title: Kinetic and mechanistic studies of geometrical isomerism in neutral square-planar methylpalladium complexes bearing unsymmetrical bidentate ligands of alpha-aminoaldimines.
abstract: 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 [R(1)R(2)NCMe(2)CH horizontal lineNR]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 = (n)Pr, R(1) = R(2) = Me (5a); R = (i)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) = (i)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)Cl with Et(2)NCMe(2)CH horizontal lineN(i)Pr 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.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Feng-Zhao
authors.initials: FZ
authors.lastname: Yang
authors.forename: Yu-Heng
authors.initials: YH
authors.lastname: Wang
authors.forename: Mu-Chieh
authors.initials: MC
authors.lastname: Chang
authors.forename: Kuo-Hsuan
authors.initials: KH
authors.lastname: Yu
authors.forename: Shou-Ling
authors.initials: SL
authors.lastname: Huang
authors.forename: Yi-Hung
authors.initials: YH
authors.lastname: Liu
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Shiuh-Tzung
authors.initials: ST
authors.lastname: Liu
authors.forename: Jwu-Ting
authors.initials: JT
authors.lastname: Chen