Kinetic and Mechanistic Studies of Geometrical Isomerism in Neutral Square-Planar Methylpalladium Complexes Bearing Unsymmetrical Bidentate Ligands of α-Aminoaldimines

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• 作者：Feng-Zhao Yang ; Yu-Heng Wang ; Mu-Chieh Chang ; Kuo-Hsuan Yu ; Shou-Ling Huang ; Yi-Hung Liu ; Yu Wang ; Shiuh-Tzung Liu ; Jwu-Ting Chen
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：August 17, 2009
• 年：2009
• 卷：48
• 期：16
• 页码：7639-7644
• 全文大小：832K
• 年卷期：v.48,no.16(August 17, 2009)
• ISSN：1520-510X

文摘

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 [R¹R²NCMe₂CH═NR]Pd(Me)Cl (R = Me, R¹ = R² = Me (3a); R = Me, R¹ = R² = Et (3b); R = Et, R¹ = R² = Me (4a); R = ⁿPr, R¹ = R² = Me (5a); R = ⁱPr, R¹ = R² = Me (6a); R = ⁱPr, R¹ = R² = Et (6b); R = ⁱPr, (R¹, R²) = c-C₄H₈ (6c); R = ⁱPr, R¹ = ⁱPr, R² = H (6d); R = ⁱPr, R¹ = ^tBu, R² = H (6e); R = ^tBu, R¹ = R² = Me (7a); R = ^tBu, R¹ = R² = Et (7b); R = ^tBu, (R¹, R²) = c-C₄H₈ (7c); R = ^tBu, R¹ = ⁱPr, R² = H (7d); R = ^tBu, R¹ = ^tBu, R² = H (7e); R = Ph, R¹ = R² = Me (8a); R = Ph, R¹ = R² = 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 R¹ and R²). The NMR studies for the substitution reaction of (COD)Pd(Me)Cl with Et₂NCMe₂CH═NⁱPr at −20 °C indicate that cis-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.