Mechanisms of Thermal Decomposition of Diethylbis( triethy lphosphine )platinum( II)

The mechanism of thermal decomposition of diethylbis(triethylphosphine)platinum(II) (L₂PtEt₂) to ethylenebis(triethylphosphine)platinum(0) and ethane in cyclohexane depends on the concentration [L] of triethylphosphine added to the solution When [L] ≃ 0 M, the overall rate-limiting step in the decomposition is dissociation of triethylphosphine from L₂PtEt₂; when [L] ≃ 0.3 M, the rate-limiting step is reductive elimination of ethane from an intermediate, ethylene(triethylphosphine)hydridoethylplatinum(II); when [L] ≥ 1.6 M, the most probable mechanism involves rate-limiting reductive elimination of ethane from ethylhydridobis(triethylphosphine)(ethylene)platinum(II). The deuterium kinetic isotope effect for reductive elimination of ethane from L(ethylene)Pt(H,D)Et is k_H/k_D ≃ 3.3 Activation parameters for each reaction indicate that entropy terms (especially of dissociation and reductive elimination of ligands from platinum) play an important role in determining which process is most rapid.