CONTRIBUTION TO THE CHEMISTRY OF BORON, 243 - SYNTHESIS AND STRUCTURES OF DIMESITYLDIBORANES(4)

An efficient route to B,B'-dihalo-B,B'-dimesityldiboranes(4) is report ed, as well as the conversion of these and of B,B'-dimesityl-B,B'-dime thoxydiborane(4) into other B,B'-dimesityldiboranes B(2)mes(2)X(2) (X = OR, SR, NR2, NHR). The substituents X influence the shielding of the B-11 nucleus in the expected manner. Hindered rotation about the B-N bond is observed for X = pyrrolyl, while in solution there is free rot ation about the B-C bond. However, X-ray structural results reveal tha t the mesityl group is almost orthogonal to the B(B)CY plane in the so lid state. The shortest B-B bond is observed in mes,B,I,, indicating t hat the iodide is the strongest Lewis acid in the reported series of m es(2)B(2)Y(2) compounds. This is also reflected in short B-C bonds. Mo reover, the two mes(Y)B units also approach orthogonality in these dib orane(4) compounds, and thus enforce this as a typical structural feat ure of diborane(4) derivatives. For this reason, the planar C (N) B-B( N)C unit of B,B'-di(benzylamino)-B,B'-dimesityldiborane(4) is regarded as exceptional for aminodiboranes(4).