Amide Complexes Research Articles

Development of a Library of Extremely Bulky Amide Ligands, and their use for the Stabilization of Germanium(I) and Germanium(II) Compounds

AbstractEleven new extremely bulky aryl/silyl substituted secondary amines, L1–11H, have been prepared. These incorporate a combination of one of the bulky aryl groups, C6H2{C(H)Ph2}2R‐2,6,4; R=Me (Ar*), Pri (Ar†); C6H2{C(H)(C6H3But2‐3,5)2}2Me‐2,6,4) (Ar#); or C6H2{C(H)(2‐naphthyl)2}2Me‐2,6,4 (Ar¥), and one of the silyl fragments, SiMe3, SiCy3 (Cy=cyclohexyl), SiPri3, Si(p‐C6H4But)3, or Si(OBor)3 (OBor=[(1S)‐endo]‐(−)‐borneoxy). Amines including the latter silyl group represent the first enantiopure examples of this ligand class. All amines are readily deprotonated with n‐butyllithium or KH. Reactions of five alkali metal amide complexes with GeCl2⋅dioxane have given monomeric amido‐germanium(II) chloride complexes, LxGeCl (x=1–4, 7). Treatment of two of these with KOBut afforded monomeric amido‐germanium(II) tert‐butoxide species, LxGeOBut (x=1 or 3). Reductions of two amido‐germanium(II) chloride systems with a dimagnesium(I) compound afforded amido‐digermyne species, LxGeGeLx (x=3 or 4), the X‐ray crystal structures of which show them to possess very short Ge−Ge bonds, with considerable implied multiple bond character.

The Contribution of Commercial Metal Amides to the Chemical Recycling of Waste Polyesters

Simple and commercially available metal amides are investigated as catalysts for the chemical depolymerization of polyesters of commercial interest such as polylactide (PLA) and polyethylene terephthalate (PET) via alcoholysis. In the alcoholysis reactions performed with methanol or ethanol at room temperature, Zn, Mg, and Y amides showed the highest activities, while the amides of group 4 metals were revealed as poor catalysts. During the ethanolysis of PLA at higher temperatures and the glycolysis of PET, the good activity of the Zn amide was preserved, while for Mg and Y amides, a significant decrease was observed. The reaction temperature had an opposite effect on the performance of group 4 amides, with the Zr amide revealed to be the best catalyst in the PET glycolysis, reaching activities comparable to the best ones reported in the literature for metal catalysts (78% BHET yield within one hour at 180 °C). These studies represent new opportunities for the sustainable recycling of plastics, which are currently being used on a large scale, and provide significant contributions to the design of a circular economy model in the plastic industry.

Hydrogen Atom Abstraction from an OsII(NH3)2 Complex Generates an OsIV(NH2)2 Complex: Experimental and Computational Analysis of the N-H Bond Dissociation Free Energies and Reactivity.

Double hydrogen atom abstraction from (TMP)OsII(NH3)2 (TMP = tetramesitylporphyrin) with phenoxyl or nitroxyl radicals leads to (TMP)OsIV(NH2)2. This unusual bis(amide) complex is diamagnetic and displays an N-H resonance at 12.0 ppm in its 1H NMR spectrum. 1H-15N correlation experiments identified a 15N NMR spectroscopic resonance signal at -267 ppm. Experimental reactivity studies and density functional theory calculations support relatively weak N-H bonds of 73.3 kcal/mol for (TMP)OsII(NH3)2 and 74.2 kcal/mol for (TMP)OsIII(NH3)(NH2). Cyclic voltammetry experiments provide an estimate of the pKa of [(TMP)OsIII(NH3)2]+. In the presence of Barton's base, a current enhancement is observed at the Os(III/II) couple, consistent with an ECE event. Spectroscopic experiments confirmed (TMP)OsIV(NH2)2 as the product of bulk electrolysis. Double hydrogen atom abstraction is influenced by π donation from the amides of (TMP)OsIV(NH2)2 into the d orbitals of the Os center, favoring the formation of (TMP)OsIV(NH2)2 over N-N coupling. This π donation leads to a Jahn-Teller distortion that splits the energy levels of the dxz and dyz orbitals of Os, results in a low-spin electron configuration, and leads to minimal aminyl character on the N atoms, rendering (TMP)OsIV(NH2)2 unreactive toward amide-amide coupling.

