Mechanistic Studies of the Palladium-Catalyzed Amination of Aryl Halides and the Oxidative Addition of Aryl Bromides to Pd(BINAP)2and Pd(DPPF)2:  An Unusual Case of Zero-Order Kinetic Behavior and Product Inhibition

Mechanistic studies of the amination of aryl bromides catalyzed by palladium complexes containing the chelating phosphines BINAP and DPPF are reported. The coupling of primary alkyl- and arylamines, secondary cyclic alkylamines, and secondary arylalkylamines with bromoarenes in the presence of stoichiometric base and Pd(BINAP)2 (1a) as catalyst, and the reaction of aniline with 4-Br-C6H4-t-Bu in the presence of base catalyzed by Pd(DPPF)2 (2), were studied. The stoichiometric oxidative additions of PhBr to 1a and to 2 were turnover limiting, and kinetic studies were also conducted on this individual step. The stoichiometric oxidative addition of PhBr to 1a showed an inverse first-order dependence on added ligand when the PhBr concentration was low but depended solely on the rate of chelating ligand dissociation at high [PhBr]. There was no measurable solvent effect. In addition, the rates were indistinguishable in the presence and in the absence of amines and salts that are present in the catalytic aminat...