Amide Ligands Research Articles

Ruthenium‐Catalyzed Chemoselective Olefin Transfer Hydrogenation of alpha, beta‐Unsaturated Carbonyl Systems By Using EtOH as Hydrogen Source

AbstractThe use of EtOH as hydrogen donor is remarkably under explored in transfer hydrogenation reactions, even though EtOH represents an appealing hydrogen source. With the cationic ruthenium complex [Ru(PYA)(cymene)]+, 1, containing a N,N‐bidentate amino‐functionalized pyridinium amidate (PYA) ligand as catalyst precursor, we here demonstrate the first example of chemoselective room temperature transfer hydrogenation of the C═C bond in α,β‐unsaturated ketones using EtOH as benign hydrogen source to yield a variety of functionalized ketones. The reaction proceeds under mild conditions with K2CO3 as base and conventiently at room temperature. A broad substrate scope, including various functionalized α,β‐unsaturated carbonyl groups, demonstrates the general applicability of this method. Preliminary mechanistic studies suggest the formation of an alkoxide complex [1]–OEt as an initially formed species, and the requirement for EtOH to induce hydride transfer, suggesting a protic activation of the catalyst.

Organometallic Iridium-Complex-Functionalized Nanographene Catalysts for Low-Temperature Hydrogenation of Carbonyl Derivatives.

An organometallic iridium (Ir)-complex-functionalized nanographene catalyst Ir-PyPh-GC was prepared via a two-step strategy involving amide ligand modification and metal Ir coordination. Ir-PyPh-GC showed ultrahigh hydrogenation capability, good recyclability, and selectivity for carbonyl derivatives (ketones, aldehydes, and quinones) at a low temperature (40 °C). The as-prepared Ir-complex-based catalyst is less expensive, making it feasible for industrial application.

Ligand-Enabled Copper-Catalyzed Ullmann-Type S-C Bond Formation to Access Sulfilimines.

A copper-catalyzed Ullmann-type cross-coupling reaction of sulfenamides with aryl iodides is developed. The key to success is the use of a 2-methylnaphthalen-1-amine-derived amide ligand, which enables the formation of an S-C bond to access functionalized sulfilimines in good to excellent yields at room temperature. This method has the advantages of mild conditions, a broad substrate scope, good functional group compatibility, and high chemoselectivity. The utility of this protocol is highlighted through late-stage modification of drug-relevant molecules and sulfilimine product derivatization.

In situ-generated mononuclear half-sandwich [(η6‐p‐cymene)RuCl(amide)] complexes as efficient catalysts in the selective oxidation of benzyl alcohol to benzaldehyde

The application of in situ-generated mononuclear Ru(II)-organometallic complexes (1–7) i.e., [(η6-p-cymene)RuCl(L)], produced by the interaction of Ru dimer [(p-cymene)RuCl2]2 with some polyfunctional amide ligands(L) as highly efficient catalystsin the oxidation of various benzyl alcohols (B-OLs) by tert-butyl hydroperoxide (TBHP) oxidant to produce selectively the benzaldehydes (B-ALs) in high yields in CH3CN is described. The in situ-generated catalysts were found to be highly active than the [(p-cymene)RuCl2]2 precursor (dimer) in the oxidation of B-OL to B-AL. The influence of various reaction parameters such as type of catalyst, reaction temperature, oxidant and solvent during the B-OL oxidation was systematically monitored to optimize the catalytic conditions. In order to confirm the formation of predicted in situ-generated mononuclear Ru(II) complex catalysts during the oxidation of B-OL, one of the Ru(II) complex (1) was synthesized and characterized by Elemental analysis (EA), Infrared (IR), Proton-NMR and Mass spectral techniques and its mono nuclear structure is proposed. Further, it was observed that the activity of in-situ generated and pre-synthesized Ru(II) catalyst was almost same in the oxidation of B-OL to B-AL.

