Strongly Electrophilic Borenium Ions for Small Molecule Activation

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The chemistry of strongly electrophilic borocations is of high current interest. Reactive borenium ions that exhibit a B-H functionality are rare. The Erker group at Münster has recently developed a convenient synthetic route to N-heterocyclic carbene-stabilized B-H borenium ion systems. We will develop a series of such boron compounds that contain N-heterocyclic carbene (NHC) or cyclic alkylamino carbene (CAAC) ligands in addition to a strongly electron-withdrawing ArF fluoroaryl substituent [ArF = pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl (Fxyl) or 2,4,6-tris(trifluoromethyl)phenyl (Fmes)] at boron. We will first determine the specific reactivities of such systems in a variety of typical B-H reactions. We will then use the strongly electrophilic B-H boreniums for the generation of advanced frustrated Lewis pairs (FLPs). These shall be employed in the current development of stoichiometric and catalytic hydrogenation processes. That shall involve novel pathways in carbon monoxide and dinitrogen reduction and in the development of active catalysts for alkene, alkyne and heterocycle conversions. The new FLPs shall be tested for their ability in C-H activation processes. We want to investigate if deprotonation of our B-H borenium cations might open a convenient route to generating reactive NHC/CAAC stabilized borylenes. Eventually we want to try making neutral [NHC/CAAC]B(ArF)=CHR systems by deprotonation routes from our alkyl borenium cations in a search for metal-free olefin and acetylene metathesis routes.