Theoretical Analysis of Group 15 Periodic Trends in the Highly Strained PnC3H3 Molecule

The synthesis of highly strained molecules has garnered significant interest from the chemical community over the last few decades. The tetrahedral isomer of the C₄H₄ molecule (tetrahedrane) is a prototypical example of a strained molecule and remains elusive to experimental chemists despite its predicted theoretical kinetic stability[1]. Earlier this year Cummins and coworkers published a groundbreaking study in which they successfully isolated the PC₃(t-Butyl)₃ derivative of tetrahedrane[2]. Motivated by their impressive success, our work provides the first theoretical examination of the PnC₃H₃ (Pn = N, P, As, Sb, Bi) series of molecules in order to inspire their synthesis in the near future. We optimized each structure at the highly reliable CCSD(T)/aug-cc-pwCVTZ(-PP) level of theory and present an analysis of the pnictogen effects upon the geometric parameters, harmonic vibrational frequencies, and electronic structure of the target system. Natural Bond Orbital analysis is performed in order to provide insight into how substituent selection affects the electronic structure of the tetrahedral center. A possible model system is also briefly discussed that may elucidate the mechanism proposed by Cummins as well as provide a route to synthesize the unsubstituted PnC₃H₃ species[2]. These results provide a firm theoretical foundation for future experimental attempts at creating PnC₃H₃ tetrahedrane derivatives.

[1] Nemirowski, A., Reisenauer, H.P., and Schreiner, P.R., Chemistry – A European Journal, 12(28), (2006) 7411.

[2] Riu, M.L.Y., Jones, R.L., Transue, W.J., M¨uller, P., and Cummins, C.C., Science Advances, 6(13), (2020) 3168.