The influence of the pyridyl substituent in N-methyl-P,P-diphenyl-N-2-pyridinyl-phosphinous amide ligand on the coordination chemistry of group 6B metal carbonyl derivatives

The reaction of N-methyl-P,P-diphenyl-N-2-pyridinyl-phosphinous amide (1) with group 6B metal hexa, tetra, and tricarbonyls yielded the same octahedral complexes cis-M(CO)4[1-κ2P,Npy] (M = Cr(2), Mo(3), W(4)) in which the ligand chelates only in a bidentate fashion through its phosphorus atom and pyridyl N-atom. Compounds 1–4 were identified and characterized by multinuclear NMR spectroscopy (1H, 13C, 31P NMR), elemental analysis, IR and UV–Vis spectroscopy. Complexes 2–4 exhibited weak metal-to-ligand charge transfer transitions unaffected by solvent polarity. Crystal structure determination is carried out on complex 4.

Synthesis and Crystal Structures of Novel Group 6B Metal Carbonyl Complexes with N‐(4‐methyl‐2‐pyridinyl)‐P,P‐diphenylphosphinous Amide Ligand

AbstractThe reaction of N‐(4‐methyl‐2‐pyridinyl)‐P,P‐diphenylphosphinous amide ligand 4‐Me‐C5H3N‐2‐NH(PPh2) (1) with M(CO)6 (M=Cr, Mo, W) in refluxing toluene afforded a mononuclear group VIB metal tetracarbonyls [M(CO)4{1‐κ2P,N}] (M=Cr(2), Mo(3), W(4)). Complexes 2–4 were characterized by multinuclear NMR (1H, 13C and 31P NMR) and IR spectroscopy, and their structures were also determined by single crystal X‐ray diffraction. 2 and 4 represent the first examples of structurally characterized complexes of such ligands with group 6B metal carbonyls.

Pincer shaped N-Mesoionic Pyridylidene Amide (PYA) for palladium catalyzed CO2 reduction

Palladium complexes (4-6) bearing mesoionic N-donor pyridylidene amide ligands (PYAs) with different pendant groups of varying size and electronic properties were successfully synthesized from their respective pro-ligands (1-3). 4-6 were proved effective catalysts for CO2 reduction to synthesis gas. The first principle quantum studies of CO2 reduction provided better insight into the mechanism of these active catalysts. The highest selectivity of 71 % (Faradaic efficiency) and minimum overpotential of 0.390 V was observed for CO. Controlled potential electrolysis (CPE) and post-CPE cyclic voltammogram manifested that all catalysts were robust.

Synthesis and characterization of Ru(II) complexes with polyfunctional amides and their application in catalytic oxidative coupling of amines

The synthesis and characterization of some new mononuclear Ru(II) complexes of the type [(Ru(L)2(DMSO)2] and [(Ru(L)2] (L = O,O-donor bidentate or N,O,O-donor tridentate or O,O,O-donor tridentate amide ligands) is described. These metal complexes were characterized by Elemental analysis (EA), IR, 1H NMR, and mass spectral data and their structures have been proposed. Next, these complexes were investigated as catalysts in the oxidative coupling of amines by tert-butyl hydroperoxide (TBHP) oxidant to produce selectively the corresponding imines in high yields in CH3CN. The influence of various reaction parameters such as selection of oxidant and solvent during the benzyl amine oxidative coupling was systematically monitored to optimize the catalytic conditions. The utility of optimized reaction conditions was further extended to investigate the amine substrate scope. Based on the experimental results and previous reports, a plausible mechanism was also deduced for the selective synthesis of imines.

Extraction of uranyl from spent nuclear fuel wastewater via complexation—a local vibrational mode study

