Showing papers in "European Journal of Inorganic Chemistry in 2012"
TL;DR: A comprehensive overview of the current state-of-the-art in first-row transition metal cooperative catalysts can be found in this article. But the focus of this paper is on the metal-ligand bifunctional substrate activation.
Abstract: Cooperative catalysis with first-row transition metals holds much promise for future developments regarding sustainable, selective transformations, including e.g. alkenes, dienes and a variety of small molecules such as CO2, N2 and water. This non-exhaustive analysis of the current state-of-the-art aims to give a comprehensive overview of the various design strategies and applications of first-row transition metal cooperative reactivity and to provide leads for new research initiatives in order to expand this emerging field. The main aspects covered involve bimetallic cooperativity, redox-noninnocent ligands in combination with first-row transition metal complexes, otherwise reactive or noninnocent scaffolds that can induce metal-ligand bifunctional substrate activation and the design of adaptive ligands and complexes thereof, wherein hemilability is a key factor for selective reactivity. The metals under review are primarily the late transition metals Fe, Co, Ni and Cu.
389 citations
TL;DR: An overview of the current investigations, developments, and possibilities of metal-organic frameworks (MOFs) for use in heat pumps is given in this paper, where a large step forward is anticipated in the field of sorption heat pumps.
Abstract: Thermally driven heat pumps can significantly help to minimize primary energy consumption and greenhouse gas emissions generated by industrial or domestic heating and cooling processes. This is achieved by using solar or waste heat as the operating energy rather than electricity or fossil fuels. One of the most promising technologies in this context is based on the evaporation and consecutive adsorption of coolant liquids, preferably water, under specific conditions. The efficiency of this process is first and foremost governed by the microporosity, hydrophilicity, and hydrothermal stability of the sorption material employed. Traditionally, inorganic porous substances like silica gel, aluminophosphates, or zeolites have been investigated for this purpose. However, metal–organic frameworks (MOFs) are emerging as the newest and by far the most capable class of microporous materials in terms of internal surface area and micropore volume as well as structural and chemical variability. With further exploration of hydrothermally stable MOFs, a large step forward in the field of sorption heat pumps is anticipated. In this work, an overview of the current investigations, developments, and possibilities of MOFs for use in heat pumps is given.
278 citations
TL;DR: In this paper, the authors introduce the reader to redox-active ligands, which range from the small archetypical NO+/•/− and O20/•−/2− systems via the classical 1,4-dihetero-1,3-diene chelates (e.g. α-diimine, dithiolene, or o-quinone redox series) to π-conjugated macrocycles.
Abstract: This essay for EurJIC's cluster issue on cooperative and redox non-innocent ligands introduces the reader to redox-active ligands, which range from the small archetypical NO+/•/– and O20/•–/2–systems via the classical 1,4-dihetero-1,3-diene chelates (e.g. α-diimine, dithiolene, or o-quinone redox series) to π-conjugated macrocycles. The increased attention paid recently to the redox activity of ligands in coordination chemistry has now prompted wider successful searches, resulting in the establishing of less-conventional examples such as cyanide, carbon monoxide, thioethers, or acetylacetonate derivatives as non-innocently behaving ligands. By considering situations with significantly covalent metal–ligand bonding, the cases of metal–oxo, metal–hydrido, and organometallic compounds will also be addressed, with a perspective on how pervasive non-innocent ligand behavior is. The materials and reactivity potential of redox-active ligands will be pointed out.
238 citations
TL;DR: In this paper, the coordination chemistry of electron-rich metal complexes with the simple aliphatic, anionic diphosphanylamido ligand {N(CH2CH2PR2)2} is covered and compared with other commonly used anionic PEP (E = C, N) pincer ligands.
Abstract: In this review, the coordination chemistry of electron-rich metal complexes with the simple aliphatic, anionic diphosphanylamido ligand {N(CH2CH2PR2)2}– is covered and compared with other commonly used, anionic PEP (E = C, N) pincer ligands. The strong π-basicity of this ligand enables both the stabilization of electronically and coordinatively highly unsaturated complexes and their use as cooperating ligands in bifunctional stoichiometric bond activation reactions and catalysis. Versatile ligand backbone dehydrogenation gives access to related enamido and dienamido ligands {(R2PCHCH)N(CH2CH2PR2)}– and {N(CHCHPR2)2}–, respectively. This oxidative functionalization enables fine-tuning of the ligand donor properties and thereby of the structural features, electronic structure, and reactivity of the respective complexes, which is discussed for several examples.
