1/11 - Faculty Candidate Seminar (inorganic): Brad Carrow, University of Tokyo
University of Tokyo
Host: Paul Chirik
Mechanism and Methods in Palladium Catalysis: From Small- to Macromolecules
A series of mechanistic studies will be discussed that have revealed fundamental information about the individual steps of palladium-catalyzed coupling reactions. In one case, a series of "ligandless," anionic arylpalladium complexes of the general structure [Pd(Ar)(Br)(m-Br)]22− were isolated, and subsequent reactions with these compounds indicate they are intermediates in Mizoroki-Heck reactions conducted under the commonly utilized ligandless (Jeffery) conditions. Additionally, evidence will be presented that olefin insertion in Mizoroki-Heck reactions conducted with highly active catalysts containing P(t-Bu)3 also proceed through the same anionic arylpalladium intermediate lacking coordinated phosphine. A comprehensive kinetic study of the mechanisms of oxidative addition of haloarenes to L2Pd(0) complexes will briefly be discussed, including an unusual autocatalytic mechanism that was identified for reactions of bromoarenes with (PtBu3)2Pd(0) in the absence of strong base. Lastly, kinetic studies between arylpalladium complexes and organoboron compounds were conducted to address an ongoing debate about the mechanism of transmetalation in the Suzuki-Miyaura reaction. The second part of the presentation concerns the recent development of a series of cationic palladium complexes ligated by a bisphosphine monoxide that exhibit broad activity for the direct polymerization of ethylene and simple vinyl monomers possessing polar functional groups to form highly linear, random copolymers. This discovery represents the first new family of transition metal polymerization catalysts that tolerate the presence of industrial monomers such as vinyl acetate, acrylonitrile, and vinyl ethers reported in over a decade of collective research toward this end.