Chiral Co3Y Propeller-Shaped Chemosensory Platforms Based on 19F-NMR.

Two propeller-shaped chiral CoIII3YIII complexes built from fluorinated ligands are synthesized and characterized by single-crystal X-ray diffraction (SXRD), IR, UV-vis, circular dichroism (CD), elemental analysis, thermogravimetric analysis (TGA), electron spray ionization mass spectroscopy (ESI-MS), and NMR (1H, 13C, and 19F). This work explores the sensing and discrimination abilities of these complexes, thus providing an innovative sensing method using a 19F NMR chemosensory system and opening new directions in 3d/4f chemistry. Control experiments and theoretical studies shed light on the sensing mechanism, while the scope and limitations of this method are discussed and presented.

Structural and Electronic Control of the Bidentate 1-(2-pyridyl)benzotriazole Ligand in Copper Chemistry with Application to Catalysis in the A3 Coupling Reaction.

The hybrid bidentate 1-(2-pyridyl)benzotriazole (pyb) ligand was introduced into 3d transition metal catalysis. Specifically, [CuII (OTf)2 (pyb)2 ]⋅2 CH3 CN (1) enables the synthesis of a wide range of propargylamines by the A3 coupling reaction at room temperature in the absence of additives. Experimental and high-level theoretical calculations suggest that the bridging N atom of the ligand imposes exclusive trans coordination at Cu and allows ligand rotation, while the N atom of the pyridine group modulates charge distribution and flux, and thus orchestrates structural and electronic precatalyst control permitting alkyne binding with simultaneous activation of the C-H bond via a transient CuI species.

Salpyran: A Cu(II) Selective Chelator with Therapeutic Potential.

We report the rational design of a tunable Cu(II) chelating scaffold, 2-(((2-((pyridin-2-ylmethyl)amino)ethyl)amino)methyl)phenol, Salpyran (HL). This tetradentate ligand is predicated to have suitable permeation, has an extremely high affinity for Cu compared to clioquinol (pCu7.4 = 10.65 vs 5.91), and exhibits excellent selectivity for Cu(II) over Zn(II) in aqueous media. Solid and solution studies corroborate the formation of a stable [Cu(II)L]+ monocationic species at physiological pH values (7.4). Its action as an antioxidant was tested in ascorbate, tau, and human prion protein assays, which reveal that Salpyran prevents the formation of reactive oxygen species from the binary Cu(II)/H2O2 system, demonstrating its potential use as a therapeutic small molecule metal chelator.

Synthesis of trans-Mono(silyl)palladium(II) Bromide Complexes.

The stoichiometric reaction of cis-[Pd(ITMe)2(SiR3)2], where (SiR3 = SiMe3 and SiMe2Ph and ITMe = 1,3,4,5-tetramethylimidazol-2-ylidene) with allyl bromide affords the corresponding allylsilanes along with complexes of the type trans-[Pd(ITMe)2(SiR3)(Br)]. The structure of trans-[Pd(ITMe)2(SiMe2Ph)Br] 2b has been determined in the solid state and displays a slightly distorted square-planar geometry with the two N-heterocyclic carbene ligands in a trans-configuration.

Recent Bio-Advances in Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) have found uses in adsorption, catalysis, gas storage and other industrial applications. Metal Biomolecule Frameworks (bioMOFs) represent an overlap between inorganic, material and medicinal sciences, utilising the porous frameworks for biologically relevant purposes. This review details advances in bioMOFs, looking at the synthesis, properties and applications of both bioinspired materials and MOFs used for bioapplications, such as drug delivery, imaging and catalysis, with a focus on examples from the last five years.

Solvent-Free Synthesis and Key Intermediate Isolation in Ni2Dy2 Catalyst Development in the Domino Ring-Opening Electrocyclization Reaction of Furfural and Amines.

A solvent-free methodology that yields trans-4,5-diaminocyclopent-2-enones, main domains of natural products and a variety of N-heterocycles, is described. The bimetallic catalyst [NiII2DyIII2L4(DMF)6] 2(OTf) 2(DMF) (1) promotes the domino reaction of furfural and amines, with loadings as low as 0.01%, under stirring or microwave-assisted conditions to afford the corresponding frameworks in very good to excellent yields. Crystallographic and theoretical studies shed light on the exclusive formation of the trans-diastereoisomers via a 4π-conrotatory electrocyclization process elucidating the key step in the catalytic process.

Twists to the Spin Structure of the Ln9-diabolo Motif Exemplified in Two {Zn2Ln2}[Ln9]{Zn2} Coordination Clusters.

