The nickelacarboranes [NEt4][2-(eta(3)-C3H4R)-closo-2,1,7-NiC2B9H11] (R = H (1a), Ph (1b)) have been synthesized via reaction between [Na](2)[nido-7,9-C2B9H11] and [Ni-2(mu-Br)(2)(eta(3)-C3H4R)(2)] in THF (THF = tetrahydrofuran), followed by addition of [NEt4]Cl. Protonation of 1a in the presence of a donor ligand L affords the complexes [2,2-L-2-closo-2,1,7-NiC2B9H11] (L = CO (2), CNBut (3)). Addition of PEt3 (1 equiv) to 2 produces quantitative conversion to [2-CO-2-PEt3-closo-2,1,7-NiC2B9H11], 4. Species 2-4 exhibit in solution hindered rotation of the NiL2 fragment with respect to the eta(5)-C2B9 cage unit. Protonation of 1a in the presence of a diene affords the neutral complexes [2-(eta(2):eta(2)-diene)-closo-2,1,7-NiC2B9H11] (diene = C5Me5H (5), dcp (6), cod (7), nbd (8), chd (9), and cot (10a); dcp = dicyclopentadiene, cod = 1,5-cyclooctadiene, nbd = norbornadiene, chd 1,3-cyclohexadiene, and cot = cyclooctatetraene). Variable temperature H-1 NMR experiments show that the {Ni(diene)} fragments are freely rotating even at 193 K A small quantity of the di-cage species [2,2'-mu-(1,2:5,6-eta-3,4:7,8-eta-cot)-(closo-2,1,7-NiC2B9H11)(2)] (10b) is formed as a coproduct in the synthesis of 10a. This species can be rationally synthesized by protonation of la and subsequent addition of 10a.