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

Reaction of [1,2-(CpRuH)(2)B(3)H(7)] (1; Cp=η(5)-C(5)Me(5)) with [Mo(CO)(3)(CH(3)CN)(3)] yielded arachno-[(CpRuCO)(2)B(2)H(6)] (2), which exhibits a butterfly structure, reminiscent of 7 sep B(4)H(10). Compound 2 was found to be a very good precursor for the generation of bridged borylene species. Mild pyrolysis of 2 with [Fe(2)(CO)(9)] yielded a triply bridged heterotrinuclear borylene complex [(μ(3)-BH)(CpRuCO)(2)(μ-CO){Fe(CO)(3)}] (3) and bis-borylene complexes [{(μ(3)-BH)(CpRu)(μ-CO)}(2)Fe(2)(CO)(5)] (4) and [{(μ(3)-BH)(CpRu)Fe(CO)(3)}(2)(μ-CO)] (5). In a similar fashion, pyrolysis of 2 with [Mn(2)(CO)(10)] permits the isolation of μ(3)-borylene complex [(μ(3)-BH)(CpRuCO)(2)(μ-H)(μ-CO){Mn(CO)(3)}] (6). Both compounds 3 and 6 have a trigonal-pyramidal geometry with the μ(3)-BH ligand occupying the apical vertex, whereas 4 and 5 can be viewed as bicapped tetrahedra, with two μ(3)-borylene ligands occupying the capping position. The synthesis of tantalum borylene complex [(μ(3)-BH)(CpTaCO)(2)(μ-CO){Fe(CO)(3)}] (7) was achieved by the reaction of [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))] [corrected] at ambient temperature with [Fe(2)(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 (1)H, (11)B, and (13)C NMR spectroscopy and the structural types were unequivocally established by crystallographic analysis of 2-6.