Synthesis and structural characterization of new divanada- and diniobaboranes containing chalcogen atoms

Abstract

The reaction of [CpnMCl_4−x] (M=V: n=2, x=2; M=Nb: n=1, x=0; Cp=η⁵-C₅H₅) with LiBH₄⋅THF followed by thermolysis in the presence of dichalcogenide ligands E₂R₂ (E=S, Te; R=2,6-(tBu) ₂-C₆H₂OH, Ph) and 2-mercaptobenzothiazole (C₇H₅NS₂) yielded dimetallaheteroboranes [{CpV(μ-TePh)} ₂(μ₃-Te)BH⋅thf] (1), [(CpV)₂(BH₃S)₂] (2), [(CpNb)₂B₄H₁₀S] (3), [(CpNb)₂B₄H₁₁S(tBu)₂C₆H₂OH] (4), and [(CpNb)₂B₄H₁₁TePh] (5). In cluster 1, the V₂BTe atoms define a tetrahedral framework in which the boron atom is linked to a THF molecule. Compound 2 can be described as a dimetallathiaborane that is built from two edge-fused V2BS tetrahedron clusters. Cluster 3 can be considered as an edge-fused cluster in which a trigonal-bipyramidal unit (Nb₂B₂S) has been fused with a tetrahedral core (Nb2B2) by means of a common Nb₂ edge. In addition, thermolysis of an in-situ-generated intermediate that was produced from the reaction of [Cp₂VCl₂] and LiBH₄⋅THF with excess BH₃⋅THF yielded oxavanadaborane [(CpV)₂B₃H₈(μ₃-OEt)] (6) and divanadaborane cluster [(CpV)₂B₅H₁₁] (7). Cluster 7 exhibits a nido geometry with C_2v symmetry and it is isostructural with [(Cp*M)₂B₅H_9+n] (M=Cr, Mo, and W, n=0; M=Ta, n=2; Cp*=η⁵-C₅Me₅). All of these new compounds have been characterized by ¹H NMR, ¹¹B NMR, and ¹³C NMR spectroscopy and elemental analysis and the structural types were established unequivocally by crystallographic analysis of compounds 1–4, 6, and 7.