Kinetic investigation of a PC(sp3)P pincer palladium (II) complex in the Heck reaction

An investigation of the kinetics of the Heck reaction between 4-iodoanisole and styrene catalysed by {cis-1,3-bis[(di-tert-butylphosphino)methyl]-cyclohexane} palladium (11) iodide (1) has been performed in DMF-d(7) solution. Based on mercury poisoning experiments a heterogeneous palladium catalyst formed from the PCsp3P Pd(II) pre-catalyst is proposed. Saturation behaviour with respect to the olefin concentration suggests a mechanism consisting of a pre-equilibrium association of the olefin followed by a rate determining reaction with aryl halide. The equilibrium constant for the olefin association, K-1, and the rate constant for the subsequent oxidative addition step, k(2), were determined to (5.7 +/- 2.5) x 10(-3) and 18.4 +/- 2.7 M-1 s(-1), respectively. (c) 2005 Elsevier B.V. All rights reserved.