Amide Ligands Research Articles

Trans‐Amidate Platinum Complexes Anchoring Water and N‐donor Molecules. The Importance of Hydrogen Bonding

A series of novel trans-amidate platinum(II) and platinum(IV) complexes are described herein. The ligand system allows to coordinate selectively one water, ammonia, hydrazine, or primary amine to the metal center. Strong hydrogen bonds are formed with the amidates, reinforcing the ligand binding to the platinum center and distorting the initially expected trans effect.

A kind of complex-based electrocatalytic sensor for monitoring the reduction of Cr(Ⅵ) by organic/inorganic reductants

In order to monitor the reduction of Cr(Ⅵ) by organic/inorganic reductants, three transition metal ions of Co2+/Ni2+/Cu2+ were selected to combine with a semi-rigid amide ligand [N, N'-bis-pyridin-3-ylmethyl-terephthalamide (L)]. As a result, [Co(L)(HIPA)](H2O)2]∙H2O (1) [Ni(L)(HIPA)](H2O)2]∙H2O (2) [Cu(L)(HIPA)]∙4H2O (3) were obtained by hydrothermal method (H2HIPA = 5-Hydroxyisophthalic acid). Complexes 1 and 2 are similar 2D cellular networks, while complex 3 has 4-connected 3D structure with semicircle 1D channel. The title complexes can act as electrochemical sensors to detect Cr(Ⅵ) by cyclic voltammetry and differential pulse method. The corresponding detection limits are 5.9 × 10−6 (1), 1.6 × 10−5 (2), 9.1 × 10−6 (3) for Cr(Ⅵ) anion, respectively. In addition, the title complexes 1–3 modified carbon paste electrode (1–3-CPEs) provide a kind of generalizable sensor for the electrochemical monitor the reduction of Cr(Ⅵ) by organic/inorganic reductants [Ascorbic acid (AA), H2O2 and Na2S2O3]. The effect of metal ions on the structures and electrochemical properties of 1–3 were discussed.

Recovery of palladium(II) from strong nitric acid solutions relevant to high-level liquid waste of PUREX process by solvent extraction with pyrazole-pyridine-based amide ligands

The extraction of Pd2+ with N,N-dialkyl-2-(3-(pyridine-2-yl)-1H-pyrazole-1-yl) acetamide (A-C-PzPy) and N,N-dialkyl-3-(pyridine-2-yl)-1H-pyrazole-1-carboxamide (A-PzPy) from HNO3 medium, as well as the complexation of Pd2+ with A-C-PzPy were investigated. The use of tert-butyl benzene (TBB) as a diluent for A-C-PzPy offered significantly better extractability toward Pd2+, compared to that of A-PzPy. This study demonstrated strong extractability, high selectivity, high loading capacity, and fast extraction kinetics for DOct-C-PzPy toward Pd2+ from highly acidic HNO3 solution (up to 5.0 mol/L). Slope analysis showed the formation of 1:1 type of extracted species of Pd2+ with DOct-C-PzPy ligand. The extraction was a spontaneous and endothermic process with increased entropy. The analyses of electrospray ionization mass spectrometry (ESI-MS), Fourier transform infrared (FT-IR) and UV–vis spectrophotometric titration revealed that the composition of the extracted neutral complex species was Pd(NO3)2(DOct-C-PzPy). Combining the results of solvent extraction and complexation study, a neutral complexation extraction model is proposed. Furthermore, the stability constants (log β) for the complexation of Pd2+ with A-C-PzPy are also presented.

Metal-organic framework-based magnetic dispersive micro-solid-phase extraction for the gas chromatography–mass spectrometry determination of polycyclic aromatic compounds in water samples

A magnetic hybrid material based on the use of the mixed-ligand Metal-Organic Framework (MOF) PUM198 is proposed for the magnetic dispersive micro solid-phase extraction (MD-μSPE) of the 16 polycyclic aromatic hydrocarbons (PAHs) included in the US-EPA priority pollutants list. PUM198 is a thermally robust MOF characterized by a doubly interpenetrated microporous framework in which Zn2+ ions and carboxylate groups define 2D planes that are pillared by a bis-pyridine-bis amide ligand containing a biphenyl scaffold. PUM198 revealed to be ideal to adsorb PAHs efficiently through non-covalent interactions. A Plackett-Burman Design followed by a Central Composite Design and the multicriteria method of the desirability functions were applied to find the optimal conditions for the extraction of the investigated PAHs, resulting in a reduced solvent consumption, i.e., 50 μL of solvent per extraction for 5 mL of sample, approximatively 3–20 times lower than those reported in previous studies, thus satisfying the principles of green analytical chemistry. Method validation proved the reliability of the method for the determination of PAHs at trace level, obtaining detection limits in the 6.7–27 ng/L range, good precision with RSDs% lower than 19% and recovery rates in the 99 (±13)–126 (±8)% range near the quantitation limit. Finally, the applicability of the method was demonstrated by analyzing underground water samples taken from contaminated sites

Complexes of zinc halides with amide ligands having a high dipole moment

Complexes [Zn(C6H5CONH2)2Br2] and [Zn((NH2)2CO)2Br2] were synthesized and characterized by elemental analysis, IR spectroscopy, and X-ray diffraction and compared to other complexes of zinc halides with benzamide and urea. In all complexes, the zinc ion has a tetrahedral coordination environment of two halide ligands and two oxygen atoms of two amide ligands. The structure of [Zn(C6H5CONH2)2Br2] (orthorhombic, Pna21, a = 29.207(6), b = 7.5826(14), c = 14.753(3) Å, Z = 8) is not isostructural to the chloride and iodide compounds. The [Zn((NH2)2CO)2Br2] complex (triclinic, P-1, a = 6.4435(9), b = 7.096(1), c = 11.7079(18) Å, α = 88.119(9)°, β = 77.005(9)°, γ = 66.320(8)°, Z = 2) is isostructural to [Zn((NH2)2CO)2Cl2], and they both differ from [Zn((NH2)2CO)2I2]. Dipole moments of complexes of various zinc halides with benzamide, urea, and dimethylformamide were calculated; they vary in the 9–13 D range. Complexes of zinc halides with amides were used to prepare films with the use of cellulose diacetate as a polymer matrix. Dielectric measurements showed the presence of a pronounced electret effect.

Conformational Engineering of Two-Coordinate Gold(I) Complexes: Regulation of Excited-State Dynamics for Efficient Delayed Fluorescence.

Carbene-Au-amide (CMA) type complexes, in which the amide and carbene ligands act as an electron donor (D) and acceptor (A), respectively, can exhibit strong delayed fluorescence (DF) from a ligand to ligand charge transfer (LLCT) excited state. Although the coplanar donor-acceptor (D-A) conformation has been suggested to be a crucial factor favoring radiative decay of the charge-transfer excited state, the geometric structural factor underpinning the excited-state mechanism of CMA complexes remains an open question. We herein develop a new class of carbene-Au-carbazolate complexes by introducing large aromatic substituents onto the carbazolate ligand, the presence of which are conceived to restrict the rotation of the Au-N bond and thus confine a twisted D-A conformation in both ground and excited states. A highly twisted D-A orientation is found for the complexes in their crystal structures. Photophysical studies reveal that the twisted conformation induces a decrease in the gap (ΔEST) between the lowest singlet excited state (S1) and the triplet manifold (T1) and thus a faster reverse intersystem crossing (RISC) from T1 to S1 at the expense of oscillator strength for an S1 radiative transition. In comparison with the coplanar analogue, the twisted complexes exhibit comparable or improved DF with quantum yields of up to 94% and short emission lifetimes down to sub-microseconds. The tuning of excited-state dynamics has been well interpreted by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, which unveil much faster RISC rates for twisted complexes. Solution-processed organic light-emitting diodes (OLEDs) based on the new CMA complexes show promising performances with almost negligible efficiency rolloff at a brightness of 1000 cd m-2. This work implies that neither a coplanar ground-state D-A conformation nor a dynamic rotation of the M-N bond is the key to the realization of efficient DF for CMA complexes.

Metal and bis(pyridyl)-bis(amide) ligands – tuned three new nickel(II)/copper(II) coordination polymers: Syntheses, structures and properties

Three new Ni(II)/Cu(II) coordination polymers (CPs), [Ni(L1)1.5(HBTC)(H2O)] (1), [Ni(L2)2(HBTC)]·2H2O (2) and [Cu2(L2)0.5(BTC)(μ3-OH)]·2H2O (3) {H3BTC = benzene-1,3,5-tricarboxylic acid, L1 = (E)-4,4′-(ethene-1,2-diyl)bis[N-(pyridin-3-yl)benzamide] and L2 = (E)-4,4′-(diazene-1,2-diyl)bis[N-(pyridin-3-yl)benzamide]}, were prepared under hydrothermal and solvothermal conditions by regulating different metals and ligands. The structures of CPs 1–3 were characterized by single crystal X-ray diffraction analyses, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). CP1 displays a 4-connected 3D topological structure based on [Ni(HBTC)]n chains and [Ni(L1)1.5]n chains. When L2 was used, CP2 demonstrates a 1D chain structure. CP3 is a 3D metal–organic network with the binodal (3,8)-connected {4·62}2{42·622·7·83} topology constructed from {Cu4} clusters and L2 ligands. The photocatalytic properties and electrochemical behaviors of CPs 1–3 were explored. The effect of solvent on the formation of the title CPs as well as the influence of the central metals and ligands on the structures and properties are discussed.

