Collect. Czech. Chem. Commun. 1979, 44, 3688-3694

The electronic effects in and the oxygen basicity of some oxygen-containing boranes

Josef Pola, Marie Jakoubková and Václav Chvalovský

Institute of Chemical Process Fundamentals, Czechoslovak Academy of Sciences, 165 02 Prague 6-Suchdol


The oxygen relative basicity of di-n-butylboronous anhydride ((n-C4H9)2B)2O, ethyl di-n-butylboronite (n-C4H9)2BOC2H5 and some orthoborates (RO)3B having electrondonating and electronwithdrawing groups R was measured from the IR spectra of hydrogen bonds of phenol interacting with these compounds in CCl4 and analysed by means of the Taft equation. The substituent electronic effect of (n-C4H9)2B- and (RO)2B-groups attached to the oxygen of the-OR and -OB= moieties has been estimated asa more electronwithdrawing than that of structurally alike R2Z- and (RO)2Z-groups having Z = CH and SiCH3 and is discussed in terms of the vacant 2p orbital of the boron and a weak, if any, mutual polarizability effect of the alkoxy groups in orthoborates. The trimethylsiloxy group in trimethylsilyl borate possesses reduced electronwithdrawing ability compared to that in ((CH3)3SiO)3SiCH3 as a consequence of its great polarizability.