421 Journal of Organometallic Chemistry, 414 (1991) 421-431 Elsevier Sequoia S.A., Lausanne JOM 21935 Chemistry of platinum( IV), platinum( II) and palladium( II) cyclometallates of benzylthio- or benzosulphinyl-substituted azobenzenes Surajit Chattopadhyay, Chittaranjan Sinha, Partha Basu and Animesh Chakravorty * Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032 (India) (Received February 21st, 1991) Abstract Cydometallated platinum(IV) complexes of the type [Pt(RL)CI 3 ) incorporating azobenzene (R = H) or 4-methylazobenzene (R = Me) with an SCH 2 Ph (L = Ll) or an S(O)CH 2 Ph (L = L2) substituent in an ortho position are described. These were obtained by oxidative addition of chlorine to [PtII(RL)Cl). Analogous palladium(I1) complexes, however, gave chloro-substituted azobenzenes upon reaction with chlorine. The platinum(IV) complexes show an irreversible cyclic voltammetric metal reduction peak near - 0.3 V vs SCE. Constant potential coulometric reduction at - 0.5 V or chemical reduction by hydrazine hydrate regenerated [PtII(RL)Cl). The structures of [Pt(HL 1 )CI 3 ), [Pt(Mee)Cl) and [Pd(MeLl)Cl) have been determined by an X-ray diffraction study. The S(O)CH 2 Ph group is coordinated via the sulphur atom. Introduction The platinum(II)-azobenzene system provided the first example of ortho-metalla- tion [1] but the corresponding platinum(IV) organometallics have not been char- acterised. Indeed, there are few authentic o-metallated platinum(IV) species of any type [2-10]. We report here the chemistry of several platinum(IV) azobenzene cyclometallates of the coordination type Pt(C,N,s)Cl 3 , along with their platinum(II) analogues of the type Pt(C,N,S)Cl. A PdlI(C,N,S)CI species is also discussed. Results and discussion Synthesis In the ortho-metallation reaction the azobenzene ligand is known to chelate platinum(II) in the bidentate (C,N) fashion [1]. The presence of a suitably posi- tioned donor substituent has been found to be very effective in giving rise to stable platinum(IV) cyclometallates, the azobenzene ligand becoming potentially triden- 0022-328X/91/$03.50 © 1991 - Elsevier Sequoia S.A.