Journal of Organometallic Chemistry, 467 (1994) 165-167 165 Siloxane clusters of higher valence transition metals: redox properties G. Gavioli, M. Borsari, C. Zucchi and G. P6lyi Department of Chemistry, University of Modena, Vii Campi 183, I-41100 Modena (Italy) R. Psaro and R. Ugo Department of Inorganic and Orgarwmetallic Chemistry, University of Milano, via Venezian 21, I-20133 Milan0 (Italy) 0.1. Shchegolikhina and A.A. Zhdanov A.N. Nesmeyarwv Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilova Str., V-334, Moscow 117813 (Russian Federation) (Received June 25, 1993) Abstract Cyclic voltammetric behaviour of polymetallic complexes of hexaphenylcyclohexasiloxane-hexaol with Ni, Mn and dodecaphenyl- cyclododecasiloxane-dodecaol with Cu was studied. The complexes react electrochemically as a unit assembly of the complexed metals. Key words: Siloxane; Manganese; Nickel; Copper; Sodium 1. Introduction The exploration of the true structure and nature of the surface species formed on oxide supports from transition metal complexes is one of the most impor- tant goals in present catalysis research [l]. One of the most efficient methods of exploration of this problem is the preparation of model compounds which, in some cases, could be isolated and structurally characterized. Early examples include silanolate osmium [2] and rhodium 131 complexes. Very recently monometallic and dimetallic [4] as well as polymetallic [5] complexes of oligosiloxane ligands were reported. These com- pounds can be regarded as models of metals on the silica surface. The latter type is of particular interest since these compounds contain assemblies of four to six transition metal atoms in higher oxidation state (e.g. Ni”). Structural studies reveal no direct metal- metal bonding in these complexes. On the contrary it Correspondence to: Professor G. Pblyi. 0022-328X/94/$7.00 SSDI 0022-328X(93)24036-5 would be important to know whether these compounds react as assemblies of individual (independent) metal atoms or collectively as interacting groups, i.e. a novel kind of (higher valence) metal “cluster”. The answer to this question could be important from the viewpoint of catalytic [6], bioinorganic [7] or materials 181 chemistry. 2. Results and discussion Electrochemical study of the redox properties of low valence transition metal clusters has provided useful structural information about the number of skeletal electrons [9] or even about the reactivity of a given fragment of the molecule [lo]. This prompted us to start a systematic electrochemical study of the oligosiloxane complexes, which were obtained by ex- change reaction of sodium phenylsiloxanolate with transition metal chlorides and reported recently by one of our teams [51. The preliminary results of this work are described in the present paper. The oligo-cyclo- siloxane derivatives investigated in the course of this work were sandwich-type complexes of four to six transition metal atoms between two hexaphenyl-cyclo- 0 1994 - Elsevier Sequoia. All rights reserved