BORON-NITROGEN COMPOUNDS. XCVI. STUDIES OF THE CHEMICAL BEHAVIOR OF MONOMERIC PYRAZOL-1-YLBORANES

Article abstract of DOI:10.1016/S0022-328X(00)82505-X

Two 1,3-dimethyl-2-(methylpyrazol-1'-yl)-1,3,2-diazaboracyclopentanes have been prepared.The interaction of such monomeric pyrazol-1-ylboranes containing trigonal boron with pyrazoles has been examined and 1/1 molar addition compounds have been identified and isolated.Labelling experiments support spectroscopic evidence to suggest a mobile bridging hydrogen in the cited adducts at ambient temperature and above.Monomeric 1,3-dimethyl-2-(pyrazol-1'-yl)-1,3,2-diazaboracyclopentane reacts with (dimethylamino)dialkylboranes by an exchange of the pyrazolyl with the dimethylamino group.A cyclic transition state involving a B2N3 ring system is suggested for this process in which the corresponding 2-dimethylamino-1,3,2-diazaboracyclopentane and B-tetraalkylpyrazaboles are the final products.The latter are also found among the reaction products of pyrazole adducts of monomeric pyrazol-1-ylboranes with (dimethylamino)dialkylboranes.The interaction of (dimethylamino)dialkylboranes with pyrazole gives B-tetraalkylpyrazaboles in essentially quantitative yield.