Methine Hydrogen Atoms Research Articles

Stabilization of NH- Group Adjacent to Naked Silicon(II) Atom in Base Stabilized Aminosilylenes.

Aminosilylene, comprising reactive NH- and Si(II) sites next to each other, is an intriguing class of compounds due to its ability to show diverse reactivity. However, stabilizing the reactive NH- group next to the free Si(II) atom is challenging and has not yet been achieved. Herein, we report the first examples of base stabilized free aminosilylenes Ar*NHSi(PhC(Nt Bu)2 ) (1 a) and Mes*NHSi(PhC(Nt Bu)2 ) (1 b) (Ar*=2,6-dibenzhydryl-4-methylphenyl and Mes*=2,4,6-tri-tert-butylphenyl), tolerating a NH- group next to the naked Si(II) atom. Remarkably, 1 a and 1 b exhibited interesting differences in their reactivity upon heating. With 1 a, an intramolecular C(sp3 )-H activation of one of the benzhydryl methine hydrogen atoms to the Si(II) atom produced the five-membered cyclic silazane 2. However, with 1 b, a rare 1,2-hydrogen shift to the Si(II) atom afforded a silanimine 3, with a hydride ligand attached to an unsaturated silicon atom. Further, the coordination capabilities of 1 a were also tested with Ru(II) and Fe(0) precursors. Treatments of 1 a with [Ru(η6 -p-cymene)Cl2 ]2 led to the isolation of a η6 -arene tethered complex [RuCl2 {Ar*NHSi(PhC(t BuN)2 )-κ1 -Si-η6 -arene}] (4), whereas with the Fe(CO)5 precursor a Fe(0) complex [Fe(CO)4 {Ar*NHSi(PhC(t BuN)2 )-κ1 -Si}] (5) was obtained. Density functional theory (DFT) calculations were conducted to shed light on the structural, bonding, and energetic aspects in 1-5.

Stabilization of NH− Group Adjacent to Naked Silicon(II) Atom in Base Stabilized Aminosilylenes

AbstractAminosilylene, comprising reactive NH− and Si(II) sites next to each other, is an intriguing class of compounds due to its ability to show diverse reactivity. However, stabilizing the reactive NH− group next to the free Si(II) atom is challenging and has not yet been achieved. Herein, we report the first examples of base stabilized free aminosilylenes Ar*NHSi(PhC(NtBu)2) (1 a) and Mes*NHSi(PhC(NtBu)2) (1 b) (Ar*=2,6‐dibenzhydryl‐4‐methylphenyl and Mes*=2,4,6‐tri‐tert‐butylphenyl), tolerating a NH− group next to the naked Si(II) atom. Remarkably, 1 a and 1 b exhibited interesting differences in their reactivity upon heating. With 1 a, an intramolecular C(sp3)−H activation of one of the benzhydryl methine hydrogen atoms to the Si(II) atom produced the five‐membered cyclic silazane 2. However, with 1 b, a rare 1,2‐hydrogen shift to the Si(II) atom afforded a silanimine 3, with a hydride ligand attached to an unsaturated silicon atom. Further, the coordination capabilities of 1 a were also tested with Ru(II) and Fe(0) precursors. Treatments of 1 a with [Ru(η6‐p‐cymene)Cl2]2 led to the isolation of a η6‐arene tethered complex [RuCl2{Ar*NHSi(PhC(tBuN)2)‐κ1‐Si‐η6‐arene}] (4), whereas with the Fe(CO)5 precursor a Fe(0) complex [Fe(CO)4{Ar*NHSi(PhC(tBuN)2)‐κ1‐Si}] (5) was obtained. Density functional theory (DFT) calculations were conducted to shed light on the structural, bonding, and energetic aspects in 1–5.

Crystal structures of sixteen phosphane chalcogenide complexes of gold(I) chloride, bromide and iodide.

