1,721,011 research outputs found
A survey of titanium fluoride complexes, their preparation, reactivity, and applications
No full textA significant amount of information regarding the synthesis, reactivity, and catalytic activity of titanium fluoride complexes is available in the literature. However, the reports are mostly nonsystematic and spread over a large number of specific journals. An attempt is made to collect and organize all available information. Emphasis is given on work published after 1990 with links to the previous reviews, but earlier work is also included if no systematic report was done before. Published synthetic methods to access titanium fluoride complexes are covered in the present review, as well as the properties and reactivity of titanium fluoride complexes. In particular, the behavior of TiF4 in non-aqueous solvents, as well as the interaction of TiF4 with neutral and charged ligands in non-aqueous solvents is reviewed. All published tetrafluoride complexes TiF4L2 (L - neutral ligand) are presented. Mixed chloro and fluoro titanium complexes supported by neutral ligands, their preparation, and isomerism are surveyed. DFT calculations were performed to estimate the relative basicities of molecular ligands in titanium fluoride complexes as well as the relative stability of fluoride bridged titanium complexes. The reactivity of heterometallic titanium-alkali metal, titanium-alkaline earth metal fluoride complexes, the interaction of titanium fluoride complexes with silicon substrates, and the reactivity of titanium complexes toward organofluorine compounds are presented later in the review. Titanium fluoride complexes have found numerous applications in organic synthesis, and in many cases, the fluoride complex shows better performance than do complexes supported by other types of ligands. Organotitanium fluoride complexes show antitumor activity, and their values of cytotoxicity are comparable to that of the "gold standard" cisplatin. (C) 2013 Elsevier B.V. All rights reserved
Cyclic Alkyl(amino) Carbene Stabilized Biradical of Disilicontetrachloride
No full textOne and a half decades ago the formation of Si2Cl4 from the intermediate species SiCl2 was theoretically predicted to be exothermic. The hypothetical Si2Cl4 has never been experimentally synthesized and isolated. Herein, we report that the Si2Cl4 species was stabilized as singlet biradical (Cy-cAAC center dot)(2)Si2Cl4 utilizing two cAAC (cyclic alkyl(amino) carbene). This compound is stable, isolable, and storable at it under an inert atmosphere. The electronic structure and bonding were studied by theoretical calculations which revealed that the molecule possesses a singlet biradical ground state with an unpaired electron on each carbene C atom having opposite spin
Neutral, Cationic, and Anionic Low-Spin Iron(III) Complexes Stabilized by Amidophenolate and Iminobenzosemiquinonate Radical in N,N,O Ligands
No full textA brownish-black complex [Fe-III(L)(2)] (1) (S = 0), supported by two tridentate redox-active azo-appended o-amidophenolates [H2L = 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol], has been synthesized and structurally characterized. In CH2Cl2 1 displays two oxidative and two reductive 1e(-) redox processes at E-1/2 values of 0.48 and 1.06 V and -0.42 and -1.48 V vs SCE, respectively. The one-electron oxidized form [1](+) isolated as a green solid [Fe-III(L)(2)][BF4] (2) (S = 1/2) has been structurally characterized. Isolation of a dark ink-blue one-electron reduced form [1](-) has also been achieved [Co-III(eta(5)-C10H15)(2)][Fe-III(L)(2)] (3) (S = 1/2). Mossbauer spectral parameters unequivocally establish that 1 is a low-spin (LS) Fe-III complex. Careful analysis of Mossbauer spectral data of 2 and 3 at 200 and 80 K reveal that each complex has a major LS Fe-III and a minor LS Fe-II component (redox isomers): [Fe-III{(L-ISQ)(-center dot)}(2)](+) and [Fe-II{(L-IBQ)(0)}{(L-ISQ)(-center dot)}](+) (2) and [Fe-III{(L-AP)(2-)}(2)](-) and [Fe-II{(L-ISQ)(-center dot)}{(L-AP)(2-)}](-) (3). Notably, for both at 8 K mainly the major