Synthetic,Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(Tp^Me2)Ir(H){?C(CH₂R)ArO }] (Tp^Me2=hydrotris(3,5‐dimethylpyrazolyl)borate; R=H, Me; Ar=substituted C₆H₄ group), and their corresponding hydride olefin isomers, [(Tp^Me2)Ir(H){R(H)C? C(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(Tp^Me2)Ir(C₆H₅)₂] with o‐C₆H₄(OH)CH₂R, or with the substituted anisoles 2,6‐Me₂C₆H₃OMe, 2,4,6‐Me₃C₆H₂OMe, and 4‐Br‐2,6‐Me₂C₆H₂OMe. The reactions with the substituted anisoles require not only multiple C? H bond activation but also cleavage of the Me? OAr bond and the reversible formation of a C? C bond (as revealed by ¹³C labeling studies). Equilibria between the two tautomeric structures of these complexes were achieved by prolonged heating at temperatures between 100 and 140 °C, with interconversion of isomeric complexes requiring inversion of the metal configuration, as well as the expected migratory insertion and hydrogen‐elimination reactions. This proposal is supported by a detailed computational exploration of the mechanism at the quantum mechanics (QM) level in the real system. For all compounds investigated, the equilibria favor the alkylidene structure over the olefinic isomer by a factor of between approximately 1 and 25. Calculations demonstrate that the main reason for this preference is the strong Ir–carbene interactions in the carbene isomers, rather than steric destabilization of the olefinic tautomers.     

A Novel Coordination Polymer Based on Decavanadate Units Linked by Copper(II) Ethylenediamine Complexes

Summary: A novel coordination polymer[{Cu(en)₂}(V₁₀O₂₈)]_n · 2n[Cu(en)₂(H₂O)] · 2n(H₃BO₃) · 2n(H₂O) was obtained by hydrothermal reaction. The compound crystallizes in the monoclinic crystal system, in the C2/c space group, with a = 26.490 (3) Å; b = 11.6558 (11) Å; c = 19.8426 (19) Å; β = 124.011 (1)°; V = 5078.6(8) ų. The solid structure is formed by polymeric chains, [Cu(en)₂(H₂O)]²⁺ cations, and boric acid and water solvate molecules, stabilized through a multiple hydrogen bond network.     

[Cu(H2btec)(bipy)]∞: Reusable Metal Organic Polymer Catalyst for Epoxidation Reactions

Summary: The search of new inorganic materials with better catalytic properties is an important field of research. Reusability, efficiency and atom economy correspond to the main parameters to characterize a catalyst. In this work, we inform the effectiveness of [Cu(H₂btec)(bipy)]_∞ (H₄btec = 1,2,4,5-benzenetetracarboxylic acid) as an heterogeneous coordination polymer catalyst for the oxidation of olefins. The catalyst exhibits good atom economy, high turnover numbers and good selectivity for a ratio of 4000/1 substrate/catalyst for cyclohexene and styrene oxidation. Furthermore, the catalyst was recycled and reused for seven consecutive cycles, retaining the structural integrity and effectiveness as catalyst in all the performed experiments.     

Extraction of arsenic as the diethyl dithiophosphate complex with supercritical fluid and quantitation by cathodic stripping voltammetry

The separation of arsenic based on in situ chelation with ammonium diethyl dithiophosphate (ADDTP) has been carried out using methanol-modified supercritical CO₂. Aliquots of extract were added to an electroanalytical cell and arsenic was determined by square wave cathodic stripping voltammetry (SWCSV) at a hanging mercury drop electrode (HMDE). Quantitative extractions of As(DDTP)₃ were achieved when the experiments were carried out at a pressure of 2500 psi, a temperature of 90 °C, 2.0 mL of methanol, 20.0 min of static extraction and 5.0 min of dynamic extraction in the presence of 18 mg of ADDTP. Analysis of arsenic was made using 150 mg L⁻¹ of Cu(II) in 1 M HCl solution as supporting electrolyte in the presence of ADDTP as ligand. Preconcentration was carried out by deposition at a potential of −0.50 V and the intermetallic compound Cu_xAs_y was reduced at a potential of −0.77 to −0.82 V, depending on ligand concentration. The results showed that the presence of ligand plays an important role, increasing the method's sensitivity and preventing the oxidation of As(III). The calibration graph of the As(DDTP)₃ solution was linear from 0.8 to 12.5 μg L⁻¹ of arsenic (LOD 0.5 μg L⁻¹, R = 0.9992, t_acc = 60 s). The method was validated using carrot pulp spiked with arsenic solution. This method was applied to the determination of arsenic in samples of carrots, beets and irrigation water. Arsenic in beets was: skin 4.10 ± 0.18 mg kg⁻¹; pulp 3.83 ± 0.19 mg kg⁻¹ and juice 0.71 ± 0.09 mg L⁻¹; arsenic in carrots was: skin 2.15 ± 0.09 mg kg⁻¹; pulp 0.59 ± 0.11 mg kg⁻¹ and juice 0.71 ± 0.03 mg L⁻¹. Arsenic in water were: Chiu-Chiu 0.08 mg L⁻¹, Inacaliri 1.12 mg L⁻¹, and Salado river 0.17 ± 0.07 mg L⁻¹.     