ContextThe efficient extraction of uranyl from spent nuclear fuel wastewater for subsequent reprocessing and reuse is an essential effort toward minimization of long-lived radioactive waste. N-substituted amides and Schiff base ligands are propitious candidates, where extraction occurs via complexation with the uranyl moiety. In this study, we extensively probed chemical bonding in various uranyl complexes, utilizing the local vibrational modes theory alongside QTAIM and NBO analyses. We focused on (i) the assessment of the equatorial O-U and N-U bonding, including the question of chelation, and (ii) how the strength of the axial U=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$=$$\\end{document}O bonds of the uranyl moiety changes upon complexation. Our results reveal that the strength of the equatorial uranium-ligand interactions correlates with their covalent character and with charge donation from O and N lone pairs into the vacant uranium orbitals. We also found an inverse relationship between the covalent character of the equatorial ligand bonds and the strength of the axial uranium-oxygen bond. In summary, our study provides valuable data for a strategic modulation of N-substituted amide and Schiff base ligands towards the maximization of uranyl extraction.MethodQuantum chemistry calculations were performed under the PBE0 level of theory, paired with the relativistic NESCau Hamiltonian, currently implemented in Cologne2020 (interfaced with Gaussian16). Wave functions were expanded in the cc-pwCVTZ-X2C basis set for uranium and Dunning’s cc-pVTZ for the remaining atoms. For the bonding properties, we utilized the package LModeA in the local modes analyses, AIMALL in the QTAIM calculations, and NBO 7.0 for the NBO analyses.Graphical abstract

Unique Selectivity Reversal in the Complexation of Uranium(VI) and Plutonium(IV) with Two Novel C-Pivoted Tripodal Amide Ligands: Extraction and Liquid Membrane Transport Studies

ABSTRACT Two new carbon pivoted tripodal amide-containing ligands with different spacers (L I : -CH2- spacer; L II : -CH2-CH2- spacer) have been investigated for the liquid–liquid extraction of tetravalent plutonium and hexavalent uranium from nitric acid feed solutions. The studies were carried out using the ligand solutions prepared in 95% n-dodecane + 5% isodecanol. Pu(IV) extraction was higher than that of U(VI) at 3 M HNO3 for ligand L I which was just the opposite for ligand L II . Increase of the nitric acid concentration resulted in increasing extraction of both metal ions. Isodecanol variation studies exhibited decrease in the extraction of Pu(IV) and U(VI) with increasing isodecanol content in the organic phase. Greater that 98% stripping of Pu(IV) and U(VI) was obtained from the complexes of L I and L II using 0.5 M HNO3 + 0.1 M HEDTA and 1 M Na2CO3, respectively. The slope analysis study suggested the formation of 1:2 (ML2) species with Pu(IV) as well as U(VI) with both ligands at 3 M HNO3. Temperature variation studies showed that the extraction of U(VI) and Pu(IV) with both ligands is exothermic in nature. Supported liquid membrane transport experiments using 0.11 M ligands (L I and L II ) in 95% n-dodecane + 5% isodecanol indicated poor transport (<10% after 2 h) of U(VI) and Pu(IV).

Synthesis of phosphonic acid and amide functionalized core–shell magnetic composite and its mechanisms for synergistic adsorption of thorium from strongly acidic solution

To develop adsorbents for the preeminent extraction of thorium in strongly acidic solutions is very imperative, due to strong inorganic acids are frequently used in the fuel cycle of thorium. Herein, a robust core–shell magnetic nanocomposite Fe3O4@SiO2/P (MBA-VPA-AM) possessing phosphonic acid and amide was developed via distillation-precipitation copolymerization of N, N'-methylene diacrylamide (MBA), vinylphosphonic acid (VPA) with acrylamide (AM) employing Fe3O4 decorated by SiO2 (Fe3O4@SiO2) as magnetic core. Due to the synergistic effect of phosphonic acid and amide ligand, the sorbent could capture thorium from concentrated HNO3 media efficiently, and the maximum adsorption capacity (qmax) at 4 mol L−1 of HNO3 solution reached up to 232.5 mg g−1, superior to that of all magnetic sorbents reported previously. Furthermore, the sorbent displayed good selectivity towards thorium in the presence of competitive metal ions including La3+, Nd3+, and Ce3+. The excellent thorium sorption behavior in strong hydrogen nitrate solution was merely ascribed to the complexation of thorium with phosphonic acid ligand, and the amide ligand could not complex with thorium, evidenced by XPS, FT-IR and DFT method. However, the presence of amide ligand could enhance the hydrophilicity of the sorbent and the free movement degree of phosphonic acid ligand to a certain extent, both of which could help to promote the thorium sorption on the sorbent in strong HNO3 media. Besides, due to its core–shell structure and superparamagnetism, the sorbent not only exhibited excellent acidic resistance in strong acid medias, but could be magnetically recouped, which could avoid tedious centrifugation or filtration of traditional adsorbents. This work provides a novel strategy to develop magnetic sorbent for the preeminent entrapment of thorium from strong acid solutions.

