Orbital Interaction and Electron Density Transfer in PdII([9]aneB2A)L2 Complexes: Theoretical Approaches

The geometric structures of Pd-complexes {Pd([9]ane B 2 A) L 2 and Pd([9]ane BAB) 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]ane B 2 A tridentate to Pd L 2, and electron density transfer from the electron-rich trans L-ligand to the low-lying unfilled a 1g(5s)-orbital of Pd L 2 were investigated using B3P86/lanl2DZ for Pd and 6-311+G** for other atoms. The pentacoordinate endo-[Pd([9]ane B 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 Pd L 2 was formed. The pentacoordinate endo-Pd([9]ane B 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]ane BAB) L 2 complex with one equatorial (soft A-Pd) bond is found to be more stable than the Pd([9]ane B 2 A) L 2 isomer without the equatorial ( A-Pd) bond. In particular, the geometric configuration of endo-[Pd([9]ane PNP)( L-donor) 2] 2+ could not be optimized.