NH Functionality Research Articles

Fluorescent MOF and Its Gel Composite for the Fluorescence Recovery "Turn-On" Detection of Al3+ Ions and "Turn-Off" Detection of Oxo-Anions.

The exploration of smart sensors is of great significance for the selectivity, sensitivity, and ability to show the low detection limit for the target analyte. Here, we have used the linker H2L (5-((anthracen-9-ylmethyl)amino)isophthalic acid) for the construction of {[Cd(L)(DMF)(H2O)2]·H2O}n (1) which is in order with the chromophore anthracene moiety and the free -NH functionality as a guest interaction site. This framework showed the luminescence recovery "turn-on" detection of the Al3+ ion in an aqueous solution. An exhaustive mechanism study disclosed that the Lewis acid-base-type interaction between the Al3+ ion and the -NH functionality of the linker in the framework revealed that the absorbance caused an enhancement for the "turn-on" sensing event. Besides the "turn-on" sensing event, the "turn-off" sensing phenomenon of 1 is also noticed when it detects the hazardous oxo-anions (MnO4- and CrO42-) with limit of detection values of 17.08 and 19.91 ppb, respectively. The detection of these diverse analytes are very fast (10 s) and they can also be recognized through a colorimetric response. The sensing mechanisms for these analytes are established by photoinduced electron transfer, Forster resonance energy transfer, and inert filter effect along with theoretical investigation. Furthermore, to show the sensing application of 1 in a versatile podium, a MOF gel composite, 1@AA (AA = Agar-Agar), was developed from 1 with AA. Interestingly, 1@AA showed the colorimetric detection of these analytes under UV light. Therefore, sensor 1 behaves as a smart sensory material for the recognition of the above analytes through a simultaneous "turn-on" and "turn-off" effect.

BODIPY Immobilized MCM‐41 Based Multianalyte Sensor: Application in Detection and Removal of Trivalent (Al3+, Cr3+) and Divalent (Cu2+, Hg2+) Metal Ions in Aqueous Media

AbstractIn the present study, a novel p‐phenylcarboxylic acid BODIPY (L) immobilized MCM‐41 based solid chemosensor material L‐propylsilyl@MCM‐41 (MS4) was developed to detect multiple metal ions in a pure aqueous medium. The synthesized solid chemosensor material MS4 shows high sensitivity and removal ability towards trivalent (Al3+, Cr3+) and divalent (Cu2+, Hg2+) metal ions. The emission intensity of MS4 enhanced multifold selectively in the presence of trivalent (Al3+, Cr3+) metal ions and shows quenching in the presence of divalent (Cu2+, Hg2+) metal ions. The limit of detection was calculated to be in the nanomolar range with Al3+, Cr3+, Cu2+, and Hg2+ metal ions in the aqueous medium. The spectroscopic and analytical results suggest that MS4 selectively binds with Al3+ and Cr3+ through −NH functionality and with Hg2+ and Cu2+ through −COOH functionality of p‐phenylcarboxylic acid BODIPY (L). Further, MS4 selectively removes Al3+, Cr3+, Cu2+, and Hg2+ metal ions from the aqueous media with removal efficiency of 97.28 %, 96.34 %, 87.19 %, and 95.63 %, respectively. No noticeable change in the concentration was observed for other metal ions. The recycling potential of MS4 was evaluated using EDTA for up to seven cycles with no significant reduction in sensing capability.

Highly Selective MOF-Based Turn-Off Luminescence Detection of Hg2+ Ions in an Aqueous Medium and Its Dual Functional Catalytic Activity toward Aldol Condensation and β-Enamination Reactions.

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M3(C10H4O7N1)2(8H2O)]·H2O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg2+ ions in an aqueous medium with good selectivity. The interactions between Hg2+ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg2+ ions and in the range mandated by the WHO. The interactions between Hg2+ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.

Targeting KRAS Mutant Cancers via Combination Treatment: Discovery of a 5-Fluoro-4-(3H)-quinazolinone Aryl Urea pan-RAF Kinase Inhibitor.

