190,121 research outputs found
Cationic Group 3 Alkyl Complexes with Isopropyl-Substituted Triazacyclononane-amide Ligands: Synthesis, Structure, and Thermal Decomposition Processes
Yttrium and lanthanum dialkyl complexes with the isopropyl-substituted triazacyclononane-amide monoanionic ligands [iPr2TACN-(B)-NtBu] (B = (CH2)2, L1; SiMe2, L2) are described. For Y, these were obtained by reaction of Y(CH2SiMe3)2(THF)2 with HL, whereas for La in situ peralkylation of LaBr3(THF)4 preceded reaction with HL. In C6D5Br solvent, reaction of LMR2 with [PhNMe2H][B(C6F5)4] results in rapid decomposition involving loss of propene from the ligand. This decomposition is prevented (Y) or retarded (La) in THF solvent. For yttrium, salts of the cations [LYR(THF)]+ were isolated and structurally characterized. ES-MS of these cations revealed facile desolvation. At increased nozzle voltages, fragmentation is observed with initial loss of SiMe4, followed by loss of propene. Thus decomposition is likely to involve initial cyclometalation of a ligand iPr group, followed by propene extrusion. Decomposition of [L2LaR(THF)x]+ in THF solution yields the dinuclear dication {[tBuN(Me2Si)N(C2H4)2N(C2H4)NiPr]2La2(THF)2}2+, which was structurally characterized. Kinetic data of the decomposition suggest that the process involves initial THF dissociation.
Multimetallic lithium complexes derived from the acids Phâ‚‚C(X)COâ‚‚H (X = OH, NHâ‚‚) : synthesis, structure and ring opening polymerization of lactides and lactones
Reaction of LiOR (R=t-Bu, Ph) with the acids 2,2/-Ph₂C(X)(CO₂H), X=OH (benzH), NH₂ (dpgH) was investigated. For benzH, one equivalent LiOt-Bu in THF afforded [Li(benz)]2⋅2THF (1⋅2THF), which adopts a 1D chain structure. If acetonitrile is used (mild conditions), another polymorph of 1 is isolated; LiOPh also led to 1. Robust work-up afforded [Li₇(benz)₇(MeCN)] 2MeCN THF (2⋅2MeCN⋅THF). Use of LiOt-Bu (2 equivalents) led to {Li₈(Ot-Bu)₂[(benz)](OCPh₂CO₂CPh₂CO2t-Bu)₂(THF)₄} (3), the core of which comprises two open cubes linked by benz ligands. For dpgH, two equivalents of LiOt-Bu in THF afforded [Li6(Ot-Bu)₂(dpg)₂(THF)₂] (4), which contains an Li₂Ov 6-step ladder. Similar reaction of LiOPh afforded [Li₈(PhO)₄(dpg)₄(MeCN)₄] (5). Complexes 1–5 were screened for their potential as catalysts for ring opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL), rac-lactide (rac-LA) and δ-valerolactone (δ-VL). For ROP of ϵ-CL, conversions > 70 % were achievable at 110 °C with good control. For rac-LA and δ-VL, temperatures of at least 110 °C over 12 h were necessary for activity (conversions > 60 %). Systems employing 2 were inactiv
Visible and Ultraviolet Laser Spectroscopy of ThF
The molecular ion ThF is the species to be used in the next generation of
search for the electron's Electric Dipole Moment (eEDM) at JILA. The
measurement requires creating molecular ions in the eEDM sensitive state, the
rovibronic ground state , , . Survey spectroscopy of
neutral ThF is required to identify an appropriate intermediate state for a
Resonance Enhanced Multi-Photon Ionization (REMPI) scheme that will create ions
in the required state. We perform broadband survey spectroscopy (from 13000 to
44000~cm) of ThF using both Laser Induced Fluorescence (LIF) and
REMPI spectroscopy. We observe and assign 345 previously unreported vibronic
bands of ThF. We demonstrate 30\% efficiency in the production of ThF ions
in the eEDM sensitive state using the [32.85] intermediate
state. In addition, we propose a method to increase the aforementioned
efficiency to 100\% by using vibrational autoionization via
core-nonpenetrating Rydberg states, and discuss theoretical and experimental
challenges. Finally, we also report 83 vibronic bands of an impurity species,
ThO.Comment: 49 pages, 7 figure
Solvent effect and fluorescence response of the 7-tert-butylpyrene-dipicolylamine linkage for the selective and sensitive response toward Zn(II) and Cd(II) ions
The different binding behaviour of 7-tert-butylpyrene based chemosensors bearing dipicolylamine (Dpa) linkages at the 1,3-positions was investigated in various solvents for the sensing of Zn(II) and Cd(II).The potential mono-chelating ligand L1 follows the same binding pattern in both THF and methanol–water solvent systems, exhibiting higher selectivity and sensitivity for Cd(II) over Zn(II) mainly in THF solvent system. The potential bis-chelate ligand L2 can selectively bind both Zn(II) and Cd(II) in a 1:1 ratio in THF, whereas in methanol–water (7:3) at pH = 7.0; a 1:2 binding ratio was observed. In THF, two sites of ligand L2 can only selectively and sensitively bind one Zn(II) or Cd(II). The different complexation behaviour of L1 and L2 in different solvents were studied by means of fluorescence spectra and ¹H-NMR titration experiments in the presence of Zn(II) and Cd(II)
