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Abstract Herein, we report the first systematic study of the oxidative addition of aryl bromides to a Pd^Icenter to generate organometallic Pd^IIIcomplexes. These isolable Pd^IIIcomplexes stabilized by tetradentate macrocyclic pyridinophane ligands exhibit distinct UV–vis and EPR spectroscopic signatures that allowed for the monitoring of their generation in situ. These ligand scaffolds were sterically and electronically tuned using a modular synthetic approach to probe the kinetic properties and activation parameters of the oxidative addition reaction, and a combination of UV–vis and cryo stopped‐flow spectroscopic studies reveal a rapid oxidative addition step occurring at a Pd^Icenter. In addition, these results are in strong agreement with our recent reactivity studies, which demonstrated that mononuclear Pd^Isystems are competent catalysts in Kumada cross‐coupling reactions, and thus set the stage for an improved understanding of potential catalytic applications for odd‐electron Pd systems. 

Herein we report the direct observation of C–H bond activation at an isolated mononuclear Pd( iii ) center. The oxidation of the Pd( ii ) complex ( Me N4)Pd II (neophyl)Cl (neophyl = –CH 2 C(CH 3 ) 2 Ph; Me N4 = N , N ′-dimethyl-2,11-diaza[3.3](2,6)pyridinophane) using the mild oxidant ferrocenium hexafluorophosphate (FcPF 6 ) yields the stable Pd( iii ) complex [( Me N4)Pd III (neophyl)Cl]PF 6 . Upon the addition of an acetate source, [( Me N4)Pd III (neophyl)Cl]PF 6 undergoes Csp 2 –H bond activation to yield the cyclometalated product [( Me N4)Pd III (cycloneophyl)]PF 6 . This metalacycle can be independently prepared, allowing for a complete characterization of both the starting and final Pd( iii ) complexes. The C–H activation step can be monitored directly by EPR and UV-Vis spectroscopies, and kinetic isotope effect (KIE) studies suggest that either a pre-association step such as an agostic interaction may be rate limiting, or that the C–H activation is partially rate-limiting in conjunction with ligand rearrangement. Density functional theory calculations support that the reaction proceeds through a κ 3 ligand coordination and that the flexible ligand structure is important for this transformation. Overall, this study represents the first example of discrete C–H bond activation occurring at a Pd( iii ) center through a concerted metalation–deprotonation mechanism, akin to that observed for Pd( ii ) and Pd( iv ) centers. 

Scientists of the Steward Observatory and Wyant College of Optical Sciences at the University of Arizona created a highly energy efficient adaptable method of forming precision freeform metal panels utilizing the combined effects of induction heating, electromagnetic force, an adjustable mold assembly, and infrared and visible metrology. This transformative component-level manufacturing technology has a broad application in industries requiring custom shaped high accuracy metal sheets (radio communication, automotive, aerospace, renewable energy, architecture).