Synthesis and structure of a boron cation supported by a β-diketiminate ligand

The salt [HC(CMe)₂(NAr)₂BPh][Al₂Cl₇] (3); Ar = 2,6-i-Pr₂C₆H₃) has been synthesized via the in situ preparation of [HC(CMe)₂(NAr)₂BClPh], followed by treatment with AlCl₃. X-ray analysis of 3 reveals that the BN₂C₃ ring of the boron cation is planar and DFT calculations indicate π-type interactions in the HOMO-6 and HOMO-7 orbitals.     

Chemistry of nitrosyliron complexes supported by a β-diketiminate ligand

Several nitrosyl complexes of Fe and Co have been prepared using the sterically hindered Ar-nacnac ligand (Ar-nacnac = anion of [(2,6-diisopropylphenyl)NC(Me)](2)CH). The dinitrosyliron complexes [Fe(NO)(2)(Ar-nacnac)] (1) and (Bu(4)N)[Fe(NO)(2)(Ar-nacnac)] (2) react with [Fe(III)(TPP)Cl] (TPP = tetraphenylporphine dianion) to generate [Fe(II)(NO)(TPP)] and the corresponding mononitrosyliron complexes. The factors governing NO transfer with dinitrosyliron complexes (DNICs) 1 and 2 are evaluated, together with the chemistry of the related mononitrosyliron complex, [Fe(NO)Br(Ar-nacnac)] (4). The synthesis and properties of the related cobalt dinitrosyl [Co(NO)(2)(Ar-nacnac)] (3) is also discussed for comparison to DNICs 1 and 2. The solid-state structures of several of these compounds as determined by X-ray crystallography are reported.     

Inclusion complexes of sulphanilamide drugs and β-cyclodextrin: a theoretical approach

PM3 theoretical methodology was used to access and compare the relative stability of inclusion complexes formed by sulphadiazene, sulphisomidine, sulphamethazine and sulphanilamide with β-cyclodextrin (β-CD). The study predicted that (i) the heterocyclic ring is encapsulated in the hydrophobic part and aniline ring is present in the hydrophilic part of the β-CD cavity and (ii) intermolecular hydrogen bonds were formed between host and guest molecules. The negative free energy and enthalpy changes indicated that all the four inclusion complexation processes were spontaneous and enthalpy driven process. HOMO and LUMO orbital investigation confirmed that the stability increased in the inclusion complexes and also proved no significant change in the electronic structure of the guest and host molecules after complexation.     

Kinetics and mechanism of thermal gas-phase elimination of α- and β- (N-arylamino)propanoic acid: experimental and theoretical analysis

2-(N-Phenylamino)propanoic acid 1a and 3-(N-phenylamino)-propanoic acid 2a together with four of their aryl analogues were pyrolysed in the gas-phase. The reactions were homogeneous and free from catalytic and radical pathways. Analysis of the pyrolysate of 1 showed the elimination products to be carbon monoxide, acetaldehyde and aniline, while the pyrolysate of 2 reveals the formation of acrylic acid in addition to aniline. Theoretical study of the pyrolysis of 2 using an ab initio SCF method lend support to a reaction pathway involving a 4-membered cyclic transition state.     

Capacity of layered cathode materials for lithium-ion batteries — a theoretical study and experimental evaluation

The theoretical capacity and the vacancy concentration of metal-ion-doped layered compounds such as LiCoO₂, LiNiO₂, and LiMnO₂, acting as cathodes in high-voltage lithium-ion batteries are calculated. The capacity shows strong dependence on valency of the doped metal ion and vacancy concentration. Experimental verification carried out to check the validity of the proposed equation for aluminium substitution into the potential layered materials shows good agreement between the experimental and theoretical capacity values. The vacancy concentration values of doped layered compounds have been found to be high when compared with that of the doped spinel compounds.     

Controlled rearrangement of lactam-tethered allenols with brominating reagents: a combined experimental and theoretical study on α- versus β-keto lactam formation

N-Bromosuccinimide (NBS) smoothly promotes the ring expansion of lactam-tethered allenols to efficiently afford cyclic α- or β-ketoamides with good yields and high chemo-, regio-, and diastereoselectivity, through controlled C-C bond cleavage of the β- or γ-lactam nucleus. Interestingly, in contrast to the rearrangement reactions of 2-azetidinone-tethered allenols, which lead to the corresponding tetramic acid derivatives (β-keto lactam adducts) as the sole products, the reactions of 2-indolinone-tethered allenols under similar conditions give quinoline-2,3-diones (α-keto lactam adducts) as the exclusive or major products. To rationalize the experimental observations, theoretical studies have been performed.     

