Bond dissociation energies of ligands in square planar Pd(II) and Pt(II) complexes: An assessment using trans influence

Abstract: DFT calculations using MPWB1K method with COSMO continuum solvation model have been carried out to quantify the trans influence of various X ligands (E X) in [PtIICl3X]n− complexes as well as the mutual trans influence of two X and Y ligands (E XY) in [PtIICl2XY]n− complexes. A quantitative structure energy relationship (QSER) is derived for predicting the E XY using E X and E Y and this relationship showed a strong similarity to a QSER derived for predicting E XY of [PdIICl2XY]n− complexes. Quantification of the contributions of E X and E XY to the bond dissociation energy of the ligand X (BDE X) in complexes of the type [MIIX(Y)X′(Y′)] (M = Pd, Pt) is also achieved. The BDE X of any ligand X in these complexes can be predicted using the equations, viz. BDE X(Pd) = 1.196E X − 0.603E XY − 0.118E X’Y’ + 0.442D X + 15.169 for Pd(II) complexes and BDE X(Pt) = 1.420E X − 0.741E XY − 0.125E X’Y’ + 0.498D X + 13.852 for Pt(II) complexes, where D X corresponds to the bond dissociation energy of X in [MIICl3X]n− complexes. These expressions suggest that the mutual trans influence from X and Y is more dominant than the mutual trans influence from X′ and Y′ and both factors contribute significantly to the weakening of M–X bond. We also obtained a strong linear relationship between E X and the electron density ρ(r) at the bond critical point of M–Cl bond trans to the X in [MIICl3X]n− and this allows us to express the BDE X(Pd) and BDE X(Pt) in terms of only the ρ(r) and D X. We have demonstrated that using a database comprising of D X and the ρ(r), the bond dissociation energy of X in complexes of the type [MIIX(Y)X′(Y′)] can be predicted. [Copyright &y& Elsevier]