Polyhedral Iridamonocarbaborane Chemistry. The Isolation and Characterisation of the Nine-Vertex closo-Type Species [(CO)(PPh3)2IrCB7H8] and the Partially Open Structures of Formally closo Nine-Vertex Clusters

Abstract

Reaction of [Ir(CO)Cl(PPh3)2] with the [closo-CB7H8]- anion in dichloromethane solution at room temperature results in oxidative insertion into the cluster to give the novel nine-vertex closo-type species [(CO)(PPh3)2IrCB7H8] in 87% yield as a pale-yellow air-stable solid. Crystals (from hexane-benzene) are orthorhombic, space group P212121, with a = 1056.7(1), b = 1597.6(2), c = 2150.5(2) pm, and Z = 4. The crystal and molecular structure was refined to R (Rw) = 0.0244 (0.0250) for 3338 observed reflections with F0 > 4.0σ(F0). The cluster structure is based on a tricapped trigonal prismatic arrangement of the {IrCB7} atoms, with the iridium atom at a five-connected cluster-vertex position, and the carbon at a non-adjacent four-connected capping site. In this formally closo cluster, the distance between the two boron atoms that are bound to both iridium and carbon atoms is markedly long at 219.0(14) pm, an instance of a generally unrecognized phenomenon which is briefly discussed in the context of the other partially opened, though formally closo, nine-, ten- and eleven-vertex boron-containing cluster compounds.