Oxidation of the Pd II complex (N4)Pd IIMe 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 IIIMe 2] +, followed by selective formation of ethane and the monomethyl complex (N4)Pd IIMe(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 IIMe 2 oxidation by O 2 to generate a Pd III- superoxide intermediate. In addition, reaction of (N4)Pd IIMe 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 IIMe(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.
ASJC Scopus subject areas
- Colloid and Surface Chemistry