Atropisomerism in palladacycles derived from the chloropalladation of heterosubstituted alkynes

作者：Zanini ML; Meneghetti MR; Ebeling G; Livotto PR; Rominger F; Dupont J^*

来源：Inorganica Chimica Acta, 2003, 350: 527-536.

DOI：10.1016/S0020-1693(03)00011-2

• palladacycles
• chloropalladation
• atropisomerism
• antisymbiotic effect

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[kappa(1)-C, kappa(1)-N-C=(Y-2-C6H4)C(cl)CH2NMe2](mu-Cl)}(2). Moreover, in the case 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[kappa(1)-C, kappa(1)-N, kappa(1)-O-C=(MeO-2-C6H4)C(Cl)CH2NMe2](Cl) assisted through the weak coordination of the OMe group. Pincer palladacycles Pd[kappa(1)-C, kappa(1)-N, kappa(1)-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 antilsyn) was obtained from the reaction of 2b with 2-methylpyridine. Theoretical calculations indicated that the anti isomer of 2d is 5.42 kJ mol(-1) more stable than its syn isomer.

• 出版日期2003-7-4