By reduction with CoCp*(2) in THF or toluene, the tantalum(V) chlorocarbamato complex TaCl2(O2CNEt2)(3), 1, gives high yields of the tantalum(III) N,N-diethylcarbamate, Ta(O2CNEt2)(3), 2. On the other hand, good yields of the octanuclear mu-oxo-N,N-diethylcarbamato cage compound Ta-8(mu-O)(12)(O2CNEt2)(16), 3, were secured by reaction of 1 with sodium in THF. Compound 3 has been characterized by analytical and spectroscopic methods and by X-ray diffractometry. Crystal data for C80H160N16O44Ta8 : M = 3497.84, triclinic, space group P (1) over bar (no. 2), (1) over bar a = 15.440(3) Angstrom, b = 15.710(1).Angstrom, c = 16.090(2) Angstrom, alpha = 101.53(4)degrees, beta = 107.51(5)degrees, gamma = 118.79(3)degrees, V = 2971.4(3) Angstrom(3), Z = 1, D-c = 1.955 : Mg/m(3), mu = 7.416 mm(-1), F(000) = 1688, R1 = 0.0350, wR2 = 0.0798, T = 213 K. The eight tantalum atoms are located at the vertexes of a cube whose edges are occupied by 12 bridging oxo groups; Hexacoordination at tantalum is completed by bridging and terminal N,N-diethylcarbamato ligands. Both THF and the carbon dioxide fragments of the carbamato groups are involved in the formation of the mu-oxo cage oxides.