New oxidation reactions of palladium and platinum: Synthetic and mechanistic investigations.

摘要

Organic and inorganic oxidation reactions involving the metals palladium and platinum were developed. Palladium-catalyzed carbon-hydrogen (C-H) functionalization via acetoxylation was shown to proceed efficiently using an oxidant immobilized on a solid support. The polymer oxidant has several advantages over a traditional monomer oxidant, including, but not limited to, cost, atom economy, and recyclability. Both sp2 and sp3 C-H bonds of small molecules were transformed using this methodology.;Palladium was also employed in stoichiometric oxidation reactions. Oxidation of PdII(phpy)2 (phpy = 2-phenylpyridine) using the electrophilic chlorinating reagents, PhICl2 and NCS, accessed the elusive high oxidation state of PdIV. Novel complexes were identified and characterized, incorporating 2 chlorine ligands or 1 chlorine ligand and the succinimide ligand. Both complexes were shown to undergo facile reductive elimination to produce C-Cl, C-C, and even C-N coupled organic products. Other PdIV complexes were synthesized, examining the outcome of organic reductive elimination from a metal complex with two different ligands, acetate and chlorine. Initial results demonstrate that solvent and ligand position strongly influence the observed organic products.;Platinum complexes were also oxidized by the afore mentioned electrophilic chlorinating reagents. Using conditions from the palladium system, oxidation with PhICl2 afforded similar PtIV dichloride products, while oxidation with NCS produced a PtIII complex as the major product. The reaction conditions were found to vary the observed ratios of products in the NCS oxidations. These factors were examined in an effort to propose a mechanism to explain formation of all of the species.;Finally, platinum complexes were oxidized by a series of traditional and nontraditional oxidants to access PtIII and PtIV halogen and carboxylate complexes. Traditional oxidants included Br2 and I2, while non-traditional oxidants included XeF2, PhI(OAc)2 and PhI(C2F3O 2)2. All of the compounds formed were stable to ambient conditions. Organic reductive elimination products were not observed in any of the thermolysis experiments. Upon heating the PtIV complexes either experienced no change or isomerized to an alternate geometry.