Complexes of Oxamic Acid with La(III), Gd(III), Tb(III), Er(III), Tm(III) and Lu(III)

The preparation, for the first time, of the deprotonated complexes of oxamic acid with La(III), Gd(III), Tb(III), Er(III), Tm(III) and Lu(III) is reported. Analytical results, conductometric measurements, magnetic moments and spectral data (IR and diffuse reflectance spectra) are discussed in terms of possible structural types. The oxamate anion acts as a N, O bidentate non-bridging ligand.     

Olefin polymerization catalyzed by amide vanadium(IV) complexes: The stereo‐ and regiochemistry of propylene insertion

The reaction of VCl₃(THF)₃ with 1 equiv of the lithium salt of ligand ArNH(Me₂SiCH₂CH₂SiMe₂)NHAr or ArNH(SiMe₃) (Ar = 2,6‐Me₂C₆H₃) afforded the corresponding V(IV) amide complexes, [1,2‐CH₂CH₂(Me₂SiNAr)₂]VCl₂ ( 3 ) and (Me₃SiNAr)₂VCl₂ ( 4 ). The activation of 3 and 4 with the alkyl aluminum compound Al₂Et₃Cl₃ or AlEt₂Cl produced active ethylene polymerization catalysts exhibiting productivity values among the highest reported for vanadium amide based catalysts. Moreover, syndiotactic specific propylene polymerization was successfully conducted at ?40 °C in the presence of 3 /Al₂Et₃Cl₃ and 4 /Al₂Et₃Cl₃. Syndiotactic polypropylenes with moderate stereoregularity ([rr] = 0.66) and a concentration of regioirregular propylene of 6.9 mol % were obtained. Monomodal molecular weight distributions and polydispersity indices lower than 2 were observed in the polymerization runs carried out in heptane solutions. Thus, ethylene–propylene copolymers with propylene concentrations up to 45 mol % were synthesized and characterized by ¹³C NMR and thermal analysis. Good alternation and random distribution of the two monomers were actually obtained. Samples with elevated concentrations of propylene were completely amorphous, with a glass‐transition temperature of ?50 °C. The properties and structure of the copolymers produced with amide vanadium catalysts 3 and 4 were similar to those reported for ethylene–propylenes produced with industrial vanadium‐based catalysts, suggesting the presence of the same active catalyst species. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3279–3289, 2006     

Ironcarbonyl‐Mediated Alkene Hydroamidation of 7‐Oxabenzonorbornadiene

Iron carbonyl‐mediated alkene hydroamidation of 7‐oxabenzonorbornadiene was accomplished under very mild conditions as the result of nucleophilic attack of amines on iron‐coordinating CO to produce exo‐5‐(alkylaminocarbonyl)‐7‐oxabenzobicyclo[2.2.1]hept‐2‐ene derivatives.     

Poly(ester amide)s derived from glycine,even‐numbered diols,and dicarboxylic acids: Considerations on the packing

A new sequential poly(ester amide) derived from 1,12‐dodecanediol, sebacic acid, and glycine was synthesized and characterized. Its crystalline structure was studied with transmission electron microscopy and X‐ray diffraction. The results were compared with results for a related polymer, derived from glycine, 1,6‐hexanediol, and succinic acid, that produced a lower methylene/carbonyl ratio. The crystalline structures of both polymers corresponded to a periodic arrangement of two layers of hydrogen‐bonded molecular chains, whose polymethylene sequences mimicked the packing of polyethylene and the majority of polyesters. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1036–1045, 2001     

Aliphatic Segmented Poly(ether ester amide)s Synthesized from Hexanediamine,Sebacic Acid and Poly(ethylene glycol)s

High molecular weight aliphatic segmented poly(ether ester amide)s(PEEAs) were synthesized via melt polycondensation and chain extension. An oligomeric polyamide(PA) terminated mainly with -COOH groups(HOOC-PA-COOH) was prepared from the reaction of nylon 610 salt with sebacic acid. Melt polycondensation of HOOC-PA-COOH with polyethylene glycol(PEG), such as PEG400, PEG600, PEG1000 and PEG1500, was conducted at 200℃, and several segmented PEEA prepolymers(PrePEEAs) were prepared. Chain extension of PrePEEAs was carried out at 190℃ using 2,2'-(1,4-phenylene)-bis(2-oxazoline) and adipoyl biscaprolactamate as combination chain extenders. Chain extended PEEAs(ExtPEEAs) were characterized by gel permeation chromatography(GPC), Fourier transform infrared spectrophotometer(FTIR), proton nuclear magnetic resonance(¹H NMR), differential scanning calorimetry(DSC), wide angle X-ray scattering(WAXS), thermogravimetry analysis(TGA), and tensile test. The ExtPEEAs exhibited M_n up to 98700, T_m from 164.2℃ to 176.1℃, initial decomposition temperature above 320.6℃, tensile strength up to 34.80 MPa, and strain at break from 111.92% to 353.12%. Aliphatic segmented PEEAs with good thermal and mechanical properties were prepared.     

Synthesis and characterization of sodium bis(trimethylstannyl) amide and bis(trimethylsilyl) bis(trimethylstannyl) -phospha-tetrazene

Sodium bis(trimethylstannyl)amide NaN(SnMe₃)₂, isolated by the reaction of trimethylstannyldiethylamine with sodium amide, reacts with tris(trimethylsilyl)hydrazino—dichloro-phosphine to form bis(trimethylsilyl)bis(trimethylstannyl)-2-phospha-2-tetrazene, (Me₃Si)₂N-N=P-N(SnMe₃)₂. Both the molecules have been isolated and characterized.     

Conquering amide planarity: Structural distortion and its hidden reactivity

Amides are generally considered as a low-reactive chemical entity among the carbonyl group, and therefore fewer opportunities to be involved in catalytic transformations as substrates. The origin of the stable nature of amides is resonance stabilization in the planar structure, which has drawn considerable attention from organic and physical chemists, leading to the discovery of distorted amides that exhibit a substantially reactive nature. Recent focus in this field is on the catalytic transformation of designed amides with moderate distortion or reduced resonance stabilization. This digest reviews the brief history of the quest for highly distorted amides and introduces a collection of recent studies on catalytic transformations of designed amides.     

Chemoselective Alpha-Deuteration of Amides via Retro-ene Reaction

A synthetically convenient approach for the direct α-deuteration of amides is reported. This mechanistically unusual process relies on a retro-ene-type process, triggered by the addition of deuterated dimethyl sulfoxide to a keteniminium intermediate, generated through electrophilic amide activation. The transformation displays broad functional-group tolerance and high deuterium incorporation.     

Hydrogen bonds in human ubiquitin reflected in temperature coefficients of amide protons

Analysis of amide proton temperature coefficients (deltasigma(HN)/DeltaT) in human ubiquitin shows their usefulness in indicating hydrogen bonds. The availability of a very accurate solution structure of ubiquitin enables the precise determination of hydrogen bonds and increases the reliability of the analysis of chemical shift temperature gradients. Values of deltasigma(HN)/DeltaT more positive than -4.6 ppb/K are very good indicators of hydrogen bonds. Additionally, a weak temperature dependence of non-hydrogen-bonded amides was observed for amide protons that are significantly shifted upfield. We observed that temperature gradients of amide protons involved in short hydrogen bonds are related to donor-acceptor distances.