932013-22-4Relevant academic research and scientific papers
Mechanistic studies of platinum(II)-catalyzed ethylene dimerization: Determination of barriers to migratory insertion in diimine Pt(II) hydrido ethylene and ethyl ethylene intermediates
Shiotsuki, Masashi,White, Peter S.,Brookhart, Maurice,Templeton, Joseph L.
, p. 4058 - 4067 (2007)
The diimine platinum(II) ethylene hydride complex [(N∧N)Pt(H)(ethylene) ][BAr′4] (1, N∧N = [(2,6-Me2C6H 3)N=C(An)-C(An)=N(2,6-Me2C6H3)], An = 1,8-naphthalenediyl, Ar′ = 3,5-(CF3)2C 6H3) was prepared by protonation of the diethyl complex (N∧N)PtEt2 with [H(OEt2)2] [BAr′4], The energy barrier to interchange of the platinum hydride with the olefinic hydrogens in 1 was determined to be 19.2 kcal/mol by spin saturation transfer experiments. Complex 1 initiates ethylene dimerization; the ethyl ethylene complex (N∧N)Pt(Et)-(ethylene)+ (2) has been identified as the catalyst resting state. Trapping of 1 by ethylene to yield 2 is a second-order process; kinetic studies suggest this occurs via trapping of a reversibly formed β-agostic ethyl complex. Complex 2 has been isolated and characterized by X-ray crystallography. The barrier to migratory insertion of 2, the turnover-limiting step in catalysis, was determined to be 29.8 kcal/mol. The 1-butene hydride complex, (N∧N)Pt(H)(1-butene)+ (3), is a key intermediate in the dimerization cycle and has also been isolated and characterized. Surprisingly rapid rates of degenerate associative exchange of free ethylene with bound ethylene in complexes 1 and 2 as well as the rate of degenerate exchange of free nitrile with bound nitrile in (N∧N)Pt(Et) (CH3CN)+ are reported.