228 citations
TL;DR: The use of GdIII complexes with higher hydration number, the control of the rate of exchange of the bound water molecule(s), and the reduction of the local rotational motions of the conjugated complexes leads to significant relaxivity enhancement of the nanosized systems.
Abstract: In recent years, novel, better, and more complex systems have been developed in which GdIII chelates are attached to macromolecular substrates or incorporated into nanoparticles. These magnetic resonance imaging (MRI) nanoprobes make it possible to deliver to the site of interest a large number of Gd3+ ions, thus increasing the sensitivity of the technique. In this paper, we review the most important systems developed, the conjugation methods, and the procedures devised to optimize the relaxivity. These involve the use of GdIII complexes with higher hydration number, the control of the rate of exchange of the bound water molecule(s), and the reduction of the local rotational motions of the conjugated complexes. The increase in relaxivity of the individual Gd chelates leads to significant relaxivity enhancement of the nanosized systems.
168 citations
TL;DR: In this paper, mesoporous MIL-100(Al, Cr or Fe) metal-organic frameworks were synthesized by a microwave-assisted solvothermal route with green solvents.
Abstract: Nanoparticles of mesoporous MIL-100(Al, Cr or Fe) metal–organic frameworks were synthesized by a microwave-assisted solvothermal route with green solvents. The optimization of yield, crystallinity, and particle size was achieved through the control of synthetic parameters such as temperature, heating rate, and dwelling time. The particle size strongly depends on the metallic cation and the metal and linker precursors; nanoparticles smaller than 100 nm were obtained for iron and chromium based MIL-100. Finally, stable colloidal solutions of iron and chromium MIL-100 nanoparticles were used for thin layer dip-coating deposition, which resulted in high optical quality thin films, the porosity of which was investigated by environmental ellipsometric porosimetry.
160 citations
TL;DR: In this paper, a review of the current literature on chelation of Mn2+ chelates with variable ligand structures is presented, which allows for establishing trends of how ligand structure, the rigidity of the ligand scaffold, and its donor-acceptor properties influence the thermodynamic, kinetic, and redox stability of the Mn 2+ complex.
Abstract: Mn2+ has five unpaired d electrons, a long electronic relaxation time, and labile water exchange, which make it an attractive alternative to Gd3+ in the design of contrast agents for medical Magnetic Resonance Imaging. In order to ensure in vivo safety and high contrast agent efficiency, the Mn2+ ion has to be chelated by a ligand that provides high thermodynamic stability and kinetic inertness of the complex and has to have at least one free coordination site for a water molecule. Unfortunately, these two requirements are contradictory, as lower denticity of the ligands, which leads to more inner-sphere water molecules often implies a decreased stability of the complex, and, therefore, it is necessary to find a balance between both requirements. In the last decade, a large amount of experimental data has been collected to characterize the physico-chemical properties of Mn2+ chelates with variable ligand structures. They now allow for establishing trends of how the ligand structure, the rigidity of the ligand scaffold, and its donor–acceptor properties influence the thermodynamic, kinetic, and redox stability of the Mn2+ complex. This microreview surveys the current literature in this field.
147 citations
TL;DR: In this paper, the chemistry and applications of low-valent iron complexes bearing potentially non-innocent ligands are discussed. But the focus of this review is not on the catalytic properties of these complexes.
Abstract: Introduced in the late sixties, non-innocent (or redox) ligands have been extensively studied for their unusual and intriguing chemical behavior. Their ability to delocalize and/or provide electrons to the metal center of organometallic complexes confers them undisputable chemical interest and has proved valuable in the development of novel synthetic methodologies. This review will focus on the chemistry and applications of low-valent iron complexes bearing potentially non-innocent ligands. Because of the elusive nature of these ligands, and whenever possible, theoretical calculations and analysis of spectroscopic data will be presented in an effort to provide insights into the catalytic activity of the complexes.
136 citations
TL;DR: In this paper, an analysis of the conjugative possibilities of dienes carrying two terminal heteroatom donors shows some generalizations of these as possible redox-active (redox "noninnocent") ligands.
