QM evaluation of the intramolecular aromatic & pi;-& pi; interactions of Ir(I) complex transition states

Major p-p interactions within Ir(I) complex Cp*Ir(I)PPh3 were quantum mechanically characterized using the major hybrid DFT, MP2 and CCSD(T) methods. Almost all the neighborhood p-p interactions are found to be slightly repulsive, and MP2 interaction energies range from -0.49 to 19.16 kcal/mol. The representative A-B p-p pair (See Figure 2) is further addressed using DFT methods. Interaction energies of the A-B p-p pair calculated from 6 hybrid DFT methods ranges from 0.52 kcal/mol by the SVWN method to 8.23 kcal/mol by the O3LYP method. The interaction energies calculated with unrestricted open shell MP2 theory can be up to 25% higher than those computed using restricted open shell MP2 method. Comparison between the DFT results and the benchmark CCSD(T) results shows that the DFT calculations of p-p interaction are reasonable but still need to be interpreted with caution. This study helps to pinpoint intramolecular aromatic p-p interactions of transition state for alkyl C-H bond activation of saturated hydrocarbons and rational molecular design.