Optimization of a series of aryl urea RAF inhibitors led to the identification of type II pan-RAF inhibitor GNE-0749 (7), which features a fluoroquinazolinone hinge-binding motif. By minimizing reliance on common polar hinge contacts, this hinge binder allows for a greater contribution of RAF-specific residue interactions, resulting in exquisite kinase selectivity. Strategic substitution of fluorine at the C5 position efficiently masked the adjacent polar NH functionality and increased solubility by impeding a solid-state conformation associated with stronger crystal packing of the molecule. The resulting improvements in permeability and solubility enabled oral dosing of 7. In vivo evaluation of 7 in combination with the MEK inhibitor cobimetinib demonstrated synergistic pathway inhibition and significant tumor growth inhibition in a KRAS mutant xenograft mouse model.

Metal-ligand bifunctional based Mn-catalysts for CO2 hydrogenation reaction

A series of monoligated bidentate aminophosphine (PN) based Noyori-type bifunctional Mn(I)-complexes has been studied for CO2 hydrogenation. The NH functionality of the PN ligand shows a metal–ligand cooperation (MLC) mechanism for CO2 hydrogenation. We show here that it is not essential for a NH functionality to show cooperation via cleavage/formation of NH bond as reported in the case of classical Noyori mechanism for ketone hydrogenation. Rather than this, the NH functionality can work as a chemically innocent ligand for stabilizing the formate anion via NH⋯O hydrogen bonding. More importantly, such stabilized formate anion favours the heterolytic H2 cleavage, which is otherwise a rate determining step. Furthermore, we show that the NH functionality plays a key role for such metal–ligand cooperation mechanism. Therefore, present study will provide an exclusive feature of chemically innocent cooperation in bifunctional catalysts for the development of more efficient catalysts design for CO2 hydrogenation reaction.

Models for Cooperative Catalysis: Oxidative Addition Reactions of Dimethylplatinum(II) Complexes with Ligands Having Both NH and OH Functionality.

The role of NH and OH groups in the oxidative addition reactions of the complexes [PtMe2(κ2-N,N′-L)], L = 2-C5H4NCH2NH-x-C6H4OH [3, x = 2, L = L1; 4, x = 3, L = L2; 5, x = 4, L = L3], has been investigated. Complex 3 is the most reactive. It reacts with CH2Cl2 to give a mixture of isomers of [PtMe2(CH2Cl)(κ3-N,N′,O-(L1-H)], 6, and decomposes in acetone to give [PtMe3(κ3-N,N′,O-(L1-H)], 7, both of which contain the fac tridentate deprotonated ligand. Complex 3 reacts with MeI to give complex 7, whereas 4 and 5 react to give [PtIMe3(κ2-N,N′-L2))], 8, or [PtIMe3(κ2-N,N′-L3)], 9, respectively. Each complex 3, 4, or 5 reacts with either dioxygen or hydrogen peroxide to give the corresponding complex [Pt(OH)2Me2(κ2-N,N′-L)], 10, L = L1; 11, L = L2; 12, L = L3. The ligand L3 in complexes 9 and 12 is easily oxidized to the corresponding imine ligand 2-C5H4NCH=N-4-C6H4OH, L4, in forming the complexes [PtIMe3(κ2-N,N′-L4)], 13, and [Pt(OH)2Me2(κ2-N,N′-L4)], 14, respectively. The NH and OH groups play a significant role in supramolecular polymer or sheet structures of the complexes, formed through intermolecular hydrogen bonding, and these structures indicate how either intramolecular or intermolecular hydrogen bonding may assist some oxidative addition reactions.

A controlled blue-shift in meso-nitrogen aryl fused DIPY and BODIPY skeletons

An aryl-amine attached to the meso-position of the BODIPY skeleton quenches the fluorescence. The observed edge fusion creates a new heterocyclic subunit simultaneously increasing the efficiency of emission. The quantitative deprotonation of meso NH functionality leads to absorbance blue shift and increased emission quantum yield showing potential for formation of BODIPY based changeable chromophores.

Rapid transfer hydrogenation of acetophenone using ruthenium catalysts bearing commercially available and readily accessible nitrogen and phosphorous donor ligands

The screening, synthesis and testing of Ru complexes generated from commercially available ligands or ligands that can be synthesised in one step, is described. The catalysts were tested for activity in the transfer hydrogenation of acetophenone by isopropanol, a probe reaction for hydrogen transfer processes between oxygenated species, often found in applications such as biomass upgrading and fine and specialty chemical synthesis. Ligand screening was conducted by in situ catalyst generation and examined NPN and NNN pincer type ligands bearing NH or CN functional groups. The most active transfer hydrogenation catalysts were found to be those bearing NH functionality, either as amino groups or as benzimidazole groups. Well-defined catalyst precursors were subsequently synthesised, including the novel complex [Ru(1)PPh3(Cl)2] (where (1) = bis(3-aminopropyl)phenylphosphine), the first reported Ru complex for this NPN ligand. Established (PN)2 and PP/NN ketone hydrogenation catalysts were also screened for transfer hydrogen capability, of which [Ru(PhPN)2Cl2] (where PhPN = 2-(diphenylphosphino)ethylamine) was the most active. Subsequently, [Ru(1)PPh3(Cl)2], [Ru(PhPN)2Cl2] and [Ru(4)(PPh3)2Cl][Cl] (where (4) = 2,6-bis(2-benzimidazolyl)pyridine) were investigated more closely to compare rate constants (determined by reaction profile regression analysis) as a more accurate measure of catalyst activity over commonly reported turn over frequencies (TOF). The effect of the reaction products on the catalyst activity was evaluated using feed spiking experiments. Catalyst deactivation was shown to be prevalent and subsequently incorporated into a simple kinetic model which enabled more accurate reaction profile fitting and provided rate constants for both the transfer hydrogenation step and deactivation reaction.

A long wavelength colourimetric chemosensor for fluoride

A family of chemosensors based on the squaramidoquinoxaline moiety (cyclobuta[b]quinoxaline-1,2(3H,8H)-dione) (1–3) have been assembled by a simple room temperature one step synthesis. X-ray crystallographic analysis of 2 demonstrated both strong hydrogen bond donor ability and tendency to π stack in the solid state. Moreover, Compound 2, with its strongly electron withdrawing nitro-substituent, showed an obvious F− selective colour change (when measured against other halides) clearly visible to the naked eye from pink to green in DMSO solution. Further addition of F− led to a second colour change from green to yellow. Using TD-DFT, UV/Vis and NMR analysis we conclude that the observed colour changes are likely to be due to a two-step process involving two NH deprotonation steps. Colour changes of 1 and 3 were not as apparent in the presence of F− owing to the reduced acidity of the NH functionality of the squaramidoquinoxaline. The results of this study again demonstrate the use of squaramide derivatives as valuable building blocks in the field of anion recognition and demonstrate that the electron withdrawing aryl substituent is directly related to the sensing ability/acidity of the squaramide protons and can be used to tune their anion recognition behavior.

Novel amide-functionalized chloramphenicol base bifunctional organocatalysts for enantioselective alcoholysis of meso-cyclic anhydrides.

A family of novel chloramphenicol base-amide organocatalysts possessing a NH functionality at C-1 position as monodentate hydrogen bond donor were developed and evaluated for enantioselective organocatalytic alcoholysis of meso-cyclic anhydrides. These structural diversified organocatalysts were found to induce high enantioselectivity in alcoholysis of anhydrides and was successfully applied to the asymmetric synthesis of (S)-GABOB.

Cooperative N–H and CH2 Skeleton Effects on the Catalytic Activities of Bimetallic Ru(II)–NNN Complexes: Experimental and Theoretical Study

Bimetallic ruthenium(II) complexes bearing a bis(pyrazolylimidazolylpyridine) ligand bridged by a rotatable single C–C bond or methylene linker were synthesized, structurally characterized, and exhibited diverse catalytic activities for the transfer hydrogenation (TH) reactions of ketones in refluxing isopropyl alcohol. Both the unprotected NH functionality and bridging methylene moiety demonstrated an acceleration effect on such TH reactions. Combination of the NH and CH2 skeleton functionalities into the bimetallic Ru(II)–NNN complexes remarkably enhanced the catalytic activities of the complex catalysts. Density functional theory calculations have suggested that the difference in the catalytic activities of these Ru(II)–NNN complexes is attributed to the inherent nucleophilic character of the coordinative nitrogen atoms in the bis(NNN) ligand, and the metal–metal interaction resulted from the number of net natural bond orbital charges on these nitrogen atoms.