Abstract: An analysis of the conjugative possibilities of dienes carrying two terminal heteroatom donors shows some generalizations of these as possible redox-active (redox “noninnocent”) ligands. If the two E=C functionalities (E = O,S, NR, CHR) are connected by an odd number of sp2-hybridized atoms, full conjugation between the two terminal E donors is not possible, a situation which is found both in 2,6-bis(imino)pyridine (BIMPY) and beta-diketiminate ligands; the character of their redox noninnocence is thus altered, compared to 1,4-diheterodienes. Some insight into the BIMPY ligand comes from the analog where one imino arm is absent. The traditional stereochemical relationships which govern conjugation in arenes are analyzed for their implications for different bis(imino)pyridine isomers, and also for 2,6-dipyrimidyl- and dipyridazinyl-pyridines, as generalizations of the classic terpyridyl ligands. Factors which favor oxidized vs. reduced ligand forms are discussed.
124 citations
TL;DR: In this article, the authors describe their efforts to produce Mn 3 O 4 -graphene nanocomposites based on a convenient andfeasible solution based synthetic route under mild conditions.
Abstract: In this work, we describe our efforts to produce Mn 3 O 4 –graphene nanocomposites based on a convenient andfeasible solution based synthetic route under mild conditions. According to transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) results porous Mn 3 O 4 nanocrystals (NCs), 20–40 nm in size, are uniformly deposited on both sides of the graphene nanosheet (GNS) matrix. Significantly, the as-prepared Mn 3 O 4 –graphene nanocomposites exhibit remarkable pseudocapacitive activity including high specific capacitance (236.7 F g –1 at 1 A g –1 ), good rate capability (133 F g –1 at 8 A g –1 ), and excellent cyclability (the specific capacitance only decreases by 6.32 % of the initial capacitance after 1000 cycles). The excellent pseudocapacitive performance of the Mn 3 O 4 –graphene nanocomposites electrode is probably due to the positive synergistic effects between the Mn 3 O 4 and GNS. Namely, the intimate combination of the conductive graphene network with uniformly dispersed porous Mn 3 O 4 NCs not only greatly improves the electrochemical utilization of Mn 3 O 4 , but also increases the double-layer capacitance of the graphene sheets. These characteristics make this nanocomposite a very promising electrode material for high performance supercapacitors.
121 citations
TL;DR: In this article, a new Mo6 cluster complex and its silica and polyurethane composites have been synthesized and characterized, which are highly luminescent with emission above 650 nm, produce singlet oxygen with high efficiency, and can be excited up to 580 nm.
Abstract: A new Mo6 cluster complex and its silica and polyurethane composites have been synthesized and characterized. These materials are highly luminescent with emission above 650 nm, produce singlet oxygen with high efficiency, are photostable, and can be excited up to 580 nm. These properties are desirable for the construction of luminescent probes of oxygen, photoactive materials for oxidation reactions with easily separable active carriers, and bactericidal textile surfaces upon daylight irradiation.
Abstract: Ring-opening polymerisation of cyclic esters represents a growing field of research, because the resulting polymers are biodegradable and mostly based on renewable raw materials, which ensures increasing interest in this process within the context of green chemistry. Up to now, neutral N-donor ligands have been overlooked in their potential to stabilise catalytically active systems. This contribution summarises recent developments in this area as well as their applicability in lactide polymerisation with special regard to the reaction conditions. When a use on the industrial scale is targeted, tolerance towards moisture, air, lactide impurities and high temperatures is an important issue to be considered during catalyst design. A multitude of sodium, calcium and zinc complexes with amines, carbenes, guanidines, phosphinimines, pyridines and tris(pyrazolyl)methanes is discussed and their activity in lactide polymerisation is highlighted.
TL;DR: The state of the art of manganese-based MRI contrast agents is highlighted with a particular focus on the chemical structures of these agents and on their chronological evolution from simple chelates to complex nanohybrid systems.
Abstract: During the last decades, a wide range of molecular and cellular imaging techniques have been developed and optimized, resulting in important progress in the understanding of diagnostic and biological processes. Among these techniques, magnetic resonance imaging (MRI) is certainly one of the most popular, because of its high spatial resolution and the fact that it does not require the use of radioisotopes. Although gadolinium has long been the most commonly used paramagnetic metal to design efficient MRI contrast agents, the discovery of its potential toxicity has driven researchers to give priority to other paramagnetic metals, as, for example, manganese. With this microreview we would like to highlight the state of the art of manganese-based MRI contrast agents with a particular focus on the chemical structures of these agents and on their chronological evolution from simple chelates to complex nanohybrid systems.
