The prevalence of isocloso deltahedra in low-energy hypoelectronic metalladicarbaboranes with a single metal vertex: manganese and rhenium derivatives

Abstract

Theoretical studies on the hypoelectronic metalladicarbaboranes CpMC₂B_n−3H_n−1 (M = Mn, Re; n = 9, 10, 11) having 2n skeletal electrons indicate that true isocloso MC₂B_n−3 deltahedra are highly energetically favored in which the metal atom occupies the single degree 6 vertex. This contrasts with the previously studied isoelectronic diferradicarbaboranes Cp₂Fe₂C₂B_n−3H_n−1 for which the isocloso structure is clearly favored only for the 10-vertex system. For the 12-vertex hypoelectronic manganadicarbaborane CpMnC₂B₉H₁₁ with 2n (= 24) skeletal electrons the lowest energy structures have central MnC₂B₉ icosahedra. However, for the corresponding rhenadicarbaborane CpReC₂B₉H₁₁ the lowest energy structures have central non-icosahedral ReC₂B₉ deltahedra with two degree 6 vertices, one of which is occupied by the rhenium atom. The low-energy structures for the metalladicarbaboranes studied in this work relate to the preferences of transition metal atoms for degree 6 vertices but those of boron and carbon for degree 5 and 4 vertices, respectively.