Protonation and coordination ability of small peptides – theoretical and experimental approaches for elucidation

This review deals with modern theoretical and experimental approaches as well as structural elucidation of small peptides (SP), their protonated forms and metal complexes. Free peptide bond rotation in amino acids (AA) and peptides yielded various conformers, which may possess differing biological activities. Inter- and/or intramolecular stacking observed in aromatic SP is another phenomenon typical for both peptide salts and complexes. These phenomenological effects can be successfully studied, both theoretically and experimentally, using a combination of the theoretical approximations and physical methods, such as electronic absorption spectroscopy, vibrational spectroscopy (including IR and Raman), nuclear magnetic resonance, mass spectrometry, as well as single-crystal X-ray diffraction. The physical and chemical properties of these systems can be precisely calculated by ab initio and DFT methods, varying basis sets and the results obtained allow elucidation of their conformations as a function of the reaction conditions (pH, type of the solvent, temperature, metal to ligand molar ratio). Although the 3-D structures of many peptides have been determined over the past decades, peptide crystallization is still a major obstacle to crystallographic work and the presence of chiral center/s adds further difficulties. For this reason, a specific part of the review is focused on the study of the absolute structure of the peptides, their salts and metal complexes, discussing the conformational preferences of the peptides during these processes. The available crystallographic data for metal complexes are successfully used for the correlation between the structures and the spectroscopic properties.     

Direct experimental evidence for the high chemical reactivity of α- and β-xylopyranosides adopting a (2,5)B conformation in glycosyl transfer

The effect of a (2,5)B boat conformation on xyloside reactivity has been investigated by studying the hydrolysis and glycosylation of a series of synthetic xyloside analogues based on a 2-oxabicyclo[2.2.2]octane framework, which forces the xylose analogue to adopt a (2,5)B conformation. The locked β-xylosides were found to hydrolyze 100-1200 times faster than methyl β-D-xylopyranoside, whereas the locked α-xylosides hydrolyzed up to 2×10(4) times faster than methyl α-D-xylopyranoside. A significant rate enhancement was also observed for the glycosylation reaction. The high reactivity of these conformers can be related to the imposition of a (2,5)B conformation, which approximates a transition state (TS) boat conformation. In this way, the energy penalty required to go from the chair to the TS conformation is already paid. These results parallel and support the observation that the GH-11 xylanase family force their substrate to adopt a (2,5)B conformation to achieve highly efficient enzymatic glycosidic bond hydrolysis.     

Experimental and theoretical thermochemistry of β-tetralone

The standard (p^° = 0.1 MPa) molar enthalpy of formation β-tetralone was measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, was obtained using Calvet microcalorimetry.These values were used to derive the standard molar enthalpy of formation of the compound in the gaseous phase, at T = 298.15 K, ?(75.2 ± 2.5) kJ · mol^?1.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy function with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed.     

Magnesium complexes containing β-ketiminate and β-diketiminate ligands with dimethylamino substituents on the ligand core nitrogen atoms

Treatment of dibutylmagnesium with two equivalents of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (L¹H) in diethyl ether afforded Mg(L¹)₂ (76%), which contains η²-L¹ ligands with tetrahedral coordination at the magnesium ion. Similar treatment of dibutylmagnesium with 4-(2,2-dimethylhydrazino)-3-penten-2-one (L²H) or 5-(2,2-dimethylhydrazino)-2,6-dimethyl-4-hepten-3-one (L³H) and 4-tert-butylpyridine (4-tBupy) in diethyl ether afforded the octahedral complexes Mg(L²)₂(4-tBupy)₂ (85%) and Mg(L³)₂(4-tBupy)₂ (79%). Treatment of dibutylmagnesium with two equivalents of L²H or L³H in the absence of 4-tBupy afforded [Mg(L²)₂]₂ and Mg(L³)₂, however, these complexes were difficult to isolate due to the sticky nature of the crude products. A better synthetic approach entailed sublimation of Mg(L²)₂(4-tBupy)₂ or Mg(L³)₂(4-tBupy)₂ at 95-100 °C/0.05 Torr, which afforded [Mg(L²)₂]₂ (94%) and Mg(L³)₂ (80%) as colorless crystalline solids that were easily isolated. Treatment of [MgCp(CH₃)(OEt₂)]₂ with two equivalents each of 4-tBupy and L¹H afforded MgCp(L¹)(4-tBupy) (65%). Similar treatment of [MgCp(CH₃)(OEt₂)]₂ with two equivalents of L²H or L³H afforded the dimeric complexes [MgCp(L²)]₂ (81%) and [MgCp(L³)]₂ (84%), respectively. [MgCp(L²)]₂ and [MgCp(L³)]₂ decompose upon attempted sublimation at 125-130 °C/0.05 Torr to afford Cp₂Mg (47-53%) and [Mg(L²)₂]₂ (67%) or Mg(L³)₂ (74%). The X-ray crystal structures of Mg(L¹)₂, Mg(L³)₂(4-tBupy)₂, [Mg(L²)₂]₂, Mg(L³)₂, MgCp(L¹)(4-tBupy), [MgCp(L²)]₂, and [MgCp(L³)]₂ are described. The thermal stability and volatility of the complexes were determined through preparative sublimation experiments. Many of the complexes sublime without decomposition at moderate temperatures and low pressures, and thus represent new potential precursors for thin film growth using chemical vapor deposition and related techniques.     

