www.elsevier.nl/locate/jorganchem Journal of Organometallic Chemistry 599 (2000) 166 – 169 Solvent effects on the rate of oxidative addition of methyl iodide to di(4-thiocresol)(2,2-bipyridyl) platinum(II) Ja’afar K. Jawad a, *, Faisal N.K. Al-Obaidy a , Jasim A. Hammud a , Fathi Al-Azab b a Department of Chemistry, Faculty of Education, Uniersity of Salahaddin, Erbil, Iraq b Department of Chemistry, Faculty of Science, Sana’a Uniersity, Sana’a, Yemen Received 24 November 1998; received in revised form 9 December 1999 Abstract The reaction of methyl iodide with di(4-thiocresol)(2,2-bipyridyl) platinum(II) to give iodo (methyl) di(4-thiocresol)(2,2- bipyridyl) platinum(IV) follows the rate law, rate =K 2 [Pt-(4-thiocresol) 2 (2,2-bipyridyl)] [MeI]. The values of K 2 increase with increasing polarity of the solvent, suggesting a polar transition state for the reaction. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Oxidative addition; Platinum; Solvent effects 1. Introduction It has been shown [1] that the UV–vis spectra of bipyridyl platinum(II) complexes contain two intense metal to ligand charge-transfer (MLCT) bands, whose energies are strongly dependent on the nature of the other ligands bound to platinum and on the solvent. More electronegative substituents on platinum and more polar solvents cause the bands to move to higher energy. The reactivity of alkyl and aryl-(2,2-bipyridyl) plat- inum(II) complexes towards oxidative addition reac- tions can be correlated with the energy of the lowest-energy MLCT band [2], suggesting that it is the energy of the platinum d-orbitals that primarily deter- mines the reactivity [1,3 – 5], and since in such reactions the metal centre acts as a nucleophile [6]. We are looking for this effect by studying the oxidative addi- tion of methyl iodide to the complexes [4X-C 6 H 4 S) 2 Pt(2,2-bipyridyl)] as a function of the substituent X. Thus steric effects due to X should be negligible in these compounds, and it has already been shown [1] that the energy of the first MLCT band (and hence the energy of the platinum d orbitals) correlates well with Hammett -values of X. The ability of the aryl platinum(II) complexes to undergo oxidative addition at all is remarkable since similar complexes stabilized by tertiary phosphine lig- ands do not give stable aryl platinum(IV) complexes [7]. This is probably due to the greater -donor and poorer -acceptor power of 2,2-bipyridyl with respect to ter- tiary phosphines and to its lower steric requirements. The oxidative-addition reactions of methyl iodide to (2,2-bipyridyl) and (1,10-phenanthroline) platinum (II) complexes has been reported [8]. The solvent effects on the rate of oxidative addition of methyl iodide to [PtPh 2 -(bipy)] indicate a polar transition state in the reaction such as is predicted for the S N 2 mechanism [16], provided the platinum atom acts as a nucleophilic centre during the oxidative addition. Bipyridine platinum (II) thiolates have been synthe- sized and characterized [9]. Some transition-metal thio- late complexes have been synthesized recently [10 – 14]. This prompted us to report the solvent effects on the rate of oxidative addition of methyl iodide to di(4- thiocresol) (2,2-bipyridyl) platinum(II). 2. Results Orange solutions of di(4-thiocresol)(2,2-bipyridyl) platinum(II) in common organic solvents turned yellow * Corresponding author. Present address: Ma’een Post Office, PO Box 13220, Sana’a, Yemen. 0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0022-328X(99)00759-7