Structure, reactivity and catalytic properties of manganese-hydride amidate complexes.

The high efficiency of widely applied Noyori-type hydrogenation catalysts arises from the N-H moiety coordinated to a metal centre, which stabilizes rate-determining transition states through hydrogen-bonding interactions. It was proposed that a higher efficiency could be achieved by substituting an N-M' group (M' = alkali metals) for the N-H moiety using a large excess of metal alkoxides (M'OR); however, such a metal-hydride amidate intermediate has not yet been isolated. Here we present the synthesis, isolation and reactivity of a metal-hydride amidate complex (HMn-NLi). Kinetic studies show that the rate of hydride transfer from HMn-NLi to a ketone is 24-fold higher than that of the corresponding amino metal-hydride complex (HMn-NH). Moreover, the hydrogenation of N-alkyl-substituted aldimines was realized using HMn-NLi as the active catalyst, whereas HMn-NH is much less effective. These results highlight the superiority of M/NM' bifunctional catalysis over the classic M/NH bifunctional catalysis for hydrogenation reactions.

Hyaluronic Acid Methacrylate Hydrogel-Modified Electrochemical Device for Adsorptive Removal of Lead(II).

This paper presents the development of a compact, three-electrode electrochemical device functionalized by a biocompatible layer of hyaluronic acid methacrylate (HAMA) hydrogel for the adsorptive removal of detrimental lead (Pb(II)) ions in aqueous solutions. An adsorption mechanism pertaining to the observed analytical performance of the device is proposed and further experimentally corroborated. It is demonstrated that both the molecular interactions originating from the HAMA hydrogel and electrochemical accumulation originating from the electrode beneath contribute to the adsorption capability of the device. Infrared spectral analysis reveals that the molecular interaction is mainly induced by the amide functional group of the HAMA hydrogel, which is capable of forming the Pb(II)–amide complex. In addition, inductively coupled plasma mass spectrometric (ICP-MS) analysis indicates that the electrochemical accumulation is particularly valuable in facilitating the adsorption rate of the device by maintaining a high ion-concentration gradient between the solution and the hydrogel layer. ICP-MS measurements show that 94.08% of Pb(II) ions present in the test solution can be adsorbed by the device within 30 min. The HAMA hydrogel-modified electrochemical devices exhibit reproducible performance in the aspect of Pb(II) removal from tap water, with a relative standard deviation (RSD) of 1.28% (for n = 8). The experimental results suggest that the HAMA hydrogel-modified electrochemical device can potentially be used for the rapid, on-field remediation of Pb(II) contamination.

In situ Grignard Metalation Method, Part II: Scope of the One-Pot Synthesis of Organocalcium Compounds.

The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot strategy to synthesize alkaline-earth metal amides in multi-gram scale with high yields via addition of bromoethane to an ethereal suspension of a primary or secondary amine and magnesium (Part I) or calcium (Part II). This method is highly advantageous because no activation of calcium is required prior to the reaction. Contrary to the magnesium-based iGMM, there are some limitations, the most conspicuous one is the large influence of steric factors. The preparation of Ca(hmds)2 succeeds smoothly within a few hours with excellent yields opening the opportunity to prepare large amounts of this reagent. Side reactions and transfer of the iGMM to substituted anilines and N-heterocycles as well as other H-acidic substrates such as cyclopentadienes are studied. Bulky amidines cannot be converted directly to calcium amidinates via the iGMM but stoichiometric calciation with Ca(hmds)2 enables their preparation.

Heavy Alkali Metal Manganate Complexes: Synthesis, Structures and Solvent-Induced Dissociation Effects.

