An ab initio study on the stability of isolated borata-alkene synthons

Abstract

• Isolated (H 2 C = BH 2 ) – synthon is a thermodynamically stable system. • (H 2 C = B R 2 ) – synthons ( R = CH 3 , C 6 H 5 , C 6 F 5 , Mes) are also stable as isolated species. • The presence of C = B double bond is confirmed in all borata-alkene systems studied. • Excess electron binding energies of (H 2 C = B R 2 ) – synthons span the 1.70–3.29 eV range. • Na + (H 2 C = B R 2 ) – salts preserve the structure and bonding pattern of embedded synthons. Using ab initio electronic structure methods with flexible basis sets, we examined the electronic, geometric, and thermodynamic stability of selected borata-alkene synthons (H 2 C = B R 2 ) – ( R = H, CH 3 , C 6 H 5 , C 6 F 5 , Mes). The isolated (H 2 C = BH 2 ) – synthon was found to be electronically stable and susceptible to neither fragmentation nor isomerization processes. Geometric and electronic stabilities of the remaining (H 2 C = B R 2 ) – anions were confirmed likewise. The structures of borata-alkene synthons studied contain planar H 2 C = B < fragment with the apparent double-bond character of the C–B connection confirmed by natural bond orbital occupancies of σ(C–B) and π(C–B) bonds approaching 2 e and by the shapes and spatial localizations of the corresponding NBOs. Vertical electron detachment energies (1.70–3.29 eV) of the (H 2 C = B R 2 ) – synthons were predicted and compared to those of the representative alkenyl carbanions. The stability and structures of sodium salts comprising the (H 2 C = B R 2 ) – unit and their ability to preserve the basic properties of the borata-alkene synthons were determined and discussed.