312925-34-1Relevant academic research and scientific papers
Activation volume measurement for C-H activation. Evidence for associative benzene substitution at a platinum(II) center
Procelewska, Joanna,Zahl, Achim,Eldik, Rudi van,Zhong, H. Annita,Labinger, Jay A.,Bercaw, John E.
, p. 2807 - 2810 (2008/10/08)
The reaction of the platinum(II) methyl cation [(N-N)Pt(CH3)(solv)]+ (N-N = ArN=C(Me)C(Me)=NAr, Ar = 2,6-(CH3)2C6H3, solv = H2O (1a) or TFE = CF3CH2OH (1b)) with benzene in TFE/H2O solutions cleanly affords the platinum(II) phenyl cation [(N-N)Pt-(C6H5)(solv)]+ (2). High-pressure kinetic studies were performed to resolve the mechanism for the entrance of benzene into the coordination sphere. The pressure dependence of the overall second-order rate constant for the reaction resulted in ΔV? = -(14.3 ± 0.6) cm3 mol-1. Since the overall second order rate constant k = Keqk2, ΔV? = ΔV°(Keq) + ΔV?(k2). The thermodynamic parameters for the equilibrium constant between 1a and 1b, Keq = [1b][H2O]/[1a][TFE] = 8.4 × 10-4 at 25°C, were found to be ΔH° = 13.6 ± 0.5 kJ mol-1, ΔS° = -10.4 ± 1.4 J K-1 mol-1, and ΔV° = -4.8 ± 0.7 cm3 mol-1. Thus ΔV?(k2) for the activation of benzene by the TFE solvento complex equals -9.5 ± 1.3 cm3 mol-1. This significantly negative activation volume, along with the negative activation entropy for the coordination of benzene, clearly supports the operation of an associative mechanism.
