Stability of Methyl Platinum Complexes in Water: The Role of pH and Geometry

Several water-soluble platinum(II) complexes containing methyl ligands have been prepared, PtMe 2 L 2 and Pt(Cl)(Me)L 2 (L 2 = two P( m -C 6 H 4 SO 3 Na) 3, TPPTS; ( m -C 6 H 4 SO 3 Na) 2 PCH 2 CH 2 P( m -C 6 H 4 SO 3 Na 2 ), DPPETS; ( m -C 6 H 4 SO 3 Na) 2 PCH 2 CH 2 CH 2 P( m -C 6 H 4 SO 3 Na) 2, DPPPTS; or ( m -C 6 H 4 SO 3 Na) 2 PCH 2 CH 2 CH 2 CH 2 P( m -C 6 H 4 SO 3 Na) 2, DPPBTS), to establish the stability of the platinum methyl bond in aqueous solution. From pH = 3 to 14 there is no reaction other than ligand substitution of H 2 O or OH - for Cl -; there is no CH 3 OH elimination. At lower pH's protonolysis of the Pt−Me bond occurs, producing CH 4 . Dissolving PtMe 2 L 2 into a solution of HCl at pH = 1 rapidly produces PtCl 2 L 2 for the bidentate ligands, but trans -Pt(Cl)(Me)L 2 is observed for the monodentate ligands. trans -PtClMe(TPPTS) 2 undergoes protonolysis very slowly, indicating an important role for geometry in protonolysis reactions. The protonolysis reactions occur stereospecifically but are sometimes accompanied by cis − trans isomerization. The cis or trans thermodynamic preferences, cis -PtCl 2 L 2, cis -PtMe 2 L 2, cis -Pt(OH)(Me)L 2, trans -Pt(Cl)(Me)L 2, and trans -Pt(H 2 O)(Me)L 2 +, are not easily explained.