TL;DR: In this paper, the second-order nonlinear optical (NLO) response of a series of 2D polyoxometalate-based terpyridine-substituted compounds was studied.
Abstract: DFT calculations were carried out in order to study the second-order nonlinear optical (NLO) response of a series of proposed 2D polyoxometalate-based terpyridine-substituted compounds. These compounds can be formulated as [Mo6O17{N4C25H16(X)2}{N4C25H16(X)2}]2– (X = H, F, Cl, Br, I, CF3, or CN), which has a wedge Λ-shaped acceptor––π-conjugated bridge––donor––π-conjugated bridge––acceptor (A-π-D-π-A) configuration. The calculations showed that these compounds possess significantly large molecular second-order polarizabilities that range from approximately 1000 × 10–30 to 4300 × 10–30 esu. The combination of trifluoromethyl (CF3) and cyanide (CN) groups at the end of the terpyridine ligand strengthens the bridge conjugation, which is useful for the enhancement of the NLO response. In addition, the greatest contributions to the βvec values are dervied from the charge transfer (CT) from the Mo≡N bond and the organoimido ligand to the terpyridine-substituted segments. This report demonstrates that various combinations of the acceptor(s) remarkably affect the second-order NLO response. The electronic transitions to the crucial excited states indicated that the y polarized transition contributed to the off-diagonal second-order polarizabiliy tensor (βzyy) and that the z polarized transition accounted for the diagonal second-order polarizabiliy tensor (βzzz). Thus, itsteered towards in-plane nonlinear anisotropy (u = βzyy/βzzz) along with a good 2D second-order NLO response. These compounds can be used as good 2D second-order NLO materials from the point of view of their large β values.
TL;DR: A belt-like V2O3@C core-shell-structured composite was successfully synthesized by thermal treatment with the precursor V3O7·H2O@C composite under an inert atmosphere.
Abstract: A beltlike V2O3@C core–shell-structured composite was successfully synthesized by thermal treatment with the precursor V3O7·H2O@C composite under an inert atmosphere. The phase, composition, structure, and morphology of the as-obtained samples were confirmed by XRD, elemental analysis, FTIR, energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), IR Raman, SEM, and TEM measurements. The process of the formation of V2O3@C is briefly discussed. The carbon coated onto the surface of V2O3 is disordered, and V2O3 keeps the original morphology of V3O7·H2O. V2O3@C has an average length that ranges from 0.4 to 5.2 μm, a width of about 80–170 nm, and an average thickness of the shells of about 15.6 nm. The possible formation mechanism of V2O3@C is proposed as follows: the reaction undergoes a solid-state reaction by the interface reaction between V3O7 cores and carbon shells. It was found that the V2O3@C composite possesses the same phase-transition properties as V2O3, which could expand the possible applications of materials related to V2O3 in the future. Furthermore, a V2O3 sphere, a V2O3 nanobelt, and the beltlike V2O3@C composite were explored as cathode materials for application in lithium-ion batteries. The beltlike V2O3@C composite electrode exhibited the best electrochemical properties among them, thereby achieving our aim of improving the electrochemical properties of V2O3.
TL;DR: In photocatalytic H2 formation, tertiary amines are commonly used as sacrificial electron donors, thereby limiting the pH range for studies in water and the concentration of free protons as mentioned in this paper.
Abstract: In photocatalytic H2 formation, tertiary amines are commonly used as sacrificial electron donors, thereby limiting the pH range for studies in water and the concentration of free protons. We found that ascorbate rapidly reductively quenches the excited state of [Re(CO)3(bipy)(py)]+ (bpy = 2,2′-bipyridyl; py = pyridine). In combination with the water reduction catalyst (WRC) [Co{(DO)(DOH)pn}Br2] [(DO)(DOH)pn = N2,N2′-propanediylbis(2,3-butanedione 2-imine 3-oxime)], this system produces H2 upon irradiation with light under acidic conditions (pH range 2–6) and with significantly enhanced turnover numbers. Furthermore, we observed that, in contrast to similar systems with tertiary amines, oxidized ascorbate (dehydroascorbic acid) is slowly re-reduced during the course of photocatalysis.