The structures of 16 phosphane chalcogenide complexes of gold(I) halides, with the general formula R 1 3- nR 2 nPEAuX (R 1 = t-butyl; R 2 = isopropyl; n = 0 to 3; E = S or Se; X = Cl, Br or I), are presented. The eight possible chlorido derivatives are: 1a, n = 3, E = S; 2a, n = 2, E = S; 3a, n = 1, E = S; 4a, n = 0, E = S; 5a, n = 3, E = Se; 6a, n = 2, E = Se; 7a, n = 1, E = Se; and 8a, n = 0, E = Se, and the corresponding bromido derivatives are 1b-8b in the same order. However, 2a and 2b were badly disordered and 8a was not obtained. The iodido derivatives are 2c, 6c and 7c (numbered as for the series a and b). All structures are solvent-free and all have Z' = 1 except for 6b and 6c (Z' = 2). All mol-ecules show the expected linear geometry at gold and approximately tetra-hedral angles P-E-Au. The presence of bulky ligands forces some short intra-molecular contacts, in particular H⋯Au and H⋯E. The Au-E bond lengths have a slight but consistent tendency to be longer when trans to a softer X ligand, and vice versa. The five compounds 1a, 5a, 6a, 1b and 5b form an isotypic set, despite the different alkyl groups in 6a. Compounds 3a/3b, 4b/8b and 6b/6c form isotypic pairs. The crystal packing can be analysed in terms of various types of secondary inter-actions, of which the most frequent are 'weak' hydrogen bonds from methine hydrogen atoms to the halogenido ligands. For the structure type 1a, H⋯X and H⋯E contacts combine to form a layer structure. For 3a/3b, the packing is almost featureless, but can be described in terms of a double-layer structure involving borderline H⋯Cl/Br and H⋯S contacts. In 4a and 4b/8b, which lack methine groups, Cmeth-yl-H⋯X contacts combine to form layer structures. In 7a/7b, short C-H⋯X inter-actions form chains of mol-ecules that are further linked by association of short Au⋯Se contacts to form a layer structure. The packing of compound 6b/6c can conveniently be analysed for each independent mol-ecule separately, because they occupy different regions of the cell. Mol-ecule 1 forms chains in which the mol-ecules are linked by a Cmethine⋯Au contact. The mol-ecules 2 associate via a short Se⋯Se contact and a short H⋯X contact to form a layer structure. The packing of compound 2c can be described in terms of two short Cmethine-H⋯I contacts, which combine to form a corrugated ribbon structure. Compound 7c is the only compound in this paper to feature Au⋯Au contacts, which lead to twofold-symmetric dimers. Apart from this, the packing is almost featureless, consisting of layers with only translation symmetry except for two very borderline Au⋯H contacts.

Synthesis of α‐Heterocycle Anchored Spirocyclic Azetidin‐2‐ones in a Minute by p‐TSA Catalyzed Cyclocondensation of Azetidin‐2,3‐diones with Difunctionalized Substrates

AbstractMonocyclic azetidin‐2,3‐diones provide easy extensions to spiro‐fused azetidin‐2‐ones upon p‐toluenesulfonic acid (p‐TSA) catalyzed cyclocondensation reaction with difunctionalized substrates [mercaptoacids (mercaptoacetic acid, 2‐mercaptopropionic acid, 3‐mercaptopropionic acid), ethan‐1,2‐dithiol, ortho‐difunctionalized benzenes (ortho‐phenylenediamine, ortho‐aminothiophenol)]. 1,3‐Oxathiolan‐5‐one/6‐one, 1,3‐dithiolane, 2,3‐dihydrobenzo[d]imidazole and 2,3‐dihydrobenzo[d]thiazole tethered spirocyclic azetidin‐2‐ones were obtained in good overall isolated yields (69–89 %) in a very short‐time duration (max 1 min) using toluene Dean‐Stark reflux/dichloromethane rt stirring conditions. The stereochemical and spectral studies, stabilities and diastereoisomeric ratio for trans and cis spiro‐fused products are reported. The trans and cis configuration has been assigned to spiro‐β‐lactams wrt the stereochemical relationship between sulfur atom (at spiro centre) and the vicinal methine hydrogen atom at C3/C2. The absolute configuration of one trans 1,3‐oxathiolan‐5‐one fused spirocyclic azetidin‐2‐one was clearly identified by X‐ray single crystal structure analysis.

Fluorinated Bambusurils as Highly Effective and Selective Transmembrane Cl−/HCO3− Antiporters

Summary The exchange of chloride and bicarbonate across lipid bilayers is an important biological process. Synthetic molecules can act as mobile carriers for these anions, although most show little selectivity. Here we report on three bambus[6]uril macrocycles functionalized with fluorinated benzyl groups, which are able to exchange Cl− and HCO3− efficiently. Remarkably, rates for Cl−/NO3− exchange are two orders of magnitude lower. The higher rates of Cl−/HCO3− transport can be explained by the ability of the bambusurils to complex Cl− and HCO3− simultaneously, facilitating their exchange at the bilayer interface. Furthermore, the exceptionally high affinity and selectivity of these systems for NO3− appear to contribute to the poor Cl−/NO3− exchange. This work not only demonstrates the importance of anion binding characteristics on anion transport but also the potential relevance of bambusurils for anion transport applications considering the high rate observed for Cl−/HCO3− exchange.

Theoretical study on complexation of the perchlorate, permanganate, pertechnate and perrhenate anions with dodecabenzylbambus[6]uril

ABSTRACTBy using quantum chemical calculations, the most probable structures of the anionic complex species dodecabenzylbambus[6]uril–ClO4−, dodecabenzylbambus[6]uril–MnO4−, dodecabenzylbambus[6]uril–TcO4− and dodecabenzylbambus[6]uril–ReO4− were derived. In these four complexes, each of the considered anions, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion. Further, the corresponding interaction energies of the investigated four anionic complexes were calculated; the absolute values of these calculated energies increase in the series of ReO4− < TcO4− < MnO4− < ClO4−.

2-Prenylated m-dimethoxybenzenes as potent inhibitors of 15-lipo-oxygenase: inhibitory mechanism and SAR studies.

15-lipo-oxygenases are one of the iron-containing proteins capable of performing peroxidation of unsaturated fatty acids in animals and plants. The critical role of enzymes in the formation of inflammations, sensitivities, and some cancers has been demonstrated in mammals. The importance of enzymes has led to the development of mechanistic studies, product analysis, and synthesis of inhibitors. In this study, a series of allyl and prenyl dimethoxybenzenes were synthesized and their inhibitory potency against soybean 15-Lipo-oxygenase (L1; EC 1,13,11,12) was determined. Among the synthetic compounds, 2,6-dimethoxy-1-isopentenyl-4-methylbenzene, 2,6-dimethoxy-1-geranyl-4-methylbenzene, and 2,6-dimethoxy-1-farnesyl-4-methylbenzene showed the most potent inhibitory activity with IC50 values of 7.6, 5.3, and 0.52μm, respectively. For some of the compounds, SAR studies showed acceptable relationship between inhibitory potency and enzyme-ligand interactions. Radical scavenging assessment results apart from the SAR studies indicate that electronic properties are the major factors for lipo-oxygenase inhibition potency of the mentioned compounds. Based on the theoretical studies, it was suggested that CH…O intramolecular hydrogen bond between ortho-methoxy oxygen and methine hydrogen atoms is one of the major factors in the stability of 2,6-dimethoxyallyl(or prenyl)benzenes radical via the planarity fixation between phenyl and allyl (or prenyl) pi orbitals.

Theoretical study on the complexation of the chloride, bromide, and iodide anions with dodecabenzylbambus[6]uril

Using quantum mechanical calculations, the most probable structures of the anionic complex species dodecabenzylbambus[6]uril–Cl−, dodecabenzylbambus[6]uril–Br−, and dodecabenzylbambus[6]uril–I− were derived. In these three complexes, each of the considered univalent halide anions, included in the center of the macrocyclic cavity, is bound by 12 weak C–H···X− (X− = Cl−, Br−, I−) hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion. The lengths of these C–H···X− hydrogen bonds increase in the series of Cl− < Br− < I−.

Protonolysis and amide exchange reactions of a three-coordinate cobalt amide complex supported by an N-heterocyclic carbene ligand.

A three-coordinate cobalt species, IPrCoCl{N(SiMe3)2} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], was synthesized by the reaction of {IPrCoCl2}2 with NaN(SiMe3)2. Compound 1 is a useful starting material for low-coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-methylphenol (BHT-H) via aminolysis of the Co-N bond to generate a three-coordinate phenoxide complex, IPrCoCl(O-2,6-(t)Bu2-4-MeC6H2) (2). The reaction of 1 with 2,6-diisopropylaniline (NH2DIPP) generates IPrCoCl(NHDIPP) (4), which undergoes disproportionation to form a mixture of 4, {IPrCoCl2}2, and IPrCo(NHDIPP)2 (3). The same product mixture is formed by the reaction of 1 with Li[NH(DIPP)], which unexpectedly proceeds by amide exchange. Compound 3 was synthesized independently by the reaction of {IPrCoCl2}2 with 4 equiv of Li[NH(DIPP)]. The reaction of 1 with the bulkier lithium 2,6-dimesitylanilide (LiNHDMP) also proceeds by amide exchange to generate IPrCoCl(NHDMP) (5), which is stable toward disproportionation. Compounds 1 and 2 exhibit trigonal-planar geometries at cobalt in the solid state. The solid-state structure of 3 also contains a trigonal-planar cobalt center and exhibits close Co---H contacts involving the methine hydrogen atoms of the NH(DIPP) groups in the axial positions. The solid-state structure of 5 features an interaction between cobalt and a flanking aryl group of the anilide ligand, resulting in pyramidalization of the cobalt center.

Theoretical study on the complexation of bambus[6]uril with the methanesulfonate and trifluoromethanesulfonate anions

By using quantum mechanical DFT calculations, the most probable structures of the bambus[6]uril—CH3SO 3 − and bambus[6]uril—CF3SO 3 − anionic complex species were derived. In these two complexes having C 3 symmetry, each of the considered anions, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion.

Bambus[6]uril as a novel example of a ditopic ion-pair molecular receptor for sodium iodide

By using quantum mechanical DFT calculations, the most probable structure of the bambus[6]uril-Na+I− electroneutral complex species was derived. In this complex with a plane of symmetry, the considered anion I−, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the I− anion, while the sodium cation Na+ interacts only with two carbonyl oxygen atoms of the parent macrocyclic receptor. The interaction energy of the resulting complex, involving the Boys-Bernardi counterpoise corrections of the basis set superposition error, was found to be −593.8 kJ mol−1.

Theoretical study on the complexation of bambus[6]uril with the hydrogen sulfide anion

By using quantum mechanical DFT calculations, the most probable structure of the bambus[6]uril-SH− anionic complex species was derived. In this complex having C 3 symmetry, the sulfur atom of the SH− anion, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds with 12 methine hydrogen atoms on the convex face of glycoluril units of the bambus[6]uril macrocycle. The interaction energy of the resulting anionic complex, involving the Boys–Bernardi counterpoise corrections of the basis set superposition error, was found to be −238.3 kJ/mol.

Bambus[6]uril as a novel macrocyclic receptor for the cyanide anion

By using quantum mechanical DFT calculations, the most probable structure of the bambus[6]uril·CN− anionic complex species was derived. In this complex having C3 symmetry, the considered anion CN−, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units of the parent macrocyclic receptor and the anion CN−. The interaction energy of the resulting complex, involving the Boys–Bernardi counterpoise corrections of the basis set superposition error, was found to be −324.3kJmol−1, which confirms the formation of the mentioned anionic complex.

