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] [Pt^IV₂Me₈ (μ-SMe₂)₂] + 2 Me₂S ^kf⇌_kd 2 [Pt^IVMe₄(SMe₂)₂] [2] [Pt^II₂Me₄ (μ-SMe₂)₂] + 2 Me₂S ^kf→ 2 [Pt^IIMe₂(SMe₂)₂] and [3] [Pt^IV₂Me₈ (μ-SMe₂)₂] + 2NN → 2 [Pt^IVMe₄(NN)] + 2 Me₂S where NN = bipy or 4,4′-Me₂-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: [Pt^IV₂Me₈(μ-SMe₂)₂] + 2 Me₂S ⇌ 2 [Pt^IVMe₄(SMe₂)₂] and [Pt^IVMe₄(SMe₂)₂] + NN → [Pt^IVMe₄(NN)] + 2 Me₂S The rate constants and activation parameters for the reactions areas follows: k_f= 3.16 ± 0.06 M^-1 s^-1 (25°C), ΔH^≠_f = 51.8 ± 1.7 kJ mol^-1, ΔS^≠_f = -61.0 ± 5.8 J mol^-1 K^-1, k_d= 1.18 ± 0.22 M^-1 s^-1 (25°C), ΔH^≠_d = 65 ± 22 kJ mol^-1, ΔS^≠_d = -26 ± 73 J mol^-1 K^-1 for reaction [1] in n-hexane; k_f = 6.68 ± 0.06 M_-1 s^-1 (25°C), ΔH^≠_f = 58.0 ± 3.1 kJ mol^-1, ΔS^≠_f = -34.5 ± 10.5 J mol^-1 K^-1, ΔV^≠_f = -10.7 ± 1.3 cm³ mol^-1 for reaction [2] in dichloromethane; k₂= (7.09 ± 1.89) × 10^-4 M^-1 s^-1, ΔH^≠₂ = 95 ± 21 kJ mol^-1, and ΔS^≠₂ = 18 ± 70 J mol^-1 K^-1, ΔV^≠₂ = 9 ± 9 cm³ mol^-1 for reaction [3] with bipy, and k_l = (1.10 ± 0.10) × 10^-2 s^-1, k₃/k^-1 = (4.33 ± 0.30) × 10^-2, and k₂= (6.09 ± 1.35) × 10^-4 M^-1 s^-1 for reaction [3] with 4,4′-Me₂-bipy. It was shown that reactions [1] and [2] proceed nucleophilically without any intermediates, and reaction [3] proceeds through a mainly k₂ path for NN = bipy and through both k₁ and k₂ paths for NN = 4,4′-Me₂-bipy, without appreciable participation of the direct reaction between the dimer and NN as shown by the following reaction scheme.