TL;DR: In this article, a ternary nanocomposite of graphene-TiO2-Fe3O4 (GTF) was developed as a low-cost, recollectable and stable photocatalyst for the degradation of organic dyes.
Abstract: We developed a ternary nanocomposite of graphene–TiO2–Fe3O4 (GTF) as a low-cost, recollectable, and stable photocatalyst for the degradation of organic dyes. The nanocomposite has been successfully prepared by successively growing TiO2 and Fe3O4 nanoparticles on the reduced graphene oxide (RGO). The as-synthesized GTF nanocomposite shows higher photocatalytic activity as compared with that of pure TiO2 nanoparticles and can be easily collected from water using a magnet. More importantly, benefiting from the presence of RGO, GTF can suppress the photodissolution behavior of Fe3O4 nanoparticles that usually occurrs in TiO2–Fe3O4 binary nanocomposites, rendering it a highly stable photocatalyst. Furthermore, the GTF nanocomposite works well in different pH environments and is capable of eliminating mixtures of various dyes. In addition, the GTF is also able to degrade the dyes under sunlight. These attractive features make the GTF nanocomposite a promising photocatalyst for practical use in wastewater treatment.
TL;DR: In this paper, seven cyclopentadienyl-NHC piano-stool iron complexes were prepared and studied in the catalytic hydrosilylation of aldehydes and ketones under visible light irradiation.
Abstract: Seven cyclopentadienyl-NHC piano-stool iron complexes were prepared and studied in the catalytic hydrosilylation of aldehydes and ketones under visible light irradiation. A significant acceleration of the rate was observed when the reactions were carried out under solvent-free conditions. Single-crystal X-ray structural analyses were performed for complexes 5 and 7.
TL;DR: In this article, a novel porous coordination polymer (PCP), Zr-abdc, composed of Zrbased secondary building units (SBUs), [Zr6O4(OH)4]12+, and 4,4′-azobenzenedicarboxylate (abdc2)-linkers, has been synthesized by a modulated synthetic approach.
Abstract: A novel porous coordination polymer (PCP), Zr–abdc, composed of Zr-based secondary building units (SBUs), [Zr6O4(OH)4]12+, and 4,4′-azobenzenedicarboxylate (abdc2–) linkers, has been synthesized by a modulated synthetic approach. In accord with the twelve-fold connecting SBU, Zr–abdc has a topology similar to the PCP series UiO-66–UiO-68, which is proposed from single-crystal XRD and powder (P)XRD experiments. The linkers are strongly disordered, which made it impossible to determine the exact structure. The compound was further characterized by thermogravimetric analysis, scanning electron microscopy and Ar sorption measurements. Soxhlet extraction with ethanol instead of simple washing was helpful to remove guest molecules present in the pores after the synthesis. PXRD patterns measured at elevated temperatures show that a material stable up to 400 °C in air was obtained. After activation, it showed a specific surface area of 3000 m2 g–1 and a pore volume of 1.41 cm3 g–1.
TL;DR: Progress made in the application of metallodendrimers as scaffolds for drug delivery, as metal-based drugs in their own right, and as agents for biosensing, photothermal and photodynamic therapy are described.
Abstract: The field of biomedical metallodendrimers is an emerging discipline that is attracting prolific attention. Metallodendrimers, like their organic counterparts, are known for their multivalency (high concentration of peripheral end-groups), well-defined architectures and narrow polydispersity. These are characteristics that make metallodendrimers well-suited as innovative scaffolds for the development of new therapeutic agents. Coupled with the surge of interest in the use of various metal complexes to treat various diseases, the application of metallodendrimers in medicinal chemistry is an attractive strategy for therapies involving macromolecules and the advancement of new metal-based therapeutics. In this review, we describe the progress made in the application of metallodendrimers as scaffolds for drug delivery, as metal-based drugs in their own right, and as agents for biosensing, photothermal and photodynamic therapy.
TL;DR: A short overview of hybrid inorganic-organic materials can be found in the European Journal of Inorganic Chemistry (EJIC) as mentioned in this paper, where the authors discuss the future potential of hybrid materials based on some of the most exciting areas of development, such as artificial photosynthetic leaves, metamaterials, molecular machines, theranostics, 3D printing, nuclear waste storage, and the exploration of life's extraordinary evolutionary origins.
