Shmuel Cohen

Ligand–Metal Cooperation in PCP Pincer Complexes: Rational Design and Catalytic Activity in Acceptorless Dehydrogenation of Alcohols

Cooperative ligands are non-innocent ligands that actively participate in reversible structural transformations of catalytic species over the course of a catalytic cycle. The ligand– metal cooperation often brings about unusual and exciting reactivity and plays a very important role in natural and artificial systems. Among others, this concept is of great interest for the design of new catalytic bond-breaking and bond-forming processes, as it offers a non-oxidative mechanistic alternative to the classical oxidative addition/reductive elimination sequence. The initial interest in this concept has been translated into practice, and efficient catalytic processes, which exploit conceptually different cooperating systems, have been discovered since the prominent reports on bifunctional hydrogenation catalysts by Noyori and co-workers (1; Figure 1)

First utilization of a homochiral ruthenium porphyrin as enantioselective epxidation catalyst

Abstract The enantioselectivity in the first catalytic conversion of styrene to its epoxide by a homochiral ruthenium porphyrin- 1 -Ru(O) 2 - displayed a remarkable sensitivity to the solvent and the identity of the oxidant. The latter phenomenon clearly indicates that several high valent intermediates with different selectivities participate in oxygen atom transfer from catalyst to substrate. These observations are anticipated to significantly affect research of metal complexes of other homochiral porphyrins as well.

Metal atom dynamics in four triferrocenylmethane derivatives and the crystal structure of Fc3COH

The metal atom dynamics of four triferrocenylmethane derivatives have been elucidated, using temperature-dependent 57Fe Mössbauer effect (ME) spectroscopy. The hyperfine parameters (IS and QS) at 90 K are compared to each other and those of related ferrocenoids. The metal atom vibrational amplitudes as a function of temperature have been extracted from the ME recoil-free fraction data, and are compared to the X-ray U(i,j) values for two of the compounds. The single crystal structural data for triferrocenylmethanol have been determined at 173 and 295 K. The vibrational anisotropy of the metal atom for all of the compounds is negligibly small over the accessible temperature range.

IL-10 Mediates Resistance to Adoptive Transfer Experimental Autoimmune Encephalomyelitis in MyD88−/− Mice

MyD88 is an adaptor molecule that functions in the innate signaling induced by proinflammatory adjuvants that interact with TLRs. Mice lacking MyD88, for example, resist active experimental autoimmune encephalomyelitis (EAE) induced by immunization with an encephalitogenic myelin oligodendrocyte glycoprotein (MOG) peptide in CFA. We reasoned that MyD88−/− mice, nevertheless, should be susceptible to EAE mediated by adoptive transfer of activated encephalitogenic T cell lines, which do not require adjuvant signaling for their effector functions. We now report, however, that mice lacking MyD88 also resist adoptive EAE mediated by an anti-MOG T cell line that is strongly encephalitogenic in wild-type (WT) mice. The transferred anti-MOG T cells proliferated, secreted INF-γ, and migrated to the CNS in the MyD88−/− mice, as they did in WT mice, but inflammatory infiltrates did not progress and clinical EAE did not develop. The resistance of the MyD88−/− mice to adoptive EAE mediated by the otherwise encephalitogenic T cells was found to result from the secretion of IL-10 by recipient T cells of two different specificities: those specific for MOG and those responding to the T cell clone itself—both anticlonotypic and antiergotypic T regulators were detected. IL-10–producing anti-MOG T cells isolated from immunized MyD88−/− mice suppressed the induction of active EAE in WT recipients. Moreover, the absence of IL-10 production in MyD88/IL-10 double-knockout mice rendered the mice susceptible to adoptive transfer of EAE. Thus, MyD88 signaling appears to be a key factor in determining the cytokine phenotype of T cells involved in autoimmune inflammation and regulation.

Potassium, Cesium, and Ammonium Peroxogermanates with Inorganic Hexanuclear Peroxo Bridged Germanium Anion Isolated from Aqueous Solution

Potassium (K6[Ge6(μ-OO)6(μ-O)6(OH)6]·14H2O, 1), cesium ammonium (Cs4.2(NH4)1.8[Ge6(μ-OO)6(μ-O)6(OH)6]·8H2O, 2), and potassium ammonium (K2.4(NH4)3.6[Ge6(μ-OO)6(μ-O)6(OH)6]·6H2O, 3) peroxogermanates were isolated from 3% hydrogen peroxide aqueous solutions of the corresponding hydroxogermanates and characterized by single crystal and powder X-ray diffraction studies and by Raman spectroscopy and thermal analysis. The crystal structure of all three compounds consists of cations of potassium and/or ammonium and cesium, water molecules, and centrosymmetric hexanuclear peroxogermanate anion [Ge6(μ-OO)6(μ-O)6(OH)6](6-) with six μ-oxo- and six μ-peroxo groups. Peroxogermanates demonstrate relatively high thermal stability: the peroxide remains in the structure even after water release after heating to 100-120 °C. DFT calculations of the peroxogermanate [Ge6(μ-OO)6(μ-O)6(OH)6](6-) anion confirm its higher thermodynamic stability compared to the hydroperoxo- and oxogermanate analogues.

