The title compound, C10H30B2N2Si, was synthesized in 98% yield. It has a zwitterionic heterocyclic carborane ring in which an N, N, N', N'-tetramethylethy lenediamine (TMEDA) unit is coordinated via two donor N atoms to two BH2 units that are separated by a CH(SiMe3) moiety to form a novel seven-membered ring. The bond distances (Angstrom) within the ring are B-C 1.613(3) and 1.618(3), B-N 1.652(3) and 1.659(3), C-N 1.483(3) and 1.505(3), and C-C 1.510(3).