Abstract: We introduce this themed issue of the European Journal of Inorganic Chemistry with a short overview of hybrid inorganic–organic materials. Hybrid materials have been used in society since antiquity, in fact the creative musings regarding hybridization began in ancient mythology. Now hybrid materials are ubiquitous, and so for clarity they have been divided into different classes and subgroups. These are explained and illustrated with notable synthetic and natural examples. The second half of this overview is devoted to some speculation about the future potential of hybrid materials based on some of the most exciting areas of development, such as artificial photosynthetic leaves, metamaterials, molecular machines, theranostics, 3D printing, nuclear waste storage, and the exploration of life's extraordinary evolutionary origins.
TL;DR: In this paper, three trinuclear heterometallic nickel(II)manganese (II) complexes were synthesized by using [NiL] as the so-called ligand complex, where H2L = N,N-bis(salicylidene)-1,3-propanediamine.
Abstract: Three new trinuclear heterometallic nickel(II)manganese(II) complexes, [(NiL)2Mn(NCS)2] (1), [(NiL)2Mn(NCO)2] (2), and [{NiL(EtOH)}2Mn(NO2)2]center dot 2EtOH (3), have been synthesized by using [NiL] as the so-called ligand complex [where H2L = N,N'-bis(salicylidene)-1,3-propanediamine] and have been structurally characterized. Crystal structure analyses revealed that complexes 1 and 2 are angular trinuclear species, in which two terminal four-coordinate square planar [NiL] moieties are coordinated to a central MnII through double phenoxido bridges. The MnII is in a six-coordinate distorted octahedral environment that is bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1) and cyanate (in 2). In complex 3, in addition to the double phenoxo bridge, the two terminal NiII ions are linked to the central MnII by means of a nitrite bridge (1?N:2?O) that, together with a coordinated ethanol molecule, gives rise to an octahedral environment around the NiII ions and consequently the structure becomes linear. Catecholase activity of these three complexes was examined by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. All three complexes mimic catecholase activity and the rate of catechol oxidation follows saturation kinetics with respect to the substrate and first-order kinetics with respect to the catalyst. The EPR spectra of the complexes exhibit characteristic six line spectra, which indicate the presence of high-spin octahedral MnII species in solution state. The ESI-MS positive spectrum of 1 in the presence of 3,5-DTBC has been recorded to investigate possible complexsubstrate intermediates.
TL;DR: In this paper, metal-ligand cooperativity was investigated as a strategy for promoting nickel-catalyzed alkene hydrogenation, and it was shown that the catalytic reaction proceeds through a pathway involving initial insertion of the alkene into the Ni-H bond.
Abstract: To investigate metal–ligand cooperativity as a strategy for promoting nickel-catalyzed alkene hydrogenation, cationic and neutral nickel(II) hydride complexes of the aliphatic pincer ligand PNHPCy {PNHPCy = HN[CH2CH2P(Cy)2]2} have been synthesized and characterized. Cationic hydride complex [(PNHPCy)Ni(H)]BPh4 (2) catalyzed the hydrogenation of styrene and 1-octene under mild conditions. Only low conversion was observed in the hydrogenation of 3,5-dimethoxybenzaldehyde using 2. The neutral hydride complex (PNPCy)Ni(H) (3) was also found to be an alkene hydrogenation catalyst. Mechanistic experiments suggest that for catalyst 2, the hydrogenation reaction proceeds through a pathway involving initial insertion of the alkene into the Ni–H bond. Contrary to the initial hypothesis, reactivity comparisons with the methyl-substituted hydride complex [(PNMePCy)Ni(H)]BPh4 {PNMePCy = (CH3)N[CH2CH2P(Cy)2]2} suggest that metal–ligand cooperativity is not involved in these rare examples of mild and homogeneous nickel hydrogenation catalysis.
TL;DR: In this article, the authors used density functional theory computations to investigate the mechanism of the reaction of an amine with a primary alcohol catalyzed by the ruthenium(II)-PNP pincer complex.
