Synthesis and multinuclear NMR studies of 3-aminopropyl(aryl)chalcogenides, NH2CH2CH2CH2EAr (E = Se, Te), and their complexes with Pt(II) and Pd(II)

Organosulphur and organoselenium compounds as emerging building blocks for catalytic systems for O-arylation of phenols, a C-O coupling reaction

Diaryl ethers form an important class of organic compounds. The classic copper-mediated Ullmann diaryl ether synthesis has been known for many years and involves the coupling of phenols with aryl halides. However, the use of high reaction temperature, high catalyst loading and expensive ligands has created a need for the development of alternative catalytic systems. In the recent past, organosulphur and organoselenium compounds have been used as building blocks for developing homogeneous, heterogeneous and nanocatalysts for this C-O coupling reaction. Homogeneous catalytic systems include preformed complexes of metals with organosulphur and organoselenium ligands. The performance of such complexes is influenced dramatically by the nature of the chalcogen (S or Se) donor site of the ligand. Nanocatalytic systems (including Pd₁₇Se₁₅, Pd₁₆S₇ and Cu_1.8S) have been designed using a single-source precursor route. Heterogeneous catalytic systems contain either metal (Cu or Pd) or metal chalcogenides (Pd₁₇Se₁₅ or Cu_1.8S) as catalytically active species. This article aims to cover the simple and straightforward methodologies and approaches that are adopted for developing catalytically relevant organosulfur and organoselenium ligands, their homogeneous metal complexes, heterogeneous and nanocatalysts. The effects of chalcogen (S or Se) donor, halogen (Cl/Br/I) of aryl halide, nature (electron withdrawing or electron donating) of substituents present on the aromatic ring of aryl halides or substituted phenols and position (ortho or para) of substitution on the results of catalytic reactions have been critically analyzed and summarized. The effect of composition (Pd₁₇Se₁₅ or Pd₁₆S₇) on the performance of nanocatalytic systems is also highlighted. Substrate scope has also been discussed in all three types of catalysis. The superiority of heterogeneous catalytic systems (e.g., Pd₁₇Se₁₅ immobilised on graphene oxide) indicates the bright future possibilities for the development of efficient catalytic systems using similar or tailored ligands for this reaction.

Organoselenium ligands for heterogeneous and nanocatalytic systems: development and applications

Organoselenium ligands have attracted great attention among researchers during the past two decades. Various homogeneous, heterogeneous and nanocatalytic systems have been designed using such ligands. Although reports on selenium ligated homogeneous catalysts are quite high in number, significant work has also been done on the development of heterogeneous and nanocatalytic systems using organoselenium ligands. A review article, focusing on the utility of organoselenium compounds in the development of catalytic systems, was published in 2012 (A. Kumar, G. K. Rao, F. Saleem and A. K. Singh, Dalton Trans., 2012, 41, 11949). Moreover, it mainly covered the homogeneous catalysts. There are no review articles in the literature on heterogeneous and nanocatalytic systems designed using organoselenium compounds and their applications. Hence, this perspective aims to cover the developments pertaining to the synthetic aspects of such catalytic systems (using organoselenium compounds) and their applications in catalysis of a variety of chemical transformations. Salient features and advantages of organoselenium compounds have also been highlighted to justify the rationale behind their use in catalyst development. Their performance in various chemical transformations [viz. Suzuki-Miyaura coupling, Heck coupling, Sonogashira coupling, O-arylation of phenol, transfer hydrogenation of aldehydes and ketones, aldehyde-alkyne-amine (A3) coupling, hydration of nitriles, conversion of aldehydes to amides, cross-dehydrogenative coupling (CDC), photodegradation of substrates (formic acid, methylene blue), reduction of nitrophenols, electrolysis (hydrogen evolution reaction and oxygen reduction reactions), organocatalysis and dye sensitized solar cells] and relevant aspects of catalytic processes (such as recyclability, substrate scope and green aspects) have been critically analyzed. Future perspectives have also been discussed.

Synthesis and antioxidant activity of new selenium-containing quinolines

Background:

Quinoline derivatives have been attracted much attention in drug discovery and synthetic derivatives of these scaffolds present a range of pharmacological activities. Therefore, organoselenium compounds are valuable scaffolds in organic synthesis because their pharmacological activities and their use as versatile building blocks for regio-, chemio-and stereoselective reactions. Thus, the synthesis of selenium-containing quinolines has great significance, and their applicability range from simple antioxidant agents, to selective DNA-binding and photocleaving agents.

