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[摘要]：Reaction of [CpnMCl4-x] (M=V: n=x=2; M=Nb: n=1, x=0) or [Cp*TaCl4] (CP=eta(5)-C5H5, Cp*=eta(5)-C5Me5), with [LiBH4 center dot thf] at -70 degrees C followed by thermolysis at 85 degrees C in the presence of [BH3 center dot thf] yielded the hydrogen-rich metallaboranes [(CpM)(2)-(B2H6)(2)] (1: M=V; 2: M=Nb) and [(Cp*Ta)(2)(B2H6)(2)] (3) in modest to high yields. Complexes 1 and 3 are the first structurally characterized compounds with a metal-metal bond bridged by two hexahydroborate (B2H6) groups forming a symmetrical complex. Addition of [BH3 center dot thf] to 3 results in formation of a metallaborane [(Cp*Ta)(2)B4H8(mu-BH4)] (4) containing a tetrahydroborate ligand, [BH4](-), bound exo to the bicapped tetrahedral cage [(Cp*Ta)(2)B4H8] by two Ta-H-B bridge bonds. The interesting structural feature of 4 is the coordination of the bridging tetrahydroborate group, which has two B-H bonds coordinated to the tantalum atoms. All these new metallaboranes have been characterized by mass, H-1, B-11, and C-13 NMR spectroscopy and elemental analysis and the structural types were established unequivocally by crystallographic analysis of 1-4. |
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