Preparation of (η-cyclo-octa-1,5-diene)halogenohydridobis(phosphine)-iridium(III) salts and kinetic study of the oxidative-addition reactions of (η-cyclo-octa-1,5-diene)bis(phosphine)iridium(I) salts with hydrohalogenic acids: evidence for anionic intermediates

Abstract

The complexes [IrH(X)(cod)L₂][PF₆][cod = cyclo-octa-1,5-diene, X = Cl, Br, or I, L = PPh₂(OMe) or PMePh₂; X = Cl or Br, L = PEtPh₂] and [IrHX₂(cod)L](X = Br or I, L = PMePh₂ or PEtPh₂) have been synthesised from HX (X = Cl, Br, or I) and the salts [Ir(cod)L₂][PF₆][L = PPh₂(OMe), PMePh₂, or PEtPh₂]. The equilibrium (i)[Ir(cod)L₂]⁺+ Cl^–⇌[IrCl(cod)L]+ L (i) exists due to steric crowding, and explains the presence of the second chloride in the end product. Kinetic studies on both the oxidative-addition reactions of [Ir(cod)L₂]⁺ and [lrCl(cod)L] with HCl have revealed that the nucleophilic attack of Cl^– precedes the protonation of the complexes.