Search results for "Rate"
showing 10 items of 22191 documents
Cooperative N–H bond activation by amido-Ge(ii) cations
2020
N-heterocyclic carbene (NHC) and tertiary phosphine-stabilized germylium-ylidene cations, [R(L)Ge:]+, featuring tethered amido substituents at R have been synthesized via halide abstraction. Characterization in the solid state by X-ray crystallography shows these systems to be monomeric, featuring a two-coordinate C,N- or P,N-ligated germanium atom. The presence of the strongly Lewis acidic cationic germanium centre and proximal amide function allows for facile cleavage of N-H bonds in 1,2-fashion: the products resulting from reactions with carbazole feature a tethered secondary amine donor bound to a three-coordinate carbazolyl-GeII centre. In each case, addition of the components of the N…
Photochemistry and Redox Chemistry of an Unsymmetrical Bimetallic Copper(I) Complex
2016
The bimetallic copper(I) complex Cu2L2 (cis-1) is formed with high diasteroselectivity from [Cu(NCCH3)4][BF4] and HL (4-tert-butyl phenyl(pyrrolato-2-yl-methylene)amine) in a kinetically controlled reaction. cis-1 features a rather short Cu···Cu distance of 2.4756(6) A and is weakly emissive at room temperature in solution. Oxidatively triggered disproportionation of cis-1 yields elemental copper and the mononuclear copper(II) complex CuL2 (trans-2). One-electron reduction of trans-2 gives cuprate [2]– with a bent bis(pyrrolato) coordinated copper(I) entity. The imine donor atoms of [2]– can insert an additional copper(I) ion giving exclusively the bimetallic complex cis-1 closing the oxida…
Mononuclear Rearrangement of the Z-Phenylhydrazones of Some 3-Acyl-1,2,4-oxadiazoles: Effect of Substituents on the Nucleophilic Character of the >…
2019
The reaction rates for the mononuclear rearrangement of the Z-phenylhydrazones of 3-acyl-1,2,4-oxadiazoles 3a-c into the relevant 2-phenyl-2 H-1,2,3-triazoles (4a-c) have been measured in dioxane/water at different temperatures in a large range of proton concentrations. The occurrence of two different reaction pathways (one uncatalyzed, water assisted, and the other general base catalyzed) has- been observed. The obtained results have been able to furnish information about the effects of the nature of the 3-acyl structure and of the 5-substituents in the 1,2,4-oxadiazole ring on the reactivity of the examined rearrangements: they are well in line with the previsions carried out considering …
Bis(2-methylbenzimidazole-κN1)copper(I) dichlorocuprate(I)
2004
By using alternating-current electrochemical synthesis, crystals of the copper(I) ionic compound composed of [Cu(C8H8N2)2]+ and [CuCl2]− ions have been obtained and structurally investigated. Both crystallographically independent Cu atoms lie on centres of inversion and exhibit the less-common coordination number 2. A linear arrangement of the metal atoms includes two N atoms of the different organic moieties in the [Cu(2-methylbenzimidazole)2]+ cation and two Cl atoms in the case of the inorganic anion.
Tetracationic and Tetraanionic Manganese Porphyrins: Electrochemical and Spectroelectrochemical Characterization
2017
International audience; The electrochemistry and spectroelectrochemistry of four tetrapositively charged and two tetranegatively charged porphyrins were characterized in two nonaqueous solvents (dimethyl sulfoxide and N,N-dimethylformamide) containing 0.1 M tetra-n-butylammonium perchlorate. The tetrapositively charged compounds are represented by the tetrapyridylporphyrins [TRPyPM]4+(X-)4, where R is a methyl or [2-[2-(2-methoxy)ethoxy]ethoxy]ethyl group, M = MnIIII, MnIIICl, CuII, or PdII, and X = I- or Cl-. The tetranegatively charged porphyrins are represented by the tetrasulfonato derivatives [TPPSMn(OAc)]4-(NH4+)4 and [TArPSMn(OAc)]4-(NH4+)4, where Ar = 4-O-[2-[2-(2-methoxy)ethoxy]eth…
Photolysis of Tertiary Amines in the Presence of CO2: The Paths to Formic Acid, α-Amino Acids, and 1,2-Diamines
2017
The photolysis of triethylamine (1a) in the presence of carbon dioxide leads to the hydrogenation of CO2, the α-C-C coupling of triethylamine (1a), and the CO2-insertion into the α-C-H σ-bond of amine 1a. This reaction is proposed to proceed through the radical ion pair [R3N·+·CO2·-] generated by the photoionization of amine 1a and the electron capture by CO2. The presence of lithium tetrafluoroborate in the reaction medium promotes the efficient and stereoselective α-C-C coupling of 1a by enhancing the production of α-dialkylamino radicals and the isomerization of N,N,N',N'-tetraethylbutane-2,3-diamine (4a).
A water molecule in the interior of a 1H-pyrazole Cu2+ metallocage
2016
Water has a great tendency to associate through hydrogen bonding with water molecules or other hydrogen bond donor or acceptor groups. Here the case of a water molecule encapsulated in the interior of a metallocage receptor is presented. The association of four copper(II) ions and two aza-macrocyclic receptors in which two 1H-pyrazole units are connected by cadaverine diamines leads to the inclusion of a water molecule into the cage, as proved by X-ray analysis and infrared spectroscopy. The included water molecule shows no hydrogen bonding with any component of the cage presenting only a weak hydrogen bond with an oxygen atom of a perchlorate counter-anion. The IR stretching vibrations pre…
Energetic study of bifurcated hydrogen bonds in secondary structures of salts composed with dicarboxylic acids and ethylamine
2020
Abstract The nature of bifurcated hydrogen bonds prompted us to analyze the energy of supramolecular motifs on the example of new structures of carboxylic acids salts with amines, which guarantee a multitude of such interactions. Experimental and theoretical studies of four dicarboxylic salts with primary amine: ethylammonium succinate hydrate (1), tartrate hydrate (2) phthalate hydrate (3) and terephthalate (4) has been investigated along with study of the strength of interactions between the anions and cations. The complete topological analysis of the charge density for all new structures allowed designation of the estimated Cumulative Dissociation Energy (eCDE).
Reversible O–H bond activation by an intramolecular frustrated Lewis pair
2019
The interactions of the O-H bonds in alcohols, water and phenol with dimethylxanthene-derived frustrated Lewis pairs (FLPs) have been probed. Within the constraints of this backbone framework, the preference for adduct formation or O-H bond cleavage to give the corresponding zwitterion is largely determined by pKa considerations. In the case of the PPh2/B(C6F5)2 system and p-tBuC6H4OH, an equilibrium is established between the two isomeric forms which allows the thermodynamic parameters associated with zwitterion formation via O-H bond cleavage to be probed.
Protonation of a Spherical Macrotricyclic Tetramine: Water Inclusion, Allosteric Effect, and Cooperativity
2017
The spherical macrotricyclic cryptand tetramine "C24" (1) displays remarkable protonation behaviour. It undergoes protonation in four successive steps for which pKa values of 11.17±0.05, 10.28±0.04, 6.00±0.06 and 3.08±0.08 have been determined at 298 K. The unusually close values for the first two protonations provide evidence for the encapsulation of a water molecule serving as effector for the second protonation, which is consistent with earlier observations that the exchange of protons bound in the diprotonated species with solvent protons is unusually slow and that 17 O NMR spectra show the presence of an oxygen centre in the same species quite distinct from that of solvent water. Encap…