The structure of pyrazoles in the solid state: a combined CPMAS, NMR, and crystallographic study

The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1H-pyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G level justify the great stability of this tautomer by the presence of an intramolecular N-H...pi interaction, present in solution.     

Multiphoton reactive surfaces using ruthenium(II) photocleavable cages

Photoreactive surfaces derived from a new photocleavable surface modification agent and with photosensitivity in the Vis and IR region are described. A ruthenium(II) caged aminosilane, [Ru(bpy)(2)(PMe(3))(APTS)](PF(6))(2), was synthesized and attached to silica surfaces. Light irradiation removed the cage and generated surface patterns with reactive amine groups. The photosensitivity of this compound under single (460 nm) and two-photon (900) excitation is demonstrated. Functional patterns with site-selective attachment of other molecular species are described.     

A phosphine-free Pd catalyst for the selective double carbonylation of aryl iodides

The first phosphine-free Pd-catalysed double carbonylation of aryl iodides is reported as a general and practical method, giving excellent conversions and selectivities for a wide range of aryl iodides and amine nucleophiles under atmospheric CO pressure.     

Synthesis of the O-linked hexasaccharide containing β-D-Galf-(1→2)-β-D-Galf in Trypanosoma cruzi mucins

The hexasaccharide β-D-Galp-(1→2)-[β-D-Galp-(1→3)]-β-D-Galp-(1→6)-[β-D-Galf(1→2)-β-D-Galf(1→4)]-D-GlcNAc (1) is the largest carbohydrate structure released as alditol by reductive β-elimination from mucins of some strains of T. cruzi. The terminal β-D-Galp units are sites of sialylation by trans-sialidase which transfers sialic acid from the host to the parasite. Hexasaccharide 1 was synthesized by a [3 + 3]-convergent strategy based on a nitrile assisted glycosylation, using the trichloroacetimidate method. The β-D-Galf-(1→2)-β-D-Galf-D-GlcNAc synthon was sequentially constructed from the reducing end to the non-reducing end employing benzyl α-D-galactofuranoside as starting material for the internal Galf unit. The choice of this novel precursor, obtained in one-reaction step from galactose, allowed the introduction of an orthogonal and participating levulinoyl group at O-2. Thus, the diastereoselective construction of the Galf-β(1→4)-GlcNAc linkage by the trichloroacetimidate method of glycosylation was achieved. The (1)H NMR spectrum of alditol 2 was identical to the product released by β-elimination from the parasite mucin.     

Every Banach ideal of polynomials is compatible with an operator ideal

We show that for each Banach ideal of homogeneous polynomials, there exists a (necessarily unique) Banach operator ideal compatible with it. Analogously, we prove that any ideal of n-homogeneous polynomials belongs to a coherent sequence of ideals of k-homogeneous polynomials.     

Synthesis of branched dithiotrisaccharides via ring-opening reaction of sugar thiiranes

Satisfactory procedures are described for the synthesis of 5,6- and 3,4-thiirane derivatives from the respective hexofuranose or hexopyranose epoxide precursors. The controlled ring-opening reaction of thiiranes by 1-thioaldoses was successfully accomplished to afford, regio- and stereoselectively, β-S-(1→4)-3,4-dithiodisaccharides. For instance, the regioselective attack of per-O-acetyl-1-thioglucose (16) to C-4 of 2-propyl 2,6-di-O-acetyl-3,4-epithio-α-D-galactopyranoside (14) gave the derivative of Glcp-β-S-(1→4)-3,4-dithioGlcp-O-iPr (17). This thiodisaccharide was accompanied by the (1→3)-disulfide 18, formed between 16 and 17, and the symmetric (3→3)-disulfide 19, which resulted from the oxidative dimerization of 17. However, the S-acetyl derivative of 17 could be obtained in good yield (62%) by LiAlH(4) reduction of the crude mixture 17-19, followed by acetylation. The same sequence of reactions starting from 14 and the 1-thiolate of Galp afforded the per-O,S-acetyl derivative of Galp-β-S-(1→4)-3,4-dithio-α-D-Glcp-O-iPr (23), which was selectively S-deacetylated to give 25. The dithiosaccharides 17 and 25 are 3,4-di-S-analogues of derivatives of the natural disaccharides cellobiose and lactose, respectively. The ring-opening reaction of 5,6-epithiohexofuranoses of D-galacto (8) or L-altro (11) configuration with 1-thioaldoses was also regio- and stereoselective to give the respective β-S-(1→6)-linked 5,6-dithiodisaccharides 26 or 29 in excellent yields. Glycosylation of the free thiol group of 17, 25, or 26, using trichloroacetimidates as glycosyl donors, led to the corresponding branched dithiotrisaccharides. Some of them are sulfur analogues of derivatives of branched trisaccharides found in natural polysaccharides.