Heterolytic CH Activation with Electron-rich Metal Complexes

4 Heterolytic CH Activation with Electron-rich Metal Complexes 

Heterolytic CH activation (Eq. 3), where X is a heteroatom, is well suited for incorporation into catalytic cycles for the oxy-functionahzation of hydrocarbons and is relatively common with the electrophilic metals Pt(ll), Pd(II), Hg(II), Au(III)/(I) [22], 

However, this type of CH activation is not common with more electron-rich metals [23] and we have been working to develop such systems as they may be less susceptible to the water inhibition that is characteristic of more electrophihc catalytic systems. The complex trons-(acac-0,0)2lr(III)(OH)(py), Ir-OH was synthesized from the methoxo complex (acac-0,0)2lr(III)(0CH3)(CH30H) in quantitative yield by reaction with water at 70 °C, followed by treatment with pyridine [24]. 

Benzene CH activation with Ir-OH was carried out in neat CgHg at 160°C for 10 h and cleanly generates that trons-(acac)2lr(CsH5)(py), Ir-Ph in 71% yield. Typical of other well-defined CH activation reactions [4], reactions with toluene 

Consistent with these results, as shown in Fig. 7.33, the DFT calculations of the CH activation mechanism show that the lowest energy pathway involves pre-equilibrium, dissociative loss of pyridine to generate a trans-5 oordinate intermediate, followed by rate-determining trans-cis isomerization to generate the cis-benzene complex and fast CH bond cleavage by a sigma-bond metathesis transition state. 

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