Orbital interaction and electron density transfer in PdII([9]aneB2A)L2 complexes: theoretical approaches

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Coordination Chemistry

Background:

• Palladium complexes with macrocyclic ligands are crucial in catalysis.
• Understanding ligand coordination modes is key to designing stable complexes.
• Orbital interactions and electron density transfer influence complex stability.

Purpose of the Study:

• To investigate the geometric structures of palladium complexes with macrocyclic ligands.
• To analyze the selective orbital interactions and electron density transfer in these complexes.
• To determine the factors governing the stability of different coordination geometries.

Main Methods:

• Density Functional Theory (DFT) calculations using B3P86/lanl2DZ for Pd and 6-311+G** for other atoms.
• Optimization of pentacoordinate and tetracoordinate palladium complexes.
• Analysis of orbital interactions and electron density transfer.

Main Results:

• Pentacoordinate endo-[Pd([9]aneB2A)(L-donor)2]2+ complexes with an axial (soft A--Pd) quasi-bond are more stable than tetracoordinate analogs.
• A fifth (soft A--Pd) quasi-bond forms between the soft atom and the palladium 5s-orbital.
• Tetracoordinate Pd([9]aneBAB)L2 complexes with an equatorial (soft A-Pd) bond are more stable than isomers lacking this bond.
• The geometric configuration of endo-[Pd([9]anePNP)(L-donor)2]2+ could not be optimized.

Conclusions:

• Pentacoordinate palladium complexes with axial quasi-bonds exhibit enhanced stability.
• The formation of a fifth quasi-bond significantly impacts complex stability.
• Ligand structure and coordination mode (axial vs. equatorial) dictate the relative stability of palladium complexes.