Zirconium and titanium complexes supported by tridentate LX2 ligands having two phenolates linked to furan, thiophene, and pyridine donors: precatalysts for propylene polymerization and oligomerization

Zirconium and titanium complexes with tridentate bis(phenolate)-donor (donor = pyridine, furan and thiophene) ligands have been prepared and investigated for applications in propylene polymerization. The ligand framework has two X-type phenolates connected to the flat heterocyclic L-type donor at the 2,6- or 2.5- positions via direct ring-ring (sp^2-sp^2)linkages. The zirconium and titanium dibenzyl complexes have been prepared by treatment of the neutral bis(phenol)-donor ligands with M(CH_2Ph)_4 (M = Ti, Zr) with loss of 2 equiv of toluene. Titanium complexes with bis(phenolate)pyridine and -furan ligands and zirconium complexes with bis(phenolate)pyridine and -thiophene ligands have been characterized by single-crystal X-ray diffraction. The solid-state structures of the bis(benzyl)titanium complexes are roughly C_2 symmetric, while the zirconium derivatives display C_s and C^1 symmetry. The bis(phenolate)pyridine titanium complexes are structurally affected by the size of the substituents substituents (CMe_3 or CEt_3) ortho to the oxygens, the larger group leading to a larger C_2 distortion. Both titanium and zirconium dibenzyl complexes were found to be catalyst precursors for the polymerization of propylene upon activation with methylaluminoxane (MAO). The activities observed for the zirconium complexes are particularly notable, exceeding 10^6 g polypropylene/mol Zr center dot h in some cases. The bis(phenolate)pyridine titanium analogues are about 10^3 times less active, but generate polymers of higher molecular weight. When activated with MAO, the titanium bis(phenolate)furan and bis(phenolate)thiophene systems were found to promote propylene oligomerization

Methyl 3-[3-(ethoxy­carbon­yl)thio­ureido]-1H-pyrazole-5-carboxyl­ate

The title compound, C9H12N4O4S, was proven to be the product of the reaction of methyl 5-amino-1H-pyrazole-3-carboxyl­ate with ethyl isothio­cyanato­carbonate. All non-H atoms of the mol­ecule are planar, the mean deviation from the least squares plane being 0.048 Å. The intra­molecular N—H⋯O bond involving the NH-group, which links the thio­urea and pyrazole fragments, closes a six-membered pseudo-heterocyclic ring, and two more hydrogen bonds (N—H⋯O with the participation of the pyrazole NH group and N—H⋯S involving the second thio­urea NH group) link the mol­ecules into infinite chains running along [10]

4-Chloro-7-hydr­oxy-6-methyl-1,7-naphthyridin-8(7H)-one

The title compound, C9H7ClN2O2, was prepared by reaction of methyl 4-chloro-3-(prop-1-yn­yl)picolinate with hydroxy­l­amine in MeOH/KOH solution. The two essentially planar mol­ecules which make up the asymmetric unit have almost identical geometries and and are linked into dimeric aggregates via pairs of O—H⋯O hydrogen bonds. These aggregates have almost perfect inversion symmetry; however, quite unusually, the inversion center of the dimer does not coincide with the crystallographic inversion center

trans-4-(2-Amino-5-bromo-6-methyl­pyrimidin-4-ylamino)-1-methyl­cyclo­hexa­nol

The title compound, C12H19BrN4O, represents the minor component of the two products obtained in a series of transformations involving the Grignard reaction of tert-butoxy­carbonyl-protected 4-amino­cyclo­hexa­none with MeMgBr, and subsequent inter­action of the obtained amino-substituted cyclo­hexa­nol with 4-chloro-6-methyl­pyrimidin-2-amine followed by bromination with N-bromo­succinimide. The X-ray structure showed that this product represents a trans isomer with respect to the amino and hydr­oxy substituents in the cyclo­hexyl ring; the dihedral angle between the amino­pyrimidine plane and the (noncrystallographic) mirror plane of the substituted cyclo­hexyl fragment is 33.6 (3)°. Only two of the four potentially ‘active’ H atoms participate in inter­molecular N—H⋯O and O—H⋯N hydrogen bonds, linking the mol­ecules into layers parallel to the (10) plane

Lewis acid–base interactions enhance explosives sensing in silacycle polymers

The high sensitivity of silole- and silafluorene-containing polymers for detecting organic nitro, nitrate, and nitramine explosives cannot be solely attributed to favorable analyte–polymer hydrophobic interactions and amplified fluorescence quenching due to delocalization along the polymer chain. The Lewis acidity of silicon in conjugated poly(silafluorene-vinylene)s is shown to be important. This was established by examining the 29Si NMR chemical shifts (Δ) for the model trimer fragment of the polymer CH3–silafluorene–(trans-C2H2)–silafluorene–(trans-C2H2)–silafluorene–CH3. The peripheral and central silicon resonances are up-field from a TMS reference at −9.50 and −18.9 ppm, respectively. Both resonances shift down-field in the presence of donor analytes and the observed shifts (0 to 1 ppm) correlate with the basicity of a variety of added Lewis bases, including TNT. The most basic analyte studied was acetonitrile and an association constant (Ka) of 0.12 M−1 was calculated its binding to the peripheral silicon centers using the Scatchard method. Spin-lattice relaxation times (T1) of 5.86(3) and 4.83(4) s were measured for the methyl protons of acetonitrile in benzene-d6 at 20 °C in the absence and presence of the silafluorene trimer, respectively. The significant change in T1 values further supports a binding event between acetonitrile and the silafluorene trimer. These studies as well as significant changes and shifts observed in the characteristic UV–Vis absorption of the silafluorene group support an important role for the Lewis acid character of Si in polymer sensors that incorporate strained silacycles. The nitro groups of high explosives may act as weak Lewis-base donors to silacycles. This provides a donor–acceptor interaction that may be crucial for orienting the explosive analyte in the polymer film to provide an efficient pathway for inner-sphere electron transfer during the electron-transfer quenching process

Vitamin D in Prevention of Autoimmune Diseases

Vitamin D is essential for the regulation of the immune system. In recent years, the role of vitamin D in the control of several autoimmune conditions such as inflammatory bowel disease (IBD), celiac disease, type 1 diabetes mellitus (T1DM), and others has been investigated. The aim of this review was to define the level of knowledge on vitamin D's role in these disorders, as well as the preventive and therapeutic role of vitamin D supplementation. Relevant studies published over the last 20 years were identified via a PubMed/Medline (http://www.ncbi.nlm.nih.gov/pubmed/) search using the keywords: vitamin D, autoimmune disease, and prevention. Vitamin D deficiency or impaired function of the enzymes necessary for its activity has been shown to affect the onset and severity of the autoimmune diseases examined. Vitamin D supplementation appears useful in the support therapy of IBD. Its role in celiac disease, autoimmune hepatitis, T1DM, and autoimmune thyroiditis is unclear. In conclusion, further studies are needed to define whether vitamin D is a cause or a result of the most common autoimmune, extra-skeletal diseases, such as IBD. Vitamin D should be provided to all newborns during their first year of life. Afterwards, the vitamin D supplementation regimen should be tailored to the presence of risk factors for vitamin D deficiency and/or specific disease

tert-Butyl 4-(1-methyl-1H-pyrazol-5-yl)piperidine-1-carboxyl­ate

The reaction of (E)-tert-butyl 4-[3-(dimethyl­amino)acrylo­yl]piperidine-1-carboxyl­ate with methyl­hydrazine leads to the formation of the title compound, C14H23N3O2, with a 1-methyl-1H-pyrazol-5-yl substituent. The plane of the pyrazole ring forms a dihedral angle of 33.4 (1)° with the approximate mirror plane of the piperidine ring

The Quenching of Isopropyl Group Rotation in Van Der Waals Molecular Solids

X-ray diffraction experiments are employed to determine the molecular and crystal structure of 3-isopropylchrysene. Based on this structure, electronic structure calculations are employed to calculate methyl group and isopropyl group rotational barriers in a central molecule of a ten-molecule cluster. The two slightly inequivalent methyl group barriers are found to be 12 and 15 kJ mol(-1) and the isopropyl group barrier is found to be about 240 kJ mol(-1), meaning that isopropyl group rotation is completely quenched in the solid state. For comparison, electronic structure calculations are also performed in the isolated molecule, determining both the structure and the rotational barriers, which are determined to be 15 kJ mol(-1) for both the isopropyl group and the two equivalent methyl groups. These calculations are compared with, and are consistent with, previously published NMR (1)H spin-lattice relaxation experiments where it was found that the barrier for methyl group rotation was 11 +/- 1 kJ mol(-1) and that the barrier for isopropyl group rotation was infinite on the solid state NMR time scale

6-(2,6-Dimethyl­phen­yl)pyrido[2,3-d]pyrimidin-7-amine

In the title compound, C15H14N4, the pyrido[2,3-d]pyrimidine system is almost ideally planar (r.m.s. deviation 0.028 Å) with its mean plane almost orthogonal to the 2,6-dimethyl­phenyl plane. The dihedral angle formed by these planes [87.3 (2)°] is close to the predicted value (89.7°) obtained by mol­ecular-mechanics force-field calculations. Only one of the two active amine H atoms participates in hydrogen bonding, which links mol­ecules into centrosymmetric dimers