Palladium(0)-Catalyzed Allylic Aminations: Kinetics and Mechanism of the Reaction of Secondary Amines with Cationic [(η3-allyl)PdL2]+ Complexes

The mechanism of the reaction of secondary amines (piperidine, morpholine) with the cationic complexes [( η 3 -PhCHCHCHR)PdL 2 ] + BF 4 - (R = Ph, L = PPh 3 or L 2 = dppb; R = H, L 2 = dppb) has been investigated in DMF. The reaction, which affords the tertiary allylic amine, is irreversible when L is a monodentate ligand such as PPh 3, whereas the reaction is reversible when L 2 is a bidentate ligand such as dppb. In all cases, piperidine is more reactive than morpholine. The rate and equilibrium constants have been determined in DMF. These results can be combined with our previous results on the mechanism of the reversible formation of cationic [( η 3 -PhCHCHCHPh)PdL 2 ] + AcO - by reacting Pd 0 L 2 complexes with ( E )-PhCH CHCH(Ph)OAc. Fully established catalytic cycles are now proposed for the Pd-catalyzed allylic amination of ( E )-PhCH CHCH(Ph)OAc by piperidine and morpholine. The amine and AcO - are in competition in their reaction with the cationic complexes [( η 3 -PhCHCHCHPh)PdL 2 ] + . The nucleophilic attack of the amine may be faster than the attack of AcO - and thus limited by the ionization step in which [( η 3 -PhCHCHCHPh)PdL 2 ] + is formed, this ionization step being turnover limiting for the catalytic cycle.