Synthesis and Crystal Structure of a Self-Assembled, Octanuclear Oxo-Tantalum(V) Derivative Containing the First Example of a Transition Metal M(8)(&mgr;-O)(12) Cage.

By reduction with CoCp(2) in THF or toluene, the tantalum(V) chlorocarbamato complex TaCl(2)(O(2)CNEt(2))(3), 1, gives high yields of the tantalum(III) N,N-diethylcarbamate, Ta(O(2)CNEt(2))(3), 2. On the other hand, good yields of the octanuclear &mgr;-oxo-N,N-diethylcarbamato cage compound Ta(8)(&mgr;-O)(12)(O(2)CNEt(2))(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 C(80)H(160)N(16)O(44)Ta(8): M = 3497.84, triclinic, space group = P&onemacr; (no. 2), &onemacr;a = 15.440(3) Å, b = 15.710(1) Å, c = 16.090(2) Å, alpha = 101.53(4) degrees, beta = 107.51(5) degrees, gamma = 118.79(3) degrees, V = 2971.4(3) Å(3), Z = 1, D(c) = 1.955 Mg/m(3), &mgr; = 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 &mgr;-oxo cage oxides.