Study of the Square Planar Methylpalladium (II) Complexes Bearing Unsymmetrical α-Aminoaldimine Bidentate Ligands of Hetero Functionalities: Synthesis, Geometrical Isomerism and Reactivity
Date Issued
2009
Date
2009
Author(s)
Wang, Yu-Heng
Abstract
A series of unsymmetrical bidentate ligands of α-aminoaldimines in the form of R1R2NCMe2CH=NR (R1, R2 = Me, Et, c-C4H8 or R1 = iPr, tBu, R2 = H; R = Me, Et, iPr, tBu) have been synthesized using condensation of 2,2-aminoethylpropanal with such ligands can replace COD in (COD)PdMeCl to give neutral methylchloropalladium complexes contain geometrical isomers with square planar configuration, and cis-trans isomerism was observed in solutions. However, it is interested that crystallographic analysis gives only single form crystal. Which geometrical isomers could be available depending on the relative stability in solution. The equilibrium constant of the isomerization may be fine-tuned in terms of the variation of the ligand substituents. Kinetic and mechanistic studies for the substitution and isomerization reactions are investigated by varied temperature 1H NMR. The rate constant of isomerization is 6.97 × 10-5 s-1 at -10℃, 5.29 × 10-4 s-1 at 0℃, and 3.49 × 10-3 s-1 at 10℃, and the activation energy is 120 kJ/mol. The geometrical isomerization is proposed to proceed via an imine dissociation and re-coordination. The CO- and CNR- inserted products of [R1R2NCMe2CH=NR]PdMeCl also contain geometrical isomers, and the reactivity is differentiated toward DMAD. Here we report the variation in insertion rate constant and proposed mechanism between cis and trans form.
Subjects
unsymmetrical bidentate ligand
methylpalladium
geometrical isomer
crystallographic analysis
CO, DMAD Insertion
Type
thesis
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