Bisamidate-functionalized NHC ligands: Electronic and steric influences of N-substituents on the bisamidate moieties

Bis-anionic tethered NHC ligands have widely served as stable and useful catalysts. The properties of anionic donor sites make them useful for the tuning of metal complexes with the NHC ligands, and since amidate ligands can be functionalized on their nitrogen elements, they also have been applied as catalysts. There has been, however, a paucity of investigations into the influences of various N-substituents on bisamidate portions within bis-amidate functionalized NHCs. In this study, we used original NHCs, which we refer to as DHASIs, to synthesize various bisamide functionalized NHC pincer ligand precursors, and their Pd complexes also were successfully obtained. The structures of the synthesized complexes were unambiguously confirmed via XRD study, which showed that the N-substituents had a structural affect via the coordination modes of the resultant complexes. We applied the obtained pincer complexes to a Suzuki Miyaura coupling reaction and found that the strong Lewis basicity of the anionic N donors improved the catalytic performance of Pd–NCN pincer complexes.

Three Anderson-type POMOFs with bis(pyrimidine)-bis(amide) ligands: Synthesis, fascinating structures and performances of electrochemical sensing and dye adsorption

Three new Anderson-type polyoxometalate (POM)-based metal–organic frameworks (POMOFs) [Co3(L1)(TeMo6O24)(H2O)10]·8H2O (1), [Co3(L2)(TeMo6O24)(H2O)10]·8H2O (2) and [Cu3(L1)(TeMo6O24)(H2O)10]·6H2O (3) (L1 ​= ​N,N′-bis(4-pyrimidinecarboxamido)-1,2-ethane, L2 ​= ​N,N′-bis(4-pyrimidinecarboxamido)-1,4-butane) were obtained under 90 ​°C aqueous solution for two days. POMOFs 1–3 show fascinating 3D framework structures formed by transition metal linking bis(pyrimidine)-bis(amide) ligands and Anderson-type [TeMo6O24]6– anions. The carbon paste electrodes bulk-modified by POMOFs 1–3 (1-, 2-, 3-CPEs) have good bifunctional electrocatalytic performance towards the oxidation of ascorbic acid and the reduction of potassium bromate, potassium nitrite and heavy metal ions Cr(VI). 1-, 2-, 3-CPEs can be used as electrochemical sensors for the detection of Cr(VI), the limits of detection (LODs) are 0.389 ∼ 0.422 ​μM, which are lower than the 1.0 ​μM standard set by the WHO. In addition, the adsorption properties of POMOFs 1–3 on organic dyes gentian violet (GV) and methyl orange (MO) were investigated.

Aluminum(III) di- and monochlorides incorporating an N,N'-chelating iminophosphonamide ligand: synthesis and structures

Treatment of lithium iminophosphonamide with AlCl3 in Et2O led to the formation of an aluminum(III) dichloride complex as colorless crystals. The substitution reactions of aluminum(III) dichloride stabilized by an iminophosphon- amide ligand with N- and Fe-nucleophiles gave the corresponding compounds of aluminum(III) monochloride. The reaction of the aluminum(III) dichloride complex with CpNa proceeded slowly at room temperature to form an aluminum(III) monochloride complex bearing an η1(σ)-bonded cyclopentadienyl ring.

Four Keggin-type polyoxometalate-based complexes derived from bis(pyrazine)–bis(amide) ligands for electrochemical sensing of multiple analytes and adsorbing dye molecules

Four new Keggin-based complexes derived from bis(pyrazine)–bis(amide) ligands are used to detect multiple analytes (BrO3− NO2−, Cr(vi) and Fe(iii) ions) and adsorb organic dye molecules from aqueous solution.

Electronic insights into aminoquinoline-based PNHN ligands: protonation state dictates geometry while coordination environment dictates N-H acidity and bond strength.

