The cis effect of phosphines and phosphites in the reactions of chloro(1,2-diaminoethane)phosphine- and chloro(1,2-diaminoethane) trimethyl phosphite-platinum(II) cations with nucleophiles

Abstract

The kinetics of the replacement of Cl from [Pt(PR₃)(en)Cl]⁺(R = Me, Et, Buⁿ, or OCH₃; en = 1,2-diaminoethane) by a range of nucleophiles (H₂O, Br^–, N₃^–, I^–, or SCN^–) have been studied in water at 26.5 °C. Good linear relationships are observed between log k₂⁰(k₂⁰ is the nucleophile dependent second-order rate constant, extrapolated to I= 0 mol dm^–3) and the index of nucleophilicity, relative to the standard +1 cationic substrate, [Pt(NH₃)(en)Cl]⁺. The nucleophilic discrimination is similar to that of the dimethyl sulphoxide complex but the absolute rates are sensitive to steric hindrance from the cis ligand (the reactivity decreases along the sequence PMe₃ > PEt₃ PBuⁿ₃). The phosphorus in the P(OMe)₃ complex is also subject to nucleophilic attack and unambiguous kinetics could only be obtained in the reactions with Br^– and I^–.