Steric Hinderance Research Articles

Optimizing the conjugation between N,N′-dicarbazolyl-3,5-benzene and triphenylphosphine oxide as bipolar hybrids for highly efficient blue and single emissive layer white phosphorescent OLEDs

Two bipolar host materials, mCPpPO and mCPmPO have been synthesized by Ni(II)/Zn-catalyzed cross-coupling of diphenylphosphine oxide and corresponding aryl bromide. The photophysical properties, HOMO/LUMO orbital distribution and triplet levels of these host materials are investigated and optimized by tuning the linking modes between electron acceptor triphenylphosphine oxide and electron donor N,N′-dicarbazolyl-3,5-benzene (mCP). When mCP is linked to the meta-position of benzene of triphenylphosphine oxide, the hybrid (mCPmPO) shows much higher steric hinderance than the para-position linked analogue (mCPpPO) so that it possesses a higher triplet energy. Equipped with the bipolar transport properties, mCPmPO-based blue PhOLED doped FIrpic shows a maximum current efficiency (ηc,max) of 40.0cd/A, a maximum power efficiency (ηp,max) of 39.7lm/W, corresponding the maximum external quantum efficiency (ηEQE,max) of 20.3%, and the current efficiency still maintain to 34.8cd/A even at 1000cd/m2. Based on the optimized triplet energy level, the single emission layer white PhOLED hosted by mCPmPO shows ηc,max, ηp,max and ηEQE,max of 46.9cd/A, 39.7lm/W and 17.6%, respectively.

Supramolecular hydrogen-bonding networks constructed from copper(II) chlorobenzoates with nicotinamide: Structure and EPR

Nicotinamide (nia) has been employed as a supramolecular reagent in the synthesis of four copper(II) chloro- and dichlorobenzoate (Clbz/Cl2bz) complexes. The structures of the compounds [Cu(2-Clbz)2(nia)2(H2O)2] (1), [Cu(4-Clbz)2(nia)2(H2O)2] (2), [Cu(3,5-Cl2bz)2(nia)2(H2O)2] (3), and [Cu(2,5-Cl2bz)2(nia)2(H2O)]·H2O (4) were determined. All the investigated compounds 1–4 reveal water molecules as coordinated. Their structures show distorted octahedral chromophores CuIIN2O2O′2, though some are better described as square-planar or square-pyramid due to a large deviation of the axial ligand away from the octahedral z-axis along with different Cu⋯O(axial) lengths. The equatorial positions are occupied in all four cases by two nitrogen (nia-py) atoms and two carboxylate oxygen atoms of two Clbz/Cl2bz ligands, while the axial positions are occupied by water molecules. The EPR spectra reveal for all 1–4 compounds a spin state of S = ½, mostly with axial symmetry of the spectra. Their resolution is clearly dependant to the crystal symmetry related equivalence of the magnetic sites. The coordination molecules of all compounds are connected by N–H⋯O and O–H⋯O H-bonds from nicotinamide NH2 groups, carboxylate anions and/or water molecules, which create supramolecular chains or further H-bonded into 2D sheets. Steric hindering of the chlorine atoms of the Clbz/Cl2bz, especially seen at the coordination of the water molecules, demonstrates its role at the coordination sphere appearance. Despite this influence, the water molecules in 1–4 always assist at the similar supramolecular H-bonded network, almost at the same manner.

Reductive Elimination from Platinum(IV) Aminotroponiminate Dimethyl Complexes Promoted by Sterically Hindered Lewis Bases

A series of PtII and PtIV aminotroponimate (ATI = N-tolyl-aminotroponiminate) complexes has been prepared. The PtII complex (ATI)Pt(CH3)(SMe2) (1a) is synthesized from the reaction of [Li][ATI] with (Me)(Cl)Pt(SMe2)2. Addition of either ethylene or carbon monoxide to 1a results in the formation of (ATI)Pt(CH3)(η2-C2H4) (1b) or (ATI)Pt(CH3)(CO) (1c), respectively. Oxidative addition of MeOTf or MeI to 1a results in formation of the PtIV complex [(ATI)Pt(CH3)2(X)(SMe2)] (X = OTf (3), I (2)). Complex 3 reacts with isocyanides, which replace the triflate ligand to form [(ATI)Pt(CH3)2(CNR)(SMe2)][OTf] (4). Complex 3 also undergoes ligand substitution reactions with azide or cyanide to form (ATI)Pt(CH3)2(N3)(SMe2) (5a) or (ATI)Pt(CH3)2(CN)(SMe2) (5b). Addition of PR3 results in the substitution product [(ATI)Pt(CH3)2(PR3)(SMe2)][OTf] for phosphines with cone angles ≤136° (P(OMe)3, PMe3, PMe2Ph). The PtIV complex [(ATI)Pt(CH3)2(PPh2Me)(SMe2)][OTf] (6c) reductively eliminates [PMe2Ph2][OTf] or [SMe3][OTf] to form the PtII complex (ATI)Pt(CH3)(PPh2Me) (7a) in solution at room temperature. Addition of 1 equiv of PPh3, which has a cone angle of 145°, results in the formation of 50% of PtII(ATI)Pt(CH3)(PR3) and [MePPh3][OTf]. Reaction of 3 with PCy3, which has a cone angle of 170°, yields complete and immediate conversion to (ATI)Pt(CH3)(SMe2) and [MePCy3][OTf].