Rare examples of heavier alkali metal manganates [{(AM)Mn(CH2 SiMe3 )(N'Ar )2 }∞ ] (AM=K, Rb, or Cs) [N'Ar =N(SiMe3 )(Dipp), where Dipp=2,6-iPr2 -C6 H3 ] have been synthesised with the Rb and Cs examples crystallographically characterised. These heaviest manganates crystallise as polymeric zig-zag chains propagated by AM⋅⋅⋅π-arene interactions. Key to their preparation is to avoid Lewis base donor solvents. In contrast, using multidentate nitrogen donors encourages ligand scrambling leading to redistribution of these bimetallic manganate compounds into their corresponding homometallic species as witnessed for the complete Li - Cs series. Adding to the few known crystallographically characterised unsolvated and solvated rubidium and caesium s-block metal amides, six new derivatives ([{AM(N'Ar )}∞ ], [{AM(N'Ar )⋅TMEDA}∞ ], and [{AM(N'Ar )⋅PMDETA}∞ ] where AM=Rb or Cs) have been structurally authenticated. Utilising monodentate diethyl ether as a donor, it was also possible to isolate and crystallographically characterise sodium manganate [(Et2 O)2 Na(n Bu)Mn[(N'Ar )2 ], a monomeric, dinuclear structure prevented from aggregating by two blocking ether ligands bound to sodium.

Metalation of 2‐Quinolyl‐Linked (Boranophosphinoyl)methane −Alkali Metal, Alkaline Earth Metal, and Ytterbium(II) Complexes of Monoanionic [CH(iPr2P−BH3)(C9H6N‐2)]− Ligand

AbstractA series of alkali and alkaline earth metal complexes, and an ytterbium(II) complex of monoanionic [CH(iPr2P−BH3)(C9H6N‐2)]− ligand (abbreviated as LQPB−) were synthesized. Lithium complexes [Li(LQPB)(TMEDA)] (2, TMEDA=Me2NCH2CH2NMe2) and [Li(LQPB)(12‐crown‐4)] (3) were prepared by lithiation of 1 with LinBu in the presence of TMEDA and 12‐crown‐4 ether, respectively. Treatment of 2 with NaOtBu and KOtBu, respectively, followed by addition of 18‐crown‐6 ether yielded monomeric sodium complex [Na(LQPB)(18‐crown‐6)] (4) and polymeric potassium derivative [K(LQPB)(18‐crown‐6)]n (5). Metalation of 1 with MgnBu2/TMEDA afforded [Mg(LQPB)2(TMEDA)] (6). Heavier group 2 complexes [Ca(LQPB)2(DME)2] (7), [Sr(LQPB)2]2 (8) and [Ba(LQPB)2(DME)] (9) were synthesized by metalation of 1 with the corresponding alkaline earth metal amide M[N(SiMe3)2]2(DME)n (M=Ca or Ba, n=2; M=Sr, n=0) in toluene under reflux conditions. Treatment of YbI2(THF)2 with potassium complex 5 led to isolation of mononuclear Yb(II) complex [Yb(LQPB)2(18‐crown‐6)] (10).

Attochemistry of hydrogen bonded amide and thioamide model complexes in protein following vertical ionization

Hydrogen bond in protein structure is a dynamic topic in research community. 2-Pyridone attached to amide forms hydrogen bond in the protein structure. Instead of amide, a number of model complexes such as thioamide in protein structure are used in recent research. Thioamide behaves potential surrogate of amide. To develop better understanding on the effect of ionizing radiation in protein, charge migration should be studied rigorously for the hydrogen bonded complexes such as amide:2-pyridone or thioamide:2-pyridone complexes. Hydrogen bond energies of these complexes are investigated in this context. Surprisingly, thioamide hydrogen bonded complexes are stronger in nature compare to amide hydrogen bonded complexes. This investigation centered on charge migration through amide and thioamide hydrogen bonded complexes and focused on different aspects of attosecond charge migration through these bonds. It is observed that charge migration occurs in amide hydrogen bonded complexes in 600–800 attoseconds time scale whereas it ceases for thioamide hydrogen bonded complexes.