Molybdenum(VI) Nitrido Complexes with Tripodal Silanolate Ligands. Structure and Electronic Character of an Unsymmetrical Dimolybdenum μ-Nitrido Complex Formed by Incomplete Nitrogen Atom Transfer.

In contrast to a tungsten nitrido complex endowed with a tripodal silanolate ligand framework, which was reported in the literature to be a dimeric species with a metallacyclic core, the corresponding molybdenum nitrides 3 are monomeric entities comprising a regular terminal nitride unit, as proven by single-crystal X-ray diffraction (SC-XRD). Their electronic character is largely determined by the constraints imposed on the metal center by the podand ligand architecture. 95Mo nuclear magnetic resonance (NMR) and, to a lesser extent, 14N NMR spectroscopy allow these effects to be studied, which become particularly apparent upon comparison with the spectral data of related molybdenum nitrides comprising unrestrained silanolate, alkoxide, or amide ligands. Attempted nitrogen atom transfer from these novel terminal nitrides to [(tBuArN)3Mo] (Ar = 3,5-dimethylphenyl) as the potential acceptor stopped at the stage of unsymmetric dimolybdenum μ-nitrido complex 13a as the first intermediate along the reaction pathway. SC-XRD, NMR, electron paramagnetic resonance, and ultraviolet-visible spectroscopy as well as magnetometry in combination with density functional theory allowed a clear picture of the geometric and electronic structure of this mixed-valent species to be drawn. 13a is formally best described as an adduct of the type [(Mo[O])+III-(μN)-III-(Mo[N])+VI], S = 1/2 complex with (Mo[O])+III in the low-spin configuration, whereas related complexes such as [(AdS)3Mo-(μN)-Mo(NtBuAr)3] (19; Ad = 1-adamantyl) have previously been regarded in the literature as mixed-valent Mo+IV/Mo+V species. The spin population at the two Mo centers is uneven and notably larger at the more reduced Mo[O] atom, whereas the only spin present at the (μN) bridge is derived from spin polarization.

Cyclometalated Pt(II)C^N phosphors bearing a bis(diphenylphorothioyl) amide ligand: synthesis and photophysical properties

Six Pt(II) complexes bearing a primary phenylpyridine (ppy) ligand or a ppy derivative and two Pt(II) complexes bearing a primary 8-hydroxyquinoline (hqnl) or 7-bromo-8-quinolinol ligand have been prepared via coordination with an auxiliary bis(diphenylphosphothionyl) amide (HStpip) ligand. All eight complexes were characterized by NMR (1H,13C, and 31P), HRMS, and elemental analysis. In addition, complexes 2, 4, 5, and 8 were characterized by single crystal XRD. The eight complexes were not emissive in solution under N2 at room temperature (r.t.). However, they all exhibited an intense emission in the solid state and in 2 wt.% polymethyl methacrylate (PMMA) films. In particular, 5 bearing a primary 2-([1,1'-biphenyl]-3-yl)-4-phenylpyridine ligand exhibited a triplet emission at 525 and 552 nm with a quantum yield of 80% in pure solid state. Density functional theory (DFT) and time dependent (TD) DFT calculations were performed for optimization and predicting the excitation properties of 2, 4, 5, and 8. The computational results reveal that the intrinsic triplet emissions of 2, 4, and 5 are the result of combinations of ligand-to-metal charge transfer (LMCT) (π*(ppy) → d(Pt)) and ligand-to-ligand charge transfer (LLCT) (π*(ppy) → p(Stpip)), whereas the triplet emission of 8 shows a π*–π character with a small LMCT (π*(hqnl) → d(Pt)) component.

Synthesis of Superbulky Amide Ligands by Addition of Polar Reagents to Sila-Imine.

