EQUILIBRIUM STUDIES OF ALPHA-DIIMINE DISPLACEMENT IN CATIONIC ALLYLPALLADIUM(II) COMPLEXES BY MONODENTATE N-DONORS AND THE MECHANISM OF ALLYL AMINATION BY TRIETHYLAMINE AND PYRIDINE

In the cationic complexes [Pd(eta3-allyl)(L-L)]ClO4 [L-L = 1,2-bis(imino)ethanes or 2-(iminomethyl)-pyridines] the chelated alpha-diimine was rapidly and reversibly displaced by secondary amines (N-methylaniline, morpholine or piperidine), triethylamine and 4-substituted pyridines. The observed equilibrium constants K(e) increased with increasing basicity and decreasing steric requirements of the entering N-donor. They strongly depend on the alpha-diimine and decrease in the order RN=CHCH=NR much-greater-than RN=C(Me)C(Me)=NR almost-equal-to NC5H4(CH=NR)-2 (R = C6H4OMe-4). The cationic complex [Pd(eta3-C3H5){NC5H4(CH=NC6H4OMe-4)-2}]+ underwent a slow allyl amination by triethylamine or pyridine (L') in the presence of fumaronitrile (fn), yielding [Pd(eta2-fn){NC5H4(CH=NC6H4OMe-4)-2}] and Et3N+CH2CH=CH2 or C5H5N+CH2CH=CH2. Kinetic studies showed that the pseudo-first-order rate constants for amination (k(obs)) are given by k(obs) = k2[L'], suggesting a direct bimolecular attack of L' on the eta3-allyl ligand. Amination hardly proceeds in the presence of the less-activated olefin dimethyl fumarate (dmf). The pi-accepting properties of the olefinic ligands play an important role also in the reaction of Et3N+CH2CH=CH2 or C5H5N+CH2CH=CH2 with [Pd(eta2-olefin){NC5H4(CH=NC6H4OMe-4)-2}] (olefin = fn or dmf), i.e. the reverse of the amination reaction.