Orbital Interaction and Electron Density Transfer in Pd(II)([9]aneB(2)A)L(2) Complexes: Theoretical Approaches

The geometric structures of Pd-complexes {Pd([9]aneB(2)A)L(2) and Pd([9]aneBAB)L(2) where A = P, S; B = N; L = PH(3), P(CH(3))(3), Cl(−)}, their selective orbital interaction towards equatorial or axial (soft A…Pd) coordination of macrocyclic [9]aneB(2)A tridentate to PdL(2), and electron density transfer from the electron-rich trans L-ligand to the low-lying unfilled a(1g)(5s)-orbital of PdL(2) were investigated using B3P86/lanl2DZ for Pd and 6-311+G** for other atoms. The pentacoordinate endo-[Pd([9]aneB(2)A)(L-donor)(2)](2+) complex with an axial (soft A--Pd) quasi-bond was optimized for stability. The fifth (soft A--Pd) quasi-bond between the σ-donor of soft A and the partially unfilled a(1g)(5s)-orbital of PdL(2) was formed. The pentacoordinate endo-Pd([9]aneB(2)A)(L-donor)(2)](2+) complex has been found to be more stable than the corresponding tetracoordinate endo-Pd complexes. Except for the endo-Pd pentacoordinates, the tetracoordinate Pd([9]aneBAB)L(2) complex with one equatorial (soft A-Pd) bond is found to be more stable than the Pd([9]aneB(2)A)L(2) isomer without the equatorial (A-Pd) bond. In particular, the geometric configuration of endo-[Pd([9]anePNP)(L-donor)(2)](2+) could not be optimized.