Organic Catalysis Research Articles

ChemInform Abstract: Cyclometalated [Cp*M(C^X)] (M: Ir, Rh; X: N, C, O, P) Complexes

AbstractReview: synthesis, characterization and applications; 167 refs.

Visible-light organic photocatalysis for latent radical-initiated polymerization via 2e⁻/1H⁺ transfers: initiation with parallels to photosynthesis.

We report the latent production of free radicals from energy stored in a redox potential through a 2e–/1H+ transfer process, analogous to energy harvesting in photosynthesis, using visible-light organic photoredox catalysis (photocatalysis) of methylene blue chromophore with a sacrificial sterically hindered amine reductant and an onium salt oxidant. This enables light-initiated free-radical polymerization to continue over extended time intervals (hours) in the dark after brief (seconds) low-intensity illumination and beyond the spatial reach of light by diffusion of the metastable leuco-methylene blue photoproduct. The present organic photoredox catalysis system functions via a 2e–/1H+ shuttle mechanism, as opposed to the 1e– transfer process typical of organometallic-based and conventional organic multicomponent photoinitiator formulations. This prevents immediate formation of open-shell (radical) intermediates from the amine upon light absorption and enables the “storage” of light-energy without spontaneous initiation of the polymerization. Latent energy release and radical production are then controlled by the subsequent light-independent reaction (analogous to the Calvin cycle) between leuco-methylene blue and the onium salt oxidant that is responsible for regeneration of the organic methylene blue photocatalyst. This robust approach for photocatalysis-based energy harvesting and extended release in the dark enables temporally controlled redox initiation of polymer syntheses under low-intensity short exposure conditions and permits visible-light-mediated synthesis of polymers at least 1 order of magnitude thicker than achievable with conventional photoinitiated formulations and irradiation regimes.

ChemInform Abstract: Poly(ethylene glycol)‐Based Ionic Liquids: Properties and Uses as Alternative Solvents in Organic Synthesis and Catalysis

AbstractReview: 83 refs.

Photofragmentation of Gas-Phase Lanthanide Cyclopentadienyl Complexes: Experimental and Time-Dependent Excited-State Molecular Dynamics.

Unimolecular gas-phase laser-photodissociation reaction mechanisms of open-shell lanthanide cyclopentadienyl complexes, Ln(Cp)3 and Ln(TMCp)3, are analyzed from experimental and computational perspectives. The most probable pathways for the photoreactions are inferred from photoionization time-of-flight mass spectrometry (PI-TOF-MS), which provides the sequence of reaction intermediates and the distribution of final products. Time-dependent excited-state molecular dynamics (TDESMD) calculations provide insight into the electronic mechanisms for the individual steps of the laser-driven photoreactions for Ln(Cp)3. Computational analysis correctly predicts several key reaction products as well as the observed branching between two reaction pathways: (1) ligand ejection and (2) ligand cracking. Simulations support our previous assertion that both reaction pathways are initiated via a ligand-to-metal charge-transfer (LMCT) process. For the more complex chemistry of the tetramethylcyclopentadienyl complexes Ln(TMCp)3, TMESMD is less tractable, but computational geometry optimization reveals the structures of intermediates deduced from PI-TOF-MS, including several classic “tuck-in” structures and products of Cp ring expansion. The results have important implications for metal–organic catalysis and laser-assisted metal–organic chemical vapor deposition (LCVD) of insulators with high dielectric constants.

DNA from natural sources in design of functional devices

The role of DNA as structuring or templating agent has become more significant with the development of nanobiotechnology. Although short single and double stranded DNA have extensively been used as immobilization tool, as a template for nanoparticle preparation and in design of various devices such as nanomotors and biosensors, DNA from natural sources has an advantage of being abundant, cheap and readily available. Therefore, it is not surprising that there is a huge interest in making the use of natural DNA properties for both nano- and micro-applications. In this review we attempt to give an overview of the up to date applications of natural DNA, either from viral, marine or mammalian sources, in design of functional devices. This article is meant to be a starting point and a guide to the platforms in which natural DNA is employed such as DNA origami, optoelectronic devices and organic catalysis.

