# Bimetallic Redox Synergy in Oxidative Palladium Catalysis

 Title: Bimetallic Redox Synergy in Oxidative Palladium Catalysis Author: Powers, David Charles; Ritter, Tobias Note: Order does not necessarily reflect citation order of authors. Citation: Powers, David C., and Tobias Ritter. 2012. Bimetallic Redox Synergy in Oxidative Palladium Catalysis. Accounts of Chemical Research 45(6): 840-850. Full Text & Related Files: Powers_BimetallicRedox.doc (2.644Mb; Microsoft Word)  Powers_BimetallicRedox.pdf (652.9Kb; PDF) Abstract: Polynuclear transition metal complexes, which are embedded in the active sites of many metalloenzymes, are responsible for effecting a diverse array of oxidation reactions in nature. The range of chemical transformations remains unparalleled in the laboratory. With few noteworthy exceptions, chemists have primarily focused on mononuclear transition metal complexes in developing homogeneous catalysis. Our group is interested in the development of carbon–heteroatom bond-forming reactions, with a particular focus on identifying reactions that can be applied to the synthesis of complex molecules. In this context, we have hypothesized that bimetallic redox chemistry, in which two metals participate synergistically, may lower the activation barriers to redox transformations relevant to catalysis. In this Account, we discuss redox chemistry of binuclear Pd complexes and examine the role of binuclear intermediates in Pd-catalyzed oxidation reactions. Stoichiometric organometallic studies of the oxidation of binuclear $$Pd^{II}$$ complexes to binuclear $$Pd^{III}$$ complexes and subsequent C–X reductive elimination from the resulting binuclear $$Pd^{III}$$ complexes have confirmed the viability of C–X bond-forming reactions mediated by binuclear $$Pd^{III}$$ complexes. Metal–metal bond formation, which proceeds concurrently with oxidation of binuclear $$Pd^{II}$$ complexes, can lower the activation barrier for oxidation. We also discuss experimental and theoretical work that suggests that C–X reductive elimination is also facilitated by redox cooperation of both metals during reductive elimination. The effect of ligand modification on the structure and reactivity of binuclear $$Pd^{III}$$ complexes will be presented in light of the impact that ligand structure can exert on the structure and reactivity of binuclear $$Pd^{III}$$ complexes. Historically, oxidation reactions similar to those discussed here have been proposed to proceed via mononuclear $$Pd^{IV}$$ intermediates, and the hypothesis of mononuclear $$Pd^{II/IV}$$ catalysis has guided the successful development of many reactions. Herein we discuss differences between monometallic $$Pd^{IV}$$ and bimetallic $$Pd^{III}$$ redox catalysis. We address whether appreciation of the relevance of bimetallic $$Pd^{III}$$ redox catalysis is of academic interest exclusively, serving to provide a more nuanced description of catalysis, or if the new insight regarding bimetallic $$Pd^{III}$$ chemistry can be a platform to enable future reaction development. To this end, we describe an example in which the hypothesis of bimetallic redox chemistry guided reaction development, leading to the discovery of reactivity distinct from monometallic catalysts. Published Version: doi:10.1021/ar2001974 Other Sources: http://www.chem.harvard.edu/groups/ritter/pdf/2011-840acr.pdf Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10861159 Downloads of this work: