Selective N-Chelation-Directed C–H Activation Reactions Catalyzed by Pd(II) Nanoparticles Supported on Multiwalled Carbon Nanotubes

Abstract

N-Chelation-directed C-H activation reactions that utilize the Pd(II)/Pd(IV) catalytic cycle have been previously reported. To date, these reactions employ only homogeneous palladium catalysts. The first use of a solid-supported Pd(II) catalyst [Pd(II) nanoparticles on multiwalled carbon nanotubes, Pd(II)/MWCNT] to carry out N-chelation-directed C-H to C-O, C-Cl, and C-Br transformations is reported. The results presented demonstrate that the solid-supported Pd(II)/MWCNT catalyst can effectively catalyze C-H activation reactions using the Pd(II)/Pd(IV) catalytic cycle.

Directed C−H Activation and Tandem Cross‐Coupling Reactions Using Palladium Nanocatalysts with Controlled Oxidation

“…[11] Palladium-catalyzed CÀHa ctivation has been demonstrated in homogeneous systems by mechanisms including high-valent palladium species,e ither monomeric Pd IV or dimeric Pd III -Pd III complexes.Because the highly Lewis-acidic Pd IV species were predominantly generated by the oxidation of palladium NPs with PhICl 2 ,w eb egan exploring the possibility of using oxidized palladium clusters for directed CÀHchlorination of benzo[h]quinoline. [12] This reactivity had already been demonstrated in homogeneous catalysis. [13] When PhICl 2 (1.0 equiv) was added to asolution of palladium NPs (3 mol %) and benzo[h]quinoline (1.0 equiv) in benzene and stirred for 3hours at 120 8 8C, the electrophilic chlorination occurred at the 5-position of benzo[h]quinolone (2a' ' Cl , Table 1).…”

Catalytic C–H bond functionalisation chemistry: the case for quasi-heterogeneous catalysis

“…113 Intriguingly, in many of these examples reactivity distinct from that seen when using the more commonly employed Pd(OAc) 2 was realised; increased activity but reduced substrate tolerance was seen in some acetoxylation reactions (Scheme 31a), reduced yields obtained in some alkoxylations (Scheme 31b) and significantly increased rates observed in halogenations using N-bromo-or N-chlorosuccinimide (Scheme 31c). 113 Intriguingly, in many of these examples reactivity distinct from that seen when using the more commonly employed Pd(OAc) 2 was realised; increased activity but reduced substrate tolerance was seen in some acetoxylation reactions (Scheme 31a), reduced yields obtained in some alkoxylations (Scheme 31b) and significantly increased rates observed in halogenations using N-bromo-or N-chlorosuccinimide (Scheme 31c).…”

Directed C−H Halogenation Reactions Catalysed by PdII Supported on Polymers under Batch and Continuous Flow Conditions

“…CÀHh alogenation under heterogeneousc atalysis conditions has been studied in multiple instances. [32][33][34][35][55][56][57] As ap arto f our ongoing work on heterogeneous catalysis, we were interested in comparingt he activities of P1 and P2 as catalysts in CÀHh alogenation under mild reactionc onditions. As ab enchmark reaction, we chose the chlorination of 2-phenylpyridine, 7,w ith different chlorinating agents( PhICl 2 and Nchlorosuccinimide( NCS)) and solvents using different loadings of P1.A ss hown in Ta ble 1, NCS/glacial acetic acid ( G AcOH) and NCS/acetonitrile (MeCN) offered mono-chlorinated product 7-Cl in 50 and 56 %y ield, respectively (selectivity almost 100 %; only traces of di-chlorinated product 7-Cl 2 ;T able 1, entries 1 and 2).…”

“…Recently,w er eported an example of ap olymer-supportedN -heterocyclic carbenep alladium(II) (NHC-Pd II )c omplex which selectively catalysed CÀHo xygenation of unfunctionalised arenes with very good regioselectivity, [29] and there are further examples of both undirected [30,31] and N-chelation-directed C(sp 2 )-H halogenation reactions using supported catalysts. [32][33][34][35] The reactions above were run in batch mode and this does not make full use of the potential of heterogeneous catalysis. On the contrary,c ontinuous flow reactions offer attractive advantages in termso fs afety (no accumulation of highly unstablei ntermediates)a nd reaction efficiency( time and cost effective process).…”