Organic Photoredox Catalysis as a General Strategy for Anti-Markovnikov Alkene Hydrofunctionalization.

The development of a general catalyst system for the direct anti-Markovnikov hydrofunctionalization of alkenes is presented. A unique catalyst system comprised of an acridinium photooxidant and a hydrogen atom transfer reagent allows for a range of alkene anti-Markovnikov hydrofunctionalization reactions including hydroalkoxylation, hydroamination, and hydroacetoxylation.

Post-polymerization modification and organocatalysis using reactive statistical poly(ionic liquid)-based copolymers

Copoly(ionic liquid)s (coPILs) based on poly(styrene)-co-poly(4-vinylbenzylbutylimidazolium) with different anions (Cl− and HCO3−), denoted as PS-co-PVBnBuImCl 1 and PS-co-PVBnBuImHCO32, were used as reactive polymers for the purpose of post-polymerization modification and organic catalysis. While coPIL 1 could be derived into the corresponding poly(N-heterocyclic carbene)-silver transition metal complex referred to as poly(NHC–Ag) by a simple deprotonation/metallation sequence utilizing Ag2O, coPIL 2 was found to quantitatively react with various electrophiles, including CS2, isothiocyanate and transition metals (based on Pd and Au) upon formal loss of “H2CO3, affording the post-functionalized poly(NHC-CS2), poly(NHC-isothiocyanate) and poly(NHC-Met) (Met = Au, Pd) copolymers. The catalytic activity of both coPILs 1 and 2 was also examined in cyclic carbonate formation by reaction between CO2 and propylene oxide and in the benzoin condensation, respectively.

Design of novel indium oxide supported gold nanocatalysts and their application in homocoupling of arylboronic acids

Gold (Au) nanoparticles stabilized on metal oxide supports offer superior catalytic activity and recyclability in organic catalysis. We report for the first time synthesis of indium oxide stabilized gold (Au@In2O3) nanocatalysts using an electrochemical procedure and their application in homocoupling of arylboronic acids. In2O3 nanoparticles prepared via sol-gel process are subjected to sacrificial anode electrolysis (SAE) under inert condition for electrodeposition of nano Au on In2O3. Thus Au@In2O3 nanoparticles obtained are thermally annealed at high temperature to partially oxidize Au and to remove any surfactants. XPS results show the existence of both elemental (nano Au0) and cationic (Au3+) species in Au@In2O3 nanocatalysts, while SEM images confirm the presence of nanoscale Au (<10nm) particles on In2O3 surface. Au@In2O3 nanocatalysts are tested for arylboronic acids homocoupling under different conditions and it is found that they are highly active in organic medium with K2CO3 base and demonstrate excellent conversion (>97%) and selectivity (>98%). The catalyst recyclability and performance towards differently substituted arylboronic acids is also studied and a plausible mechanism of action is proposed.

ChemInform Abstract: Bio‐Based Solvents: An Emerging Generation of Fluids for the Design of Eco‐Efficient Processes in Catalysis and Organic Chemistry

AbstractReview: 146 refs.

