Theoretical studies on structure, formation and nature of bond in a Disila-, Digerma- and distannacyclobutene ring

A theoretical study on the structure, formation and nature of E-E and C-E bonds (E=Si, Ge, Sn) in catenated compounds of the group 14 elements including disila-, digerma- and distannacyclobutene ring formed from the reaction of 1-thiacyclohept-4-yne and E(NR)(2)SiR2 molecules [E = Si, Ge, Sn, R = t-Bu, H, F, Cl, Br] in 1:2 mole ratio has been investigated at the M06/def2-TZVPP level of theory. The results showed that the formation energy of the products of the reaction above with Si(NBr)(2)SiBr2 and Sn(NF)(2)SiF2 reactants has greatest and the smallest value, respectively. In agreement with the values of formation energies, both the calculated Wiberg bond indices (WBI) for E-E and C-E bonds and rho(BCP) of E-E bond in the products of two above reactants have largest and smallest values, respectively. The nature of E-E bond in the products was also studied with atoms in molecules (AIM) and natural bond orbital (NBO) analyses. The data confirmed that the E-E bond is partly covalent. In addition, the nature of C-E bond was investigated with energy decomposition analysis (EDA) and it was shown that the covalent contribution is in the range 48-53% depending on the types of E atom and corresponding substituents.