A Theoretical Study on Pd II Complexes Containing Hemilabile Pyrazole‐Derived Ligands

The properties of Pd II complexes containing hemilabile pyrazole‐derived ligands (L) of the form BPz‐(CH 2 ) x A(CH 2 ) y A(CH 2 ) x ‐PzB, with A being a donor atom and B a substituent group at the pyrazole ring, have been investigated through quantum‐chemical calculations. The geometries of the [PdLCl 2 ] and [PdL] 2+ complexes have been optimized and the reaction free energy of [PdLCl 2 ] → [PdL] 2+ + 2 Cl – computed for 32 different ligands, using the hybrid B3LYP density functional method. The formation of the tetracoordinate [PdL] 2+ complexes is more favorable for the longer (eight‐ and nine‐membered) chains than for the shorter (six‐ and seven‐membered) ones. Moreover, results show the nature of the donor atom A influences significantly the formation of [PdL] 2+ , the process becoming more favorable according to the order PH > NH > S > O. Finally, electron‐donor substituents at the pyrazole ring enhance the formation of [PdL] 2+ , whereas electron‐acceptor groups hinder the process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)