| Abstract
| - The complete reaction mechanism of the platinum-mediated arene [(N−N)PtPh2 (N−N = diimine ArNCMe−CMeNAr with Ar = 2,6-Me2C6H3)] C−H activation has been investigated by using the B3LYP density functional theory method. The calculations show that the protonation should occur at the metal center, giving a coordinately unsaturated five-coordinate Pt(IV) hydride which is trapped by acetonitrile; otherwise monophenyl solvento cations (N−N)Pt(Ph)(NCMe)+ should be isolated and characterized spectroscopically.
- The complete reaction mechanism of the platinum-mediated arene [(N−N)PtPh2 (N−N = diimineArNCMe−CMeNAr with Ar = 2,6-Me2C6H3)] C−H activation has been investigated by using theB3LYP density functional theory method. The calculations show that the protonation should occur at themetal center, giving a coordinately unsaturated five-coordinate Pt(IV) hydride which is trapped byacetonitrile; otherwise monophenyl solvento cations (N−N)Pt(Ph)(NCMe)+ should be isolated andcharacterized spectroscopically. Of the H exchange process, oxidative addition−reductive eliminationand σ-bond metathesis mechanisms (including direct σ-bond metathesis and indirect σ-bond metathesis)are considered. The indirect σ-bond metathesis, which goes through a two-step H migration, is dramaticallyhigher in energy than that of the direct one, so we can safely rule it out. The barrier associated withdirect σ-bond metathesis is 14.70 kcal/mol, to be compared with 20.56 kcal/mol found in oxidative addition.So, unlike the methane C−H activation, the direct σ-bond metathesis pathway is predicted to take placepredominantly. Furthermore, the solvent-induced associative elimination of benzene is also confirmedby the current theoretical studies for the first time. The trigonal bipyramidal transition states offer substantialevidence for this process, and the principle of microscopic reversibility then implies that benzenecoordination will also be a solvent-assisted, associative process for a C−H activation reaction. For thedifferent rates of benzene elimination, our calculations show that nucleophiles with higher electron-donating abilities and small steric effects of the diimine ligands will favor elimination greatly.
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