Palladium-catalyzed redox cascade for direct β-arylation of ketones

Herein we report a full article about the detailed design and development of two palladium-catalyzed redox cascade methods that enable direct β-arylation of ketones. Palladium-catalyzed ketone dehydrogenation, aryl-X bond activation and conjugate addition were merged into a redox-neutral catalytic cycle. Non-metal-based aryl electrophiles were used as both the oxidant and the aryl source. The β-arylation with aryl iodides was achieved site-selectively with Pd(TFA)₂/P(i-Pr)₃ as the precatalyst and AgTFA as the iodide scavenger. Both cyclic and linear ketones can react to give β-aryl ketones with excellent functional group tolerance. The β-arylation with diaryliodonium salts was realized without stoichiometric heavy metal additives, and proved to be redox-neutral. A wider substrate scope regarding aryl groups and ketones was obtained for the arylation with diaryliodonium salts, and the possible involvement of palladium nanoparticles as the active catalyst was examined and discussed.     

Derivation of ligand σ- and π-bonding parameters from density functional theoretical calculations and Bursten ligand additivity relationships

New ligand additivity equations, based on the Bursten model, describing dπ orbital energies in square-planar and square–pyramidal complexes are proposed and tested for hypothetical binary Cr(0) and Mn(I) complexes of CO and CNMe. Density functional theory calculations are used to calculate the energies of dπ orbitals of binary octahedral, square–planar, and square–pyramidal d⁶ complexes of Mn(I) and Cr(0). Combination of the modified equations for unsaturated species with Bursten’s original equations for octahedral species allows for calculation of individual ligand bonding parameters and the separation of σ- and π-bonding effects. The calculated parameters provide interesting insight into the nature of metal–ligand bonding in the species studied. The method of separating σ- and π-bonding effects, applied here to CO and CNMe, is proposed as general method for solution of the Bursten equations for low-spin d⁶ octahedral systems.     

Photo and redox dual-stimuli-responsive β-cyclodextrin-ferrocene supramolecules for drug delivery

Abstract

Amphiphilic photo and redox dual-stimuli-cleavable β-cyclodextrin-ferrocene supramolecules were synthesized through noncovalent interactions of ferrocene (Fc) and β-cyclodextrin (β-CD) born by 5-hydroxy-2-nitrobenzyl alcohol (ONB), a photodegradable linker between the β-CD and poly(4-substituted-?-caprolactone) (PXCL _n ) chain. The terminal host–guest MPEG-Fc/β-CD-ONB-PXCL _n complex can formed micelles in the aqueous phase. The critical micelle concentration ranged from 3.16 to 11.50?mg L^?1. The drug-loading content and drug entrapment efficiency of the complex were lower than those of the parent β-CD. When exposed to ultraviolet irradiation and hydrogen peroxide, complex micelles could dissociate and efficiently release the loaded drug. Nanoparticles exhibited almost no toxicity at concentrations up to 1000?μg mL^?1. The uptake of doxorubicin-incorporated micelles by HeLa cells was faster than that of free doxorubicin within the first 5?min. DOX-loaded MPEG₄₅-Fc/β-CD-ONB-PMCL₂₃ micelles effectively inhibited the proliferation of HeLa cells with a half maximal inhibitory concentration (IC₅₀) of 3.8?µg mL^?1.     

