Ligand effects on the stability of the insertion products: A DFT study of oxidative addition of NH3 to iridium(I) complex

The density functional theory (DFT) calculations were used to study the effects of PCP ancillary ligands on the relative stabilities of hydrido amido complexes and ammonia coordination complexes. Calculations on the four compounds 1a, 1b, 2a and 2b containing PCP ligands with t-butyl groups on P atoms showed that 1b is more stable than 1a and 2a is more stable than 2b. Calculations also showed that the relative energies of hydrido amido complexes with respect to the isomeric ammonia coordinated complexes vary with the different substituent groups (R = H, Me and tBu) on the P atoms of the PCP ligands. An alternative method to study the ligand effects introduced by different substituents on the P atoms is to vary the nuclear charge on the P atoms of PCP ligand. The relative energies were predicted to decrease with the nuclear charge of the P atoms on the PCP ligands, which indicates that increasing the electron donating ability tend to favor the hydrido amido complexes over the ammonia coordination complexes: