title: Palladium-catalysed directed C-H activation by anilides and ureas; water participation in a general base mechanism.
abstract: C-H activation plays a central role in organometallic catalysis. Concerted metallation-deprotonation (CMD) has been dominant as the pathway for C-H bond cleavage. In the course of studying the mechanism of C-H activation of arylamides and arylureas with Pd complexes as part of catalytic oxidative Heck reactions, DFT calculations were carried out. The turnover-limiting C-H activation is acid-catalysed and can occur readily in the absence of acetate or other coordinating bases. The calculations simulated experiment, so that ligated sulfonate and water, both previously observed by X-ray characterization, were incorporated in the model. A Wheland-type complex between acetanilide and Pd was readily located, but the reactive C-H and the coordinated sulfonate were poorly placed for intramolecular proton transfer. Involvement of a water molecule coordinated to sulfonate provides a low-energy pathway to the palladacycle. The relative reactivity of substituted acetanilides and arylureas according to this model fits well with existing literature. General-base catalysis as described here has broader potential.
authors.affiliation: Chemistry Research Laboratory, Oxford University, Mansfield Rd, Oxford OX1 3QY, UK. john.brown@chem.ox.ac.uk.
authors.forename: Waqar
authors.initials: W
authors.lastname: Rauf
authors.forename: John M
authors.initials: JM
authors.lastname: Brown
mesh_terms: D000813:Anilides / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010165:Palladium / Q000737:chemistry*; D011789:Quantum Theory; D014508:Urea / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000813:Anilides; D014867:Water; D010165:Palladium; D002244:Carbon; D006859:Hydrogen; D014508:Urea