Changes in Tricarbastannatrane Transannular N–Sn Bonding upon Complexation Reveal Lewis Base Donicities

Hypercoordinated complexes involving tricarbastannatrane cation [N­(CH2CH2CH2)3Sn]+ with various Lewis bases are investigated in the gas and solution phases using a combination of infrared multiple photon dissociation (IRMPD) spectroscopy, NMR spectroscopy, and density functional theory calculations. Coordination is found to occur at the apical position leading to a pentacoordinated Sn center. Strongly electron donating Lewis bases disrupt the N···Sn transannular interaction and induce higher degrees of geometric distortion at the metal center than weakly donating Lewis bases, an effect that manifests as anharmonic shifts in the vibrational spectra. Once characterized in the gas phase, [N­(CH2CH2CH2)3Sn­(Lewis base)]+ structures were embedded in a dichloroethane polarizable continuum model to investigate solution phase properties. Calculated 119Sn NMR chemical shifts were found to be in good agreement with those measured experimentally, thus suggesting that the bonding properties of [N­(CH2CH2CH2)3Sn]+ are essentially the same in the gas and solution phases.