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

Using ab initio electronic structure methods with flexible basis sets, we examined the electronic, geometric, and thermodynamic stability of selected borata-alkene synthons (H2C = BR2)(-) (R = H, CH3, C6H5, C6H5 Mes). The isolated (H2C = BH2)(-) synthon was found to be electronically stable and susceptible to neither fragmentation nor isomerization processes. Geometric and electronic stabilities of the remaining (H2C = BR2)- anions were confirmed likewise. The structures of borata-alkene synthons studied contain planar H2C = B < fragment with the apparent double-bond character of the C-B connection confirmed by natural bond orbital occupancies of sigma(C-B) and pi(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 (H2C = BR2)- synthons were predicted and compared to those of the representative alkenyl carbanions. The stability and structures of sodium salts comprising the (H2C = BR2)- unit and their ability to preserve the basic properties of the borata-alkene synthons were determined and discussed.