A variety of transition metal complexes bearing aminoquinoline PNHH'-R ligands R = Ph (L1H), Cy (L2H) and their amido analogues are reported for rhodium(I) ([Rh(L1H)(PPh3)]+1 and Rh(L1)(PPh3) 2), cobalt(II) (Co(L2)(Cl) 3), and iron(II) ([Fe(L1H)2]2+5, Fe(L1)26, and [Fe(C5Me5)(L1H)]PF67). The acid-base and redox properties of the amido complexes 2, 6, and their protio parent complexes 1, and 5 permit the determination of the pKa and bond dissociation free energy (BDFE) of their N-H bonds while the ligand scaffold is coordinated to metal centres of square planar and octahedral geometry, respectively. From relative concentrations obtained by the use of 31P{1H} NMR spectroscopy, a pKaTHF value of 14 is calculated for rhodium complex 1, 6.4 for iron complex 5, and 24 for iron complex 7. These data, when combined with elecrochemical potentials obtained via cyclic voltammetry, allow the calculations of BDFE values for the N-H bond of 69 kcal mol-1 for 1, and of 55 kcal mol-1 for 5.

Four Anderson-type [TeMo6O24]6−-based metal–organic complexes with a new bis(pyrimidine)-bis(amide): multifunctional electrochemical and adsorption performances

Four isostructural Anderson-type POM-based metal–organic complexes derived from a new bis(pyrimidine)-bis(amide) ligand were synthesized, showing multifunctional electrochemical sensing activities and good adsorption performances for organic dyes.

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.

Highly efficient and selective extraction of Pu(IV) using two alkyl-substituted amides of nitrilo triacetic acid from nitric acid solutions

• The extraction of U(VI), Pu(IV) and Am(III) was studied with two tripodal NTA amide ligands. • The extraction trend was Pu(IV) > >U(VI) > Am(III) with both the ligands and HONTA > HDDNTA. • The metal ion extraction was not significantly affected with U loading or absorbed gamma dose. • Stripping was facile and the encouraging reusability data promises for possible application. • Modifier content has a positive impact on water and nitric acid extraction and negative impact on metal ion extraction. Liquid-liquid extraction of the actinide ions UO 2 2+ , Pu 4+ , Am 3+ was carried out from nitric acid feed solutions using two tripodal amide extractants, viz., N,N,N’,N’,N”,N” - hexa - n -octylnitrilotriacetamide (HONTA) and N,N,N’,N’,N”,N” - hexa - n -dodecylnitrilotriacetamide (HDDNTA) in 10% isodecanol + 90% n -dodecane diluent. The metal ion extraction trend was: Pu(IV) ≫ U(VI) > Am(III) at 3 M HNO 3 , HONTA being a superior extractant than HDDNTA. Slope analysis indicated ML 2 type species for both Pu(IV) and Am(III) at 3 M HNO 3 and pH 2.0, respectively, whereas, only in case of HONTA, a ML type species was obtained with U(VI) at 3 M HNO 3 . Back extraction data suggested that a mixture of 0.5 M HNO 3 + 0.5 M oxalic acid was efficient for quantitative stripping (∼90%) of Pu(IV), whereas 1 M Na 2 CO 3 and 1 M α-HIBA gave satisfactory back extraction for U(VI) and Am(III), respectively. The ligand solutions showed reasonably good radiation stability up to an absorbed total gamma ray dose of 274 kGy. Distribution data were also obtained under U(VI) loading conditions for possible nuclear fuel cycle applications.

Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups

Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (η5-C5Me5)TiCl2(O-2,6-iPr2C6H3) (1), (η5-C5Me5)TiCl2(N=CtBu2) (2) and [Me2Si(η5-C5Me4)(NtBu)]TiCl2 (3), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex 1, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes 1 and 2, while both side insertion orientations are comparable for complex 3. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from 3. At the chain termination stage, β-H transfer was calculated to be a dominant chain termination route over β-H elimination, presumably owing to the thermodynamic perspective.

Synthesis of C,N,N-Cyclometalated Gold(III) Complexes with Anionic Amide Ligands

AbstractA series of neutral C,N,N Au(III) complexes were synthesized with N-(8-quinolinyl)benzamide derivatives or chiral N-[2-(1,3-oxazolin-2-yl)phenyl]benzamide derivatives. The convenient synthesis method for the amide ligands, together with their operationally simple complexation by direct C–H auration, permitted changes to both the steric and electronic properties of Au(III) complexes for promoting the catalytic three-component couplings of an aldehyde, an amine, and an alkyne.

