Trimetallic Chalcogenide Species: Synthesis, Structures, and Bonding.

In an attempt to isolate boron-containing tri-niobium polychalcogenide species, we have carried out prolonged thermolysis reactions of [Cp*NbCl 4 ] (Cp* = ɳ 5 -C 5 Me 5 ) with four equivalents of Li[BH 2 E 3 ] (E = Se or S). In the case of the heavier chalcogen (Se), the reaction led to the isolation of the tri-niobium cubane-like cluster [(NbCp*) 3 ( μ 3 -Se) 3 (BH)( μ -Se) 3 ] ( 1 ) and the homocubane-like cluster [(NbCp*) 3 ( μ 3 -Se) 3 ( μ -Se) 3 (BH)( μ -Se)] ( 2 ). Interestingly, the tri-niobium framework of 1 stabilizes a selenaborate {Se 3 BH} - ligand. A selenium atom is further introduced between boron and one of the selenium atoms of 1 to yield cluster 2 . On the other hand, the reaction with the sulfur-containing borate adduct [LiBH 2 S 3 ] afforded the trimetallic clusters [(NbCp*) 3 ( μ -S) 4 { μ -S 2 (BH)}] ( 3 ) and [(NbCp*) 3 ( μ -S) 4 { μ -S 2 (S)}] ( 4 ). Both clusters 3 and 4 have an Nb 3 S 6 core, which further stabilizes {BH} and mono-sulfur units, respectively, through bi-chalcogen coordination. All of these species were characterized by 11 B{ 1 H}, 1 H, and 13 C{ 1 H} NMR spectroscopy, mass spectrometry, infrared (IR) spectroscopy, and single-crystal X-ray crystallography. Moreover, theoretical investigations revealed that the triangular Nb 3 framework is aromatic in nature and plays a vital role in the stabilization of the borate, borane, and chalcogen units.