Preparation and Synthetic Applications of Sterically Hindered Secondary Amines

The preparation of sterically hindered secondary amino esters from the reaction of N-protected α-amino aldehydes and 3-, or 2-oxo esters with α-amino esters by reductive amination is described. The resulting amino esters were converted to the β-lactam or acylated to form N-acyl secondary amides.     

Reductive Methylation of Secondary Amines Containing Reducible,Hydrolyzable and Sterically Hindered Groups

Aliphatic secondary amines, including those that are sterically hindered, undergo reductive methylation under mild conditions in high yield using formaldehyde and sodium phosphite solution without reducing or hydrolyzing ethynyl, ester or cyano groups.     

Pseudohalogeno Complexes of Sterically Hindered Tripyrrinatopalladium (TrpyPd) Fragments

Eight new pseudohalogeno complexes of sterically hindered TrpyPd fragments 4 – 11 have been prepared by salt metathesis in one step from known trifluoroacetates TrpyPdOAc^F 1 – 3 , using sodium salts of N₃, NCO, NCS, NCSe, dicyanamide (dca) and tricyanomethanide (tcm) anions. Despite the propensity of the co‐ligands to bind to two or more metal centres in a bridging coordination mode all new complexes have been shown by NMR spectroscopy to be essentially monomeric in solution. X‐ray diffraction studies performed on TrpyPdNCS( 6 ), TrpyPddca( 8 ), TrpyPddca( 9 ), and TrpyPdtcm( 10 ) revealed the presence of two different conformers in the solid state, one with a helically distorted Trpy backbone for 6 and 10 , and one with an almost planar tripyrrole but a tetrahedral distortion of the Pd^II coordination, a so‐called pseudoplanar form, for 8 and 9 . Interestingly the helical forms are also detected by unusual wavenumbers for the ν_CN stretching bands in their IR spectra. The reason for the occurrence of two different conformers in the solid state appears to be the crystal packing which depends mainly on the shape of the anionic co‐ligand and on the presense of alkyl groups on the TrpyPd fragment.     

Synthesis of Sterically Hindered Secondary and Tertiary Alkyl(Aryl)Phosphines

Cross coupling of silylphosphines with 2-halobenzenecarboxylates or 2-halophenyl ethers, catalyzed with zero-valent palladium complexes can not be used as a procedure for preparing sterically hindered tertiary phosphines. The latter compounds can be successfully prepared by means of phosphorylation of corresponding o-lithiated derivatives.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 239–243.Original Russian Text Copyright © 2005 by Veits, Neganova, Vinogradova.     

Heterocycles Based on Sterically Hindered Phenols and their Derivatives. (Review)

Published data on the synthesis of heterocyclic compounds (derivatives of dibenzofuran, phenoxazine, benzodioxolane, etc.) based on sterically hindered 6-substituted 2,4-di-tert-butylphenols, 6-hydroxy-2,4- and 6-hydroxy-2,5-di-tert-butylphenols, and their redox-conjugated ortho-benzoquinones are reviewed.     

Physicochemical Study of New Mono- and Binuclear Copper(II) Complexes with Sterically Hindered Acylhydrazones and Azomethines

Series of new binuclear copper(II) complexes with acylhydrazones and azomethines of substituted derivatives of salicylaldehyde containing bulky tert-butyl substituents were synthesized. The target dimerization of the monomeric fragments of the complexes caused by the steric factors was shown to predetermine the specific features of their magnetochemical behavior. The calculated exchange parameters for the complexes based on acylhydrazones range from –110 to –138 cm^–1 and those for the complexes based on azomethines lie in the interval from –400 to –500 cm^–1.     

Electrochemical and Spectral Studies of Sterically Hindered Water-Soluble Iron Tetrakis(Sulfonatomesityl)Porphine

Sterically hindered water-soluble iron(III) tetrakis(sulfonatomesityl)porphine (FeTSMP) exists exclusively in its monomer form in neutral and basic aqueous solutions. The acid dissociation constant (pKa) for Fe^IIITSMP is 6.6. The Fe^III/IITSMP couple has a formal reduction potential at ?0.22 V (vs. Ag/AgCl) in an acidic buffer solution. The E°-pH diagram shows that E° is independent of pH until the pH is larger than the pKa. The acid dissociation constant for Fe^IITSMP is 11.7. The redox potential of Fe^III/IITSMP shifts positively when imidazole is present, indicating the ligation of imidazole to Fe^IITSMP. At pH 4.0 and 10.2 buffer solutions, two imidazoles are found to ligate at the iron(III) center with β₂ = 10^4.7 and 10^4.1, respectively. The E°-pH diagram indicates that the pKa of (ImH)₂Fe^IIITSMP is 11.3 at 0.03 M imidazole solution. The oxidation of Fe^IIITSMP could involve two one-electron transfer processes, namely, one electron oxidation at the iron center, while another at the porphyrin ring. The two one-electron oxidations are found to overlap at pH = 5.5 and separate as the pH increases by shifting of the potential at the iron center, which is pH dependent. The radical cation of porphyrin ring is not stable and decomposes rapidly in water.     

Coordinating Properties of Co(II) and Zn(II) Complexes with Sterically Hindered Porphyrins

Cobalt(II) and zinc(II) complexes with 5,15-di(o-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-buthylporphyrin and its capped analogues, where the MN₄ reaction site is shielded by bridging groups containing m-phenylene and dimethoxy-substitutedp-phenylene fragments, were synthesized. Equilibrium constants of additional coordination of pyridine and N-methylimidazole by these metalloporphyrins were determined at 298 K. It was found that steric distortion of the porphyrin core destabilizes extra complexes.     