Hydrides, Halides, and Polymers: Some Unexpected Intermediates on the Routes to First-Row Transition Metal M{N(SiMe3)2}n (n = 2, 3) Complexes.

The reaction of 2 equiv of LiN(SiMe3)2·Et2O with TiCl3(NMe3)2 or VCl3(NMe3)2 afforded the dimeric, halide bridged complexes [Ti(μ-Cl){N(SiMe3)2}2]2 (1) or [V(μ-Cl){N(SiMe3)2}2]2 (2) in moderate yields. The reduction of titanium complex 1 with 3 equiv of 5% (wt) Na/NaCl gave the mixed metal titanium/sodium hydride cluster Ti2(μ-H)2{N(SiMe3)2}3{N(SiMe3)(SiMe2CH)}(Na) (3), which was formed by activation of two C-H bonds at a single methyl group of one of the bis(trimethylsilyl)amide ligands. Attempts to form the analogous vanadium complex by reduction of 2 gave only intractable products. Treatment of Co{N(SiMe3)2}2 with 1 equiv of BrN(SiMe3)2 (which was previously shown to give the unique three-coordinate cobalt(III) trisamide Co{N(SiMe3)2}3) afforded the polymeric [(μ-Br)Co{μ-N(SiMe3)(SiMe2CH2CH2Me2Si)(Me3Si)μ-N}Co(μ-Br)]∞ (4) as a second product, which was shown by a structural analysis to possess a carbon-carbon bond formed between the two ligands. Attempts to isolate manganese and iron complexes analogous to 4 were unsuccessful. The role of bromine in these reactions was further studied by examining the reaction of 0.5 equiv of elemental bromine with [Mn{N(SiMe3)2}2]2 or [Co{N(SiMe3)2}2]2, which for manganese was shown to give the previously reported manganese trisamide Mn{N(SiMe3)2}3 but for cobalt gives the dimeric amide-bridged [Co(Br){μ-N(SiMe3)2}]2 (5).

Significant impact of lanthanide contraction on the structure of the phenanthroline complexes

The structure of La, Nd, Eu and Lu complexes with N,N,N',N'-tetrabutyl-1,10-phenanthroline-2,9-dicarbox- amide ligand was examined using X-ray diffraction analysis. Due to the effect of lanthanide contraction, lutetium forms unique type of complex having the coordination number 9 in contrast to other 10-coordinated lanthanides.

Reductive Reactivity of the 4f75d1 Gd(II) Ion in {GdII[N(SiMe3)2]3}-: Structural Characterization of Products of Coupling, Bond Cleavage, Insertion, and Radical Reactions.

The reductive reactivity of a Ln(II) ion with a nontraditional 4fn5d1 electron configuration has been investigated by studying reactions of the {GdII(N(SiMe3)2)3]}- anion with a variety of reagents that survey the many reaction pathways available to this ion. The chemistry of both [K(18-c-6)2]+ and [K(crypt)]+ salts (18-c-6 = 18-crown-6; crypt = 2.2.2-cryptand) was examined to study the effect of the countercation. CS2 reacts with the crown salt [K(18-c-6)2][Gd(NR2)3] (1) to generate the bimetallic (CS3)2- complex {[K(18-c-6)](μ3-CS3-κS,κ2S',S'')Gd(NR2)2]}2, which contains two trithiocarbonate dianions that bridge Gd(III) centers and a potassium ion coordinated by 18-c-6. In contrast, the only crystalline product isolated from the reaction of CS2 with the crypt salt [K(crypt)][Gd(NR2)3] (2) is [K(crypt)]{(R2N)2Gd[SCS(CH2)Si(Me2)N(SiMe3)-κN,κS]}, which has a CS2 unit inserted into a cyclometalated amide ligand. Complexes 1 and 2 reductively couple pyridine to form bridging dipyridyl moieties, (NC5H4-C5H4N)2-, that generate bimetallic complexes differing only in the countercation, {[K(18-c-6)(C5H5N)2]}2{[(R2N)3Gd]2[μ-(NC5H4-C5H4N)2]} and [K(crypt)]2{[(R2N)3Gd]2[μ-(NC5H4-C5H4N)2]}. Complexes 1 and 2 also show similar reactivity with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to form the (TEMPO)- complexes [K(18-c-6)][(R2N)3Gd(η1-ONC5H6Me4)] and [K(crypt)][(R2N)3Gd(η1-ONC5H6Me4)], respectively. The first example of a bimetallic coordination complex containing a Bi-Gd bond, [K(crypt)][(R2N)3Gd(BiPh2)], was obtained by treating 2 with BiPh3.