Removable bidentate directing group assisted-recyclable metal–organic frameworks-catalyzed direct oxidative amination of Sp 2 C–H bonds Nga T.T. Tran, Quan H. Tran, Thanh Truong ⇑ Department of Chemical Engineering, HCMC University of Technology, VNU-HCM, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet Nam article info Article history: Received 18 June 2014 Revised 16 September 2014 Accepted 18 September 2014 Keywords: Metal–organic frameworks C–H activation Copper-catalyzed Direct amination 8-Aminoquinoline abstract Several Cu-MOFs were showed to be efficient heterogeneous catalysts for ortho-amination of benzoic acid derivative C–H bonds by N–H amines using 8-aminoquinoline as bidentate directing group. The optimal reaction conditions involve the use of Cu-MOFs (25%), N-methylmorpholine oxide (NMO) as an oxidant, secondary or primary amine coupling partner, DMF, DMA, or NMP solvent at 90–100 °C. Furthermore, the Cu-MOFs catalyst could be facilely isolated from the reaction mixture and reused several times without remarkable degradation in catalytic reactivity. Contribution from homogeneous leached active copper species, if any, is negligible. To the best of our knowledge, C–H activation reactions using bidentate directing groups, which are increasingly gaining importance, under heterogeneous catalytic systems were not previously mentioned in the literature. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Transition metal-catalyzed carbon–nitrogen coupling reactions have offered widespread applications in the synthesis of many valuable substrates including pharmaceutical compounds, func- tional materials, and organic sensors [1–3]. Pre-functionalization of starting materials either in the aminated substrates or in the amines is required when conventional methods are employed either in homogeneous or heterogeneous manners [4,5]. Conse- quently, this adds up more chemical steps in the synthetic sequences which can significantly lengthen the procedures. From synthetic point of views, the direct coupling reactions from C–H and N–H are highly desired (Scheme 1) [6–8]. Since organic mole- cules often contain a wide range of chemically similar C–H bonds, selective transformations for non-activated C–H bonds are gener- ally difficult to achieve [9,10]. Several approaches have been employed to address this challenge, the most common involves the use of directing groups, which bind to the metal center and bring catalysts to the proximal C–H bonds. Over last several years, a wide variety of functional groups have been evaluated as direct- ing groups in the transformation of C–H bonds [11,12]. Homoge- neous palladium, iridium, and ruthenium based catalysts have been employed for ligand-assisted direct amination of C–H bonds of [13–15]. Recently, reactivity enabled by cheap and abundant copper catalysts has attracted great interest. In particular, the first copper-mediated directed amination of C–H arene bonds was described by Yu group [16]. However, stoichiometric amount of copper is required and only 2-phenylpyridine derivatives were active [17–19]. Recently, with the use of 8-aminoquinoline (8- AQ) directing group [20,21], Daugulis has firstly reported that ortho-amination of sp 2 C–H bonds is possible under copper cataly- sis [22]. The utilization of an inexpensive copper catalyst and removable directing group allows for a favorable comparison with previous direct amination methodologies. Thus, the heterogeneous catalytic system for this transformation should be targeted for practical chemical industry as well as simplifying the product puri- fication [23,24]. Metal–organic frameworks (MOFs) have recently emerged as an incredible class of crystalline porous materials with potential applications in different fields [25–28]. Although the utilization of MOFs in catalysis is a young research area, many MOFs have been investigated as heterogeneous catalysts or catalyst supports for a variety of organic transformations [29–32]. Recently, the use of MOFs and other heterogeneous systems with transition metal clusters for organic transformations, especially C–H func- tionalization reactions have increasingly gained attention [33,34]. With respect to MOFs catalysis, Sanford and Swartzers have pio- neered using Pd-MOFs for arylation of naphthalene by arene C–H bonds [34a]. Bipyridyl-containing metal–organic frameworks of palladium and iridium were demonstrated as efficient catalysts for borylation of aromatic C–H bonds [34b]. However, regioisomers were obtained in many cases where steric effect is not predomi- nant. Our group has described the deprotonative arylation of http://dx.doi.org/10.1016/j.jcat.2014.09.015 0021-9517/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. E-mail address: tvthanh@hcmut.edu.vn (T. Truong). Journal of Catalysis 320 (2014) 9–15 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat