Search results for "Protonation"
showing 10 items of 583 documents
An approach to erythrophleum alkaloids. Synthesis of methyl (−)-4-epi-cassamate
1986
Abstract A synthetic approach to Erythrophleum alkaloids, involving as a key-step the regiospecific deprotonation of the ketone 5a, is described.
Boosting Vis/NIR Charge-Transfer Absorptions of Iron(II) Complexes by N-Alkylation and N-Deprotonation in the Ligand Backbone.
2017
Reversing the 3MLCT / 3MC excited state order in iron(II) complexes is a challenging objective, yet would finally result in longsought luminescent transition metal complexes with an earthabundant central ion. One approach to achieve this goal is based on low-energy charge transfer absorptions in combination with a strong ligand field. Coordinating electron rich and electron poor tridentate oligopyridine ligands with large bite angles at iron(II) enables both low-energy MLCT absorption bands around 590 nm and a strong ligand field. Variations of the electron rich ligand by introducing longer alkyl substituents destabilizes the iron(II) complex towards ligand substitution reactions while hard…
The deprotonative metalation of [1,2,3]triazolo[1,5-a]quinoline. Synthesis of 8-haloquinolin-2-carboxaldehydes
2009
New highly functionalized triazoloquinolines were synthesized by applying polar organometallic methods. Double metalation and functionalization provided 3,9-dihalogenated triazoloquinolines. Ring opening of the triazole with loss of nitrogen has been performed for the first time with 3,9-dihalogenated triazoloquinolines allowing the access toward 8-haloquinolin-2-carboxaldehydes under oxidant-free conditions. This approach demonstrates that the triazole ring can be used as protecting group of 2-quinolinecarboxaldehydes, activating the C9-position for lithiation and functionalization by triazole ring opening. 8-Haloquinoline-2-carbaldehydes become in this way readily available.
Mn(II) complexes with sulfonamides as ligands.
2012
Abstract Sulfonamides derived from 8-aminoquinoline react with Mn(II) and Mn(III) salts to form Mn(II) complexes; the Mn(III) species are reduced to the divalent state in the presence of 1,10 phenanthroline and bipyridine. Their molecular structure, determined by single crystal X‐ray diffraction, show that all the complexes present a distorted octahedral geometry, in which the deprotonated sulfonamide acts as a bidentate ligand. UV–visible spectroscopy and changes in the melting temperature (Tm) of calf thymus DNA show a strong interaction of these complexes with DNA. The significant hypochromicity of the charge transfer transition at 370 nm without an appreciable change in wavelength and t…
Reactivity of the di-μ-hydroxo-complexes [{Pd(NN)}2(μ-OH)2][ClO4]2 (NN=bis(pyrazol-1-yl)alkanes) towards protic electrophiles. Hydration of coordin…
2000
Abstract The hydroxo-complexes [{Pd(μ-OH)(NN)}2][ClO4]2 (NN=bpzm:bis(pyrazol-1-yl) methane: a-compounds, bpzm*:bis(3,5-dimethylpyrazol-1-yl)methane; b-compounds) react with a wide variety of weak protic electrophiles H(LL) in a 1:2 molar ratio to give the mononuclear cationic palladium(II) derivatives of general formula [Pd(LL)(NN)][ClO4] [LL=2-pyridine-methoxo (OCH2-py) (1a,b); picolinate (pic) (2a,b); 8-hydroxiquinolinate (oxin) (3a,b)] or the dinuclear complexes [{Pd(NN)}2(μ-ox)][ClO4]2 [ox=oxalate: (4a,b)] and [{Pd(μ-LL)(NN)}2][ClO4]2 [LL=pyrazolate (pz) (5a,b); p-thiocresolate (SC6H4Me-p) (6a,b); triazolate (tz) (7b); thiophenolate (SPh) (8b)] when reacting with oxalic acid, azole…
Conjugate addition of organolithium reagents to α,β-unsaturated carboxylic acids
1999
Abstract Conjugate addition of primary, secondary, tertiary alkyl and phenyl lithium reagents to 2-alkenoic acids affords good yields of branched saturated carboxylic acids. Methyl groups at the α- and β-carbon of the 2-alkenoic acid decrease reactivity as acceptors, and foster deprotonation, respectively. The lithium enediolate resulting from the conjugate addition can react with electrophiles. PM3 calculations are in agreement with the substituent effects.
Macrocyclic (1,3)- and (1,4)-benzena-(1,4)-piperazinacyclophanes
1995
New large, up to 45-membered macrocycles were synthesised from piperazine and m- and p-2,6-bis(bromomethyl)xylene under high dilution conditions. X-ray structures of compounds 3a, 4a, 5a, and 8b were determined. Surprisingly, none of the macrocycles prepared showed any inclusion properties towards small guest molecules. Instead, the compounds were found to self-organize during the packing process into larger structures due to the complementary of the molecular skeletons. In the crystalline state 3a forms nets, where the macrocycles are bound by HCH…N interactions to each other. 4a exits in a dimeric structure, which, in turn, further extends to a sheet structure. The positively charged phan…
Modified photobehavior of carboxylic acid derivatives induced by protonation
1987
Abstract A series of carboxylic acid derivatives 1–6 containing a second interacting function have been converted into the corresponding O -protonated species or acylium ions upon treatment with 96% sulfuric acid or oleum, respectively, at room temperature. The resulting stable cations have been spectroscopically characterized and submitted to irradiation. Cis-trans photoisomerization was observed in the ionic speciesderived from trans -crotonic, fumaric and maleic acids, and maleic anhydride. By contrast protonated crotonolactone 5a+ was found to be photostable. Finally, protonated α-bromobutyrolactone 6a+ was clean and efficiently dehydrohalogenated to 5a+ upon irradiation. Since the norm…
Rapid Synthesis and MALDI-ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers
2009
Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well-defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5-8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30000g · …
Binding ability of N-Para-amino-phenylsulfonyl derivatives of amino acids. Potentiometric and spectroscopic studies of Cu(II) complexes
1995
Abstract N-Para-amino-phenylsulfonyl derivatives of amino acids are very effective ligands for Cu(II) ions. Potentiometric and spectroscopic results have shown that Cu(II) ions are able to deprotonate and bind to sulfonamide nitrogen below pH 5 to form stable mono- and bis-[N − , COO − ] chelates. The basicity of sulfonamide nitrogen is lower than peptide amide nitrogen and no distinct anchoring site is necessary to promote the amide nitrogen deprotonation.