Isomerization reaction of head-to-head alpha-pyridonato-bridged ethylenediaminepalladium(II) binuclear complex, [Pd2(en)2(C5H4NO)2]2+, in aqueous solution.
Head-to-head bis(alpha-pyridonato)-bridged bis(ethylenediamine)dipalladium(ii), HH-[Pd(2)(en)(2)(alpha-pyridonato)(2)](ClO(4))(2), was synthesized and structurally characterized by X-ray crystallography. The (1)H NMR spectra show that the head-to-head (HH) dimer produces the head-to-tail (HT) dimer and monomers ([Pd(en)(alpha-pyridone)(2)](2+), [Pd(en)(H(2)O)(alpha-pyridone)](2+), [Pd(en)(H(2)O)(2)](2+), etc.) in aqueous solution, and the relative amount of dimers to monomers is dependent on the total concentration of the HH dimer dissolved as well as the acidity of the solution. It was found that the formation of the HH and HT dimers from the monomers is fast, and the HT dimer is produced from the HH dimer only via coexisting monomers, i.e., there is no direct isomerization path between the HH and HT dimers. The kinetic analyses for the HH <==>HT isomerization reaction with time-resolved (1)H NMR measurements revealed that the reaction proceeds via first-order kinetics, which was explained based on a relaxation process. The rate determining step for HH <==>HT isomerization is the reaction step between the mono-alpha-pyridone complex and the bis-alpha-pyridone complex, [Pd(en)(H(2)O)(alpha-pyridone)](2+)+alpha-pyridone <==> [Pd(en)(alpha-pyridone)(2)](2+).
Iwatsuki
Satoshi
S
Graduate School of Science and Engineering, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan. s-iwatsuki@aoni.waseda.jp
Itou
Tomohiro
T
Ito
Hideaki
H
Mori
Hiroki
H
Uemura
Kuzuhiro
K
Yokomori
Yushinobu
Y
Ishihara
Koji
K
Matsumoto
Kazuko
K
D018360:Crystallography, X-Ray; D005029:Ethylenediamines / Q000737:chemistry*; D007536:Isomerism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D011728:Pyridones / Q000737:chemistry*
D005029:Ethylenediamines; D009942:Organometallic Compounds; D011728:Pyridones; D010165:Palladium