摘要
A series of hemilabile ligands of α-aminoaldimines and their methylpalladium complexes have been prepared and characterized. Neutral square-planar methylpalladium complexes in the form of [R 1 R 2 NCMe 2 CH=NR]Pd(Me)CI (R=Me, R 1 =R 2 =Me (3a); R=Me, R 1 =R 2 =Et (3b); R=B, R 1 =R 2 =Me (4a); R= n Pr, R 1 =R 2 =Me (5a); R='Pr, R 1 =R 2 =Me (6a); R= i Pr, R 1 =R 2 =Et (6b); R= i Pr, (R 1 , R 2 )=c-C 4 H 8 (6c); R= i Pr, R 1 ='Pr, R 2 =H (6d); R= i Pr, R 1 = t Bu, R 2 =H (6e); R= t Bu, R 1 =R 2 = Me (7a); R= t Bu, R 1 =R 2 =Et (7b); R= t Bu, (R 1 , R 2 )=c-C 4 H 8 (7c); R= t Bu, R 1 = i Pr, R 2 =H (7d); R= t Bu, R 1 = t Bu, R 2 =H (7e); R= Ph, R 1 =R 2 =Me (8a); R=Ph, R 1 =R 2 =Et (8b)) show geometrical isomerism. The relative ratios of trans/cis isomers appear to be predominated by the steric hindrance between the Pd-bound methyl group and imino or amino substituents (R and R 1 and R 2 ). The NMR studies for the substitution reaction of (COD)Pd(Me)CI with Et 2 NCMe 2 CH=N i Pr at -20 °C indicate that c/s-6b is the major kinetic product, which isomerizes to the thermodynamic product in trans form quantitatively above -5 °C. Kinetic results show that the ligand substitution reaction likely undergoes an associative pathway, and the isomerization reaction proceeds via an intramolecular process that comprises imine dissociation and recoordination. © 2009 American Chemical Society.