The Coordination of Benzene in Clusters: The Face-Capping Mode

Abstract The use of discrete metal cluster complexes as models of chemisorption systems in surface chemistry is an attractive hypothesis and has been emphasised by numerous workers in recent years. In this paper we shall examine possible boundary conditions to such a cluster-surface analogy, drawing extensively on the interfacial chemistry of benzene. The motivation for this work is provided by the molecular chemistry of a new class of arene clusters in which the arene molecule is bonded to an M3 triangulo-face within the cluster. The parent compounds in these studies, [M3(CO)9(μ3:η2:η2:η2-C6H6)] (M = Ru or Os), contain benzene in this important new face-capping bonding mode that accurately models benzene adsorption at a threefold site on the surface of a close-packed metal lattice. X-ray diffraction studies combined with NMR (1H and13C) and infrared spectroscopic studies lead to the conclusion that the benzene is coordinated to the metal triangle and is best viewed as a bond-localised cyclohexa-1,3,5-triene.