Small cycloalkane 1,1',2,2'-tetracyano structures are highly directional non-covalent carbon-bond donors

Abstract

[eng] High-level calculations (RI-MP2/def2-TZVP) disclosed that the s-hole in between two C atoms of cycloalkane X2C CX2 structures (X=F, CN) is increasingly exposed with decreasing ring size. The interacting energy of complexes of F , HO , N C , and H2CO with cyclopropane and cyclobutane X2C CX2 derivatives was calculated. For X=F, these energies are small to positive, while for X=CN they are all negative, ranging from 6.8 to 42.3 kcal mol 1. These finding are corroborated by a thorough statistical survey of the Cambridge Structural Database (CSD). No clear evidence could be found in support of non-covalent carbon bonding between electron-rich atoms (El.R.) and F2C CF2 structures. In marked contrast, El.R.···(CN)2C C(CN)2 interactions are abundant and highly directional. Based on these findings, the hydrophobic electrophilic bowl formed by 1,1',2,2'-tetracyano cyclopropane or cyclobutane derivatives is proposed as a new and synthetically accessible supramolecular synthon.