Structural diversity and catalytic properties in a family of Ag(I)-benzotriazole based coordination compounds

In this work we study the coordination chemistry of a series of semi-rigid benzotriazole based ligands (L1-L3) along with the low coordination number but versatile AgI ions. This has led to nine new coordination compounds formulated [Ag(L1)(CF3CO2)] (1), [Ag2(L1T)2(CF3SO3)2]·2Me2CO (2), [Ag(L2T)(ClO4)(Me2CO)] (3), [Ag(L2T)(BF4)(Et2O)] (4), [Ag2(L3T)2(ClO4)2]2 (5), [Ag(L3)(NO3)] (6), [Ag2(L3T)2(CF3CO2)2] (7), [Ag2(L3T)(CF3SO3)2] (8) and [Ag2(L3T)2(CF3CF2CO2)2]·2Me2CO (9). These compounds show structural diversity including dimers (5, 7, 9), one dimensional (1D) (3, 4, 6) and two dimensional (2D) (1, 2, 8) coordination polymers. The presence of the two -CH2- units between the three rigid backbones, benzotriazole/-C6H4-/benzotriazole, provides a limited, but significant, flexibility in L1-L3, influencing their variety coordination abilities. Interestingly, certain structures exhibit an isomerism effect (L1T-L3T) in the benzotriazole unit when in solid state; a series of studies are indicative of the 1,1- form is generally dominant in solution even in cases where the crystal structure does not contain this tautomer. The homogeneous catalytic efficacy of all compounds against the well-known multi component A3 coupling reaction and the hydration of alkynes were investigated. Compound 4 was identified as the optimal catalyst for both reactions, promoting the multicomponent coupling as well as the alkyne hydration reaction under low loadings (0.5 and 3 mol%, respectively) and in high yields (up to 99 and 93% in each case)

Metal-catalysed A3 coupling methodologies: classification and visualisation

The multicomponent reaction of aldehydes, amines, and alkynes, known as A3 coupling, yields propargylamines, a valuable organic scaffold, and has received significant interest and attention in the last years. In order to fully realise the potential of the metal-based catalytic protocols that facilitate this transformation, we summarise substrates, in situ and well-characterised synthetic methods that provide this scaffold and attempt a monumental classification considering several variables (Metal, Coordinating atom(s), Ligand type and name, in-situ or well-characterised, co-catalyst, catalyst and ligand Loading (mol%), solvent, volume, atmosphere, temperature, microwave, time, yield, selectivity (e.e. d.r.), substrate name, functionality, loading (amines, aldehydes, alkynes), and use of molecular sieves). This pioneering work creates a valuable database that contains 2376 entries and allows us to produce graphs and better visualise their impact on the reaction

Copper-promoted regioselective synthesis of polysubstituted pyrroles from aldehydes, amines and nitroalkenes via1,2-phenyl/alkyl migration

The facile Copper-catalyzed synthesis of polysubstituted pyrroles from aldehydes, amines and β-nitroalkenesis reported. Remarkably, the use of α-methyl substituted aldehydes provide efficient access to a series of tetra- and pentasubstituted pyrroles via an overwhelming 1,2-phenyl/alkyl migration. The present methodology is also accessible to non α-substituted aldehydes yielding the corresponding trisubstituted pyrroles. On the contrary, the use of ketones, in place of aldehydes, does not promote the organic transformation signifying the necessity of α-substituted aldehydes. The reaction proceeds under mild catalytic conditions with low catalyst loading (0.3 – 1 mol %), a broad scope, very good functional-group tolerance, high yields and can be easily scaled up to more than 3 mmol of product, thus highlighting a useful synthetic application of the present catalytic protocol. Based on formal kinetic studies, a possible radical pathway is proposed that involves the formation of an allylic nitrogen radical intermediate, which in turn reacts with the nitroalkene to yield the desired pyrrole framework via a radical 1,2-phenyl or alkyl migration