Theoretical studies on excited‐state properties and luminescence mechanism of a Carbene–Metal–Amide Au(I) complex with thermally activated delayed fluorescence

AbstractTwo‐coordinate Carbene−Metal−Amide (CMA) complexes with thermally activated delayed fluorescence (TADF) have attracted much attention owing to their excellent luminescence properties and potential applications in organic light‐emitting devices. However, the luminescence mechanism remains unclear. Herein, we took one CMA Au(I) complex as an example and investigate its relevant photophysics using both density functional theory (DFT) and time‐dependent DFT methods with a polarizable continuum model. The calculated absorption and emission spectra agree with the experimental data and the S1 and T1 states show mixed ligand to ligand charge transfer (CT) and ligand to metal CT characters. Small spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) minimizes the energy difference between the S1 and T1 states (ΔEST). Properly large spin‐orbit coupling promotes the reverse intersystem crossing (rISC) process. At 300 K, the rISC process is much more efficient than the T1 phosphorescent emission, which leads to the TADF emission.

Dyadic Analysis of a Speed-Dating Format between Farmers and Citizens

Alienation between farmers and citizens has increased amid complex developments of agriculture’s intensification, urbanization processes, demographic change, and specialization in food supply chains in developed countries. Traditional public relations instruments have failed to generate societal acceptance of today’s intensive agricultural practices. At the same time, the agricultural sector feels alienated from societal value changes. Other controversial contexts showed that open face-to-face encounters at eye level hold the potential to promote mutual understanding and acceptance. The study aims to analyze how speed-dating conversations between farmers and citizens, considering participants’ characteristics, impact different outcome variables. 24 farmers and 22 citizens specifically recruited for participation in the speed-dating were organized to have short conversations of 10–15 min in different farmer-citizen-constellations. Each conversation had a specific overall agricultural topic including animal welfare, agricultural technology, environmental protection, agricultural policy, and esteem for food. Four months after, different outcomes were measured in a follow-up survey. For 84 person-constellations complete dyadic data were available to be analyzed by hierarchical regression analyses. Participants were mostly satisfied with the dialogue format and gained new factual and personal information. Results indicate stronger impacts of socio-demographic characteristics and personality traits than characteristics of the conversations themselves. Constellations with male citizens, female farmers, more educated farmers, extroverted participants, emotionally stable farmers, and more open participants tended to have higher dyadic outcome variable values. The results call for a re-design of farmer-citizen dialogue formats to facilitate more direct interpersonal communication.

Group 13 complexes for methane activation

Methane is a highly stable molecule, with strong CH bonds, and hence difficult to activate. Thus, finding efficient pathways for the direct oxidation of methane is immensely important. This study explores Group 13 (triel, E) element hydroxide and amide complexes as well as larger “round” and “oblate” E4O6 cluster models for methane activation. Modeling several compounds using density functional theory, it was discovered that heavier Group 13 tris-hydroxide and tris-amide catalysts are more thermodynamically and kinetically favorable for methane activation. Interestingly, for Group 13 E4O6 cluster models there were no clear periodic trends, and these models produced significantly lower reaction free energies and activation barriers than the tris-hydroxide/amide models. Furthermore, the cluster model calculations revealed that the shape/structure of the surface greatly impacted reaction free energies and activation barriers. These findings thus shed light on potential energetically favorable catalysts for methane functionalization for the utilization of natural gas resources.

Dynamics of rotation in two‐coordinate thiazolyl copper(I) carbazolyl complexes

Two‐coordinate carbene Cu(Ι) amide complexes with sterically bulky groups such as the diisopropyl phenyl (dipp) on the carbenes have been shown to have comparable performance to the phosphorescent emitters bearing heavy atoms such as iridium and platinum. These bulky groups enforce a coplanar molecular structure and suppress the nonradiative decay rates. Here, three different two‐coordinate Cu(Ι) complexes were investigated that bear a common thiazole carbene, 3‐(2,6‐diisopropylphenyl)‐4,5‐dimethylthiazol‐2‐ylidene, with only a single dipp group, and carbazolyl ligands with substituents of varying steric bulk ortho to N. These substituents have a negligible impact on luminescence energies of the complexes but serve to modulate the rotation barriers along the metal–ligand coordinate bond. The geometric arrangement of ligands (syn‐ or anti‐conformer) in complexes with alkyl substituents were found to differ, being syn in the solid state versus anti in solution as revealed by crystallographic analysis and nuclear magnetic resonance spectroscopy. In addition, calculations were performed to determine potential energy surfaces for different conformations of the three complexes to provide a theoretical evaluation of rotation barriers around the metal–ligand bond axis. The relationship between rotation barriers and photophysical properties demonstrate that rates for nonradiative decay decrease with increasing bulk of the substituents on the carbazolyl ligand.

