Kinetics and Mechanism of the Reaction of Chloroplatinum(II) Complexes with Alkyl Radicals

Abstract

AbstractThe reaction between certain platinum(II) complexes and alky radicals produces an unstable organoplatinum(III) intermediate, {PtIII ‐R}. The kinetics of this step were evaluated by laser flash photolysis with ABTS2 (2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonate) ion) and TMPD (tetramethylphenylenediamine) as kinetic probes. The rate constants for PtCl42− are: kPt/108 L mol−1 s−1 = 5.2, 2.8 and 0.27 for CH3, C2H5, and CH2Cl in aqueous solution at pH 1. Those with cis‐Pt(NH3)2Cl2 are somewhat smaller, and those for Pt(NH3)42+ too small to measure will) this technique. The product analysis indicates that the decomposition of organoplatinum takes place by hydrolysis and (for R = C2H5 only) by β‐elimination, The kinetic isotope effect on die β‐elimination of DCH2CH2PtC4,2− is kH/kD = 1.2. The β‐elimination step produces a PtIII‐hydride that releases hydrogen gas and forms {PtIII‐OH}. The short‐lived Pt(III) intermediate may disproportionate or oxidize the CoII complex that is produced in the radical‐generating step.