Mesoporous Silica Nanomaterials Applications in Catalysis

Mesoporous silica materials benefit from unique features that have attracted substantial interest for their use as catalyst-immobilization matrices. These features include high surface area, chemical, thermal, and mechanical stability, highly uniform pore distribution and tunable pore size, high adsorption capacity, and an ordered porous network for free diffusion of substrates and reaction products. Solid supported catalysts are of great interests in both academic and industrial arenas due to their recyclability, enhanced catalytic reactivity, and selectivity. Inorganic, organic end enzymatic catalysis fields have been revolutionized by introduction of mesoporous silica nanomaterials as support due to dramatic increase of contact area and thus contributing to overall reaction yield [1-4]. Furthermore, mesoporous silica offers the opportunity of multifunctionalization and therefore, multiple catalyst immobilizations. The ability to sequester selectively molecules buy their functionality makes mesoporous silica catalyst championing high selectivities. This editorial will highlight the most important achievements in the field of mesoporous silica-supported catalysis. The first mesoporous silica material was first reported as early as 1971, where a material described as low-bulk density silica was obtained from hydrolyzing and condensing tetraethoxysilicate (TEOS) in the presence of cationic surfactants [5]. This result did not gain much attention at the time it was published because the porosity and structural properties were not reported. It was not until 1992 that the chemistry society started to realize the potential of this field, when scientists in oil giant Mobil Corporation laboratories published a series of ordered mesoporous materials (M41S) with pore sizes ranging from 1.5-10 nm. The variant called MCM-41 with 1000 m 2 g -1 and pore volumes up to 1 cm 3 g -1 , has been comprehensively studied and widely applied in many fields such as drug delivery, biosensors and catalysis [6-12]. The morphological transformations that lead to converting bulk MCM-41 mesoporous silica to functionalized mesoporous silica nanospheres (MSNs) by Lin’s group represented a step forward toward increasing control of kinetics in catalytic reactions occurring in functionalized MSN [10]. The first report of utilizing mesoporous silica in polymer synthesis catalysts initiated by Aida’s group in Japan, has opened new avenues toward modern solid-supported catalysis. The authors reported crystalline nanofibers of linear polyethylene with an ultrahigh molecular weight (6,200,000) and a diameter of 30 to 50 nanometers, formed by the polymerization of ethylene with mesoporous silica fiber–supported titanocene, with methylalumoxane as a cocatalyst. Small-angle x-ray scattering analysis indicated that the polyethylene fibers consist predominantly of extended-chain crystals. The Science article highlighted the potential utility of the honeycomb-like porous framework as an extruder for nanofabrication of polymeric materials [13].

Merging metal–organic framework catalysis with organocatalysis: A thiourea functionalized heterogeneous catalyst at the nanoscale

A new thiourea-containing metal–organic framework (MOF) catalyst was synthesized. It overcomes recycling, self-aggregation and solvation issues that exist in homogeneous thiourea catalysts. Nanomorphology was introduced to increase the dispersion of the solid catalyst in solvent. Acetalization and Morita–Baylis–Hillman reactions were catalyzed using the new thiourea MOF catalyst.

Self-assembled wire-like and honeycomb-like osmium nanoclusters (NCs) in DNA with pronounced catalytic and SERS activities

A new route to the formation of ultra-small Os nanoparticles (NPs) in DNA is reported. The Os NPs that are initially formed are self-assembled together to form Os nanoclusters (NCs) which have wire-like and honeycomb-like morphologies. The synthesis was carried out within a minute using microwave heating by the reaction of Os salt with ethanol. The size of the individual Os NPs varies between 1 and 3 nm and the synthesized particles are stabilized in DNA. The stable Os NCs showed a coupled SPR band near 600 nm in the visible region, which is useful for using the material as a potential SERS substrate. The SERS study was carried out using methylene blue (MB) as a model SERS probe molecule and the observed EF value is ∼107, which is much higher compared to a recent report for Os NPs. Apart from SERS, the Os NCs have also been tested in a catalysis reaction. The catalysis reaction was carried out for the first time for the reduction of organic nitro compounds in the presence of excess NaBH4. The catalytic reaction rate using Os NCs as a catalyst was found to be superior compared to earlier reports with other metal NPs, like Au or Ag. The improved catalytic and SERS activities of the Os NCs due to their ultra-small size with a high surface area might be useful in future in the field of biosensors, biomedicine, nano devices and other organic catalysis reactions.

