Olefin-Borane van der Waals Complexes: Intermediates in Frustrated Lewis Pair Addition Reactions

The nature of the borane-olefin interactions that take place prior to frustrated Lewis pair addition reactions has been probed employing a Lewis acidic borane tethered to a vinyl group through an alkyl chain. H-1{F-19} HOESY spectral data obtained at -50 degrees C demonstrated the spatial proximity of the boryl and vinyl groups and computational data support the initial formation of a van der Waals borane-olefin complex. Such species serve as intermediates undergoing facile addition reactions with phosphine bases to afford cyclic zwitterionic products.