Oxidation and coupling of β-diketiminate ligand in lanthanide complexes: novel eight-nuclear lanthanide clusters with μ-, μ3-Cl, and μ4-O bridge

Two novel eight-nuclear lanthanide oxide and chloride clusters Ln(8)(μ-η(2)-L(4))(2)(μ(3)-Cl)(4)(μ-Cl)(10)(μ(4)-O)(3)(THF)(8) (Ln = Er(3), Dy(4); L(4) = [OC{(Me)CN-2,6-(i)PrC(6)H(3)}(2)](2-)) have been synthesized by the reaction of β-diketiminate rare-earth metal chlorides with oxygen, providing a new oxidation and coupling reaction of the β-diketiminate ligand.     

Synthesis and properties of group 9 metal complexes bearing a β-ketophosphenato ligand

A novel β-ketophosphenato ligand bearing a bulky substituent, Tbt(2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), on the phosphorus atom was newly designed and synthesized as a heavier congener of a β-ketoiminato ligand. Rhodium and iridium complexes bearing this new β-ketophosphenato ligand have been synthesized and fully characterized by spectroscopic and elemental analyses together with X-ray crystallographic analyses. The results of NMR spectroscopic studies and the X-ray structural analyses suggested that the β-ketophosphenato ligand has unique electronic features due to the low-coordinated phosphorus atom. Comparison of properties between rhodium β-ketophosphenates 2a,b and rhodium β-ketoiminate 7 revealed the character of the β-ketophosphenato ligand, where the trans influence of the phosphorus atom should be stronger than the nitrogen atom of the β-ketoiminato ligand.     

Synthesis and fluorescence properties of novel pyrazine-boron complexes bearing a β-iminoketone ligand

A novel fluorescence dye based on pyrazine-boron complexes bearing a β-iminoketone ligand has been synthesized by using a simple two-step reaction. Synthesized complexes exhibited fluorescence in solution (F(max): 472-604 nm) and in the solid state (F(max): 496-624 nm). These complexes showed a larger Stokes shift (3690-4900 cm(-1)) than well-known boron dipyrromethene dyes (400-600 cm(-1), in most cases).     

Inclusion complexes of β-cyclodextrin with pyrazinamide and piperazine: Crystallographic and theoretical studies

The inclusion complexes of β-cyclodextrin (β-CD) with pyrazinamide (PYA) and piperazine (PIZ) have been investigated both in the solid phase by single-crystal X-ray diffraction analysis and in the gas phase by semi-empirical PM3 calculation. In the crystalline phase, the disordered PYA and PIZ molecules are entirely embedded in the β-CD cavity. The PYA pyrazine-centre displaces upwards by 1.15(1) Å from the β-CD plane, whereas the PIZ centre shifts downwards by 0.76(1) Å from the β-CD plane. The inclusion scenario changed in the gas phase. Two inclusion geometries of the PYA molecule are comparatively stable with binding energies of ? 22.28 and ? 25.29 kJ mol^? 1: the pyrazine centre shifts upwards by 0.5 Å and downwards by 2.0 Å from the β-CD plane. The PIZ molecule positioning at 2.0 Å below the β-CD plane gives a more stable inclusion complex than does the PYA molecule by 22–25 kJ mol^? 1.

Structural distinction of the β-CD–PYA and β-CD–PIZ inclusion complexes in the solid phase (by X-ray crystallography) and gas phase (by PM3 calculation) is a paradigm of the CD conformational flexibility, the induced-fit mechanism and the dynamics of the inclusion process.     

9-Oxidophenalenone: a noninnocent β-diketonate ligand?

The redox systems [Ru(L)(bpy)(2)](k), [Ru(L)(2)(bpy)](m), and [Ru(L)(3)](n) containing the potentially redox-active ligand 9-oxidophenalenone = L(-) were investigated by spectroelectrochemistry (UV-vis-near-IR and electron paramagnetic resonance) in conjunction with density functional theory (DFT) calculations. Compounds [Ru(L(-))(bpy)(2)]ClO(4) ([1]ClO(4)) and [Ru(L(-))(2)(bpy)]ClO(4) ([2]ClO(4)) were structurally characterized. In addition to establishing electron-transfer processes involving the Ru(II)/Ru(III)/Ru(IV) and bpy(0)/bpy(?-) couples, evidence for the noninnocent behavior of L(-) was obtained from [Ru(IV)(L(?))(L(-))(bpy)](3+), which exhibits strong near-IR absorption due to ligand-to-ligand charge transfer. In contrast, the lability of the electrogenerated anion [Ru(L)(2)(bpy)](-) is attributed to a resonance situation [Ru(II)(L(?2-))(L(-))(bpy)](-)/[Ru(II)(L(-))(2) (bpy(?-))](-), as suggested by DFT calculations.