- [Cr(pincer2-)]2 as an electron shuttle for reductively promoted hydrazine disproportionation. [Journal Article]
- DTDalton Trans 2019 Jul 16
- We describe here delivery of hydrazine to a reducing, low oxidation state chromium bound to a proton responsive ligand which has already been deprotonated. Reaction of PhHNNH2 at a 4 : 1 mole ratio w…
We describe here delivery of hydrazine to a reducing, low oxidation state chromium bound to a proton responsive ligand which has already been deprotonated. Reaction of PhHNNH2 at a 4 : 1 mole ratio with the bis-(pyrazolate)pyridyl pincer ligated reducing agent [CrIIL]2 gives prompt conversion to [CrIII2L2(PhNH2)2(μ-PhHNN)], with release of NH3 and C6H6, a new disproportionation of the hydrazine, with trapping of PhHNN as its dianion, bridging the two chromium centers. The redox balance of the reaction is discussed, and participation by Brønsted basic sites on the bis-(pyrazolate)pyridyl pincer ligand L2- is suggested, but no hydrazine protons remain on the pincer in the product.
- Methyl Ester Functionalized Phenalenyl Arene- and Bipyridine-Ruthenium-Based Complexes for Electroactive Langmuir-Blodgett Films. [Journal Article]
- ICInorg Chem 2019 Jul 01; 58(13):8408-8418
- We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1 H-phenalen-5-methyl carboxylate (L), and the generated compl…
We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1 H-phenalen-5-methyl carboxylate (L), and the generated complexes [Ru(bpy)2L]PF6 and [(η6-C6H6)Ru(L)Cl]. Compounds were characterized by spectroscopic and X-ray diffraction methods, and their electrochemical behavior was investigated via cyclic voltammetry and UV-vis spectroelectrochemistry. The one-electron oxidized compounds have an unpaired electron located in the phenalenyl ring, as supported by theoretical calculations (DFT) and EPR results. Langmuir-Blodgett (LB) films deposited by [Ru(bpy)2L]2+/3+ species mixed with stearic acid are electroactive, showing a quasi-reversible wave with E1/2Film1 = 0.74 V and E1/2Film2 = 0.81, which are promising systems that allow access to immobilized open-shell species in the film.
- A computational study on the identity of the active catalyst structure for Ru(ii) carboxylate assisted C-H activation in acetonitrile. [Journal Article]
- OBOrg Biomol Chem 2019 Jul 21; 17(27):6678-6686
- Density Functional Theory (DFT) calculations using a consistent methodology accounting for solvation, dispersion and thermal effects have been used to study C-H activation of the simple directing gro…
Density Functional Theory (DFT) calculations using a consistent methodology accounting for solvation, dispersion and thermal effects have been used to study C-H activation of the simple directing group substrate 2-phenylpyridine (a-H). The computational model uses acetate (-OAc) and benzene to represent the carboxylate and arene co-ligands coordinated at a Ru organometallic complex. A variety of different mechanisms ranging from cationic to neutral, ion-paired, arene free, two substrates bound, and solvent (MeCN) coordinated have been explored. Computed results indicate that the cationic pathways from "B+", [(C6H6)Ru(OAc)(a-H)]+, and "D+ (η6)", [(η6-a-H)Ru(OAc)(a-H)]+, involve the lowest overall barriers to C-H activation. Consideration of solvent coordination leads to a complex variety of isomers and conformers. Here a neutral pathway with either one or two acetonitriles coordinated to the Ru centre give very low barriers to C-H activation.
- Elucidating the Chemical Dynamics of the Elementary Reactions of the 1-Propynyl Radical (CH3CC; X2A1) with Methylacetylene (H3CCCH; X1A1) and Allene (H2CCCH2; X1A1). [Journal Article]
- JPJ Phys Chem A 2019 Jul 05; 123(26):5446-5462
- The reactions of the 1-propynyl radical (CH3CC; X2A1) with two C3H4 isomers, methylacetylene (H3CCCH; X1A1) and allene (H2CCCH2; X1A1), along with their (partially) deuterated counterparts were explo…
The reactions of the 1-propynyl radical (CH3CC; X2A1) with two C3H4 isomers, methylacetylene (H3CCCH; X1A1) and allene (H2CCCH2; X1A1), along with their (partially) deuterated counterparts were explored at collision energies of 37 kJ mol-1, exploiting crossed molecular beams to unravel the chemical reaction dynamics to synthesize distinct C6H6 isomers under single collision conditions. The forward convolution fitting of the laboratory data along with ab initio and statistical calculations revealed that both reactions have no entrance barrier, proceed via indirect (complex-forming) reaction dynamics involving C6H7 intermediates with life times longer than their rotation period(s), and are initiated by the addition of the 1-propynyl radical with its radical center to the π-electron density of the unsaturated hydrocarbon at the terminal carbon atoms of methylacetylene (C1) and allene (C1/C3). In the methylacetylene system, the initial collision complexes undergo unimolecular decomposition via tight exit transition states by atomic hydrogen loss, forming dimethyldiacetylene (CH3CCCCCH3) and 1-propynylallene (H3CCCHCCCH2) in overall exoergic reactions (123 and 98 kJ mol-1) with a branching ratio of 9.4 ± 0.1; the methyl group of the 1-propynyl reactant acts solely as a spectator. On the other hand, in the allene system, our experimental data exhibit the formation of the fulvene (c-C5H4CH2) isomer via a six-step reaction sequence with two higher energy isomers-hexa-1,2-dien-4-yne (H2CCCHCCCH3) and hexa-1,4-diyne (HCCCH2CCCH3)-also predicted to be formed based on our statistical calculations. The pathway to fulvene advocates that, in the allene-1-propynyl system, the methyl group of the 1-propynyl reactant is actively engaged in the reaction mechanism to form fulvene. Because both reactions are barrierless and exoergic and all transition states are located below the energy of the separated reactants, the hydrogen-deficient C6H6 isomers identified in our investigation are predicted to be synthesized in low-temperature environments, such as in hydrocarbon-rich atmospheres of planets and their moons such as Titan along with cold molecular clouds such as Taurus Molecular Cloud-1.