Bambus[6]uril as a ditopic ion-pair molecular receptor for Cs+I−

Quantum mechanical density functional theory (DFT) calculations were used to derive the most probable structure of the bambus[6]uril·Cs+I− electroneutral complex species. In this complex, the considered anion I−, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the I− anion, whereas the cesium cation Cs+ interacts only with two carbonyl oxygen atoms of the parent macrocyclic receptor. The interaction energy of the resulting complex, involving the Boys–Bernardi counterpoise corrections of the basis set superposition error, was found to be −472.4 kJ/mol.

Theoretical study on the complexation of bambus[6]uril with the cyanate and thiocyanate anions

Quantum mechanical density functional theory (DFT) calculations were used to derive the most probable structures of the bambus[6]uril·OCN− and bambus[6]uril·SCN− anionic complex species. In these two C 3 symmetric complexes, each of the two considered anions, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion.

Theoretical study on the complexation of bambus[6]uril with the fluoride anion

By using quantum mechanical DFT calculations, the most probable structure of the bambus[6]uril·F− anionic complex species was derived. In this complex having C3 symmetry, the fluoride anion F−, included in the macrocyclic cavity, is bound by six weak C–H⋯F− hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the considered F− ion.

Theoretical study on the complexation of bambus[6]uril with the chloride, bromide, and iodide anions

AbstractBy using quantum mechanical DFT calculations, the most probable structures of the bambus[6]uril·Cl − , bambus[6]uril·Br − , and bambus[6]uril·I − anionic complex species were derived. In these three complexes, each of the considered univalent halide anions, included in the center of the macrocyclic cavity, is bound by 12 weak C–H⋯X − (X − = Cl − , Br − , I − ) hydrogen bonds between methine hydrogen atoms on the convex face of the glycoluril units and the respective anion. The lengths of the C–H⋯X − hydrogen bonds increase in the order Cl − < Br − < I − .Graphical abstract[IMAGE]

In-Adamantane, a Small Inside-Out Molecule

The hydrocarbon in-adamantane (1), a high-energy adamantane isomer in which one methine hydrogen atom is inside the cage, is predicted by ab initio calculations to be isolable at dry ice temperature. It has 440 kJ/mol of hydrogenic strain but appears to be stable against dimerization, moisture, and air. The inverted CH bond is compressed, and the IR and NMR spectra are unusual. The symmetrical pentadecafluoro derivative (2) has an estimated half-life of 100 years at room temperature.

Stereoselective synthesis of (±)-tacamonine

We report a stereocontrolled approach to the pentacyclic indole alkaloid tacamonine by modifying an earlier route using norbornadiene to supply the nontryptamine portion. By maintaining a bridged system the reduction step of the Bischler–Napieralski reaction proceeded to deliver a bridged diol in which three methine hydrogen atoms are in an all-cis configuration. All 19 skeletal carbon atoms are fully incorporated, therefore, the only remaining steps involved cleavage of the vic-diol subunit in the seven-membered ring and further oxidation and reduction of the resulting lactam aldehyde.

Hydrogen abstraction from solvents by the triplet state of p-benzoquinone: a time-resolved electron paramagnetic resonance and laser flash photolysis study

The reaction of triplet p-benzoquinone in several solvents, such as ethanol, 2-propanol, ethylene glycol, t-butanol, 1,4-dioxane, tetrahydrofuran and cyclohexane, has been studied. The primary photochemical event was shown to be a hydrogen atom abstraction from the solvent and not an electron transfer. In the time-resolved EPR experiments, in all cases, except t-butanol and cyclohexane, the radicals from the solvent were recorded along with p-benzosemiquinone radical and the spectra were dominated by triplet mechanism of spin polarization, giving totally emissive EPR signals. The sites of abstracted hydrogen atom have been identified. In particular, whereas the methine hydrogen atom is abstracted from 2-propanol, both the methylene and hydroxyl hydrogen atoms are abstracted from ethanol. From laser flash photolysis experiments, the rate constants of the hydrogen abstraction in all solvents, except t-butanol and cyclohexane, were found to be (1–5) × 108 M−1 s−1.