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

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

New heteronuclear bridged borylene complexes that were derived from [{Cp*CoCl}₂] and mono-metal—carbonyl fragments

The synthesis, structural characterization, and reactivity of new bridged borylene complexes are reported. The reaction of [{Cp*CoCl}₂] with LiBH₄⋅THF at −70 °C, followed by treatment with [M(CO)₃(MeCN)₃] (M=W, Mo, and Cr) under mild conditions, yielded heteronuclear triply bridged borylene complexes, [(μ₃-BH)(Cp*Co)₂ (μ-CO)M(CO)₅] (1–3; 1: M=W, 2: M=Mo, 3: M=Cr). During the syntheses of complexes 1–3, capped-octahedral cluster [(Cp*Co)₂ (μ-H)(BH)₄{Co(CO)₂}] (4) was also isolated in good yield. Complexes 1–3 are isoelectronic and isostructural to [(μ₃-BH)(Cp*RuCO)₂ (μ-CO){Fe(CO)₃}] (5) and [(μ₃-BH)(Cp*RuCO)₂(μ-H)(μ-CO){Mn(CO)₃}] (6), with a trigonal-pyramidal geometry in which the μ₃-BH ligand occupies the apical vertex. To test the reactivity of these borylene complexes towards bis-phosphine ligands, the room-temperature photolysis of complexes 1–3, 5, 6, and [{(μ₃-BH)(Cp*Ru)Fe(CO)₃}₂(μ-CO)] (7) was carried out. Most of these complexes led to decomposition, although photolysis of complex 7 with [Ph₂P(CH₂)nPPh₂] (n=1–3) yielded complexes 9–11, [3,4-(Ph₂P(CH₂)nPPh₂)-closo-1,2,3,4-Ru₂Fe₂ (BH)₂] (9: n=1, 10: n=2, 11: n=3). Quantum-chemical calculations by using DFT methods were carried out on compounds 1–3 and 9–11 and showed reasonable agreement with the experimentally obtained structural parameters, that is, large HOMO–LUMO gaps, in accordance with the high stabilities of these complexes, and NMR chemical shifts that accurately reflected the experimentally observed resonances. All of the new compounds were characterized in solution by using mass spectrometry, IR spectroscopy, and ¹H, ¹³C, and ¹¹B NMR spectroscopy and their structural types were unequivocally established by crystallographic analysis of complexes 1, 2, 4, 9, and 10