- Synthesis, crystal structure, insecticidal activities, molecular docking and QSAR studies of some new phospho guanidines and phospho pyrazines as cholinesterase inhibitors. [Journal Article]
- PBPestic Biochem Physiol 2019; 157:122-137
- Novel phospho guanidine and phospho pyrazine derivatives were synthesized and characterized by 31P, 13C, 1HNMR and IR spectroscopy to obtain novel and human-safe insecticides. Compound 35 [(C4H4N2NH)…
Novel phospho guanidine and phospho pyrazine derivatives were synthesized and characterized by 31P, 13C, 1HNMR and IR spectroscopy to obtain novel and human-safe insecticides. Compound 35 [(C4H4N2NH)2P(O)(C6H6)] was investigated by X-ray crystallography. The inhibitory effects of synthesized compounds were evaluated on human and insect acetylcholinesterase (AChE) using in vitro Ellman method. A few of these compounds, which had low human toxicity, were selected for assessing the killing effects (in vivo) on the elm leaf beetle (X.luteola). The in vitro and in vivo results indicated that compounds bearing both phosphoryl groups and aromatic systems were found to possess a good selectivity for the inhibition of insect AChE over human AChE; up to 550-fold selectivity was achieved for compound 19. Docking studies were performed to explain reasons for the selective behavior of AChE inhibitors. Additionally, the quantitative structure-activity relationship (QSAR) and density functional theory (DFT) results of AChEs demonstrated that the size, shape, dipole moment, and ability to form hydrogen bond played the main role in both models. In addition, the aromatic π - π interactions and charge of the amide nitrogen had a major effect on insecticidal activity of the compounds. The present research can be helpful to gain a better understanding of the interactions between the insect AChE and its inhibitors and introduces compounds which are capable of becoming human-safe insecticides.
- Radiation-Induced Transformations of C6H6 Molecules in Solid Noble-Gas Matrices: Is Benzene Intrinsically Resistant in Condensed Media? [Journal Article]
- JPJ Phys Chem A 2019 Jun 27; 123(25):5199-5205
- The radiation resistance of aromatic compounds is one of the key concepts of basic and applied radiation chemistry in condensed phases. Usually, it is attributed to the intrinsic radiation stability …
The radiation resistance of aromatic compounds is one of the key concepts of basic and applied radiation chemistry in condensed phases. Usually, it is attributed to the intrinsic radiation stability of the benzene ring. In this work, we have demonstrated for the first time that the isolated benzene molecules undergo rather efficient radiation-induced degradation in rigid inert media at cryogenic temperatures (comparable to that of aliphatic hydrocarbons), and their stability is essentially determined by the intermolecular relaxation correlating with matrix polarizability. The principal primary products of benzene radiolysis in matrices are phenyl radicals and fulvene. The matrix environment strongly affects the proportion of these species because of external heavy atom effect on the intersystem crossing, which may trigger further reaction pathways. The obtained results may have important implications for the prediction of radiation stability of complex organic systems and polymers. Furthermore, they may contribute to a better understanding of the radiation-induced evolution of aromatic species in cold interstellar media.