A Single Organoiridium Complex Generating Highly Active Catalysts for both Water Oxidation and NAD+/NADH Transformations

The complex [Cp*Ir(pica)Cl] (1; pica = picolinamidate = κ2-pyridine-2-carboxamide) was found to be an effective catalyst for both water oxidation to molecular oxygen and NAD+/NADH transformations, which are the key reactions of light-dependent natural photosynthesis. In particular, 1 exhibits high activity in water oxidation driven by CAN and NaIO4. With the former, the initial TOF exceeds that of [Cp*Ir(pic)Cl] (2; pic = picolinate = κ2-pyridine-2-carboxylate), which is the fastest iridium catalyst reported to date, whereas with NaIO4 it compares well with the best catalysts. 1 exhibits top performances also in the hydrogenation of NAD+ with HCOOK, leading to the regiospecific formation of 1,4-NADH (pH 7) with TOF = 143 h–1, which is about 3 times higher than the previous highest value (54 h–1) reported for [Cp*Ir(4-(1H-pyrazol-1-yl-κN2)benzoic acid)(H2O)]SO4 (3). The activity seems to be critically affected by the presence of the NH functionality, as indicated by its drop of about 1 order of magnitude w...

Dimeric Ruthenium(II)-NNN Complex Catalysts Bearing a Pyrazolyl-Pyridylamino-Pyridine Ligand for Transfer Hydrogenation of Ketones and Acceptorless Dehydrogenation of Alcohols

Dimeric pincer-type ruthenium(II)-NNN complexes bearing an unsymmetrical pyrazolyl-pyridylamino-pyridine ligand were prepared and characterized by NMR, elemental analysis, and X-ray single crystal structural determination. These complexes exhibited very high catalytic activity for both transfer hydrogenation of ketones and acceptorless dehydrogenation of secondary alcohols, achieving TOF values up to 1.9 × 106 h–1 in the transfer hydrogenation of ketones. The high catalytic activity of the Ru(II) complex catalysts is attributed to the presence of the unprotected NH functionality in the ligand and hemilabile unsymmetrical coordination environment around the central metal atoms in the complex.

A new perylenediimide with NH functionality as a colorimetric and fluorescent probe for the selective detection of trivalent Fe3+ and Al3+ ions

Abstract We report the synthesis of a new colorimetric probe R1, in which the perylene tetracarboxylicdiimide fluorophore is connected with an adamantly amine unit through the NH binding site. R1 was tested with a variety of metal ions and exhibited a significant colorimetric transition in the presence of Fe3+ and Al3+ ions. No significant changes were observed with other metal ions. Absorption measurements indicated that trivalent metal ions Fe3+/Al3+ bind with R1 and generate a stable complex. The presence of Fe3+ and Al3+ ions induces new absorption bands with shoulder peaks at 525 nm and 568 nm. The fluorescence intensity of R1 at 579 nm was significantly increased by the addition of Fe3+or Al3+ ions. Furthermore, R1 was found to be sensitive towards these metal ions at micromolar concentrations. The stoichiometry of R1:Fe3+/Al3+ complexes were confirmed by ESI–MS analysis, and binding constants were calculated using Benesi–Hildebrand plots. The binding mode of R1 with metal ions was proposed based on optimized structure from DFT calculation.

ChemInform Abstract: A Novel Thiourea Type Organocatalyst Possessing a Single NH Functionality.

AbstractThe novel catalyst is designed by altering a typical H‐bonding pattern of thiourea derivatives and utilizing the potential of the bis(trifluoromethyl)phenyl motif to participate in the H‐bond formation.

A multi writable thiophene-based selective and reversible chromogenic fluoride probe with dual –NH functionality

A chromogenic fluoride probe bearing bis imine groups having dual –NH functionality (BSB) has been designed, synthesised and structurally characterized by its single crystal X-ray diffraction studies. The BSB could visually and spectroscopically recognise F− with high selectivity over other anions by exhibiting intense chromogenic response (from colourless to red) for F− in acetonitrile solution. The UV–visible titration and 1H NMR titration experiments indicated that the observed changes occur via a combined process including hydrogen bonding and deprotonation between the BSB and F−. Moreover theoretical calculations at the Density Functional Theory (DFT) level shed further light upon probe design strategy and the nature of interactions between BSB and F−. The limit of detection and binding constant of BSB towards F− were found to be 6.9×10−7M and 1.42±0.069×108M−2 respectively. Finally, by using F−and H+ as chemical inputs and the absorbance as output, a INHIBIT logic gate was constructed, which exhibits “Multi-write” ability without obvious degradation in its optical output.

