2,3,4-TRICARBA-NIDO-HEXABORANES(7) WITH A BRIDGING B-ETHYL-B MOIETY

Hydroboration of diethyl(1-propynyl)borane 1 with tetraethyldiborane(6 ) in the presence of a catalytic amount of trimethyl-or tributyltin ch loride gave two new organo-substituted carboranes 6 and 7 with 2,3,5 - tricarba-nido-hexaborane(7) and 2,3,4-tricarba-nido-hexaborane(7) skel etons, respectively, along with polymeric material and the known organ o-substituted 1-carba-arachno-pentaborane(10) (3) and pentaethyl-1,5-d icarba-closo-pentaborane(5) (4). Selective B-11(5,6) decoupled C-13-NM R spectra indicate an unprecedented B(5)-ethyl-B(6) bridge in 7. This structure is supported by the agreement between experimental and calcu lated B-11-and C-13-chemical shifts on a model compound 7d with methyl groups in the 1,2,3,5,6-positions and an ethyl group bridging B(5) an d B(6).