Theoretical Elucidation of the Platinum-Mediated Arene C-H Activation Reactions
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- 作者：Ji-Lai Li ; Cai-Yun Geng ; Xu-Ri Huang ; Xiang Zhang ; Chia-Chung Sun
- 刊名：Organometallics
- 出版年：2007
- 出版时间：April 23, 2007
- 年：2007
- 卷：26
- 期：9
- 页码：2203 - 2210
- 全文大小：477K
- 年卷期：v.26,no.9(April 23, 2007)
- ISSN：1520-6041
文摘
The complete reaction mechanism of the platinum-mediated arene [(N-N)PtPh2 (N-N = diimineArN=CMe-CMe=NAr 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 
-bond metathesis mechanisms (including direct -bond metathesis and indirect -bond metathesis)are considered. The indirect -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 -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 -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.
-bond metathesis mechanisms (including direct -bond metathesis and indirect -bond metathesis)are considered. The indirect -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 -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 -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.