Reactions leading to the first representatives of the tricarbollide series are reported. These are based on monocarbon insertion into the neutral nido-5,6-C2B8H12 (1) and its anion [nido-5,6-C2B8H11](-) (2), using the CN- anion and Bu(t)NC as monocarbon insertion agents, to give the the ligand derivatives of the 11-vertex nido family of general formula 7-L-nido-7,8,9-C3B8H10 (3), where L = H2N- (3a) or Bu(t)NH(2) (3b) as a result of endo attack by the C-atom of the carbon-insertion reagent in the open hexagonal face of the dicarbaborane substrate. The second product from the CN- reaction is the [9-CN-arachno-5,6-C2B8H12](-) anion (4) arising from an exo attack by the N-atom at the B(9) vertex of 2. Methylation of 3a and 3b leads to the isolation of N-methyl derivatives of type 3, where L, = Me(3)N (3c) and Bu(t)(Me)NH (3d). Compounds of the general structure 3, namely 3c, are essential starting materials for the parent tricarbollide chemistry. Single-crystal X-ray diffraction analysis of 3d . Me(2)CO shows a regular 11-vertex nido constitution with a slightly perturbed pentagonal open face with three adjacent {CH} vertices. Crystal data for 3d . Me(2)CO : C11H29B8NO, M = 277.83, a 13.8400(10) Angstrom, b = 10.6400(10) Angstrom, c = 16.439(2) Angstrom, alpha = 90 degrees, beta = 134.725(8)degrees, gamma = 90 degrees, Z = 4, V = 1719.9(3) Angstrom(3), mu = 0.058 mm(-1), D-calcd = 1.073 Mg/m(3), R(1) = 0.0472, wR(2) = 0.1247.