Theoretical Elucidation of the Platinum-Mediated Arene C−H Activation Reactions

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. Of the H exchange process, oxidative addition−reductive elimination and 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 dramatically higher in energy than that of the direct one, so we can safely rule it out. The barrier associated with direct 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−...