651729-30-5Relevant academic research and scientific papers
Atropisomerism in palladacycles derived from the chloropalladation of heterosubstituted alkynes
Zanini, Mara L.,Meneghetti, Mario R.,Ebeling, Günter,Livotto, Paolo R.,Rominger, Frank,Dupont, Jairton
, p. 527 - 536 (2008/10/08)
The chloropalladation of 2-substituted phenyl N,N-propargylamines, Y-2-C6H4C≡CCH2NMe2 (1a, Y=H; 2a, Y=CF3; 3a, Y=OMe; 4a, Y=SMe and 5a, Y=NH2) affords palladacycles in different ratios of isomers (geometric and atropisomers). In solution, the parent alkyne (Y=H) and the CF3 substituted derivative generate a mixture of cisoid and transoid chloro-bridged dimer palladacycles of the type {Pd[κ1-C, κ1-N-C=(Y-2-C 6H4)C(Cl)CH2NMe2](μ-Cl)} 2. Moreover, in the case of Y=CF3 palladacyclic derivative each of the geometric isomers comprises a mixture of two diastereoisomers due to the restricted rotation of the C(vinyl)-C(aryl) sigma bond (atropisomers). Palladacycles 1a (Y=H) and 2a (Y=CF3) crystallize as the single transoid and cisoid-anti isomer, respectively. The OMe substituted alkyne yields a similar dimeric compound that crystallizes as a single cisoid-anti isomer. In solution this dimeric compound is in fast equilibrium with a monomeric pincer compound of the type Pd[κ 1-C, κ1-N, κ1-O-C=(MeO-2-C 6H4)C(Cl)CH2NMe2](Cl) assisted through the weak coordination of the OMe group. Pincer palladacycles Pd[κ1-C, κ1-N, κ1-Y-C=(Y-2- C6H4)C(Cl)CH2NMe2](Cl) (Y=SMe and NH2) were the sole products obtained in the chloropalladation of alkynes 4a and 5a. The bridge splitting reaction of the dimeric palladacycles 1b-3b with pyridine is highly selective, affording exclusively the corresponding monomeric compounds 1c-3c. The monomeric palladacycle 2d, which comprises a mixture of two atropisomers (2:1 ratio of anti/syn) was obtained from the reaction of 2b with 2-methylpyridine. Theoretical calculations indicated that the anti isomer of 2d is 5.42 kJmol-1 more stable than its syn isomer.
