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The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH3]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy3)2HCl(H2)] (Cy: cyclohexyl) were studied, resulting in bis(σ)‐borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The complexes were studied by multinuclear NMR spectroscopy, mass spectrometry, X‐ray diffraction analysis, and density functional theory (DFT) calculations. The experimental and computational results suggest that the ortho‐substitution of the aryl groups is necessary for the formation of terminal borylene complexes. [ABSTRACT FROM AUTHOR]

A series of bis(σ)‐borane complexes of Group 6 transition metals were prepared by direct dihydroborane coordination to the metal center. Reaction of [M(CO)3(PCy3)2] and two dihydroboranes [DurBH2] and [(Me3Si)2NBH2] (Dur=2,3,5,6‐Me4C6H) yielded bis(σ)‐borane complexes fac‐[M(CO)3(PCy3){η2‐(H2BR)}] (R=Dur; 1: M=Cr, 2: M=W; R=N(SiMe3)2; 3: M=Cr, 4: M=W). In the case of molybdenum, we have isolated an arene complex (5) with [DurBH2] in which the Dur group acts as a η6‐bound ligand, and with [(Me3Si)2NBH2] a similar bis(σ)‐borane complex was isolated, cis,trans‐[Mo(CO)2(PCy3)2{η2‐(H2BN(SiMe3)2}] (6), with a different pattern of auxiliary ligands. The complexes were investigated by multinuclear NMR spectroscopy, mass spectrometry, X‐ray diffraction analysis, and computational methods. Quantum theory of atoms in molecules (QTAIM) calculations demonstrated that the borane complexes may be described as pure bis(σ)‐borane complexes rather than elongated or stretched examples given that the calculations do not show the presence of a ring‐critical point (RCP) at the ring formed by the interactions of the B−H with metal center. [ABSTRACT FROM AUTHOR]