First-Row Transition-Metal-Diborane and -Borylene Complexes

A combined experimental and quantum chemical study of Group 7 borane, trimetallic triply bridged borylene and boride complexes has been undertaken. Treatment of [{Cp*CoCl}2] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) with LiBH4⋅thf at −78 °C, followed by room‐temperature reaction with three equivalents of [Mn2(CO)10] yielded a manganese hexahydridodiborate compound [{(OC)4Mn}(η6‐B2H6){Mn(CO)3}2(μ‐H)] (1) and a triply bridged borylene complex [(μ3‐BH)(Cp*Co)2(μ‐CO)(μ‐H)2MnH(CO)3] (2). In a similar fashion, [Re2(CO)10] generated [(μ3‐BH)(Cp*Co)2(μ‐CO)(μ‐H)2ReH(CO)3] (3) and [(μ3‐BH)(Cp*Co)2(μ‐CO)2(μ‐H)Co(CO)3] (4) in modest yields. In contrast, [Ru3(CO)12] under similar reaction conditions yielded a heterometallic semi‐interstitial boride cluster [(Cp*Co)(μ‐H)3Ru3(CO)9B] (5). The solid‐state X‐ray structure of compound 1 shows a significantly shorter boron–boron bond length. The detailed spectroscopic data of 1 and the unusual structural and bonding features have been described. All the complexes have been characterized by using 1H, 11B, 13C NMR spectroscopy, mass spectrometry, and X‐ray diffraction analysis. The DFT computations were used to shed light on the bonding and electronic structures of these new compounds. The study reveals a dominant BHMn, a weak BBMn interaction, and an enhanced BB bonding in 1. Building bridges: The synthesis and full characterization of a new manganaborane containing a diborane(6) dianion ligand has been described. In addition, the synthesis and characterization of new hetero‐ and homotrinuclear triply bridged borylene complexes from the reaction of a cobalt intermediate with metal carbonyls ({M2(CO)10}, (M=Mn, Re); see figure) is also reported. DFT computations were used to shed light into the bonding and electronic structures of these new compounds.