Exohedral complexation of B39- with ECp*+ half-sandwich complexes (E=Si Ge, Sn, Pb): A DFT study

The hexagonal and heptagonal holes of B-39(-) allow its complexation with a half sandwich complex ECp*+ (E=Si, Ge, Sn, Pb). Structure and the nature of bonding of (eta(6/7)-B-39)E(eta(5)-Cp-*) are explored through the density functional theory based computation. (eta(6)-B-39)E(eta(5)-Cp-*) isomers are more stable than (eta(7)-B-39)E(eta(5)-Cp*) and the energy difference between these two isomers decreases down the group from Si to Pb. The dissociation path, (eta(6/7)-B-39)E(eta(5)-Cp-*) -> B-39(-)+ ECp*+ is studied. For all E, (eta(6/7)-B-39)E(eta(5)-Cp-*) is formed exergonically at 298 K temperature as given by the Delta G values of dissociation path [60.1(Si) to 68.3(Pb) kcal/mol for (eta(6)-B-39)E(eta(5)-Cp-*) and 58.3(Si) to 67.8(Pb) kcal/mol for (eta(7)-B-39)E(eta(5)-Cp-*)]. The adduct becomes bent around the central E atom when B-39(-) gets attached to ECp*+ and the amount of bending increases gradually down the group from Si to Pb. Bonding analysis of the stable isomer, (eta(6)-B-39)E(eta 5-Cp*) has been done by natural bonding orbital (NBO) and energy decomposition analyses (EDA). The electron density from B-39(-) is transferred to the ECp*+ moiety as revealed by the NBO analysis. All the complexes are mainly stabilized by the electrostatic and orbital interactions between B-39(-) and ECp*+ fragments as highlighted by the EDA results.