Abstract: We have used density functional theory computations to investigate the mechanism of the reaction of an amine with a primary alcohol catalyzed by the ruthenium(II)-PNP pincer complex [PNP = 2,6-bis(di-tert-butylphosphanylmethyl)pyridine]; the reaction produces an imine as the major product. The catalytic cycle includes four stages: (stage I) alcohol dehydrogenation to aldehyde, (stage II) coupling of aldehyde with amine to form hemiaminal, (stage III) hemiaminal dehydration to give imine, and (stage IV) catalyst regeneration by means of H2 elimination of the trans ruthenium dihydride complex produced in stage I. The mechanism is similar to that for amide formation from amine and alcohol that was catalyzed by the RuII-PNN pincer complex [PNN = 2-(di-tert-butylphosphanylmethyl)-6-(diethylaminomethyl)pyridine], the only difference being in stage III. Alcohol dehydrogenation (stage I) occurs by a bifunctional double hydrogen transfer mechanism and alcohol can facilitate stages II and III. The selectivity of imine over ester is governed by stage II: the formation of hemiaminal by means of aldehydeamine coupling is kinetically much more favorable than the alternative aldehydealcohol coupling reaction that yields hemiacetal. Furthermore, the hemiaminal dehydration to give an imine is also kinetically more favorable than the hemiacetal dehydrogenation to give an ester. The selectivity of imine over amide is determined by stage III: the hemiaminal dehydration to give an imine is kinetically much more favorable than the hemiaminal dehydrogenation to give an amide. The essential difference between the RuII-PNP-catalyzed imine synthesis and the RuII-PNN-catalyzed amide formation is that the former prefers hemiaminal dehydration whereas the latter prefers hemiaminal dehydrogenation. In addition, water produced during hemiaminal dehydration can catalyze stages II and III more effectively than alcohol can. By contrast, the water-catalyzed hemiaminal formation does not happen in the RuII-PNN-catalyzed synthesis of an amide because no water is produced in any stage of the reaction.
TL;DR: In this paper, the reaction between H2O2 and two water oxidation catalysts was studied by means of in situ 1D and 2D-NMR experiments in order to elucidate if catalyst degradation proceeds through the initial functionalization of a quaternary carbon atom (C-attack) or by hydrogen abstraction of the Cp* -C-CH3 moiety.
Abstract: The reaction between H2O2 and two water oxidation catalysts {[Cp*Ir(H2O)3](NO3)2 (1, Cp* = pentamethylcyclopentadienyl) and [Cp*Ir(bzpy)(NO3)] (2, bzpy = 2-benzoylpyridine)} was studied by means of in situ 1D- and 2D-NMR experiments in order to elucidate if catalyst degradation proceeds through the initial functionalization of a quaternary carbon atom (C-attack) or by hydrogen abstraction (H-attack) of the Cp* –C–CH3 moiety. It was shown that 1 underwent double functionalization of the –C–CH3 moiety of Cp* leading to the formation of –C(OR)–CH2OR (R = H or OH) in a strictly analogous manner to that previously observed for the reaction of 1 with Ce4+. On the contrary, two new intermediates associated with the oxidative degradation of 2, which are functionalized only at the quaternary carbon atom(s) of the –C–CH3 moiety [–C(OR)–CH3], were intercepted and characterized by NMR spectroscopy. This indicates that the oxidative degradation of water oxidation catalysts, featuring the –Cp* ancillary ligand, likely starts with preferential C-attack.
TL;DR: In this paper, the electronic structure of the five-membered electron-transfer series (n = 1+, 0, 1−) has been established by a combination of electro- and magnetochemistry, electron paramagnetic resonance (EPR) and Mossbauer spectroscopy, X-ray crystallography, and DFT calculations.