The chemistry of extremely bulky amide ligands is troubled by difficulties in deprotonation of the parent amine. As an alternative route to superbulky amide reagents, the addition of polar reagents to a sila-imine has been investigated. Attempts to synthesize the superbulky amide anion (tBu3Si)2N- by addition of tBuLi to tBu2Si=N(SitBu3) failed and gave tBu3Si(tBu2HSi)NLi and isobutene. Reaction of the sila-imine with KOtBu successfully led to tBu3Si[tBu2(tBuO)Si]NK which crystallized as a separated ion-pair. Reaction with the slightly bulkier KOAd (Ad=1-adamantyl) led in presence of THF to ether ring-opening. Reaction with tBuOH gave tBu3Si[tBu2(tBuO)Si]NH but this amine cannot be easily deprotonated. Reaction with (BDI*)MgnBu in presence of THF gave (BDI*)Mg+ ⋅ (THF)2 and the non-coordinating anion tBu3Si[tBu2(nBu)Si]N-; BDI*=ß-diketiminate ligand HC[C(tBu)N-DIPP]2, DIPP=2,6-diisopropylphenyl. Reaction of Mg(nBu)2 with tBu2Si=N(SitBu3) led to a Mg complex with one amide ligand: tBu3Si[tBu2(nBu)Si]N-. The other superbulky amide anion isomerized by internal deprotonation of a tBu-substituent to give a primary carbanion that is also coordinated to Mg. Although the amide-to-carbanion isomerization is highly contrathermodynamic, it allows for coordination of both anions to a single Mg center. The new bulky amides are rare cases of halogen-free weakly coordinating anions.

Understanding the Interaction of Uranyl Cation with Two C-Pivot Tripodal Amides: Synthesis, Complexation, Microcalorimetry, and DFT Studies.

Complexation of uranyl ions with two structurally related C-pivotal tripodal amides with varying spacer lengths, synthesized for the first time, was studied by optical spectroscopy. In the tripodal amides, the coordination was through the carbonyl O atoms where the carbonyl groups were away from the central C-atom by three spacer atoms (LI) and four spacer atoms (LII), respectively. Increasing the spacer atoms going from LI to LII favors the complexation with the linear uranyl cations and results in stronger complex formation. The complexation heat between the uranyl cations and the two amide ligands was directly measured by microcalorimetric titrations. The complexation with both the ligands was driven by exothermic enthalpy and positive entropy changes. Formation of the complex proceeded by the replacement of water molecules from the primary coordination sphere of the uranyl cation. Both ligands formed bisolvated (ML2-type) complexes in which one unit of the ligand binds in a monodentate manner and the other in a bidentate mode. Density functional theory calculations further supported our experimental observations.

Old Acquaintances and Novel Complex Structures for the Ni(II) and Cu(II) Complexes of bis-Chelate Oxime-Amide Ligands.

In the process of systematically studying the methylhydroxyiminoethaneamide bis-chelate ligands with polymethylene spacers of different lengths, L1-L3, and their transition metal complexes, a number of new Ni(II) and Cu(II) species have been isolated, and their molecular and crystal structures were determined using single-crystal X-ray diffraction. In all of these compounds, the divalent metal is coordinated by the ligand donor atoms in a square-planar arrangement. In addition, a serendipitously discovered new type of neutral Ni(II) complex, where the propane spacer of ligand L2 underwent oxidation to the propene spacer, and one of the amide groups was oxidised to the ketoimine, is also reported. The resulting ligand L2' affords the formation of neutral planar Ni(II) complexes, which are assembled in the solid state on top of each other, and yield two polymorphic structures. In both structures, the resulting infinite, exclusively parallel metal ion columns in ligand insulation may serve as precursor materials for sub-nano-conducting connectors. Overall, this paper reports the synthesis and characterisation of seven new anionic, cationic, and neutral Ni(II) and Cu(II) complexes, their crystal structures, as well as experimental and computed UV-Vis absorption spectra for two structurally similar Ni(II) complexes, yellow and red.

