An AM1 semiempirical molecular orbital investigation of the group 14 [1.1.1] propellanes and bicyclo[1.1.1]pentanes

Abstract

AM1 semiempirical calculations were performed on the group 14 [1.1.1]propellanes and bicyclo[1.1.1]pentanes. For the carbon and tin propellanes, the results were in agreement with several previous theoretical and experimental studies, predicting substantial bonding interaction between the bridgehead atoms in the case of carbon and none in the case of tin. Calculations on the silicon propellane were in sharp disagreement with ab initio calculations using a variety of basis sets. Both geometry and singlet-triplet splitting were incorrectly reproduced. The silicon propellane calculations were repeated using the HF/6-31G* basis set, and the singlet-triplet order was in agreement with the previous work. The germanium results show very strong charge localization. We suggest a possible reason for this observation.