Perceptions of living wage impacts in Aotearoa New Zealand: towards a multi-level, contextualised conceptualisation

PurposeThe study maps workplace stakeholders’ perceptions of living wage (LW) impacts in New Zealand. Empirical findings inform an inaugural model of LW impacts and contingent factors at individual, organisation, sector/industry and national levels.Design/methodology/approachData from a national employee survey, semi-structured interviews with business sector representatives, and staff in two LW organisation cases were subjected to thematic content analysis.FindingsInformants emphasised anticipated LW impacts amid complex workplace and regulatory dynamics. Employers/managers stressed its cost effects. However, employees, human resource (HR) advocates and other LW proponents highlighted employee “investment” impacts that improve worker productivity and societal circumstances.Research limitations/implicationsThis study highlights the need for further context-sensitive LW analysis. An initial model of LW impacts provides a framework for comparative and longitudinal work in other national contexts.Practical implicationsThe proposed model categorises perceived LW effects and can inform policy development. Findings also stress a need for cross-agency initiatives to address LW concerns, including a key role for HR.Social implicationsThe findings highlight perceptions of a LW impacting within and beyond the workplace. Whilst higher-quality management is seen to encourage better-informed decisions about “going living wage”, a LW's positive socio-economic impacts require multi-lateral initiatives, suggesting that those initiatives are is part of wider obligations for policy makers to encourage decent living standards.Originality/valueThis study provides a much-needed and inaugural focus on the intertwined workplace and wider impacts of a LW, extending extant econometric analyses. The paper also synthesizes different data sources to develop an inaugural, context-sensitive model of perceived LW effects.

Observing Amid the Anthropocene: An Excursus in Methodology or the How of Inquiry

Amid complex issues like those of the Anthropocene, choice of methodology in inquiry is critical to assure the validity of an inquiry’s conclusions. Confidence in its success can be gained initially through the exercise of introspection. More importantly, the complexity of inquiry needs to be commensurate with that of the subject. Since ανθρωπός (anthropos) is the cause of environmental deterioration, inquiry must be thematically anthropological and future-orientated towards the evolution of mankind amid technological advance. These themes promulgate modes of observation from which an inquirer can observe empirically. Eventually, with the need for increasing complexity of inquiry, the abilities of such a method of study become exhausted, with epistemology and empiricism consequent casualties. In a leap of theory and inspired by Haraway’s conjecture of the cyborg in posthumanism, the approach then privileges the ontological so that observers instead become beings and exploration of the relationship to the Anthropocene of the human qua human, qua transhuman and so on, can be pursued by moving inside. With the inherent sacrifice of the observing outside(r), the inquirer is deprived of communication. Academe then substitutes as the cerebral, transcendent, inquirer/communicator and survivor of posthumanism amongst beings, sans pareil, through publication and education. Some consequences of this are explored. The author borrows gratefully from Niklas Luhmann’s characterisation of observation in social systems. His assertions concur with the effects of the transformations proposed in the study, including the autopoiesis of the newly-theorised beings.

Thiazoline Carbene–Cu(I)–Amide complexes: Efficient White Electroluminescence from Combined Monomer and Excimer Emission

