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

Synthesis and Characterization of the Double Salts [Pt(bzq)(CNR)2][Pt(bzq)(CN)2] with Significant Pt···Pt and π···π Interactions. Mechanistic Insights into the Ligand Exchange Process from Joint Experimental and DFT Study

“…With the aim of gaining insight into the mechanism of this process and the role of the Pt···Pt and π···π interactions in the reaction pathway, we studied the ligand rearrangement process undergone by DCSs 1 – 3 by combined experimental and computational calculations. For this purpose 1 H NMR spectroscopy was used to follow the processes undergone by compounds 1 and 2 in CD 2 Cl 2 at three different temperatures in the range −1 to +30 °C (see Experimental Section) because the reaction does not work at low temperatures (below −5 °C) and at RT it is very fast, especially for compound 2 . Compound 3 could not be investigated because the resulting neutral complexes precipitate in the NMR tube, which precluded the possibility of obtaining accurate data from the integral values of the NMR signals.…”

Alternating ethylene-norbornene copolymerization catalyzed by cationic organopalladium complexes bearing hemilabile bidentate ligands of α-amino-pyridines

“…In general, conformationally bulky amino substituents tend to favor the trans configuration in which the coordination site cis to pyridine may accommodate a methyl better than the site cis to amino group. 8 The ortho-substituted aryl groups probably are restrained to free rotation in 6 or 7, particularly when a methyl is on the back-bone carbon. The relative yields of the isomers in the neutral and cationic species are in lack of good correlation.…”

Kinetics, Mechanism and Theoretical Studies of Norbornene-Ethylene Alternating Copolymerization Catalyzed by Organopalladium(II) Complexes Bearing Hemilabile α-Amino–pyridine

“…T -{[RHNCH 2 ( o -C 6 H 4 N)]Pd(Et)(MeCN)}(BF 4 ) ( 5a – c ), with respective yields of 29%, 50%, and 24%, were also obtained. The absence of the C - 5a – c is presumably due to the conformational steric hindrance between the amino substituent and the ethyl ligand [ 80 , 98 ]. T -forms are of the more favored configurations in 1a’ – d’ and 5a’ – e’ , again, ascribed to the steric effect ( Table 3 ).…”