From metallaborane to borylene complexes: syntheses and structures of triply bridged ruthenium and tantalum borylene complexes

Abstract

Reaction of [1,2-(Cp*RuH)₂B₃H₇] (1; Cp*=η⁵-C₅Me₅) with [Mo(CO)₃(CH₃CN)₃] yielded arachno-[(Cp*RuCO)₂B₂H₆] (2), which exhibits a butterfly structure, reminiscent of 7 sep B₄H₁₀. Compound 2 was found to be a very good precursor for the generation of bridged borylene species. Mild pyrolysis of 2 with [Fe₂ (CO)₉] yielded a triply bridged heterotrinuclear borylene complex [(μ₃-BH)(Cp*RuCO)₂ (μ-CO){Fe(CO)₃}] (3) and bis-borylene complexes [{(μ₃-BH)(Cp*Ru)(μ-CO)}₂Fe₂ (CO)₅] (4) and [{(μ₃-BH)(Cp*Ru)Fe(CO)₃}₂ (μ-CO)] (5). In a similar fashion, pyrolysis of 2 with [Mn₂(CO)10] permits the isolation of μ₃-borylene complex [(μ₃-BH)(Cp*RuCO)₂ (μ-H)(μ-CO){Mn(CO)₃}] (6). Both compounds 3 and 6 have a trigonal-pyramidal geometry with the μ₃-BH ligand occupying the apical vertex, whereas 4 and 5 can be viewed as bicapped tetrahedra, with two μ₃-borylene ligands occupying the capping position. The synthesis of tantalum borylene complex [(μ₃-BH)(Cp*TaCO)₂ (μ-CO){Fe(CO)₃}] (7) was achieved by the reaction of [(Cp*Ta)₂B₄H₈ (μ-BH₄)] at ambient temperature with [Fe₂ (CO)₉]. Compounds 2–7 have been isolated in modest yield as yellow to red crystalline solids. All the new compounds have been characterized in solution by mass spectrometry; IR spectroscopy; and ¹H, ¹¹B, and ¹³C NMR spectroscopy and the structural types were unequivocally established by crystallographic analysis of 2–6.