component exists. Broken-Symmetry (BS) Density Functional Theory (DFT) calculations at the B3LYP level reveals that in 1 the unpaired electron of LS Fe-III is strongly antiferromagnetically coupled with a pi-radical of o-iminobenzosemiquinonate(1-) (L-ISQ)(-center dot) form of the ligand, delocalized over two ligands providing 3- charge (X-ray structure). DFT calculations reveal that the unpaired electron in 2 is due to (L-ISQ)(-center dot) [LS Fe-III (S-Fe = 1/2) is strongly coupled to one of the (L-ISQ)(-center dot) radicals (S-rad = 1/2)] and 3 is primarily a LS Fe-III complex, supported by two o-amidophenolate(2-) ligands. Time-Dependent-DFT calculations shed light on the origin of UV-vis-NIR spectral absorptions for 1-3. The collective consideration of Mossbauer, variable-temperature (77-298 K) electron paramagnetic resonance (EPR), and absorption spectral behavior at 298 K, and DFT results reveals that in 2 and 3 the valence-tautomerism is operative in the temperature range 80-300 K
Organoaluminum hydrides catalyzed hydroboration of carbonates, esters, carboxylic acids, and carbon dioxide
No full textHerein, Al-catalyzed hydroboration of carbonates, esters, carboxylic acids, and CO 2 , with HBpin, is described, which provides a new route for the reduction of CO group compounds. We also conducted an in-depth study of the reduction mechanism of carbonate.The reductive functionalization of the CO unit of carbonates, carboxylic acids, esters, and CO 2 , respectively has received great attention since its introduction. This method is often used industrially for the synthesis of high value-added energy products in chemistry. This opens up a new way forward to reduce greenhouse gases and the consumption of traditional energy sources. Herein, we report an earth-abundant, cheap, and readily available aluminum dihydride, which can catalyze the reduction of a range of carbonates, esters, carboxylic acids, and CO 2 , respectively in the presence of pinacolborane as a reducing agent. Moreover, we demonstrate that the reaction can proceed to obtain good yield products under mild conditions, with low catalyst loading and solvent-free reactions. The mechanism of the catalytic reduction of carbonates has been investigated.Herein, Al-catalyzed hydroboration of carbonates, esters, carboxylic acids, and CO 2 , with HBpin, is described, which provides a new route for the reduction of CO group compounds. We also conducted an in-depth study of the reduction mechanism of carbonate.The reductive functionalization of the CO unit of carbonates, carboxylic acids, esters, and CO 2 , respectively has received great attention since its introduction. This method is often used industrially for the synthesis of high value-added energy products in chemistry. This opens up a new way forward to reduce greenhouse gases and the consumption of traditional energy sources. Herein, we report an earth-abundant, cheap, and readily available aluminum dihydride, which can catalyze the reduction of a range of carbonates, esters, carboxylic acids, and CO 2 , respectively in the presence of pinacolborane as a reducing agent. Moreover, we demonstrate that the reaction can proceed to obtain good yield products under mild conditions, with low catalyst loading and solvent-free reactions. The mechanism of the catalytic reduction of carbonates has been investigated
Monomeric siliconthiodichloride trapped by a Lewis base
No full textThiophosgene (CSCl2), a chemical reagent used in numerous organic syntheses, exists in the monomeric form while its heavier silicon analogue [siliconthiodichloride (SiSCl2)] has been isolated so far as a dimer at room temperature and as a tetramer at 180 degrees C. Herein, we report on the first synthesis, isolation, and characterization of cyclic alkyl(amino) carbene (cAAC) stabilized siliconthiodichloride (cAAC) SiSCl2 (3) in the neutral monomeric form. 3 is synthesized via reaction of (cAAC(center dot))(2)Si2Cl4 (1) or (cAAC)(2)Si2Cl2 (2) with S-8 in the temperature range of -78 to 20 degrees C. An NHC [NHC = N-heterocyclic carbene] analogue of 3 is not isolated when (NHC) SiCl2 is reacted with S-8. The bright yellow colored compound 3 is soluble in polar organic solvents. It is stable at room temperature for a month under an inert atmosphere. 3 decomposes above 160 degrees C. The monomeric molecular structure of 3 has been unambiguously confirmed by X-ray single crystal diffraction. 3 is also characterized by NMR, UV-vis, and IR spectroscopy. The bonding and electron density distributions of 3 have been further studied by theoretical calculations