High-Energy-Surface Engineered Metal Oxide Micro- and Nanocrystallites and Their Applications

Because many physical and chemical processes occur at surfaces, surface atomic structure is a critical factor affecting the properties of materials. Due to the presence of high-density atomic steps and edges and abundant unsaturated coordination sites, micro- and nanocrystallites with high-energy surfaces usually exhibit greater reactivity than those with low-energy surfaces. However, high-energy crystal surfaces are usually lost during crystal growth as the total surface energy is minimized. Therefore, the selective exposure of high-energy facets at the surface of micro- and nanocrystallites is an important and challenging research topic. Metal oxides play important roles in surface-associated applications, including catalysis, gas sensing, luminescence, and antibiosis. The synthesis of metal oxide micro- and nanocrystallites with specific surfaces, particularly those with high surface energies, is more challenging than the synthesis of metal crystals due to the presence of strong metal-oxygen bonds and diverse crystal structures. In this Account, we briefly summarize recent progress in the surface-structure-controlled synthesis of several typical metal oxide micro- and nanocrystallites, including wurtzite ZnO, anatase TiO2, rutile SnO2, and rocksalt-type metal oxides. We also discuss the improvement of surface properties, focusing on high-energy surfaces. Because of the huge quantity and diverse structure of metal oxides, this Account is not intended to be comprehensive. Instead, we discuss salient features of metal oxide micro- and nanocrystallites using examples primarily from our group. We first discuss general strategies for tuning the surface structure of metal oxide micro- and nanocrystallites, presenting several typical examples. For each example, we describe the basic crystallographic characteristics as well as the thermodynamic (i.e., tuning surface energy) or kinetic (i.e., tuning reaction rates) strategies we have used to synthesize micro- and nanocrystallites with high surface energies. We discuss the structural features of the specific facets and analyze the basis for the enhanced performance of the metal oxide micro- and nanocrystallites in water splitting, the degradation of organic pollutants, gas sensing, catalysis, luminescence, and antibiosis. Finally, we note the future trends in high-energy-facet metal oxide micro- and nanocrystallite research. A comprehensive understanding of the properties of metal oxide micro- and nanocrystallites with high-energy crystal surfaces and related synthetic strategies will facilitate the rational design of functional nanomaterials with desired characteristics.

Asymmetric Mannich reaction between (S)-N-(tert-butanesulfinyl)-3,3,3-trifluoroacetaldimine and malonic acid derivatives. Stereodivergent synthesis of (R)- and (S)-3-amino-4,4,4-trifluorobutanoic acids

Inorganic as well as organic base catalysis was found to be effective for diastereoselective Mannich additions of malonic acid derivatives to (SS)-N-(tert-butanesulfinyl)-3,3,3-trifluoroacetaldimine. In the presence of catalytic amounts of inorganic bases, n-BuLi or DMAP, the reaction gives the corresponding (R,SS)-β-aminomalonates in good yield and with diastereoselectivity up to 9/1 dr. In contrast, phosphazene bases favour the formation of the (S,SS)-diastereomer with selectivities as high as 99/1. Simple choosing of an appropriate base catalyst for the Mannich addition reaction allowed us to obtain enantiomerically pure (R)- or (S)-configured 3-amino-4,4,4-trifluorobutanoic acids after hydrolysis and decarboxylation of the corresponding β-aminomalonates.

Poly(ethylene glycol)‐Based Ionic Liquids: Properties and Uses as Alternative Solvents in Organic Synthesis and Catalysis

PEG-based ionic liquids are a new appealing group of solvents making the link between two distinct but very similar fluids: ionic liquids and poly(ethylene glycol)s. They find applications across a range of innumerable disciplines in science, technology, and engineering. In the last years, the possibility to use these as alternative solvents for organic synthesis and catalysis has been increasingly explored. This Review highlights strategies for their synthesis, their physical properties (critical point, glass transition temperature, density, rheological properties), and their application in reactions catalyzed by metals (such as Pd, Cu, W, or Rh) or as organic solvent (for example for multicomponent reactions, organocatalysis, CO2 transformation) with special emphasis on their toxicity, environmental impact, and biodegradability. These aspects, very often neglected, need to be considered in addition to the green criteria usually considered to establish ecofriendly processes.

