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

Abstract

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 = PH3, P(CH3)(3), Cl-}, their selective orbital interaction towards equatorial or axial (soft A. Pd)coordination of macrocyclic [9]aneB(2)A tridentate to PdL2, and electron density transfer from the electron-rich trans L-ligand to the low-lying unfilled a(1g)(5s)-orbital of PdL2 were investigated using B3P86/lanL(2)DZ 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 sigma-donor of soft A and the partially unfilled a1g(5s)-orbital of PdL2 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.