Topological Aspects of the Skeletal Bonding in “Isocloso” Metallaboranes Containing “Anomalous” Numbers of Skeletal Electrons

Abstract

Removal of the transition metal vertex from an "isocloso" metallaborane having 9, 10, or 11 vertices and 2nu skeletal electrons leads to a B(n)()H(n)()(2)(-) ligand or isoelectronic derivative thereof having one open hexagonal face for hexahapto bonding to the transition metal and 2nu - 7 triangular faces. The numbers of available skeletal electrons and orbitals in such isocloso metallaboranes correspond to nu 2-electron 3-center bonds in nu of the 2nu - 4 faces of the original metallaborane deltahedron. This contrasts with the 2-electron nu-center core bond and the nu surface bonds in the closo metal-free B(n)()H(n)()(2)(-) and C(2)B(n)()(-)(2)H(n)() deltahedra with 2nu + 2 skeletal electrons. A diamond-square process removing an M-B edge from an isocloso metallaborane to give an "isonido" metallaborane converts a set of six skeletal orbitals from two 2-electron 3-center bonds into three 2-electron 2-center bonds.