Subtle Ligand/Media Effects. Modulation of cis/trans Isomerism in Hydrogen Peroxide Oxidation of Pt(II) to Pt(IV) Complexes

The modulation of cis/trans isomerism on the oxidation of PtII to PtIV via subtle ligand/media effects has been established. The reaction of [PtII(O-O)(dpda)] (O-O = 1,1-cyclobutanedicarboxylate (cbdc), dibenzylmalonate (dbm); dpda = 2,2-dimethyl-1,3-propanediamine) with hydrogen peroxide in acetic acid produces cis-[PtIV (O2CCH3)2(O-O)(dpda)], while the reaction in acetic anhydride gives trans-[PtIV(O2CCH3)2(O-O)(dpda)]. The crystal structures of cis-[PtIV(O2CCH3)2(cbdc) (dpda)] (orthorhombic Pbca, a = 11.148(2) A, b = 14.188(5) A, c = 23.425(3) A, V = 3705(2) A3, Z = 8, R = 0.0525) and trans-[PtIV(O2CCH3)2(cbdc)(dpda)]· 3H2O (monoclinic P21/c, a = 11.479(2) A, b = 13.426(3) A, c = 14.640(5) A, (beta) = 108.73(2)°, V = 2136.8(9) A^3, Z = 4, R = 0.0251) have been solved and refined. The AcO-Pt-AcO angle (87.4(5)°) of the cis isomer presents a striking contrast to that (172.5(1)°) of the trans isomer. The trans isomer is retained in aqueous solution, but the cis isomer is very slowly converted to the trans isomer in both water and acetic acid.