Ring Strain Energy of Diheteropnictogeniranes El2Pn (Pn=N, P, As, Sb)– Accurate versus Additive Approaches

Abstract

AbstractAccurate ring strain energy (RSE) values for sixty‐six parent pnictogeniranes having two other identical p‐block elements, El2Pn, have been reported. A decrease in RSE was observed to correlate with an increase in the p character of the AO used in endocyclic bonds, which is particularly remarkable on descending the groups 15 and 16. The latter also parallels higher ‐NICS(1) values, which seems not to be related with an increase in aromaticity, as pointed out by other NICS‐related criteria, but to atom‐centred diatropic currents mostly arising from the presence of lone pairs. Only in case of pnictogenaditrieliranes Tr2Pn (Tr=B, Al, Ga), the decrease of ‐NICS(1) is related to a lower Hückel‐type 2π‐electron aromaticity on descending group 13. The use of an additive methodology based on atom‐strain contributions enables estimation of RSEs for a large majority of all possible three‐membered rings containing group 13–16 elements with modest accuracy (RMSE=4.371 kcal/mol), that could be remarkably improved by using bond‐strain contributions (RMSE=1.183 kcal/mol) instead.