Two pentadecanuclear Zn4Ln11 [with Ln = Gd(1) or Dy(2)] coordination clusters, best formulated as {Zn2Ln2}[Ln9]{Zn2}, are presented. The central {Ln9} diabolo core has a {Zn2Ln2} handle motif pulling at two outer Ln ions of the central core via two {ZnLn} units, which also invest the system with C2 point symmetry. The resulting cluster motif is supported on two Zn "feet", corresponding to the {Zn2} unit in the formula. A thorough investigation of the magnetic properties in the light of the properties of previously reported {Ln9} diabolo compounds was undertaken. Up to now, the spin structure of such diabolo motifs usually proves ambiguous. Our magnetic studies show that the orientation of the central spin in the {Gd9} diabolo plays a decisive role. In stabilizing the core by attachment of the {Zn}2+ "feet" and using the C2 symmetry related {ZnGd}5+ handles to influence the spin direction of the central Gd of the {Gd9} diabolo, we can understand why the "naked" {Gd9} diabolo shows ambiguous spin structure. This then allowed us to elucidate the single-molecule magnetic (SMM) properties of the Dy-based compound 2 through disentangling the magnetic properties of the isostructural Gd-based compound 1.

Copper-Promoted Regioselective Synthesis of Polysubstituted Pyrroles from Aldehydes, Amines, and Nitroalkenes via 1,2-Phenyl/Alkyl Migration.

The facile copper-catalyzed synthesis of polysubstituted pyrroles from aldehydes, amines, and ß-nitroalkenes is reported. Remarkably, the use of α-methyl-substituted aldehydes provides efficient access to a series of tetra- and pentasubstituted pyrroles via an overwhelming 1,2-phenyl/alkyl migration. The present methodology is also accessible to non α-substituted aldehydes, yielding the corresponding trisubstituted pyrroles. On the contrary, the use of ketones, in place of aldehydes, does not promote the organic transformation, signifying the necessity of α-substituted aldehydes. The reaction proceeds under mild catalytic conditions with low catalyst loading (0.3-1 mol %), a broad scope, very good functional-group tolerance, and high yields and can be easily scaled up to more than 3 mmol of product, thus highlighting a useful synthetic application of the present catalytic protocol. Based on formal kinetic studies, a possible radical pathway is proposed that involves the formation of an allylic nitrogen radical intermediate, which in turn reacts with the nitroalkene to yield the desired pyrrole framework via a radical 1,2-phenyl or alkyl migration.

Cu(II) Coordination Polymers as Vehicles in the A3 Coupling.

A family of benzotriazole based coordination compounds, obtained in two steps and good yields from commercially available materials, formulated as [CuII(L1)2(MeCN)2]·2ClO4·MeCN (1), [CuII(L1)(NO3)2]·MeCN (2), [ZnII(L1)2(H2O)2]·2ClO4·2MeCN (3), [CuII(L1)2Cl2]2 (4), [CuII5(L1)2Cl10] (5), [CuII2(L1)4Br2]·4MeCN·CuII2Br6 (6), [CuII(L1)2(MeCN)2]·2BF4 (7), [CuII(L1)2(CF3SO3)2] (8), [ZnII(L1)2(MeCN)2]·2CF3SO3 (9), [CuII2(L2)4(H2O)2]·4CF3SO3·4Me2CO (10), and [CuII2(L3)4(CF3SO3)2]·2CF3SO3·Me2CO (11), are reported. These air-stable compounds were tested as homogeneous catalysts for the A3 coupling synthesis of propargylamine derivatives from aldehyde, amine, and alkyne under a noninert atmosphere. Fine tuning of the catalyst resulted in a one-dimensional (1D) coordination polymer (CP) (8) with excellent catalytic activity in a wide range of substrates, avoiding any issues that would inhibit its performance.

3d/4f Coordination Clusters as Cooperative Catalysts for Highly Diastereoselective Michael Addition Reactions.

Michael addition (MA) is one of the most well studied chemical transformation in synthetic chemistry. Here, we report the synthesis and crystal structures of a library of 3d/4f coordination clusters (CCs) formulated as [ZnII2YIII2L4(solv)X(Z)Y] and study their catalytic properties toward the MA of nitrostyrenes with barbituric acid derivatives. Each CC presents two borderline hard/soft Lewis acidic ZnII centers and two hard Lewis acidic YIII centers in a defect dicubane topology that brings the two different metals into a proximity of ∼3.3 Å. Density functional theory computational studies suggest that these tetrametallic CCs dissociate in solution to give two catalytically active dimers, each containing one 3d and one 4f metal that act cooperatively. The mechanism of catalysis has been corroborated via NMR, electron paramagnetic resonance, and UV-vis. The present work demonstrates for the first time the successful use of 3d/4f CCs as efficient and high diastereoselective catalysts in MA reactions.

