COMPARATIVE-STUDY OF THE MECHANISM OF ALKENYLATION OF ORTHO-PALLADATED BENZYLAMINES AND ACETANILIDESстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The ortho-palladated derivative of N,N-dimethylbenzylamine, the complex [Pd(OAc)(C6H4CH2-NMe2)2, reacts with styrene in acetic acid solution with a final product of o-Me2NCH2C6H4CH = CHC6H5. Two parallel second-order pathways, are involved catalysed, respectively by acetic acid (k3) and perchloric acid (k(H)). The rate constants k3 and k(H) at 30-degrees-C are 0.021 +/- 0.005 and 6.8 +/- 0.5 dm3 mol-1 s-1, while the pK(a) is 4.6. In the case of the corresponding acetanilide derivative, the complex [Pd(OAc)(C6H4NHCOMe)]2, the catalysis by perchloric acid is much weaker than for the amine complex, the k3 and k(H) being 0.0206 +/- 0.0005 and 0.049 +/- 0.003 dm3 mol-1 s-1, respectively. The pK(a) in this case is 4.5. Despite the great difference in basicity of N,N-dimethylbenzylamine and acetanilide, the values for pK(a) are very similar, providing evidence that the perchloric acid-catalysed pathway involves the protonation of groups of comparable basicity in both complexes, that is to say the bridging acetates, while the great variation in the values of k(H) suggests the existence of other route of acid catalysis for amine complexes. The chloro-bridged acetanilidide complex [PdCl(C6H4NHCOMe)]2 reacts with styrene in various organic solvents without the perchloric acid-catalysed pathway (k(H)). The Hammett equations log k3 = -(1.58 +/- 0.02)-(1.57 +/- 0.06)-sigma-m and log k3 = -(1.49 +/- 0.02) - (0.79 +/- 0.15)-sigma-P were obtained in acetic acid solution at 30-degrees-C varying ring-substituents in the acetanilide complex and styrene, respectively. On the basis of these and previously reported results the mechanism of the k3 pathway for acetanilide complexes is discussed.