DFT Study on the Mechanism of Formic Acid Decomposition by a Well-Defined Bifunctional Cyclometalated Iridium(III) Catalyst: Self-Assisted Concerted Dehydrogenation via Long-Range Intermolecular Hydrogen Migration

DFT calculations have been performed to gain insight into the mechanism of formic acid (HCOOH) decomposition into H2 and CO2, catalyzed by a well-defined bifunctional cyclometalated iridium(III) complex (a Ir–H hydride) based on a 2-aryl imidazoline ligand with a remote NH functionality. It is shown that the reaction features the direct protonation of the Ir–H hydride by HCOOH with the hydrogen shuttling between the NH group and the carbonyl group of HCOOH. Importantly, the simultaneous presence of two HCOOH molecules is proposed to be important for the dehydrogenation, where one works as a hydrogen source and the other acts as a hydrogen shuttle to assist the long-range intermolecular hydrogen migration. The dehydrogenation mechanism is referred to as HCOOH self-assisted concerted hydrogen migration. With such a mechanism, the energetic span, i.e. the apparent activation energy of the catalytic cycle, is calculated to be 17.3 kcal/mol, which is consistent with the observed rapid dehydrogenation of HCOOH ...

A novel thiourea type organocatalyst possessing a single NH functionality.

A novel thiourea organocatalyst was rationally designed by altering a typical H-bonding pattern of thiourea derivatives and utilising the potential of the 3,5-bis(trifluoromethyl)phenyl motif to participate in the H-bond formation. This unique catalyst afforded the products of the α-amination and Michael reaction in excellent yields and with a high level of stereoselectivity. Although additional studies are necessary to establish the full potential of the catalyst and to broaden its application further, the presented results may indicate alternative routes for further exploration of the thiourea class of organocatalysts.

Coordination of β-Ketoimine-Derived Ligands at Main Group and Transition Metals

The β-ketoimine HC[MeC(O)][MeC(NHt-Bu)] (1H) (Me = methyl) was used as a ligand in the synthesis of organo-aluminium and gallium compounds. With Al, the NH functionality was deprotonated to form the N,O-chelating β-ketoiminate ligand in Al{HC[MeC(O)][MeC(Nt-Bu)]}Me2 (3) (t-Bu = tertiary butyl), whereas the neutral form coordinated to trimethylgallium via the oxygen atom to form the adduct GaMe3·{HC[MeC(O)][MeC(NHt-Bu)]} (4). Reaction of 1H with Ar†NH2 (Ar† = 2-t-BuC6H4) afforded the new N-aryl β-ketoimine HC[MeC(O)][MeC(NHAr†)] (2H), which reacted with Pd(OAc)2 (OAc = acetate = CH3CO2–) to afford the heteroleptic dimer {Pd[HC(MeC(O))(MeC(NAr†))](μ-OAc)}2 ([5]2). The homoleptic bis(β-ketoiminate) Pd{HC[MeC(O)][MeC(NAr†)]}2 (6) was isolated as a minor product of this reaction. The crystal structures of compounds 3, 4, [5]2, and 6 are reported.

Ruthenium Complex Catalysts Supported by a Bis(trifluoromethyl)pyrazolyl–Pyridyl-Based NNN Ligand for Transfer Hydrogenation of Ketones

Ru(III) and Ru(II) complexes bearing a tridentate 2-(3′,5′-dimethylpyrazol-1′-yl)-6-(3″,5″-bis(trifluoromethyl)pyrazol-1″-yl)pyridine or 2-(benzimidazol-2′-yl)-6-(3″,5″-bis(trifluoromethyl)pyrazol-1″-yl)pyridine ligand were synthesized and applied to the transfer hydrogenation of ketones. The Ru(II) complex was structurally confirmed by the X-ray crystallographic analysis and achieved up to 2150 turnover numbers and final TOFs up to 29700 h–1 in the transfer hydrogenation of ketones. The benzimidazolyl moiety with an unprotected NH functionality in the ligand exhibited an enhancement effect on the catalytic activity of its RuCl3 complex in the ketone reduction reactions, reaching a final TOF value up to 35640 h–1. The controlled experiments have revealed that the compatibility of the trifluoromethylated pyrazolyl and unprotected benzimidazolyl is crucial for the establishment of the highly active catalytic system.