Abstract: The five-membered electron-transfer series [M(bpy)3]n and [M(tpy)2]n (M = Fe, Ru; bpy = 2,2′-bipyridine, tpy = 2,2′:6′,2″-terpyridine) and [Fe(tbpy)3]n (tbpy = 4,4′-di-tert-butyl-2,2′-bipyridine; n = 3+, 2+, 1+, 0, 1–) have been investigated and the electronic structure of the so called “low-valent” complexes (n = 1+, 0, 1–) have been established by a combination of electro- and magnetochemistry, electron paramagnetic resonance (EPR) and Mossbauer spectroscopy, X-ray crystallography, and DFT calculations. These complexes are accessed by reduction of the d6 S = 0 dicationic starting materials [M(bpy)3]2+ and [M(tpy)2]2+ (M = Fe, Ru) and [Fe(tbpy)3]2+. The monocations [M(bpy·)(bpy0)2]1+ (S = 1/2) and [M(tpy·)(tpy0)]1+ (S = 1/2) (M = FeII, RuII) also contain a low-spin (t2g)6 divalent metal center, plus a single radical monoanion (bpy·)1– or (tpy·)1–, and two or one neutral (bpy0) or (tpy0) ligands, respectively. The unpaired electron resides in a ligand π* orbital. The neutral complexes [FeII(bpy·)2(bpy0)]0 and [RuII(tpy·)2]0 were found, by DFT calculations, to possess an S = 1 ground state that is attained by weak intramolecular ferromagnetic coupling between two ligand radical anions and a singlet excited state (S = 0). In contrast, the neutral species [RuII(bpy·)2(bpy0)]0 possesses an S = 0 ground state. The metal centers of these neutral complexes retain a low-spin (t2g)6 configuration. Remarkably, the corresponding neutral complex [FeII(tpy·)2]0 contains high-spin FeII (SFe = 2). Strong intramolecular antiferromagnetic metal–radical coupling yields an experimentally observed S = 1 ground state. The monoanions [MII(bpy·)3]1– (M = Fe, Ru) are composed of a low-spin metal ion [Fe, Ru; (t2g)6; SM = 0] and three (bpy·)1– radical anions.
TL;DR: In this paper, a microreview of transition metal-catalyzed cross-coupling reactions with pincer ligands is presented, including Kumada, Negishi, Suzuki, and Sonogashira reactions for the formation of different types of C-C bonds.
Abstract: Transition-metal-catalyzed cross-coupling reactions are powerful tools for constructing carbon–carbon and carbon–heteroatom bonds. In this microreview we summarize the nickel-catalyzed cross-coupling reactions with pincer ligands. The reactions presented here include Kumada, Negishi, Suzuki, and Sonogashira reactions for the formation of different types of C–C bonds, as well as the thiolation of aryl iodides.
TL;DR: In this article, the synthesis of monocrystalline Prussian blue (PB) analogue hollow nanocubes by applying a controlled chemical etching method with assistance of polyvinylpyrrolidone (PVP) was reported.
Abstract: We report the preparation of monocrystalline Prussian blue (PB) analogue hollow nanocubes by applying a controlled chemical etching method with assistance of polyvinylpyrrolidone (PVP). The hollow particles obtained possess the original single-crystalline structures, with retention of the high surface areas. Our synthetic route based on chemical etching is quite simple, and it can be scaled up for mass production.
TL;DR: The physicochemical basis of probe design for 19F MRS and MRI applications is reviewed in this article, where complexes that give a single major resonance in solution are described, in which the Ln3+ ion is about 6 A from the 19F label.
Abstract: The physicochemical basis of probe design for 19F MRS and MRI applications is reviewed. Complexes that give a single major resonance in solution are described, in which the Ln3+ ion is about 6 A from the 19F label. Sensitivity improvements of 15-fold are reported in both imaging and spectroscopy based on longitudinal relaxation enhancement. The pseudocontact shift allows an amplification of chemical shift non-equivalence in responsive 19F probes, e.g. for monitoring pH in the range between 5 and 8.
TL;DR: A series of allyl 1,2,3-triazol-5-ylidene (tzNHC) palladium complexes were prepared, and the structures of the complexes were fully characterized by NMR and X-ray diffraction analyses as discussed by the authors.
Abstract: A series of allyl 1,2,3-triazol-5-ylidene (tzNHC) palladium complexes was prepared, and the structures of the complexes were fully characterized by NMR and X-ray diffraction analyses. The donor properties of these ligands were evaluated by studying the vibrational spectra of their carbonyliridium complexes and their X-ray photoelectron spectra. These evaluations showed that the structures of the tzNHC palladium complexes are almost identical to those of the corresponding imidazole carbene palladium complexes, and that the tzNHC ligands have stronger donor properties than the imidazole carbene ligands. The relationship between catalytic activity and structure was examined by carrying out a room-temperature Suzuki–Miyaura coupling reaction, and the cinnamylpalladium complex bearing 1,4-bis(2,6-diisopropylphenyl)-3-methyl-1,2,3-triazol-5-ylidene (TPr) was found to be the most active catalyst. (cinnamyl)(TPr)PdCl showed high activity in the room-temperature reaction performed with aryl chlorides regardless of the electronic and steric properties of the substituents, and was effective in reactions with sterically crowded arylboronic acids.