Objective:

In the present study we describe the synthesis and antioxidant activity in vitro of new 7-chloroN(arylselanyl)quinolin-4-amines 5 by the reaction of 4,7-dichloroquinoline 4 with (arylselanyl)-amines 3.

Methods:

For the synthesis of 7-chloro-N(arylselanyl)quinolin-4-amines 5, we performed the reaction of (arylselanyl)- amines 3 with 4,7-dichloroquinoline 4 in the presence of Et3N at 120 °C in a sealed tube. The antioxidant activities of the compounds 5 were evaluated by the following in vitro assays: 2,2- diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), ferric ion reducing antioxidant power (FRAP), nitric oxide (NO) scavenging and superoxide dismutase-like activity (SOD-Like).

Results:

7-Chloro-N(arylselanyl)quinolin-4-amines 5a-d has been synthesized in yields ranging from 68% to 82% by the reaction of 4,7-dichloroquinoline 4 with arylselanyl-amines 3a-d using Et3N as base, at 120 °C, in a sealed tube for 24 hours and tolerates different substituents, such as -OMe and -Cl, in the arylselanyl moiety. The obtained compounds 5a-d presented significant results with respect to the antioxidant potential, which had effect in the tests of inhibition of radical’s DPPH, ABTS+ and NO, as well as in the test that evaluates the capacity (FRAP) and in the superoxide dismutase-like activity assay (SOD-Like). It is worth mentioning that 7-chloro-N(arylselanyl)quinolin-4-amine 5b presented excellent results, demonstrating a better antioxidant capacity when compared to the others.

Conclusion:

According to the obtained results 7-chloro-N(arylselanyl)quinolin-4-amines 5 were synthesized in good yields by the reaction of 4,7-dichloroquinoline with arylselanyl-amines and tolerates different substituents in the arylselanyl moiety. The tested compounds presented significant antioxidant potential in the tests of inhibition of DPPH, ABTS+ and NO radicals, as well as in the FRAP and superoxide dismutase-like activity assays (SOD-Like).

Base free N-alkylation of anilines with ArCH2OH and transfer hydrogenation of aldehydes/ketones catalyzed by the complexes of η5-Cp*Ir(iii) with chalcogenated Schiff bases of anthracene-9-carbaldehyde

The condensation of anthracene-9-carbaldehyde with 2-(phenylthio/seleno)ethylamine results in Schiff bases [PhS(CH₂)₂C[double bond, length as m-dash]N-9-C₁₄H₉](L1) and [PhSe(CH₂)₂C[double bond, length as m-dash]N-9-C₁₄H₉] (L2). On their reaction with [(η⁵-Cp*)IrCl(μ-Cl)]₂ and CH₃COONa at 50 °C followed by treatment with NH₄PF₆, iridacycles, [(η⁵-Cp*)Ir(L-H)][PF₆] (1: L = L1; 2: L = L2), result. The same reaction in the absence of CH₃COONa gives complexes [(η⁵-Cp*)Ir(L)Cl][PF₆] (3-4) in which L = L1(3)/L2(4) ligates in a bidentate mode. The ligands and complexes were authenticated with HR-MS and NMR spectra [¹H, ¹³C{¹H} and ⁷⁷Se{¹H} (in the case of L2 and its complexes only)]. Single crystal structures of L2 and half sandwich complexes 1-4 were established with X-ray crystallography. Three coordination sites of Ir in each complex are covered with η⁵-Cp* and on the remaining three, donor atoms present are: N, S/Se and C^-/Cl^-, resulting in a piano-stool structure. The moisture and air insensitive 1-4 act as efficient catalysts under mild conditions for base free N-alkylation of amines with benzyl alcohols and transfer hydrogenation (TH) of aldehydes/ketones. The optimum loading of 1-4 as a catalyst is 0.1-0.5 mol% for both the activations. The best reaction temperature is 80 °C for transfer hydrogenation and 100 °C for N-alkylation. The mercury poisoning test supports a homogeneous pathway for both the reactions catalyzed by 1-4. The two catalytic processes are most efficient with 3 followed by 4 > 1 > 2. The mechanism proposed on the basis of HR-MS of the reaction mixtures of the two catalytic processes taken after 1-2 h involves the formation of an alkoxy and hydrido species. The real catalytic species proposed in the case of iridacycles results due to the loss of the Cp* ring.