Synthesis of Functionalized Hydrazines: Facile Homogeneous (N-Heterocyclic Carbene)-Palladium(0)-Catalyzed Diboration and Silaboration of Azobenzenes.

The bis(N-heterocyclic carbene)(diphenylacetylene)palladium complex [Pd(ITMe)2(PhC≡CPh)] (ITMe=1,3,4,5-tetramethylimidazol-2-ylidene) acts as a highly active pre-catalyst in the diboration and silaboration of azobenzenes to synthesize a series of novel functionalized hydrazines. The reactions proceed using commercially available diboranes and silaboranes under mild reaction conditions.

An Undecanuclear Ferrimagnetic Cu9Dy2 Single Molecule Magnet Achieved through Ligand Fine-Tuning.

We describe the concept of increasing the nuclearity of a previously reported high-spin Cu5Gd2 core using a "fine-tuning" ligand approach. Thus, two Cu9Ln2 coordination clusters, with Ln = Dy (1) and Gd (2), were synthesized with the Gd compound having a ground spin state of (17)/2 and the Dy analogue showing single-molecule-magnet behavior in zero field.

Effect of Ligand Field Tuning on the SMM Behavior for Three Related Alkoxide-Bridged Dysprosium Dimers.

The synthesis and characterization of three Dy2 compounds, [Dy2(HL1)2(NO3)4] (1), [Dy2(L2)2(NO3)4] (2), and [Dy2(HL3)2(NO3)4] (3), formed using related tripodal ligands with a central tertiary amine bearing picolyl and alkoxy arms, 2-[(2-hydroxy-ethyl)-pyridin-2-ylmethylamino]-ethanol (H2L1), 2-(bis-pyridin-2-ylmethylamino)-ethanol (HL2), and 2-(bis-pyridin-2-ylmethylamino)-propane-1,3-diol (H2L3), are reported. The compounds are rare examples of alkoxide-bridged {Dy2} complexes and display capped square antiprism coordination geometry around each Dy(III) ion. Changes in the ligand field environment around the Dy(III) ions brought about through variations in the ligand donors can be gauged from the magnetic properties, with compounds 1 and 2 showing antiparallel coupling between the Dy(III) ions and 3 showing parallel coupling. Furthermore, slow relaxation of the magnetization typical of SMM behavior could be observed for compounds 2 and 3, suggesting that small variations in the ligand field can have a significant influence on the slow relaxation processes responsible for SMM behavior of Dy(III)-based systems.

Efficient Ni(II)2Ln(III)2 Electrocyclization Catalysts for the Synthesis of trans-4,5-Diaminocyclopent-2-enones from 2-Furaldehyde and Primary or Secondary Amines.

A series of heterometallic coordination clusters (CCs) [Ni(II)2Ln(III)2(L1)4Cl2(CH3CN)2] 2CH3CN [Ln = Y (1Y), Sm (1Sm), Eu (1Eu), Gd (1Gd), or Tb (1Tb)] were synthesized by the reaction of (E)-2-(2-hydroxy-3-methoxybenzylidene-amino)phenol) (H2L1) with NiCl2·6(H2O) and LnCl3·x(H2O) in the presence of Et3N at room temperature. These air-stable CCs can be obtained in very high yields from commercially available materials and are efficient catalysts for the room-temperature domino ring-opening electrocyclization synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere. Structural modification of the catalyst to achieve immobilization or photosensitivity is possible without deterioration in catalytic activity.

Chemically and thermally stable silica nanowires with a ß-sheet peptide core for bionanotechnology.

BACKGROUND: A series of amyloidogenic peptides based on the sequence KFFEAAAKKFFE template the silica precursor, tetraethyl orthosilicate to form silica-nanowires containing a cross-ß peptide core. RESULTS: Investigation of the stability of these fibres reveals that the silica layers protect the silica-nanowires allowing them to maintain their shape and physical and chemical properties after incubation with organic solvents such as 2-propanol, ethanol, and acetonitrile, as well as in a strong acidic solution at pH 1.5. Furthermore, these nanowires were thermally stable in an aqueous solution when heated up to 70 °C, and upon autoclaving. They also preserved their conformation following incubation up to 4 weeks under these harsh conditions, and showed exceptionally high physical stability up to 1000 °C after ageing for 12 months. We show that they maintain their ß-sheet peptide core even after harsh treatment by confirming the ß-sheet content using Fourier transform infrared spectra. The silica nanowires show significantly higher chemical and thermal stability compared to the unsiliconised fibrils. CONCLUSIONS: The notable chemical and thermal stability of these silica nanowires points to their potential for use in microelectromechanics processes or fabrication for nanotechnological devices.

