Multiply borylated arenes: X-ray crystal structure analyses and quantum chemical calculations

Optimised synthesis procedures and results of X-ray single crystal structure analyses for 4-(dibromoboryl)toluene, 1,3-bis(dibromoboryl)benzene, 1,4-bis(dibromoboryl)benzene, and 1,3,5-tris(dibromoboryl)benzene are reported. These compounds have also been studied by Hartree-Fock (HE), density functional theory (DFT), and Moller-Plesset second-order perturbation (MP2) methods in combination with the polarized double-zeta valence (SVP) and polarized triple-zeta valence (TZVP) basis sets of Ahlrichs and coworkers. A comparison of the quantum chemical results for optimised geometries and computed NMR chemical shifts with experiment is presented to test the quality of the various methods for this class of compounds. All DFT methods tested yield optimised geometries within the experimental error bars of 3sigma for bond lengths, whereas larger deviations among the methods are observed for computed NMR chemical shifts. This calibration recommends the B3LYP/SVP combination as a reliable and computationally efficient level of theory to assess the structures and absolute and relative H-1-, C-13- and B-11 NMR shift values of borylated aromatic compounds in future investigations.