Computational study of unsaturated and saturated cyclic (alkyl) (amino) carbene borane complexes

In this study, several density functional theory (DFT) and CBS-QB3 calculations were performed to explore the properties of different conformers of cyclic (alkyl) (amino) carbene (CAAC) borane complexes with the chemical formula BH(C4NH5)2. In 2011, Kinjo et al. successfully synthesized a Lewis-basic boron derivative using two saturated CAACs (Kinjo et al., 2009). In this work, the properties of the boron atom attached to two unsaturated CAACs and two saturated CAACs were compared. According to our results, the unsaturated CAAC shows reduced proton affinity of the boron atom as compared to the saturated CAAC; the insertion of two CC double bonds into CAAC makes the BCcarbenic bonds stronger. The results of natural bond orbital analysis indicated that the lone pair of the central boron atom can be viewed as a pure π-type p orbital.