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 [Pt(II)Cl(3)X](n-) complexes as well as the mutual trans influence of two X and Y ligands (E(XY)) in [Pt(II)Cl(2)XY](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 [Pd(II)Cl(2)XY](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 [M(II)X(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 [M(II)Cl(3)X](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 rho(r) at the bond critical point of M-Cl bond trans to the X in [M(II)Cl(3)X](n-) and this allows us to express the BDE(X(Pd)) and BDE(X(Pt)) in terms of only the rho(r) and D(X). We have demonstrated that using a database comprising of D(X) and the rho(r), the bond dissociation energy of X in complexes of the type [M(II)X(Y)X'(Y')] can be predicted.