A second monoclinic polymorph ofN-(2,4-dinitrophenyl)-2,4-dinitroaniline

The title compound, C12H7N5O8, was previously described in space group P21/n with Z = 4 [Wu et al. (2007 ▶). Acta Cryst. E63, o4194]. The current monoclinic P21/c polymorph was obtained from a mixed solution of dichloro­methane and hexane. The dihedral angle between the benzene rings is 44.16 (5)°, smaller than in the previously reported polymorph [56.3 (2)°]. As a result of the steric hinderance of the nitro groups, hydrogen bonding is limited intramolecularly. The dihedral angles between the phenyl rings and their attached nitro groups are 18.97 (6) and 17.71 (5)° at the 2-position, and 18.52 (6) and 32.41 (6)° at the 4-position.

Synthesis of a ChiralC2-Symmetric Sterically Hindered Pyrrolidine Nitroxide Radical via Combined Iterative Nucleophilic Additions and Intramolecular 1,3-Dipolar Cycloadditions to Cyclic Nitrones

A sterically hindered bis-spirocyclic C(2)-symmetric chiral pyrrolidine-type nitroxide has been successfully synthesized starting from an l-tartaric derived nitrone. Starting from a pyrrolidine flanked by two methylene groups, complete quaternization of the two α-carbon atoms has been accomplished through iteration of completely regio- and stereoselective intramolecular cycloaddition reactions and organometallic additions to key nitrone intermediates, formed in turn by oxidation procedures. This method appears to be very useful for building up bulky spirocyclic moieties adjacent to a nitroxide group and provides an important supplementation to traditional methods of nitroxide synthesis. The synthesized chiral nitroxide showed a very high stability to reduction with ascorbate (k ≈ 8 × 10(-3) M(-1) s(-1)).

Synthesis and characterization of original N-meso chiral substituted diarylporphyrins

A first palladium catalyzed cross-coupling amination with chiral auxiliaries at the two meso positions of diarylporphyrins was reported. We noticed that, the non-metallation of porphyrins and steric hinderance of the chiral auxiliary play an essential role to the effectiveness of this cross coupling-reaction. Here, when two methyl pyroglutamates were added, the reaction leads to atropisomers and their behaviors were investigated by NMR spectroscopy. Finally, functionalizations of these chiral porphyrins were performed onto the pyrroglutamate moiety to give new original chiral porphyrins.

ChemInform Abstract: Synthesis of a Novel Sterically Hindered Imidazolinium Chloride: An N‐Heterocyclic Carbene Precursor.

ChemInformVolume 43, Issue 42 Heterocyclic Compounds ChemInform Abstract: Synthesis of a Novel Sterically Hindered Imidazolinium Chloride: An N-Heterocyclic Carbene Precursor. Xiang Liu, Xiang Liu Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorKaiqi Ge, Kaiqi Ge Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorPei Guan, Pei Guan Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorPang He, Pang He Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorYunfei Li, Yunfei Li Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorYanhui Shi, Yanhui Shi Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorChangsheng Cao, Changsheng Cao Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this author Xiang Liu, Xiang Liu Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorKaiqi Ge, Kaiqi Ge Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorPei Guan, Pei Guan Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorPang He, Pang He Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorYunfei Li, Yunfei Li Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorYanhui Shi, Yanhui Shi Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this authorChangsheng Cao, Changsheng Cao Sch. Chem. Chem. Eng., Xuzhou Norm. Univ., Jiangsu, Xuzhou 221116, Peop. Rep. ChinaSearch for more papers by this author First published: 20 September 2012 https://doi.org/10.1002/chin.201242126Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume43, Issue42October 16, 2012 RelatedInformation

Lipase-catalyzed esterification of steric hindered fructose derivative by continuous flow and batch conditions

The lipase catalyzed sugar ester synthesis is an interesting strategy for producing biodegradable, non-ionic surfactants. The main disadvantage of this protocol is the long reaction time required for achieving moderated to good yields. Here, we report the esterification of steric hindered fructose derivative where important variables for batch conditions were identified by the use of a RSM protocol and then translated to the continuous flow regime with high conversions and short residence times.

