Over the past decade, numerous reports have focused on the development and applications of Cu-mediated C−H functionalization reactions; however, to date, little is known about the Cu intermediates involved in these transformations. This paper details the observation and characterization of Cu II and Cu III intermediates in aminoquinoline-directed C(sp 2 )−H functionalization of a fluoroarene substrate. An initial C(sp 2 )−H activation at Cu II occurs at room temperature to afford an isolable anionic cyclometalated Cu II complex. This complex undergoes singleelectron oxidation with ferrocenium or Ag I salts under mild conditions (5 min at room temperature) to afford C(sp 2 )−C(sp 2 ) or C(sp 2 )−NO 2 coupling products. Spectroscopic studies implicate the formation of a transient diamagnetic Cu III -σ-aryl intermediate that undergoes either (i) a second C(sp 2 )−H activation at Cu III followed by C−C bond-forming reductive elimination or (ii) reaction with a NO 2 − nucleophile and C(sp 2 )−NO 2 coupling.

The reaction of (cod)PtMe2 (cod = 1,5-cyclooctadiene) with trifluoroacetic acid to release methane is an important system because it represents the microscopic reverse of desirable methane activation and because it has an unusually large kinetic isotope effect (KIE) that has been tentatively attributed to proton tunneling. A detailed kinetic and mechanistic investigation of this system was conducted using stopped-flow and traditional time-dependent UV–vis spectroscopy, supported by NMR and density functional theory studies. Consistently large KIE values (∼14) in line with previous reports were obtained over a large range of reactant concentrations (0.1–1.6 mM (cod)PtMe2 and 3.2 mM to 6.0 M acid). At lower concentrations of acid, the KIE decreased significantly (KIE = ∼6 for 0.1 mM (cod)PtMe2 and 0.2 mM acid). This concentration-dependent KIE suggests a multistep reaction mechanism, eliminating the need to invoke proton tunneling. The reaction exhibits first-order dependence on (cod)PtMe2 and approximately second-order dependence on acid, with at least 2 equiv of acid required for complete conversion. Overall, the kinetic data indicate a multimolecular, multistep reaction mechanism for the protonolysis of (cod)PtMe2, thus ruling out the previously accepted bimolecular single-step mechanism. A mechanistic alternative consistent with the kinetic data is proposed, in which sequential oxidative addition and reductive elimination occur, and the second equivalent of acid serves to stabilize the trifluoroacetate anion in solution.

The reaction of (cod)PtMe2 (cod = 1,5-cyclooctadiene) with trifluoroacetic acid (TFAH) to release methane is an important system because it represents the microscopic reverse of desirable methane activation, and because it has an unusually large kinetic isotope effect (KIE) that has been tentatively attributed to proton tunneling. A detailed kinetic and mechanistic inves-tigation of this system was conducted using stopped-flow and traditional time-dependent UV-vis spectroscopy, supported by NMR and DFT studies. Consistently large KIE values (~14) in line with previous reports were obtained over a large range of reactant concentrations (0.1 – 1.6 mM (cod)PtMe2 and 3.2 mM to 6.0 M acid). At lower concentrations of acid, the KIE decreased significantly (KIE = ~6 for 0.1 mM (cod)PtMe2 and 0.2 mM acid). This concentration-dependent KIE suggests a multi-step reaction mechanism, eliminating the need to invoke proton tunneling. The reaction exhibits first-order dependence on (cod)PtMe2 and approximately second-order dependence on acid, with at least 2 equivalents of acid required for complete conversion. Overall, the kinetic data indicate a multi-molecular, multi-step reaction mechanism for the protonolysis of (cod)PtMe2, thus ruling out the previously accepted bimolecular single-step mechanism. A mechanistic alternative consistent with the kinetic data is proposed, in which sequential oxidative addition and reductive elimination occur, and the second equivalent of acid serves to stabilize trifluoroacetate anion in solution.

The reaction of (cod)PtMe2 (cod = 1,5-cyclooctadiene) with trifluoroacetic acid (TFAH) to release methane is an important system because it represents the microscopic reverse of desirable methane activation, and because it has an unusually large kinetic isotope effect (KIE) that has been tentatively attributed to proton tunneling. A detailed kinetic and mechanistic inves-tigation of this system was conducted using stopped-flow and traditional time-dependent UV-vis spectroscopy, supported by NMR and DFT studies. Consistently large KIE values (~14) in line with previous reports were obtained over a large range of reactant concentrations (0.1 – 1.6 mM (cod)PtMe2 and 3.2 mM to 6.0 M acid). At lower concentrations of acid, the KIE decreased significantly (KIE = ~6 for 0.1 mM (cod)PtMe2 and 0.2 mM acid). This concentration-dependent KIE suggests a multi-step reaction mechanism, eliminating the need to invoke proton tunneling. The reaction exhibits first-order dependence on (cod)PtMe2 and approximately second-order dependence on acid, with at least 2 equivalents of acid required for complete conversion. Overall, the kinetic data indicate a multi-molecular, multi-step reaction mechanism for the protonolysis of (cod)PtMe2, thus ruling out the previously accepted bimolecular single-step mechanism. A mechanistic alternative consistent with the kinetic data is proposed, in which sequential oxidative addition and reductive elimination occur, and the second equivalent of acid serves to stabilize trifluoroacetate anion in solution.