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 [CpNbCl] (Cp = -CMe) with four equivalents of Li[BHE] (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*)(-Se)(BH)(-Se)] () and the homocubane-like cluster [(NbCp*)(-Se)(-Se)(BH)(-Se)] (). Interestingly, the tri-niobium framework of stabilizes a selenaborate {SeBH} ligand. A selenium atom is further introduced between boron and one of the selenium atoms of to yield cluster . On the other hand, the reaction with the sulfur-containing borate adduct [LiBHS] afforded the trimetallic clusters [(NbCp*)(-S){-S(BH)}] () and [(NbCp*)(-S){-S(S)}] (). Both clusters and have an NbS core, which further stabilizes {BH} and mono-sulfur units, respectively, through bi-chalcogen coordination. All of these species were characterized by B{H}, H, and C{H} NMR spectroscopy, mass spectrometry, infrared (IR) spectroscopy, and single-crystal X-ray crystallography. Moreover, theoretical investigations revealed that the triangular Nb framework is aromatic in nature and plays a vital role in the stabilization of the borate, borane, and chalcogen units.