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 LiBH 4 ⋅ thf at −78 °C, followed by room‐temperature reaction with three equivalents of [Mn 2 (CO) 10 ] yielded a manganese hexahydridodiborate compound [{(OC) 4 Mn}(η 6 ‐B 2 H 6 ){Mn(CO) 3 } 2 (μ‐H)] ( 1 ) and a triply bridged borylene complex [(μ 3 ‐BH)(Cp*Co) 2 (μ‐CO)(μ‐H) 2 MnH(CO) 3 ] ( 2 ). In a similar fashion, [Re 2 (CO) 10 ] generated [(μ 3 ‐BH)(Cp*Co) 2 (μ‐CO)(μ‐H) 2 ReH(CO) 3 ] ( 3 ) and [(μ 3 ‐BH)(Cp*Co) 2 (μ‐CO) 2 (μ‐H)Co(CO) 3 ] ( 4 ) in modest yields. In contrast, [Ru 3 (CO) 12 ] under similar reaction conditions yielded a heterometallic semi‐interstitial boride cluster [(Cp*Co)(μ‐H) 3 Ru 3 (CO) 9 B] ( 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 1 H, 11 B, 13 C 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 BHMn, a weak BBMn interaction, and an enhanced BB bonding in 1 .