Synthesis and luminescence properties of two novel lanthanide (III) complexes of acetophenonylcarboxymethyl sulphoxide

A novel ligand containing multiple coordinating groups (sulfinyl, carboxyl and carbonyl groups), acetophenonylcarboxymethyl sulphoxide, was synthesized. Its corresponding two lanthanide (III) binary complexes were synthesized and characterized by element analysis, molar conductivity, FT-IR, TG-DTA and UV spectroscopy. Results showed that the composition of these complexes was REL3 L(-) (ClO4)2 · 3H2O (RE = Eu (III), Tb (III); L = C6 H5 COCH2 SOCH2 COOH; L(-) = C6H5 COCH2 SOCH2 COO(-)). FT-IR results indicated that acetophenonylcarboxymethyl sulphoxide was bonded with an RE (III) ion by an oxygen atom of the sulfinyl and carboxyl groups and not by an oxygen atom of the carbonyl group due to high steric hinderance. Fluorescent spectra showed that the Tb (III) complex had excellent luminescence as a result of a transfer of energy from the ligand to the excitation state energy level ((5)D4) of Tb (III). The Eu (III) complex displayed weak luminescence, attributed to low energy transfer efficiency between the triplet state energy level of its ligand and the excited state ((5)D0 ) of Eu (III). As a result, the Tb (III) complex displayed a good antenna effect for luminescence. The fluorescence decay curves of Eu (III) and Tb (III) complexes were also measured.

Preparation and spectroscopic studies on charge-transfer complexes of famciclovir drug with different electron acceptors

The CT-interaction of electron acceptors such as chloranilic acid (H2CA), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and and 7,7′,8,8′-tetracyano-p-quinodimethane (TCNQ) with the antiviral drug famciclovir (FCV) have been investigated spectrophotometrically in the defined solvent. The data indicate the formation of CT-complexes with the general formula [(FCV)(acceptor)]. The 1:1 stoichiometry of the (FCV)-acceptors were based on elemental analysis, IR spectra and thermogravimetric analysis of the solid CT-complexes along with the photometric titration measurements for the reactions. The formation constants (KCT) for the CT-complexes are shown to be strongly dependent on the type and structure of the electron acceptor. Factors affecting the CT-processes such as redox potentials and steric hinderance of reactants are discussed.

Photophysics of novel 22π porphyrinoids

The photophysical properties of toluene solutions of two new 22π expanded porphycene compounds were measured using a combination of various steady-state and time-resolved techniques. The determined triplet energy (E T = 109 ± 3) kJ.mol-1, coincident with the calculated E T = (96.0 ± 10) kJ.mol-1, of both red absorbing compounds is higher than the energy required to excite ground state molecular oxygen to singlet molecular oxygen. However, the intersystem crossing yield is very low (ca. 10-2), which makes these compounds poor photosensitizers. The triplet state yield of the two expanded 22π porphyrinoid compounds is much lower than that of the parent porphycene, whereas their fluorescence is as high (ca. 30%) as the value for porphycene. The slower than diffusional quenching rate constant of a porphycene triplet state by the two new compounds reflects a steric hindering factor of the exothermic energy transfer.

Atropisomerism in a Belt‐Persistent Nanohoop Molecule: Rotational Restriction Forced by Macrocyclic Ring Strain

Enough strain! Strain in a macrocyclic ring hinders the rotation of an arylene panel in a nanohoop molecule containing four chrysenylene units (see picture). Unlike conventional rotational restrictions in biaryl systems, the new atropisomerism does not require any steric hinderance from the substituents. The study of atropisomerism also provides the first experimental insights into the relative stability of nanohoop structures.

The selective dealkylations: the formylations of the three easily accessible calix[4]arene conformers immobilized by propyl and isopropyl groups

Formyl groups were introduced to the para positions of the three easily accessible calix[4]arene conformers immobilized by four propyl or isopropyl groups by Duff reaction. Propyl group led to exhaustively formylated products due to the weak steric hinderance effect. While as for the isopropoxy calix[4]arenes, with the increase of steric hinderance, 1,3-alternate conformer gave exhaustively formylated product with no alkyl group dealkylating; partial cone conformer gave the tetraformylated proximal A,B-diether in 1,3-alternate conformation; and cone conformer led to triformylated derivatives accompanied by the selective dealkylations of three or two diametrical alkyl groups. The results indicated that the structures of the products were greatly influenced by the steric hinderance effect of the starting compounds.