大位阻手性吡咯烷(salen)Mn(III)配合物在烯烃不对称环氧化反应中的应用

设计合成了具有大位阻的手性吡咯烷(salen)Mn(III)配合物Mn3,并研究了其在NaClO水/有机两相氧化体系中催化烯烃的不对称环氧化反应性能。 具有叔胺基团的配合物Mn3具有比Jacobsen催化剂更高的反应活性、以及近似的产率和略高的对映选择性。 尤其是过量CH₃I的加入可以极大地缩短环氧化反应的时间,而高产率和高对映选择性依然保持。     

Synthesis of Sterically Hindered Heteroaromatic Ketones under Phase-transfer and Metal-complex Catalysis Conditions. (Review)

We have correlated data on methods for obtaining sterically hindered ketones, derivatives of furan, thiophene, pyrrole, and pyridine. We examine routes to arylation of chroman-4-ones and synthesis of sterically hindered unsaturated and silicon-containing heteroaromatic ketones.     

位阻型钴卟啉的结构及其在催化氧化2,6—二叔丁基苯酚反应中活性的研究

本文报道了在４０℃和０．１ＭＰａ氧气的条件下，以系列带有不同吸电子基团的位阻型钴卟啉作催化剂，研究２，６－二叔丁基苯酚的催经氧化反应，根据实验数据及对反应动力学的研究，提出了该催化氧化反应的机制，结果表明，钴卟啉催化氧化２，６－二叔丁基苯酚的反应符合酶的催化反应机制，催化剂的催化活性随着取代基团的吸电子效应和位阻效 增加而降低，即：ＴＰＰＣｏ（Ⅱ）〉ＴＰ－ＣＩＰＰＣｏ（Ⅱ）〉Ｔｏ－ＣＩＰＰＣｏ（Ⅱ     

Organobismuth(III) Derivatives of Sterically Hindered Bifunctional Tetradentate Schiff Bases: Synthesis and Spectroscopic Characterization

The equimolar reactions of Ph 3 Bi with the bifunctional tetradentate Schiff bases proceed with cleavage of two Bi--C bond of Ph 3 Bi and result in the formation of phenylbismuth(III) derivatives PhBi[RC(NC 6 H 4 S)CH 2 (NC 6 H 4 S)CCOOCH 3 ] where R = C 6 H 5 , 4-ClC 6 H 4 ,4-BrC 6 H 4 , and 4-CH 3 C 6 H 4 . Physico-chemical, IR, and NMR ( 1 H and 13 C) spectral studies have been carried out to investigate the structural aspect of these derivatives which reveal a penta coordination around the central Bi atom.     

New Sterically Hindered Bis-o-Benzoquinones with Electron-Donor Bridging Groups and Related Binuclear Triphenylantimony(V) Catecholate Complexes

Russian Journal of Coordination Chemistry - New bis-o-benzoquinones (3,5-Q)-6-CH2O–(CH2)n–OCH2-6-(3,5-Q) (n = 2 (L1), 4 (L2), and 6 (L3)) and (3,5-Q)-6-(CH2OCH2)3-6-(3,5-Q) (L4) (3,5-Q...     

Photoinduced Electron Transfer (PET) between C_(60) and Amines in Micelle Solution A Kinetic ESR Study

Fullerene chemistry has been one of the most exciting research subjects in the recent decade1,2. However, the predominant hydrophobic character and the spherical carbon allotrope of C60 hinder its solubility in an aqueous solution. In order to efficiently slow down charge recombination in the PET system containing C60, water was selected as optimal polar media to stabilize charge separation state. Accordingly, solubility of fullerene in water had to be achieved by incorporating it into th…     

Photoinduced superoxide radical anion and singlet oxygen generation in the presence of novel selenadiazoloquinolones (an EPR Study)

Novel 7‐substituted 6‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐h]quinoline ( SeQ(1–6) ) and 8‐substituted 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f ]quinoline derivatives ( SeQN(1–5) ) with R₇, R₈ = H, COOC₂H₅, COOCH₃, COOH, COCH₃ or CN were synthesized and their spectral characteristics were obtained by UV/Vis spectroscopy. Ultraviolet A photoexcitation of the selenadiazoloquinolones in dimethylsulfoxide or acetonitrile resulted in the formation of paramagnetic species coupled with molecular oxygen activation generating the superoxide radical anion or singlet oxygen, evidenced by electron paramagnetic resonance spectroscopy. The cytotoxic/photocytotoxic impact of selenadiazoloquinolones on murine and human cancer cell lines was demonstrated using the derivative SeQ5 (with R₇ = COCH₃).     

Efficient Red Electroluminescent Devices with Sterically Hindered Phosphorescent Platinum(II) Schiff Base Complexes and Iridium Complex Codopant

Sterically hindered platinum(II) Schiff base complexes were prepared. Complex 4 , which displays red emission with a quantum yield of 0.29 in a thin film and a self‐quenching rate constant of 1×10^?7 dm³ mol^?1 s^?1, was used to fabricate organic light‐emitting diodes with single or double emissive layers (EMLs). An iridium(III) complex with a wide band gap was codoped into the electron‐dominant EML to act as a deep electron trapper, and red‐light‐emitting devices with the highest current, power, and external quantum efficiencies of 20.43 cd A^?1 18.33 Lm W^?1, and 11.7 %, respectively, were fabricated. A high current efficiency and EQE of up to 14.69 cd A^?1 and 8.3 %, respectively, were achieved at a high brightness of 1000 cd m^?2. The significant delay of efficiency roll‐off is attributed to the bulky 3D structure of the norbornene moiety at the periphery of the Schiff base ligand of 4 and to the new device design strategy. The fabricated device had a projected lifetime (LT50) of 18 000 h.