1613145-78-0Relevant articles and documents
Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base
Liu, Junyang,Johnson, Samuel A.
, p. 2970 - 2982 (2021/06/28)
Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp3)-H arylation with iodoarenes were carried out, to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes undergo the key C-H activation step. The ubiquitous base Na2CO3is found to hinder catalysis; replacement of Na2CO3with NaOtBu gave improved catalytic turnovers under milder conditions. Deprotonation of the 8-aminoquinoline derivativeN-(quinolin-8-yl)pivalamide (1a) at the amide nitrogen using NaH, followed by reaction with NiCl2(PPh3)2allowed for the isolation of complex Ni([AQpiv]-κN,N)2(3) with chelating N-donors (where [AQpiv] = C9NH6NCOtBu). Complex3is a four-coordinate disphenoidal high-spin Ni(II) complex, excluding short anagostic Ni-tBu hydrogen interactions. Complex3reacts with the paddle-wheel [Ph3PNi(μ-CO2tBu)2]2(6·PPh3) ortBuCO2H to give insoluble {[AQpiv]Ni(O2CtBu)}2(5). Dissolution of5in donor solvents L (L= DMSO and DMF) gave a paramagnetic intermediate assigned by NMR as [AQpiv]Ni(O2CtBu)L (5·L) and equilibrium reformation of3and6·L. DFT calculations support this equilibrium in solution. Both3and5undergo C-H activation at temperatures as low as 80 °C and in the presence of PR3(PR3= PPh3, PiBu3) to give Ni(C9NH6NCOCMe2CH2-κN,N,C)PR3(7·PR3). The C-H functionalization reaction orders with respect to7·PiBu3, iodoarenes, and phosphines were determined. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C-H functionalization step; DFT calculations were also carried out to support this finding. When Na2CO3is used as the base, the rate determination step for C-H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR-inactive low-energy off-cycle resting state in catalysis. Replacement of Na2CO3with NaOtBu improved catalysis at milder conditions and made carboxylic acid and phosphine additives unnecessary. Complex3and its functionalized analogues were observed as the catalyst resting state under these conditions.
Nickel-Catalyzed Aminoxylation of Inert Aliphatic C(sp3)-H Bonds with Stable Nitroxyl Radicals under Air: One-Pot Route to α-Formyl Acid Derivatives
Wang, Chunxia,Zhang, Luoqiang,You, Jingsong
supporting information, p. 1690 - 1693 (2017/04/11)
Nickel-catalyzed aminoxylation of an unactivated C(sp3)-H bond with a stable nitroxyl radical has been accomplished for the first time to offer various N-alkoxyamine derivatives, which further enables a one-pot approach to α-formyl acid derivatives. The aminoxylation process reported also provides direct evidence for the oxidative addition of a cyclometallic intermediate with a free radical, which is helpful for the reaction-mechanism study in transition-metal-catalyzed functionalization of inert C(sp3)-H bonds.
Intermolecular Amination of Unactivated C(sp3)?H Bonds with Cyclic Alkylamines: Formation of C(sp3)?N Bonds through Copper/Oxygen-Mediated C(sp3)?H/N?H Activation
Gou, Quan,Yang, Yu-Wen,Liu, Zi-Ning,Qin, Jun
supporting information, p. 16057 - 16061 (2016/10/26)
The first example of intermolecular amination of unactivated C(sp3)?H bonds by cyclic alkylamines mediated by Cu(OAc)2/O2is reported. This method avoids the use of benzoyloxyamines as the aminating reagent, which are normally prepared from alkylamines in extra steps. A variety of unnatural β2, 2-amino acid analogues are synthesized by this simple and efficient procedure. This approach offers a solution to the previous unmet challenge of C(sp3)?H/N?H activation for the formation of C(sp3)?N bonds.
