作者:Bernd Wrackmeyer、Gerald Kehr
DOI:10.1016/0022-328x(95)05619-z
日期:1995.10
1,4,6,9-Tetraalkyl-3,8-diethyl-2,7-bis(diethylboryl[4.4]mona-1,3,6,8-tetraenes (alkyl = Pt (2a), Pr (2b), Pr-i (2c), ''Bu (2d)) react with four equivalents of boron tribromide to give 2,3,4,5-tetraalkyl-1,6-dibromo-2,3,4,5-tetracarba-nido-hexaboranes(6) (3a-d) in high yield. By monitoring the progress of the reactions using C-13 NMR spectroscopy, 2,5-diboryl-substituted 3-borolenes (10) were identified as intermediates that rearrange to the carboranes via elimination of ethylboron dibromide. Treatment of 2 with boron triiodide affords the analogous 1,6-diodo-substituted carboranes 4. The reaction of 2 with an excess of boron trichloride proceeds rather slowly, again with a 3-borolene (9) as intermediate, and leads finally to a mixture of the carboranes 5 and 6 as a result of elimination of EtBCl(2) or BCl3. Treatment of 2 with BF3 leads to decomposition without any defined products. The carboranes 3 react stepwise with Li[Et(3)BH] to give first the monohydride with a B(6)-H bond (17) and the dihydride with B(6)-H and B(1)-H bonds (18).