Monohaloboryls (BHX−) as Bridging Ligands: Observable Dinuclear σ-(Halo)boranyl Intermediates in the Synthesis of Metalloborylenes

Abstract

Upon treating transition-metal–dihaloboryl complexes of the form [L_nMBX₂] with K[(η⁵-C₅H₅)MnH(CO)₂], salt elimination occurs along with a migration of the Mn-bound hydride ligand onto the boron atom, thereby forming dinuclear σ-(halo)boranyl complexes of the form [L_nM(μ-BHX)Mn(CO)₂(η⁵-C₅H₅)]. Most of these complexes react further at room temperature to lose HX and provide metalloborylene complexes [L_nM-B=Mn(CO)₂(η⁵-C₅H₅)]; however, when ML_n=Re(CO)₅ the σ-(halo)boranyl complex decomposes into unidentifiable products. We found through DFT calculations that two electronically and structurally distinct forms of the intermediate σ-(halo)boranyl complexes exist, one of which easily loses HX and one that does not.