Mangiferin glucuronidation: Important hepatic modulation of antioxidant activity

Mangiferin displays an extensive spectrum of pharmacological properties, including antioxidant activity. Its phase II metabolism in the presence of Aroclor 1254-induced and un-induced microsomal and cytosolic fractions from rat liver and the antioxidant potency of the glucuronidated conjugates were investigated. Mangiferin was not a substrate for the cytosolic sulphotransferases. Glucuronidation led to the formation of two monoglucuronidated metabolites of mangiferin and a monoglucuronidated metabolite of homomangiferin (a minor constituent of the mangiferin standard). Deconjugation utilising glucuronidase resulted in the disappearance of the metabolites, with the concomitant formation of the two parent compounds. Considering steric hinderance caused by the C-2 glucosyl moiety and the relative acidity of the xanthone OH groups, the 6-OH of mangiferin and, to a lesser degree the 7-OH, are likely to be the primary glucuronidation targets. The ferric iron reducing ability of the glucuronidated reaction mixture was reduced, while the free radical scavenging abilities of mangiferin, utilising on-line post-column HPLC-DAD-DPPH and HPLC-DAD-ABTS+ assays, were eliminated, providing further evidence that the catechol arrangement at C-6 and C-7 was the preferred site of conjugation. This paper provides the first evidence that the glucuronidated metabolites of mangiferin resulted in a loss in free radical scavenging and ferric iron reducing ability.

Synthesis of hyper-branched quaternary ammonium salt and its application into montmorillonite

Hyper-branched quaternary ammonium salts (HQAS) were synthesized by condensation polymerization between quaternary ammonium salt (QAS) and the monomer we prepared. The chemical structure, molecular weight, and thermal properties of these salts were determined by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), ultraviolet spectra (UV), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). The onset and center temperatures of decomposition (T-5% and Tmax) were improved from 113°C and 270°C, to 191°C and 275°C, respectively.Sodium-montmorillonite (Na+-MMT) was modified with these two types of intercalation agents, QAS and HQAS, via ion-exchange reactions. The interlayer space, interlamellar structure, thermal stability, and surface morphology of these organic montmorillonites (OMMTs) were investigated by FTIR, TGA, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The HQAS modified montmorillonites had expanded interlayer space and possessed good thermal stabilities due to steric hindering and thermal stability of the hyper-branched polymers. The basal spacing of QAS modified samples was 1.6-4.9nm, indicating a monolayer, bilayer, and pseudo-trilayer arrangement of quaternary ammonium ions in the interlayer space. The HQAS modified samples had basal spacing ranging from 1.9 to 2.5nm, and the intensive degree was much decreased. These experimental results and phenomena indicated bilayer and pseudo-trilayer arrangements of hyper-branched molecular chains, together with some exfoliated silicate layers.

Activity of homobimetallic ruthenium alkylidene complexes on intermolecular [2+2+2] cyclotrimerisation reactions of terminal alkynes

The activity of homobimetallic ruthenium alkylidene complexes, [( p-cymene)Ru(Cl)(μ-Cl) 2Ru(Cl)( CHPh)(PCy 3)] [ Ru- I] and [( p-cymene)Ru(Cl)(μ-Cl) 2Ru(Cl)( CHPh)(IPr)] [ Ru- II], on intermolecular [2+2+2] cyclotrimerisation reactions of monoynes has been investigated for the first time. It was found that these complexes can catalyse the chemo and regioselective cyclotrimerisation reactions of alkynes at both 25 and 50 °C in polar, aprotic solvents. The catalytic activity of [ Ru- I] and [ Ru- II] was compared to other well-known ruthenium catalysts such as Grubbs first generation catalyst [RuCl 2( CHPh)(PCy 3) 2] [ Ru- III], [RuCl(μ-Cl)( p-cymene)] 2 [ Ru- IV] and [RuCl 2( p-cymene)PCy 3] [ Ru- V] complexes. To examine the effect of the steric hinderance of substrates on the regioselectivity of the reaction, a series of sterically hindered silicon containing alkynes ( 1a, 1b, 1c) were used. It was shown that the isomeric product distribution of the reaction shifts from 1,2,4-trisubstituted arenes to 1,3,5-trisubstituted arenes as the steric hinderance on the substrates increases. These homobimetallic ruthenium alkylidene complexes also catalysed regio- and chemo-selective cross-cyclotrimerisation reactions between silicon-containing alkynes ( 1a, 1b, 1c) and aliphatic alkynes ( 1d– g).

