Mechanistic insight into protonolysis and cis-trans isomerization of benzylplatinum(II) complexes assisted by weak ligand-to-metal interactions. A combined kinetic and DFT study.

Low-temperature NMR measurements showed that protonolysis and deuterolysis by H(D)X acids on meta- and para-substituted dibenzylplatinum(II) complexes cis-[Pt(CH2Ar)2(PEt3)2] (Ar = C6H4Y−; Y = 4-Me, 1a; 3-Me, 1b; H, 1c; 4-F, 1d; 3-F, 1e; 4-Cl, 1f; 3-Cl, 1g; 3-CF3, 1h) in CD3OD leads directly to the formation of trans-[Pt(CH2Ar)(PEt3)2(CD3OD)]X (4a−4h) and toluene derivatives. The reaction obeys the rate law kobsd = kH[H+]. For CH2Ar = CH2C6H5−, kH = 176 ± 3 M−1 s−1 and kD = 185 ± 5 M−1 s−1 at 298.2 K, ΔH⧧ = 46 ± 1 kJ mol−1 and ΔS⧧ = −47 ± 1 J K−1 mol−1. In contrast, in acetonitrile-d3, three subsequent stages can be distinguished, at different temperature ranges: (i) instantaneous formation of new benzylhydridoplatinum(IV) complexes cis-[Pt(CH2Ar)2(H)(CD3CN)(PEt3)2]X (2a−2h, at 230 K), (ii) reductive elimination of 2a−2h to yield cis-[Pt(CH2Ar)(CD3CN)(PEt3)2]X (3a−3h) and toluene derivatives (in the range 230−255 K), and finally (iii) spontaneous isomerization of the cis cationic solvento species to the c...