S-Block metal complexes of superbulky (tBu3Si)2N-: a new weakly coordinating anion?

Sterically hindered amide anions have found widespread application as deprotonation agents or as ligands to stabilize metals in unusual coordination geometries or oxidation states. The use of bulky amides has also been advantageous in catalyst design. Herein we present s-block metal chemistry with one of the bulkiest known amide ligands: (tBu3Si)2N- (abbreviated: tBuN-). The parent amine (tBuNH), introduced earlier by Wiberg, is extremely resistant to deprotonation (even with nBuLi/KOtBu superbases) but can be deprotonated slowly with a blue Cs+/e- electride formed by addition of Cs0 to THF. (tBuN)Cs crystallized as a separated ion-pair, even without cocrystallized solvent. As salt-metathesis reactions with (tBuN)Cs are sluggish and incomplete, it has only limited use as an amide transfer reagent. However, ball-milling with LiI led to quantitative formation of (tBuN)Li and CsI. Structural characterization shows that (tBuN)Li is a monomeric contact ion-pair with a relatively short N-Li bond, an unusual T-shaped coordination geometry around N and extremely short Li⋯Me anagostic interactions. Crystal structures are compared with Li and Cs complexes of less bulky amide ligands (iPr3Si)2N- (iPrN-) and (Me3Si)2N- (MeN-). DFT calculations show trends in the geometries and electron distributions of amide ligands of increasing steric bulk (MeN- < iPrN- < tBuN-) and confirm that tBuN- is a rare example of a halogen-free weakly coordinating anion.

A mesoionic carbene stabilized nickel(II) hydroxide complex: a facile precursor for C-H activation chemistry.

We report the synthesis of a new nickel(II) hydroxide complex 2 supported by a rigid, tridentate triazolylidene-carbazolid ligand. The complex can be accessed in high yields following a simple and stepwise extraction protocol using dichloromethane and aqueous ammonium chloride followed by aqeous sodium hydroxide solution. We found that complex 2 is highly basic, undergoing various deprotonation/desilylation reactions with E-H and C-H acidic and silylated compounds. In this context we synthesized a variety of novel, functionalized nickel(II) complexes with trimethylsilylolate (3), trityl sulfide (4), tosyl amide (5), azido (6), pyridine (7), acetylide (8, 9), fluoroarene (10 & 11) and enolate (12) ligands. We furthermore found that 2 reacts with malonic acid dimethyl ester in a knoevennagel-type condensation reaction, giving access to a new enolate ligand in complex 13, consisting of two malonic acid units. Furthermore, complex 2 reacts with acetonitrile to form the cyanido complex 14. The formation of complexes 13 and 14 is particularly interesting, as they underline the potential of complex 2 in both C-C bond formation and cleavage reactions.

Reactions of the ˙NO3 radical with nuclear extraction ligands in alkane solution.

The reactivity of the nitrate radical (NO3˙) with organophosphorus and amidic actinide and lanthanide complexing agents of interest to nuclear solvent extraction applications was measured, resulting in the first-ever reported bimolecular rate constants for this radicals' reactions in dodecane solution. The order of reactivity for neutral organophosphorus compounds showed faster rate constants with increasing electron density on the phosphoryl phosphorus atom, indicating an increasing facility for electron abstraction reactions occurring in addition to H-atom abstraction from the ligand alkane chains. The only acidic organophosphorus compound investigated, HEH[EHP], showed low reactivity with the NO3˙ radical, attributed to its dimerization in this non-polar solvent. Amide ligand reaction rates were faster than for organophosphorus molecules, suggesting more facile H-atom abstraction from carbonyl activated methylene and amyl groups. While all rate constants were slower than the diffusion-limited rate they were still rapid enough to result in significant oxidation of solvent extraction ligands in dodecane solution.

A regenerative dual-functional platform combining dendritic silica and anthraquinone amide: advancing seawater lithium detection and recovery with biosensing capabilities

A novel material with a dendritic silica substrate and anthraquinone amide ligand enables simultaneous lithium detection and adsorption in water, offering green-emissive sensing, high adsorption capacity, fast kinetics, and biosensing.