Electronic Directing Group Modification for Improved Ni(II)-Mediated C(sp³)–H Activation: A Hammett Investigation of 8-Aminoquinoline

Untangling ancillary ligand donation versus locus of oxidation effects on metal nitride reactivity

“…The Hammett parameter (s p ) quanties the electron-donating ability of a para-ring substituent and is commonly compared to a rate constant to gain a mechanistic understanding of a particular reaction. 13,87,94 Herein, if the electron-donating capacity of the para-ring substituents in [Mn(Sal R )N] + is the main contributor to the nitride reactivity with (p-CF 3 Ph) 3 P, a linear correlation will be expected for all derivatives (R]CF 3 , H, tBu, O i Pr, NMe 2 , NEt 2 ), assuming the reaction mechanism remains unchanged. 95,96 However, a substantial deviation from linearity could indicate that the locus of oxidation (metal or ligand), and not the electron-donating ability of a para-ring substituent, plays a more signicant role in the reaction, in the absence of a change in reaction mechanism.…”

Reactions of cyclonickelated complexes with hydroxylamines and TEMPO˙: isolation of new TEMPOH adducts of Ni(ii) and their reactivities with nucleophiles and oxidants

“…Therefore, expediting progress on the mechanistic front requires greater efforts toward interception of the envisaged intermediates and examination of their stabilities and reactivities. Indeed, such efforts have begun already and recent reports by the groups of Schafer and Love, 26,27 and Sanford 28 have provided valuable mechanistic insights on Ni-based systems.…”

Speciation and Reactivity of Mono- and Binuclear Ni Intermediates in Aminoquinoline-Directed C–H Arylation and Benzylation

“…6−10 To date, organometallic investigations of Ni-catalyzed AQdirected C−H arylation have largely focused on individual steps of the catalytic cycle. For instance, Love and Schafer, 6 Johnson, 7 and others 8 have interrogated C−H activation at Ni II centers to generate NNC pincer intermediate B (Scheme 1, steps i and ii). These studies show the initial formation of Ni II aminoquinoline coordination complexes of general structure A (Scheme 1, step i).…”

“…The speciation of these paramagnetic and often fluxional coordination complexes has been shown to vary as a function of stoichiometry, base, and quinoline electronics; furthermore, the formation/reactivity of A has been implicated as a key factor in the rate of C−H activation to generate B (step ii). 6,7 Despite these advances, the detection and characterization of paramagnetic coordina-tion complexes have largely been limited to what crystallizes from solution, as there are no good ways to track their formation and evolution in situ. Additionally, isolation of the cyclometalated intermediate (B) typically requires trapping with an exogenous donor ligand (e.g., phosphine, pyridine, and CO) that would not be present during catalysis.…”