Mechanistic Studies on Oxidative Addition of Aryl Halides and Triflates to Pd(BINAP)2 and Structural Characterization of the Product from Aryl Triflate Addition in the Presence of Amine

Kinetic studies of the oxidative addition of phenyl iodide and phenyl triflate to Pd(BINAP)2 (1) are reported. The products of the oxidative addition of phenyl trifluoromethanesulfonate to 1 in the presence of the primary amines n-octylamine and isoamylamine are the cationic aryl palladium(II) complexes [(BINAP)Pd(Ph)(H2NR)]OTf (2a,b), and the product of the oxidative addition of phenyl iodide to 1 is the phenylpalladium iodide {(BINAP)Pd(Ph)I} (3). Structural characterization of the rare, stable σ-aryl Pd(II) triflate complex (2b), in this case coordinated by isoamylamine, is reported. Initial mechanistic studies focused on measuring the rates of reactions containing concentrations of aryl electrophile ranging from 8.94 × 10-7 to 0.2 M. Under these conditions, the oxidative addition of PhOTf and PhI to 1 was inverse first-order in added BINAP ligand when the concentration of ArX was low. The oxidative addition reaction was first-order in ArX when the concentration of ArX was low and was zero order in ArX when the concentration of ArX was high. At these high concentrations, the reaction rate depended solely on the rate for dissociation of BINAP from 1. However, additional experiments using concentrations of aryl iodide and aryl bromide up to 4.0 M led to a measurable increase in observed rate constants and detection of a second concurrent reaction mechanism. This effect was not observed with phenyl triflate. The relevance of this phenomenon to catalytic coupling and oxidative addition of aryl bromides is discussed. Reactions of triflate complex 2a with several bases to form N-octylaniline are also reported.