KINETIC STUDIES OF RING CLOSURES IN PLATINUM(II) CHELATES - RATE CONSTANTS AND ACTIVATION PARAMETERS FOR CHELATION OF PLATINUM(II) BY BIS-(2-AMINOETHYL) SULFIDE IN AQUEOUS-SOLUTION

The complexes [PtCl3(basH2)]+ and [PtCl2(basH)]+ (bas=bis(2-aminoethyl) sulfide) have been prepared, and the kinetics of Pt-bas ring closures have been studied. In basic media the rate constants for closure of the first and second chelate rings are 3.6±0.2 and 0.173±0.005 s-1 (μ=0.4 M, 25 °C), respectively. Corresponding activation parameters are ΔH*=14.2±0.3 kcal/mol and ΔS*=-8.2±0.8 cal/(deg mol) (first ring) and ΔH*=15.7±0.1 kcal/mol and ΔS*=-9.0±0.5 cal/(deg mol) (second ring). The results when compared with data obtained for ring closures in tridentate nitrogen-donor Pt(II) chelates suggest that ring strain is involved in reaching the transition states, with the second closure involving more strain than the first. © 1979, American Chemical Society. All rights reserved.