title: The aerobic oxidation of a Pd(II) dimethyl complex leads to selective ethane elimination from a Pd(III) intermediate.
abstract: Oxidation of the Pd(II) complex (N4)Pd(II)Me(2) (N4 = N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) with O(2) or ROOH (R = H, tert-butyl, cumyl) produces the Pd(III) species [(N4)Pd(III)Me(2)](+), followed by selective formation of ethane and the monomethyl complex (N4)Pd(II)Me(OH). Cyclic voltammetry studies and use of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap suggest an inner-sphere mechanism for (N4)Pd(II)Me(2) oxidation by O(2) to generate a Pd(III)-superoxide intermediate. In addition, reaction of (N4)Pd(II)Me(2) with cumene hydroperoxide involves a heterolytic O-O bond cleavage, implying a two-electron oxidation of the Pd(II) precursor and formation of a transient Pd(IV) intermediate. Mechanistic studies of the C-C bond formation steps and crossover experiments are consistent with a nonradical mechanism that involves methyl group transfer and transient formation of a Pd(IV) species. Moreover, the (N4)Pd(II)Me(OH) complex formed upon ethane elimination reacts with weakly acidic C-H bonds of acetone and terminal alkynes, leading to formation of a new Pd(II)-C bond. Overall, this study represents the first example of C-C bond formation upon aerobic oxidation of a Pd(II) dimethyl complex, with implications in the development of Pd catalysts for aerobic oxidative coupling of C-H bonds.
authors.affiliation: Department of Chemistry, Washington University, One Brookings Drive, St. Louis, Missouri 63130-4899, USA.
authors.forename: Julia R
authors.initials: JR
authors.lastname: Khusnutdinova
authors.forename: Nigam P
authors.initials: NP
authors.lastname: Rath
authors.forename: Liviu M
authors.initials: LM
authors.lastname: Mirica
mesh_terms: D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D010165:Palladium