A coupled-cluster approach to the relative strains in [1.1.1]propellane, its derivatives and hetero[1.1.1]propellanes

Abstract

The molecule [1.1.1]propellane and its neutral boron, nitrogen, oxygen, sulphur, S–O, and SO₂ analogs as well as the methyl, hexafluoro, and tri-carbonyl substituted derivatives have been investigated by theoretical calculations at the coupled-cluster singles and doubles level with an augmented polarized double zeta basis set. The geometries were optimized and vibrational analysis was carried out for each species. The main objective of this study was to determine the relative strain in these systems, which in turn is a predictor of stability and reactivity providing valuable information about potentially viable synthetic targets. The systems with the least strain are the nitrogen, boron and the S–O analogs, whereas the SO₂ substituted molecule and the hexafluoride and tricarbonyl substituted analogs exhibited the largest amount of strain. Geometrical features are also investigated and it is demonstrated that non-bonded repulsive interactions contribute significantly to the strain in some of the systems since cage-like structures force relatively short non-bonded distances.

Keywords:

• coupled-cluster
• relative strains
• propellanes
• isodesmic equations

Acknowledgements

The computational resources were provided by the Mississippi Center for Supercomputing Research (MCSR) and the National Center for Supercomputing Applications (NCSA) under grant number CHE090067. H. Xu would like to thank Dr. Brian Hopkins of MCSR for his helpful technical support. The technical support provided by Drs. Fox and Clemente of Gaussian, Inc. regarding the Gaussian03/09 programs is also appreciated.