Heteronuclear 3 d/Dy(III) coordination clusters as catalysts in a domino reaction.

Three isoskeletal tetranuclear coordination clusters with general formula [M(II) 2 Dy(III) 2 L4 (EtOH)6 ](ClO4 )2 ⋅2 EtOH, (M=Co, 1; M=Ni, 2) and [Ni(II) 2 Dy(III) 2 L4 Cl2 (CH3 CN)2 ]⋅2 CH3 CN (3), have been synthesized and characterized. These air-stable compounds, and in particular 3, display efficient homogeneous catalytic behavior in the room-temperature synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere.

A Strongly Spin-Frustrated Fe(III) 7 Complex with a Canted Intermediate Spin Ground State of S=7/2 or 9/2.

A disk-shaped [Fe(III) 7 (Cl)(MeOH)6 (µ3 -O)3 (µ-OMe)6 (PhCO2 )6 ]Cl2 complex with C3 symmetry has been synthesised and characterised. The central tetrahedral Fe(III) is 0.733 Šabove the almost co-planar Fe(III) 6 wheel, to which it is connected through three µ3 -oxide bridges. For this iron-oxo core, the magnetic susceptibility analysis proposed a Heisenberg-Dirac-van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The (57) Fe Mössbauer (MS) analysis verifies that the central Fe(III) ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral Fe(III) ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology.

Developing a "highway code" to steer the structural and electronic properties of Fe(III)/Dy(III) coordination clusters.

In the recently established field of 3d/4f coordination cluster (CC) chemistry several burning questions still need to be addressed. It is clear that combining 3d and 4f metal ions within a coordination cluster core has the potential to lead to electronic structures that will be very difficult to describe but can also be extremely interesting. Furthermore, understanding why certain core topologies seem to be favored is difficult to predict. Here we show that the secondary coordination sphere provided by the ligands influences the favored product, as demonstrated for the compound [Fe4Dy2(µ3-OH)2(n-bdea)4(C6H5CO2)8]·MeCN (1), which has a 2Fe:2Dy:2Fe core and was made using [Fe(III)3O(C6H5)CO2)(L)3](+) as starting material plus Dy(NO3)3 and N-n-butyl-diethanolamine (n-bdeaH2), compared with the compound made using a methyl meta-substituent (R) on the phenyl ring of the benzoate, [Fe(III)3O(C6H4Me)CO2)(L)3](+) as starting material, which resulted in the "square-in-square" compound [Fe4Dy4(µ3-OH)4(n-bdea)4(O2CC6H4CH3)12]·MeCN (2) when using ambient conditions. Changing reaction conditions from ambient to solvothermal leads to "double-propeller" compounds [Fe4Dy4(µ4-O)3(n-bdea)3(C6H5CO2)12]·13MeCN (3) and [Fe4Dy4(µ4-O)3(n-bdea)3(O2CC6H4CH3)12]·MeCN (4) forming with this core, resulting irrespective of the substitution on the iron benzoate starting material. Furthermore, compounds 1 and 2 can be transformed into compounds 3 and 4, respectively, using a solvothermal method. Thus, compounds 3 and 4 appear to be the thermodynamically most stable species. The factors steering the reactions toward these products are discussed. The electronic structures have been investigated using magnetic and Mössbauer studies. All compounds are cooperatively coupled 3d/4f systems, with compound 1 showing single-molecule magnet behavior.

Tetradecanuclear Iron(III)-Oxo Nanoclusters Stabilized by Trilacunary Heteropolyanions.

The tetrameric, multi-Fe(III)-containing polyoxotungstates [Fe14O6(OH)13(P2W15O56)4](31-) (1) and [Na2Fe14(OH)12(PO4)4(A-α-XW9O34)4](20-) (X = Si(IV) (2), Ge(IV) (3)) have been successfully synthesized under conventional reaction conditions in aqueous, slightly acidic (1), or basic (2 and 3) media. Polyanions 1-3 were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and magnetic studies, and in solution by electrochemistry.

Enhancement of spin relaxation in an FeDy2 Fe coordination cluster by magnetic fields.

Two [FeLn2 Fe(µ3 -OH)2 (teg)2 (N3 )2 (C6 H5 COO)4 ] compounds (where Ln=Y(III) and Dy(III) ; teg=triethylene glycol anion) have been synthesized and studied using SQUID and Mössbauer spectroscopy. The magnetic measurements on both compounds indicate dominant antiferromagnetic interactions between the metal centers. Analysis of the (57) Fe Mössbauer spectra complement the ac magnetic susceptibility measurements, which show how a static magnetic field can quench the slow relaxation of magnetization generated by the anisotropic Dy(III) ions.