A kinetic study of the reactions of dimethyl sulfide bridged tetramethylplatinum(II) and octamethylplatinum(IV) complexes with dimethyl sulfide and bidentate ligands

Kinetics for the reactions of [1] [(Pt2Me8)-Me-IV (mu-SMe2)(2)] + 2 Me2S reversible arrow(kd)(kf) 2 [(PtMe4)-Me-IV(SMe2)(2)] [2] [(Pt2Me4)-Me-II (mu-SMe2)(2)] + 2 Me2S -->(kf) 2 [(PtMe2)-Me-II(SMe2)(2)] and [3] [(Pt2Me8)-Me-IV (mu-SMe2)(2)] + 2NN --> 2 [(PtMe4)-Me-IV(NN)] + 2 Me2S where NN = bipy or 4,4'-Me-2-bipy, have been studied at various temperatures and pressures. Reaction [3] was shown to consist of the rapid conversion of the dimer to a monomer and the much slower subsequent substitution of the dimethyl sulfide with bidentate ligand NN: [(Pt2Me8)-Me-IV(mu-SMe2)(2)] + 2 Me2S reversible arrow 2 [(PtMe4)-Me-IV(SMe2)(2)] and [(PtMe4)-Me-IV(SMe2)(2)] + NN --> [(PtMe4)-Me-IV(NN)] + 2 Me2S The rate constants and activation parameters for the reactions are as follows: k(f) = 3.16 +/- 0.06 M-1 s(-1) (25 degrees C), Delta H-f double dagger = 51.8 +/- 1.7 kJ mol(-1), Delta S-f double dagger= -61.0 +/- 5.8 J mol(-1) K-1, k(d) = 1.18 +/- 0.22 M-1 s(-1) (25 degrees C), Delta H-d double dagger = 65 +/- 22 kJ mol(-1), Delta S-d double dagger = -26 +/- 73 J mol(-1) K-1 for reaction [1] in n-hexane; k(f) = 6.68 +/- 0.06 M-1 s(-1) (25 degrees C), Delta H-f double dagger = 58.0 +/- 3.1 kJ mol(-1), Delta S-f double dagger = -34.5 +/- 10.5 J mol(-1) K-1, Delta V-f double dagger = -10.7 +/- 1.3 cm(3) mol(-1) for reaction [2] in dichloromethane; k(2) = (7.09 +/- 1.89) x 10(-4) M-1 s(-1), Delta H-2 double dagger = 95 +/- 21 kJ mol(-1), and Delta S-2 double dagger= 18 +/- 70 J mol(-1) K-1, Delta V-2 double dagger = 9 +/- 9 cm(3) mol(-1) for reaction [3] with bipy, and k(1) = (1.10 +/- 0.10) x 10(-2) s(-1), k(3)/k(-1) = (4.33 +/- 0.30) x 10(-2), and k(2) = (6.09 +/- 1.35) x 10(-4) M-1 s(-1) for reaction [3] with 4,4'-Me-2-bipy. It was shown that reactions [1] and [2] proceed nucleophilically without any intermediates, and reaction [3] proceeds through a mainly k(2) path for NN = bipy and through both k(1) and k(2) paths for NN = 4,4'-Me-2-bipy, without appreciable participation of the direct reaction between the dimer and NN as shown by the following reaction scheme.