β-Amino alcohol selectors for enantioselective separation of amino acids by ligand-exchange capillary zone electrophoresis in a low molecular weight organogel

A new family of copper ligand‐exchange selectors, L‐ or D‐β‐amino alcohols, is employed for the chiral separation of D,L‐dansyl‐amino acids, unmodified amino acid racemates, phenylalanine and tryptophan, and β‐blocker L,D‐propranolol by SDS–micellar electrokinetic chromatography and by electrophoretic chromatography in a low molecular weight organogel (LMOG)‐filled capillary. The LMOG comprised a self‐assembled fibrillar gel of trans‐(1S,2S)‐1,2‐bis‐(dodecylamido) cyclohexane in methanol. The di‐L‐valinol–copper complex exhibited the best performance on LMOG–CE compared with all other β‐amino alcohol–copper selectors. The dependence of chiral resolution on the pH*, the ratio between the copper and the L‐valinol ligand and the concentration of added selector complex in the run buffer were investigated revealing a marked difference between the activity of the copper–valinol and the previously studied copper–valine selector. The optimal separation conditions were achieved using a 2:1 valinol/copper ratio, in accordance with the 2:1 structure of the complex, which was proven by single crystal and powder X‐ray diffractions and by elemental analysis. Unlike the copper–valine selectors that could be used only under acidic conditions (pH* 3.5), the copper–valinol selectors could be used under near‐neutral conditions and even at pH* 9.1. A comparison between SDS–micellar electrokinetic chromatography and LMOG–CE under otherwise identical conditions revealed a significant superior separation on the LMOG‐filled capillaries.

Peri Interactions in Naphthalene Diketones: A Preference for (Z,Z) Conformations

The crystal structures of 1,8-dibenzoylnaphthalene (9), 1,4,5,8-tetrabenzoylnaphthalene (10), and 1,8-diacetylnaphthalene (11) have been determined by X-ray diffraction. Diketone 9 crystallizes in triclinic space group P—1 with a = 7.924(2), b = 14.068(3), c = 7.876(1) Å, α = 99.47(2), β = 90.58(1), γ = 91.43(2)°. Tetraketone 10 crystallizes in monoclinic space group P21/c a = 7.374(4), b = 11.960(5), c = 15.524(5) Å, β = 93.15(5)°. Diketone 11 crystallizes in orthorhombic space group Pbca a = 6.986(3), b = 15.946(4), c = 8.257(1) Å. Each of these naphthalene ketones adopt a (Z,Z) conformation, with torsion angles O—C—C1—C8a/O—C—C8—C8a of 49.8°/44.5° (9), 52.1°/46.6° (10), and 44.8°/42.4° (11). The structures 9–11 are overcrowded with the distances between two neighboring carbonyl carbon atoms being significantly shorter than the sum of the van der Waals radii of two carbon atoms (342 pm): 293.4 pm (9), 281.6 pm (10), and 293.0 pm (11).

Self assembly assisted preparation of a homochiral porphyrin

Abstract The multiple alkylation of porphyrin 3 by four equivalents of the homochiral ditosylthreitol 4 proceeded in high yields, and only one of the two possible isomers was formed. The crystal structure of the product 5 suggests that that this novel phenomenon is a consequence of conformational changes, induced by the first alkylation. The formation of the first bridge completely eliminates the possibility of obtaining one of the isomers, while at the same time it seems to assist in the formation of the other isomer in a self assembly fashion.

Crystallization of carbamazepine pseudopolymorphs from nonionic microemulsions.

Crystallization of carbamazepine (CBZ), an antiepileptic drug, precipitated from confined spaces of nonionic microemulsions was investigated. The study was aimed to correlate the structure of the microemulsion [water-in-oil (W/O), bicontinuous, and oil-in-water (O/W)] with the crystalline structure and morphology of solid CBZ. The precipitated CBZ was studied by DSC, TGA, powder XRD, single-crystal XRD, SEM, and optical microscopy. The results suggest that the microstructure of the microemulsions influences the crystallization process and allows crystallizing polymorphs that exhibit different crystal structure and habits. W/O nanodroplets orient the crystallizing CBZ molecules to form a prismlike anhydrous polymorphic form with monoclinic unit cell and P21/n space group. Bicontinuous structures lead to platelike dihydrate crystals with orthorhombic unit cell and Cmca space group. The O/W nanodroplets cause the formation of needlelike dihydrate crystals with monoclinic unit cell and P21/c space group. The morphological features of solid CBZ remain predetermined by the basic symmetry and parameters of its unit cell. Precipitation of CBZ pseudopolymorphs from supersaturated microemulsion is discussed in terms of oriented attachment that provides perfect packing of numerous separately nucleated ordered nuclei of CBZ into microscale platelets and then into macroscopic crystals. Crystallization from microemulsion media enabling one to obtain the drug (CBZ) with predicted structure and morphology should be of great significance for pharmaceutical applications.

A linear mixed oxidation state trinuclear cobalt complex with six bridging sulfito ligands

Abstract A linear mixed oxidation state trinuclear cobalt complex {CoII[(O3S)3CoIII(NH3)3]2}4− (1), having six bridging sulfito ligands, was obtained by the reaction between Na2S2O4 and an oxidized solution of CoCl2 in ammonia. The structure of 1, as found in the crystals of [(NH3)5CoSO3]4·1·16H2O, was determined by X-ray crystallography. The compound is triclinic, space group P 1 with a=11.956(2), b=13.260(3), c=11.480(2) A,α=96.50(3),β=111.86(3), γ=81.61(3)o, V=1668(1) A3 and Z=1. Complex 1 can be regarded as two tridentate [(NH3)3Co(SO3)3]3− ligands, oxo coordinated to a Co2+ ion, forming an octahedral geometry. The dimensions of 1 correspond closely to full D3d symmetry.