- Elusive hypervalent phosphorusπ interactions: evidence for paradigm transformation from hydrogen to phosphorus bonding at low temperatures. [Journal Article]
- PCPhys Chem Chem Phys 2019 Jun 21; 21(23):12250-12264
- The π electron systems are the conventional electron donors to the hydrogen acceptors in hydrogen bonding. Apart from the hydrogen atom, halogens, chalcogens, pnicogens and triel/tetrel atoms can als…
The π electron systems are the conventional electron donors to the hydrogen acceptors in hydrogen bonding. Apart from the hydrogen atom, halogens, chalcogens, pnicogens and triel/tetrel atoms can also be envisaged as electron acceptors involving π clouds. Markedly, in pnicogenπ interactions, the bonding of the hypervalent (predominantly pentavalent) state of the phosphorus atom with π electron donors is elusive and can be thought of as an intuitive extension to trivalent phosphorusπ interactions. In this work, on the one hand, POCl3 was taken as a prototypical molecule to explore these pentavalent phosphorus interactions and on the other hand, acetylene (C2H2), ethylene (C2H4) and benzene (C6H6), in which phosphorusπ bonding can be expected to compete with hydrogen and halogen bonding interactions, were taken as π electron donors. All three POCl3-C2H2, POCl3-C2H4 and POCl3-C6H6 heterodimers were experimentally generated at low temperatures in Ar and N2 matrices and were characterized by both infrared spectroscopy and state-of-the-art quantum chemical computations. Though hydrogen bonding dominates in POCl3-C2H2 and POCl3-C2H4 heterodimers, phosphorus bonding plays a definite and non-trivial role in their overall stabilization. An interesting paradigm transformation was noticed in the POCl3-C6H6 system, where pentavalent phosphorusπ bonding was observed to completely influence the hydrogen bonding interaction. To further shed light on these Pπ systems, the interaction characteristics were analyzed with the help of electrostatic potential mapping, natural bond orbital and energy decomposition analyses.
- Carbene Formation and Transfer at a Dinickel Active Site. [Journal Article]
- OOrganometallics 2018 Aug 13; 37(15):2437-2441
- The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [ i-PrNDI]Ni2(C6H6) complex (NDI = naphthyridine-diimine) reacts with Ph2CN2 to generate a metastable…
The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [ i-PrNDI]Ni2(C6H6) complex (NDI = naphthyridine-diimine) reacts with Ph2CN2 to generate a metastable diazoalkane adduct, which eliminates N2 at 60 °C to yield a paramagnetic Ni2(μ-CPh2) complex. The Ni2(μ-CPh2) complex undergoes carbene transfer to t-BuNC via an initial isonitrile adduct, which, upon heating, releases free t-BuNCCPh2. Based on this sequence of stoichiometric reactions, a catalytic carbene transfer reaction is demonstrated.
- Incorporation of Pt Nanoparticles on the Surface of TeO₂-Branched Porous Si Nanowire Structures for Enhanced Room-Temperature Gas Sensing. [Journal Article]
- JNJ Nanosci Nanotechnol 2019 Oct 01; 19(10):6647-6655
- A new gas sensor working in room temperature, which is compatible with silicon fabrication technology is presented. Porous silicon nanowires (NWs) were synthesized by metal-assisted chemical etching …
A new gas sensor working in room temperature, which is compatible with silicon fabrication technology is presented. Porous silicon nanowires (NWs) were synthesized by metal-assisted chemical etching method and then TeO₂ NWs branches were attached to their stem by thermal evaporation of Te powders in the presence of air. Afterwards TeO₂ branched porous Si NWs were functionalized by Pt via sputtering followed by low temperature thermal annealing. Scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy collectively confirmed successful formation of TeO₂ branched porous Si NWs functionalized by Pt nanoparticles. Their gas sensing properties in the presence of CO, C6H6 and C7H8 were tested at room temperature, for Si wafer, pristine porous Si NWs, pristine TeO₂ branched porous Si NWs, and Pt functionalized TeO₂ branched porous Si NWs sensors. Pt functionalized TeO₂ branched porous Si NWs have higher responses to all tested gases than the other sensors. The origin of high response is discussed in detail. This new room temperature gas sensor can open a new aperture for development of gas sensors with minimum energy consumption which are compatible with silicon fabrication technology.
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- Study of Benzene Fragmentation, Isomerization, and Growth Using Microwave Spectroscopy. [Journal Article]
- JPJ Phys Chem Lett 2019 May 16; 10(10):2408-2413
- Using a combination of broadband and cavity Fourier transform microwave spectroscopies, and newly developed analysis and assignment tools, the discharge products of benzene have been extensively stud…
Using a combination of broadband and cavity Fourier transform microwave spectroscopies, and newly developed analysis and assignment tools, the discharge products of benzene have been extensively studied in the 2-18 GHz frequency range. More than 450 spectral features with intensities greater than 6σ of the noise RMS were identified, of which of roughly four-fifths (82%) constituting 90% of the total spectral intensity were assigned to 38 species previously detected in the radio band, and nine entirely new hydrocarbon molecules were identified. The new species include both branched and chain fragments of benzene, high energy C6H6 isomers, and larger molecules such as phenyldiacetylene and isomers of fulvenallene; taken together they account for roughly half of the number of observed transitions and 51% of the spectral line intensity. Transitions from vibrationally excited states of several molecules were also identified in the course of this investigation. A key aspect of the present analysis was implementation of a rapid and efficient workflow to assign spectral features from known molecules and to identify line progressions by pattern recognition techniques.