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

Theoretical studies on the hypoelectronic metalladicarbaboranes CpMC(2)B(n-3)H(n-1) (M = Mn, Re; n = 9, 10, 11) having 2n skeletal electrons indicate that true isocloso MC(2)B(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 Cp(2)Fe(2)C(2)B(n-3)H(n-1) for which the isocloso structure is clearly favored only for the 10-vertex system. For the 12-vertex hypoelectronic manganadicarbaborane CpMnC(2)B(9)H(11) with 2n (= 24) skeletal electrons the lowest energy structures have central MnC(2)B(9) icosahedra. However, for the corresponding rhenadicarbaborane CpReC(2)B(9)H(11) the lowest energy structures have central non-icosahedral ReC(2)B(9) 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.