Formation of Trichlorosilyl-Substituted Carbon-Centered Stable Radicals through the Use of pi-Accepting Carbenes
No full textAmidinate based indium( iii ) monohalides and β-diketiminate stabilized In( ii )–In( ii ) bond: synthesis, crystal structure, and computational study
No full textEstimation of Donation and Backdonation of Cyclic Alkyl(amino) Carbene-Containing Compounds
No full textHerein, we present a general method for a reliable estimation of the extent of pi-backdonation of the bonded element (E) to the carbene carbon atom and C-cAAC -> E, sigma-donation. The C-cAAC E), the chemical shift values of the N-15 nuclei are around 160 ppm. In case the cAAC is bound to a cationic species, the numerical chemical shift value of the N-15 nucleus is downfield-shifted (-130 to 148 ppm). The numerical values of the N-15 nuclei fall in the range from 170 to 200 ppm when a-donation (C-cAAC -> E) of cAAC is stronger than C-cAAC <- E pi-backacceptance. The pi-backacceptance of cAAC is stronger than a-donation, when the chemical shift values of the N-15 nuclei are observed below 220 ppm. Electron density and charge transfer between C-cAAC and E are quantified using natural bonding orbital analysis and charge decomposition analysis techniques. The experimental results have been correlated with the theoretical calculations. They are in good agreement
Reactivity Studies of a Disilene with N<sub>2</sub>O and Elemental Sulfur
No full textIn a previous contribution, we have reported on a convenient and high yield synthesis of the disilene trans-[(TMS)(2)N(eta(1)-Me5C5)-Si=Si(eta(1)-Me5C5)N(TMS)(2)] (2). Herein, we show the reactions of 2 with N2O and S-g. The former reaction affords two isomeric (cis- and trans-) dioxadisiletane ring compounds. To the best of our knowledge, this is the first report where both cis- and trans-isomers are isolated from the same disilene precursor and characterized structurally by single-crystal X-ray diffraction (XRD) studies. The reaction of 2 with elemental sulfur yields only the trans-isomer. To investigate this dissimilar reaction pattern exhibited by 2, computational studies were performed. Density functional theory (DFT) calculations showed that the two dioxadisiletane ring isomers are isoenergetic, with the trans isomer being slightly more stable than the cis counterpart, by 3.3 kcal/mol, while that is not the case with sulfur. All the isolated compounds are characterized by single-crystal XRD studies, multinuclear NMR spectroscopy, and electron ionization mass spectrometry (EI-MS)
Addition Reactions of Me3SiCN with Aldehydes Catalyzed by Aluminum Complexes Containing in their Coordination Sphere O, S, and N Ligands
No full textThe reaction of oneequivalent of LAlH2 (1; L=HC(CMeNAr)(2), Ar=2,6-iPr(2)C(6)H(3), -diketiminate ligand) with twoequivalents of 2-mercapto-4,6-dimethylpyrimidine hydrate resulted in LAl[(-S)(m-C4N2H)(CH2)(2)](2) (2) in good yield. Similarly, when N-2-pyridylsalicylideneamine, N-(2,6-diisopropylphenyl)salicylaldimine, and ethyl 3-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-2-carboxylate were used as starting materials, the corresponding products LAl[(-O)(o-C6H4)CN(C5NH4)](2) (3), LAlH[(-O)(o-C4H4)CN(2,6-iPr(2)C(6)H(3))] (4), and LAl[(-NH)(o-C8SH8)(COOC2H5)](2) (5) were isolated. Compounds 2-5 were characterized by H-1 and (CNMR)-C-13 spectroscopy as well as by single-crystal X-ray structural analysis. Surprisingly, compounds 2-5 exhibit good catalytic activity in addition reactions of aldehydes with trimethylsilyl cyanide (TMSCN)
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