray photoelectron spectroscopy (XPS), and attenuated total reflection Fourier transform infrared (ATR FTIR). When is combined with solution-phase Lewis bases PR (R = CF, CH, mesityl), six associated silica nanopowder supported frustrated Lewis pairs (FLPs) are formed. In another set of six reactions, the interactions between the supported Lewis bases and solution-phase Lewis acids BR with R = CF, CH, mesityl produced six more associated supported FLPs. The capture of CO by these FLPs producing FLP-CO Lewis pair adducts and were highlighted by ATR FTIR, and it was found that FLP with R = CH on both the supported Lewis acid and solution-phase Lewis base trapped the largest quantities of CO on the silica nanopowder supports. Conversion of CO to HCOOH was achieved by first activating H to generate activated FLP-H surfaces and . Addition of CO then generated HCOOH via the silica nanopowder supported FLP-HCOOH adducts and . Qualitative identification of HCOOH generation was achieved by ATR FTIR measurements, and surface with R = CH proved to be the most successful silica nanopowder surface bound FLP in HCOOH generation. In some cases, diborano formates (-BO(CH)OB-) and were also identified as side products during HCOOH formation. Spectroscopic characterization of purposefully synthesized and included B and P CP MAS NMR.