CATALYTIC METHODS OF CREATION AND FUNCTIONALIZATION OF THE COUMARIN SKELETON

Methods of synthesis and functionalization of coumarins using metal complex and organic catalysis are considered in the review. Authors: A. Yu. Fedorov, A. V. Nyuchev, and I. P. Beletskaya. English translation in Chemistry of Heterocyclic Compounds , 2012, 48 (1), pp 166-178 http://link.springer.com/article/10.1007/s10593-012-0980-8

Do organic ligands affect forsterite dissolution rates?

Far-from equilibrium, steady state forsterite dissolution rates were measured at pH ∼3 and 25°C in aqueous solutions containing 0.1m/kg NaCl and up to 0.1mol/kg of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those common in Earth surface environments and those considered as potential catalysts for use in CO2 sequestration efforts: acetate, oxalate, citrate, EDTA4−, glutamate, gluconate, malonate, aspartate, tartrate, malate, alginate, salycilate and humate. The presence of up to 0.1mol/kg of each organic ligand altered forsterite dissolution rates less than 0.2 log units, which is the estimated uncertainty of the measured rates. Results obtained in this study, therefore, suggest that the presence of aqueous organic anions negligibly affects forsterite far-from equilibrium dissolution rates in most natural environments, and indicate that forsterite carbonation may not be appreciably accelerated by organic ligand catalysis.

ChemInform Abstract: Stereoselective Bioreduction of β‐Carboline Imines Through Cell‐Free Extracts from Earthworms (Eisenia foetida).

Abstract Although remarkable advances have been made over the last decade in organic synthesis, catalysis, and biotechnology, there is still a need to introduce and develop new processes for chemical production to achieve sustainable and cleaner approaches to support the increasing global pharmaceutical/chemical industry. There is a growing need to produce optically active compounds in high yields to maintain and support areas such as pharmaceutical and natural product synthesis. Thus, chemists today are looking for alternative reactions carried out under green conditions. In this context, we describe β-carboline imine reductions employing cell-free extracts from red Californian earthworms ( Eisenia foetida ) in high yields and enantiomeric excesses. The enantiomeric excess values of the bioreduction showed no dependence on the imine 1a – g substituents to afford amines with an ( R )-configuration. Based on these data, a model for the cell-free extract from the earthworm is proposed.

Solid-Phase Organic Synthesis and Catalysis: Some Recent Strategies Using Alumina, Silica, and Polyionic Resins

Solid-phase organic synthesis (SPOS) and catalysis have gained impetus after the seminal discovery of Merrifield’s solid-phase peptide synthesis and also because of wide applicability in combinatorial and high throughput chemistry. A large number of organic, inorganic, or organic-inorganic hybrid materials have been employed as polymeric solid supports to promote or catalyze various organic reactions. This review article provides a concise account on our approaches involving the use of (i) alumina or silica, either having doped with metal salts or directly, and (ii) polyionic resins to either promote various organic reactions or to immobilize reagents/metal catalysts for subsequent use in hydrogenation and cross-coupling reactions. The reaction parameters, scopes, and limitations, particularly in the context of green chemistry, have been highlighted with pertinent approaches by other groups.

Applications of ionic liquids in organic synthesis and catalysis

In recent years, various novel and greener methodologies have been developed using ionic liquids (ILs). In these reactions, IL has played multiple roles like catalyst, solvent, and catalyst support. In some cases, it was observed that IL enables efficient catalytic reactions in comparison with conventional molecular solvents. On the other hand, although a number of catalytic reaction processes in which ILs are used have been established in industry, there were also some unexpected problems, such as unintelligible aberrance or degradation of so-called task-specific ILs occurring in reaction processes and on the pilot plant scale. Also, several urgent questions regarding the fundamental aspects of ILs particularly toxicity and greener preparation methods need to be clarified. Several industrial applications of ILs are also discussed.