Donor Properties of a Series of Two-Electron Ligands

A large group of two-electron donor ligands were compared and ranked with the help of DFT calculations. The following characteristics were considered: (a) C≡O stretching frequencies and distances of Ni(CO)3L, IrCl(CO)2L, and IrCp(CO)L, (b) Ir−(η2-C2H4) bond enthalpies, stretching frequencies, and distances of IrCp(η2-H2C═CH2)L, (c) enthalpies of the ligand exchange reactions IrCp(CO)L + IrCpXe(PF3) → IrCp(CO)(PF3) + IrCpXeL and Ir(III)H2CpL + Ir(I)CpXe(PF3) → Ir(III)H2Cp(PF3) + Ir(I)CpXeL, (d) Ir−(η2-H2) bond enthalpies and H−H distances of Os(η2-H2)Cl2(CO)L2. Useful trends and correlations have been established for several common ligand types.