Cu(II) coordination polymers as vehicles in the A³ coupling

A family of benzotriazole based coordination compounds, obtained in two steps and good yields from commercially available materials, formulated [CuII(L 1 )2(MeCN)2]·2(ClO4)·MeCN (1), [CuII(L 1 )(NO3)2]·MeCN (2), [ZnII(L 1 )2(H2O)2]·2(ClO4)·2MeCN (3), [CuII (L 1 )2Cl2]2 (4), [CuII 5(L 1 )2Cl10] (5), [CuII 2(L 1 )4Br2]·4MeCN·(CuII 2Br6) (6), [CuII(L 1 )2(MeCN)2]·2(BF4) (7), [CuII(L 1 )2(CF3SO3)2] (8), [ZnII(L 1 )2(MeCN)2]·2(CF3SO3) (9), [CuII 2(L 2 )4(H2O)2]·4(CF3SO3)·4Me2CO (10) and [CuII 2(L 3 )4(CF3SO3)2]·2(CF3SO3)·Me2CO (11) are reported. These air stable compounds were tested as homogeneous catalysts for the A3 coupling synthesis of propargyl amine derivatives from aldehyde, amine and alkyne under a non-inert atmosphere. Fine-tuning of the catalyst resulted in a one dimensional (1D) coordination polymer (CP) (8) with excellent catalytic activity in a wide range of substrates, avoiding any issues that would inhibit its performance

Application of Silver Nanoparticles in the Multicomponent Reaction Domain:A Combined Catalytic Reduction Methodology to Efficiently Access Potential Hypertension or Inflammation Inhibitors

The catalytic efficacy of silver nanoparticles was investigated toward the chemoselective reduction of nitro-tetrazole or amino acid-substituted derivatives into the corresponding amines in high isolated yields. This highly efficient protocol was thereafter applied toward the multi-component reaction synthesis of heterocyclic dihydroquinoxalin-2-ones with high isolated yields. The reaction proceeds with low catalyst loading (0.8-1.4 mol %) and under mild catalytic conditions, a very good functional-group tolerance, and high yields and can be easily scaled up to more than 1 mmol of product. Thus, the present catalytic methodology highlights a useful synthetic application. Different molecules are designed and accordingly synthesized with the current protocol that could play the role of inhibitors of the soluble epoxide hydrolase, an important target for therapies against hypertension or inflammation

Copper(II)-benzotriazole coordination compounds in click chemistry: a diagnostic reactivity study

This diagnostic study aims to shed light on the catalytic activity of a library of Cu(II) based coordination compounds with benzotriazole-based ligands. We report herein the synthesis and characterization of five new coordination compounds formulated [CuII(L4)(MeCN)2(CF3SO3)2] (1), [CuII(L5)2(CF3SO3)2] (2), [CuII(L6)2(MeCN)(CF3SO3)]·(CF3SO3) (3), [CuII(L6)2(H2O)(CF3SO3)]·(CF3SO3)·2(Me2CO) (4), [CuI4(L1)2(L1’)2(CF3SO3)2]2·4(CF3SO3)·8(Me2CO) (5), derived from similar nitrogen-based ligands. The homogeneous catalytic activity of these compounds along with our previously reported coordination compounds (6 -13), derived from similar ligands, is tested against the well-known Cu(I)-catalysed azide-alkyne cycloaddition reaction. The optimal catalyst [CuII(L1)2(CF3SO3)2] (10) activates the reaction to afford 1,4-disubstituted 1,2,3-triazoles with yields up to 98% and without requiring a reducing agent. Various control experiments are performed to optimize the method as well as examine parameters such as ligand variation, metal coordination geometry and environment, in order to elucidate the behaviour of the catalytic system

Supported Gold Nanoparticle-Catalyzed Selective Reduction of Multifunctional, Aromatic Nitro Precursors into Amines and Synthesis of 3,4-Dihydroquinoxalin-2-Ones

