title: Pd(OAc)2-catalyzed C-H activation/C-O cyclization: mechanism, role of oxidant-probed by density functional theory.
abstract: A series of density functional theory determinations have been carried out to characterize Pd(OAc)2-catalyzed C-H activation and subsequent intramolecular C-O bond-coupling of phenyl-tert-butanol in perfluorobenzene (C6F6) solvent. Full, nontruncated models of the real chemical transformations were studied, with structures in agreement with recent X-ray determinations. Conformational analyses have provided thermodynamic validity of the geometric structures used. The B3LYP/DZVP and B3LYP/BS1 methods (BS1 = TZVP(H,C,O) + SDD(Pd,I)) were comparatively employed, with C6F6 solvent contributions accounted for by the IDSCRF method; key transition states were confirmed by intrinsic reaction coordinate determinations. The novel reaction mechanism proposed was divided into the following four steps: C-H activation, oxidation, reductive elimination, catalyst recovery. Two competing reaction routes were quantitatively compared, differing in the oxidation state of Pd (+2 vs +4). Results reveal the pathway involving Pd(IV) intermediates to be more spontaneous and, therefore, more probable than the Pd(II) path, the latter hindered by a kinetically inaccessible reductive elimination step, with total energy and free energy barriers of 41.0 and 38.6 kcal·mol(-1), respectively. The roles played by the oxidant and Pd(IV) species have also been addressed through Bader's atoms-in-molecules wave function analyses, providing a quantitative electronic metric for C-H activation chemistry.
authors.affiliation: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Lian
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Gregory Adam
authors.initials: GA
authors.lastname: Chass
authors.forename: De-Cai
authors.initials: DC
authors.lastname: Fang
mesh_terms: D000085:Acetates / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D004987:Ethers / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D000085:Acetates; D004987:Ethers; D009942:Organometallic Compounds; D016877:Oxidants; C516071:palladium(II) acetate