First-row transition-metal-diborane and -borylene complexes

Abstract

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[BOND]H[BOND]Mn, a weak B[BOND]B[BOND]Mn interaction, and an enhanced B[BOND]B bonding in 1.