A series of hemilabile ligands of alpha-aminoaldimines and their methylpalladium complexes have been prepared and characterized. Neutral square-planar methylpalladium complexes in the form of [(RRNCMe2CH)-R-1-N-2=NR]Pd(Me)Cl (R=Me, R-1=R-2=Me (3a); R=Me, R-1=R-2 =Et (3b); R=Et, R-1=R-2=Me (4a); R=Pr-n, R-1=R-2=Me (5a); R=Pr-i, R-1=R-2=Me (6a); R=Pr-i, R-1=R-2 =Et (6b); R=Pr-i, (R-1,R-2)=c-C4H8 (6c); R=Pr-i, R-1=Pr-i, R-2 =H (6d); R=Pr-i, R-1=Bu-t, R-2=H (6e); R=Bu-t, R-1=R-2=Me (7a); R=Bu-t, R-1=R-2=Et (7b); R=Bu-t, (R-1, R-2)=c-C4H8 (7c); R=Bu-t, R-1=Pr-i, R-2 =H (7d); R=Bu-t, R-1=Bu-t, 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)Cl with Et2NCMe2CH=(NPr)-Pr-I at -20 degrees C indicate that cis-6b is the major kinetic product, which isomerizes to the thermodynamic product in trans form quantitatively above -5 degrees 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.