Palladacycles of sulfated and selenated Schiff bases of ferrocene-carboxaldehyde as catalysts for O-arylation and Suzuki–Miyaura coupling

Palladacycles of Schiff-bases having a ferrocene core catalyze O-arylation of ArBr and Suzuki–Miyaura coupling of ArBr/Cl with a yield up to 93%.

Reactions of nitroxides 16. First nitroxides containing tellurium atom

Five- and six-membered nitroxides with a tellurium containing moiety were synthesized by the addition of nitroxyl amines to phenyltellanyl alkylene isothiocyanates.

Tetragonal Cu2Se nanoflakes: synthesis using selenated propylamine as Se source and activation of Suzuki and Sonogashira cross coupling reactions

The metastable tetragonal Cu2Se phase as nanoflakes has been synthesized for the first time by treating CuCl2 taken in a mixture (1:1) of 1-octadecene and oleylamine with H2N-(CH2)3-SePh dissolved in 1-octadecene. Powder X-ray diffraction (PXRD), HRTEM, SEM-EDX and XPS have been used to authenticate the nanoflakes. The XPS of Cu2Se nanoflakes indicates oxidation states of Cu and Se as +1 and -2 respectively. The size of the majority of Cu2Se nanoflakes was found to be between 12 and 14 nm. The nanoflakes have been explored for Suzuki and Sonogashira cross coupling reactions in the presence of TBAB in DMF and DMSO respectively. For Suzuki coupling conversion was found upto ∼86% in 15 h at 110 °C when loading of Cu was 1 mol%. In case of Sonogashira coupling conversion was found upto 82% in 15 h at 160 °C (Cu loading: 1 mol%). The catalytic efficiency of Cu2Se nanoflakes for Suzuki coupling reaction is greater than that for Sonogashira coupling. These nanoflakes have been found reusable for a second time. Most probably TBAB facilitates the release of CuBr from the nanoflakes which catalyze both reactions, as catalytic efficiency is very low in the absence of TBAB and CuBr has been found to activate readily both the coupling reactions. In comparison to many other copper based nano-crystals, the present nanoflakes are a better activator.

Efficient catalysis of Suzuki-Miyaura C-C coupling reactions with palladium(II) complexes of partially hydrolyzed bisimine ligands: a process important in environment context

Potentially hexadentante [O(-),N,E:E,N,O(-)] chalcogenated bisimine ligands L1-L3 have been synthesized by reaction of 1,1'-(4,6-dihydroxy-1,3-phenylene)bisethanone with H2N(CH2)2SPh, H2N(CH2)2SePh and H2N(CH2)2TeC6H4-4-OMe respectively. The L1-L3 react with Na2PdCl4 resulting in their partial hydrolysis, which appears to be metal-promoted. Of the two [(CH3)CN(CH2)2EAr] fragments of L1-L3, one is converted to (CH3)CO and H2N(CH2)2EAr eliminated. The hydrolysis products 1-[C(CH3)N(CH2)2SPh]-3-[C(CH3)O]-4,6-[OH]2C6H2 (L1'), 1-[C(CH3)N(CH2)2SePh]-3-[C(CH3)O]-4,6-[OH]2C6H2 (L2') and 1-[C(CH3)N(CH2)2TeC6H4-4-OMe]-3-[C(CH3)O]-4,6-[OH]2C6H2 (L3') have formed complexes [PdCl(L'-H)] (1, 3 and 5). The other product of hydrolysis H2N(CH2)2EAr (L″) reacted with Na2PdCl4 yielding the complexes [PdL"Cl2] (2, 4 and 6). All the complexes (1-6) were found thermally and air stable. Complexes 1, 3 and 5 have been investigated as catalysts for Suzuki-Miyaura CC coupling reactions. The catalytic activities of 1 and 3 which are palladium complexes of S- and Se-containing Schiff base derivatives respectively, were found good for the Suzuki-Miyaura cross-coupling of aryl bromides with phenylboronic acid under mild reaction conditions. The Pd(II) complex (3) of selenated ligand was found active to catalyze the coupling of 2-chlorobenzaldehyde and 3-chlorotoluene. The activity of Te analog was found to be the lowest one as it failed in catalyzing the coupling of electronically deactivated aryl bromides.