Cross‐Metathesis Reactions of Homoallyl Methyl Malonates with Sterically Hindered Allylic Esters

AbstractThe methyl malonate esters of 3‐buten‐1‐ol and 2‐methyl‐3‐buten‐1‐ol can be coupled efficiently to different methallylic esters in the presence of the second‐generation Grubbs catalyst to yield trisubstituted olefins by the cross‐metathesis reaction. Product selectivity and yields depend on the relative amounts of reagents and to a minor extent on the methallylic ester functional group. Alkyl substituents at either the allylic or the geminal positions significantly affect the product yields and the E/Z stereoselectivity.

CVD of Poly(α,α′‐dimethyl‐p‐xylylene) and Poly(α,α,α′, α′‐tetramethyl‐p‐xylylene)‐co‐poly(p‐xylylene) from Alkoxide Precursors I: Optical Properties and Thermal Stability

AbstractThe parylene CVD platform is a unique one since it enables the room temperature deposition of high‐performance polymers from the resonance‐stabilization of the p‐xylylene intermediate. This intermediate, or the derivatives of it, have the same stabilization. Regardless of the precursor, albeit the more common [2.2] paracyclophane or monomer routes, there are two sites to derivatize the parylene precursor, the alpha or benzylic position or the phenyl ring. The work here explores the addition of methyl groups to the alpha position of p‐xylylene or parylene. The results show that the resulting polymer, poly(α,α′‐dimethyl‐p‐xylylene) shares many of the properties of parylene E (phenyl‐modified ethylated parylene); however, with a higher thermal stability, 400 °C. A homopolymer of poly(α,α,α′,α′‐tetramethyl‐p‐xylylene) is not possible due to steric hinderance of the methyl groups, but an alternating copolymer, poly(α,α,α′,α′‐tetramethyl‐p‐xylylene)‐co‐poly(p‐xylylene), is deposited.

A sensitive and specific LC-MS/MS method for rapid diagnosis of Niemann-Pick C1 disease from human plasma

Niemann-Pick type C1 (NPC1) disease is a rare, progressively fatal neurodegenerative disease for which there are no FDA-approved therapies. A major barrier to developing new therapies for this disorder has been the lack of a sensitive and noninvasive diagnostic test. Recently, we demonstrated that two cholesterol oxidation products, specifically cholestane-3β,5α,6β-triol (3β,5α,6β-triol) and 7-ketocholesterol (7-KC), were markedly increased in the plasma of human NPC1 subjects, suggesting a role for these oxysterols in diagnosis of NPC1 disease and evaluation of therapeutics in clinical trials. In the present study, we describe the development of a sensitive and specific LC-MS/MS method for quantifying 3β,5α,6β-triol and 7-KC human plasma after derivatization with N,N-dimethylglycine. We show that dimethylglycine derivatization successfully enhanced the ionization and fragmentation of 3β,5α,6β-triol and 7-KC for mass spectrometric detection of the oxysterol species in human plasma. The oxysterol dimethylglycinates were resolved with high sensitivity and selectivity, and enabled accurate quantification of 3β,5α,6β-triol and 7-KC concentrations in human plasma. The LC-MS/MS assay was able to discriminate with high sensitivity and specificity between control and NPC1 subjects, and offers for the first time a noninvasive, rapid, and highly sensitive method for diagnosis of NPC1 disease.

Exploiting the Facile Release of Trifluoroacetate for the α-Methylenation of the Sterically Hindered Carbonyl Groups on (+)-Sclareolide and (−)-Eburnamonine

An efficient method for the α-methylenation of carbonyl groups is reported, and this transformation is accomplished by a facile elimination of trifluoroacetate during the formation of the olefin. This method represents an improvement beyond existing protocol in cases of steric hindrance, and we have demonstrated the utility of the process across a series of ketones, lactams, and lactones. Additionally, we have applied this method to produce semisynthetic derivatives of the natural products (+)-sclareolide and (-)-eburnamonine, in which the carbonyl group is proximal to bulky functional groups. Mechanistic insight is also provided from a time course of (19)F NMR. Biological evaluation of the natural-product-derived enones led to the identification of a derivative of (-)-eburnamonine with significant cytotoxicity (LC(50) = 14.12 μM) in drug-resistant MDA-MB-231 breast cancer cells.