The synthesis of 3,4-dihydroquinoxalin-2-ones via the selective reduction of aromatic, multifunctional nitro precursors catalyzed by supported gold nanoparticles is reported. The reaction proceeds through the in situ formation of the corresponding amines under heterogeneous transfer hydrogenation of the initial nitro compounds catalyzed by the commercially available Au/TiO2-Et3SiH catalytic system, followed by an intramolecular C-N transamidation upon treatment with silica acting as a mild acid. Under the present conditions, the Au/TiO2-TMDS system was also found to catalyze efficiently the present selective reduction process. Both transfer hydrogenation processes showed very good functional-group tolerance and were successfully applied to access more structurally demanding products bearing other reducible moieties such as chloro, aldehyde or methyl ketone. An easily scalable (up to 1 mmol), low catalyst loading (0.6 mol%) synthetic protocol was realized, providing access to this important scaffold. Under these mild catalytic conditions, the desired products were isolated in good to high yields and with a TON of 130. A library analysis was also performed to demonstrate the usefulness of our synthetic strategy and the physicochemical profile of the derivatives

Simple Synthetic Approach to <i>N</i>-(Pyridin-2-yl)imidates from Nitrostyrenes and 2-Aminopyridines via the <i>N</i>-(Pyridin-2-yl)iminonitriles as Intermediates

A facile, green, synthetic protocol of several substituted N-(pyridin-2-yl)imidates from nitrostyrenes and 2-aminopyridines via the corresponding N-(pyridin-2-yl)iminonitriles as intermediates is reported. The reaction process involved the in situ formation of the corresponding α-iminontriles under heterogeneous Lewis acid catalysis in the presence of Al2O3. Subsequently, α-iminonitriles were selectively transformed into the desired N-(pyridin-2-yl)imidates under ambient conditions and in the presence of Cs2CO3 in alcoholic media. Under these conditions, 1,2- and 1,3-propanediols also led to the corresponding mono-substituted imidates at room temperature. The present synthetic protocol was also developed on one mmol scale, providing access to this important scaffold. A preliminary synthetic application of the present N-(pyridin-2-yl)imidates was carried out for their facile conversion into the N-heterocycles 2-(4-chlorophenyl)-4,5-dihydro-1H-imidazole and 2-(4-chlorophenyl)-1,4,5,6-tetrahydropyrimidine in the presence of the corresponding ethylenediamine and 1,3-diaminopropane

Reduction of Nitroarenes into Aryl Amines and N-Aryl hydroxylamines via Activation of NaBH4 and Ammonia-Borane Complexes by Ag/TiO2 Catalyst

In this study, we report the fabrication of mesoporous assemblies of silver and TiO2 nanoparticles (Ag/MTA) and demonstrate their catalytic efficiency for the selective reduction of nitroarenes. The Ag/TiO2 assemblies, which show large surface areas (119–128 m2·g−1) and narrow-sized mesopores (ca. 7.1–7.4 nm), perform as highly active catalysts for the reduction of nitroarenes, giving the corresponding aryl amines and N-aryl hydroxylamines with NaBH4 and ammonia-borane (NH3BH3), respectively, in moderate to high yields, even in large scale reactions (up to 5 mmol). Kinetic studies indicate that nitroarenes substituted with electron-withdrawing groups reduced faster than those with electron-donating groups. The measured positive ρ values from the formal Hammett-type kinetic analysis of X-substituted nitroarenes are consistent with the proposed mechanism that include the formation of possible [Ag]-H hybrid species, which are responsible for the reduction process. Because of the high observed chemo selectivities and the clean reaction processes, the present catalytic systems, i.e., Ag/MTA-NaBH4 and Ag/MTA-NH3BH3, show promise for the efficient synthesis of aryl amines and N-aryl hydroxylamines at industrial levels

Homogeneous Decatungstate-Catalyzed Photooxygenation of Tetrasubstituted Alkenes:~ A Deuterium Kinetic Isotope Effect Study

The decatungstate W10O324- homogeneous photocatalyzed oxygenation of tetrasubstituted alkenes has been mechanistically studied. In all cases, allylic hydroperoxides are the major products. The primary inter- and intramolecular as well as the remote δ-secondary deuterium kinetic isotope effects for the photooxidation of the 2,3-dimethyl-2-butene and 1,1,1-trideuterio-7-methyl-2-(trideuteriomethyl)octa- 2,6-diene along with product analysis suggest a hydrogen abstraction in the rate-determining step. For comparison, singlet oxygen photosensitized oxidations of the above substrates were also studied. © 2006 American Chemical Society