A DFT and crystallographic reinvestigation of the [L 2RuC 2B 7H 9] and [L 3RuC 2B 7H 9] ‘ hypercloso’ and closo systems

Abstract

A reinvestigation of the [L 2RuC 2B 7H 9] ‘ hypercloso’ 10-vertex cluster compounds, where L = PPh 3, PEt 3, which were first reported some 30 years ago, has been carried out. At that time no single-crystal X-ray diffraction structural analysis was obtained for the compounds and their description as featuring a ‘ hypercloso’ cluster constitution, where the descriptor hypercloso is defined as being a closed polyhedral structure possessing n skeletal bonding electron pairs, where n is the number of vertices, was largely based on a combination of chemical and NMR spectroscopic evidence, together with the application of Polyhedral Skeletal Electron Pair Theory as it was then understood. Reported here is a single-crystal X-ray diffraction study of the PPh 3 ligated ruthenacarborane allied with density functional calculations (DFT). The cluster structure is shown to be of isocloso geometry, albeit with considerable distortion towards isonido. Addition of excess PMe 3 leads to the formation of an [(PMe 3) 3RuC 2B 7H 9] species of conventional 10-vertex closo geometry but it undergoes a cluster rearrangement, resulting in a different isomer to that originally proposed.