Luminescent carbene-metal-amide complexes bearing group 11 metals (Cu, Ag, Au) have recently attracted great attention due to their exceptional emission efficiency and high radiative decay rates (kr). These materials provide a less costly alternative to organic light-emitting diode (OLED) emitters based on more scarce metals, such as Ir and Pt. Herein, a series of eight Cu(I) complexes bearing as yet unexplored 1,3-thiazoline carbenes have been investigated and analyzed with respect to their light emission properties and OLED application. For the first time among the class of copper-based organometallic compounds the formation of efficient electroluminescent excimers is demonstrated. The prevalence of electroluminescence (EL) from either the monomer (bluish green) or the excimer (orange-red) can be adjusted in vacuum-deposited emissive layers by altering the extent of steric encumbrance of the emitter or its concentration. Optimized conditions in terms of the emitter structure and mass fraction allowed a simultaneous EL from the monomer and excimer, which laid the basis for a preparation of a single-emitter white OLED (WOLED) with external quantum efficiency of 16.5% and a maximum luminance of over 40000 cd m-2. Wide overlapping emission bands of the monomer and excimer ensure a device color rendering index (CRI) of above 80. In such a way the prospects of copper complexes as cost-effective materials for lighting devices are demonstrated, offering expense reduction through a cheaper emissive component and a simplified device architecture.

Complex Metal Borohydrides: From Laboratory Oddities to Prime Candidates in Energy Storage Applications.

Despite being the lightest element in the periodic table, hydrogen poses many risks regarding its production, storage, and transport, but it is also the one element promising pollution-free energy for the planet, energy reliability, and sustainability. Development of such novel materials conveying a hydrogen source face stringent scrutiny from both a scientific and a safety point of view: they are required to have a high hydrogen wt.% storage capacity, must store hydrogen in a safe manner (i.e., by chemically binding it), and should exhibit controlled, and preferably rapid, absorption–desorption kinetics. Even the most advanced composites today face the difficult task of overcoming the harsh re-hydrogenation conditions (elevated temperature, high hydrogen pressure). Traditionally, the most utilized materials have been RMH (reactive metal hydrides) and complex metal borohydrides M(BH4)x (M: main group or transition metal; x: valence of M), often along with metal amides or various additives serving as catalysts (Pd2+, Ti4+ etc.). Through destabilization (kinetic or thermodynamic), M(BH4)x can effectively lower their dehydrogenation enthalpy, providing for a faster reaction occurring at a lower temperature onset. The present review summarizes the recent scientific results on various metal borohydrides, aiming to present the current state-of-the-art on such hydrogen storage materials, while trying to analyze the pros and cons of each material regarding its thermodynamic and kinetic behavior in hydrogenation studies.

Six-coordinated dinuclear lanthanide(III) amide complexes: investigation of magnetization relaxation dynamics and their electronic structures.

A series of rare six-coordinated dinuclear Ln(III) complexes [Ln2(μ-Cl)2Cl4Li2(L)2(THF)6] were structurally characterized using a bulky amide ligand (L; Ln = Gd(1), Dy(2) and Y(3)). Detailed magnetic studies disclose that a weak antiferromagnetic coupling exists within 1 (-0.09 cm-1) and 2 (-0.07 cm-1; -2J Hamiltonian). Additionally, this study unveils the importance of the amide ligand at the coordination site of Dy(III), which manifests a slow relaxation of magnetization in the absence of an external magnetic field. This has been rationalized by detailed ab initio calculations as well as the electronic structure determination of 1 and 2.

Insights into the degradation mechanism of carbene–metal–amide organic light-emitting diodes

Organic light-emitting diodes (OLEDs) based on carbene–metal–amide (CMA) material are fabricated to investigate the fundamental processes that drive degradation in operational CMA OLEDs.

Reaction of lithium hexamethyldisilazide (LiHMDS) with water at ultracold conditions.

Alkali metal amides are highly reactive reagents that are broadly applied as strong bases in organic synthesis. Here, we use a combined helium nanodroplet IR spectroscopic and theoretical (DFT calculation) study to show that the reaction of the model compound lithium hexamethyldisilazide (LiHMDS) with water is close to barrierless even at ultra-cold conditions. Upon complex formation of dimeric (LiHMDS)2 with water in helium nanodroplets as ultra-cold nano-reactors (0.37 K) we observed the reaction product (LiOH)2(HMDS)2. This can be rationalized as aggregation induced reation upon stepwise addition of water. With increasing water partial pressure, only the product (LiOH)2(HMDS)2 is observed experimentally. This implies that the large interaction energy (69 kJ mol-1) of (LiHMDS)2 with water is sufficient to overcome the follow-up reaction barriers, in spite of the rapid cooling rates in He nanodroplets.