SOLVOLYSIS OF PLATINUM COMPLEXES WITH SUBSTITUTED ETHYLENEDIAMINES IN DIMETHYL-SULFOXIDE

The solvolysis of platinum complexes with substituted ethylenediamines, [PtCl2(L)] (L = 1, 4-diazabutane (dab) (1), 2-Me-dab (2), 2,3-Me2-dab (3), 2,3-[μ-(CH2)4]-dab (4), 1,4-Me2-dab (5), 1,4-(i-Pr)2-dab (6), and 1,4-(r-Bu)2-dab (7)), in DMSO has been investigated by 195Pt NMR and UV-vis spectroscopy. A chloride ion is displaced by DMSO in all cases with the exception of 7. The rate of chloride substitution in compounds 1–6 decreases with increasing number and bulk of substituents in the ligand chain; the effect is more marked when the substituents are on the coordinated nitrogen atoms rather than on the adjacent carbon atoms. In the case of compounds 3–6 having a disubstituted dab ligand, the rate of solvolysis is greater when both substituents are on one side of the coordination plane (cis configuration) than on opposite sides (trans configuration). In the solvato species, the configuration at nitrogen is not as stable as it was in the dichloro complexes because of the trans-labilizing effect of the DMSO ligand. Complex 7, unlike all the others, reacts with DMSO, displacing one end of the diamine rather than a chloride ion. At room temperature, the monodentate diamine undergoes a fast head-to-tail rearrangement that makes the t-Bu groups equivalent on the NMR time scale (ΔG* = 52 kJ mol−1). The different behavior of complexes 6 and 7 (containing respectively i-Pr and t-Bu substituents) is a consequence of the steric interaction, between the nitrogen substituents and the Cl ligands, which is far greater in the case of t-Bu than it is in the case of i-Pr. © 1990, American Chemical Society. All rights reserved.