Neutral and Cationic Rare Earth Metal Alkyl and Benzyl Compounds with the 1,4,6-Trimethyl-6-pyrrolidin-1-yl-1,4-diazepane Ligand and Their Performance in the Catalytic Hydroamination/Cyclization of Aminoalkenes
A new neutral tridentate 1,4,6-trimethyl-6-pyrrolidin-1-yl-1,4-diazepane (L) was prepared. Reacting L with trialkyls M(CH2SiMe3)3(THF)2 (M = Sc, Y) and tribenzyls M(CH2Ph)3(THF)3 (M = Sc, La) yielded trialkyl complexes (L)M(CH2SiMe3)3 (M = Sc, 1; M = Y, 2) and tribenzyl complexes (L)M(CH2Ph)3 (M = Sc, 3; M = La, 4). Complexes 1 and 2 can be converted to their corresponding ionic compounds [(L)M(CH2SiMe3)2(THF)][B(C6H5)4] (M = Sc, Y) by reaction with [PhNMe2H][B(C6H5)4] in THF. Complexes 3 and 4 can be converted to cationic species [(L)M(CH2Ph)2]+ by reaction with [PhNMe2H][B(C6F5)4] in C6D5Br in the absence of THF. The neutral complexes 1-4 and their cationic derivatives were studied as catalysts for the hydroamination/cyclization of 2,2-diphenylpent-4-en-1-amine and N-methylpent-4-en-1-amine reference substrates and compared with ligand-free Sc, Y, and La neutral and cationic catalysts. The most effective catalysts in the series were the cationic L-yttrium catalyst (for 2,2-diphenylpent-4-en-1-amine) and the cationic lanthanum systems (for N-methylpent-4-en-1-amine). For the La catalysts, evidence was obtained for release of L from the metal during catalysis.
Unprecedented layered coordination polymers of dithiolene group 10 metals: Magnetic and electrical properties
One-pot reactions between Ni(ii), Pd(ii) or Pt(ii) salts and 3,6-dichloro-1,2-benzenedithiol (HSC6H2Cl2SH) in KOH medium under argon lead to a series of bis-dithiolene coordination polymers. X-ray analysis shows the presence of a common square planar complex [M(SC6H2Cl2S)2]2- linked to potassium cations forming either a two-dimensional coordination polymer network for {[K2(μ-H2O)2(μ-thf)(thf)2][M(SC6H2Cl2S)2]}n [M = Ni (1) and Pd (2)] or a one-dimensional coordination polymer for {[K2(μ-H2O)2(thf)6][Pt(SC6H2Cl2S)2]}n (3). In 3 the coordination environment of the potassium ions may slightly change leading to the two-dimensional coordination polymer {[K2(μ-H2O)(μ-thf)2][Pt(SC6H2Cl2S)2]}n (4) that crystallizes together with 3. The physical characterization of compounds 1-3 show similar trends, they are diamagnetic and behave as semiconductorsWe thank financial support from MICINN (MAT2013-46753-C2-1-P, CTQ2014-52758-P and MAT2014-56143-R) and Generalitat Valenciana (PrometeoII/2014/076
Highly Efficient Hydrosilylation of Alkenes by Organoyttrium Catalysts with Sterically Demanding Amidinate and Guanidinate Ligands
The sterically demanding guanidine ArNHC(NMe2)NAr (Ar = 2,6-diisopropylphenyl, HL) reacts with Y(CH2SiMe3)3(THF)2 to give the yttrium dialkyl complex (L)Y(CH2SiMe3)2(THF) (1), which was structurally characterized. Electronic interaction of the -NMe2 group with the conjugated ligand backbone can be inferred from structural and spectroscopic data. The new yttrium guanidinate complex 1 and its related amidinate analogue [PhC(NAr)2]Y(CH2SiMe3)2(THF) are highly active and selective catalysts for alkene hydrosilylation with PhSiH3 (tof > 600 h-1 at 23 °C). For unfunctionalized olefins, full selectivity toward anti-Markovnikov products was obtained. The more electron donating guanidinate ligand affords the highest activities with heteroatom-functionalized substrates.
Understanding the Initial Stages of Reversible Mg Deposition and Stripping in Inorganic Non-Aqueous Electrolytes
Multi-valent (MV) battery architectures based on pairing a Mg metal anode
with a high-voltage ( 3 V) intercalation cathode offer a realistic design
pathway toward significantly surpassing the energy storage performance of
traditional Li-ion based batteries, but there are currently only few
electrolyte systems that support reversible Mg deposition. Using both static
first-principles calculations and molecular dynamics, we perform
a comprehensive adsorption study of several salt and solvent species at the
interface of Mg metal with an electrolyte of Mg and Cl dissolved in
liquid tetrahydrofuran (THF). Our findings not only provide a picture of the
stable species at the interface, but also explain how this system can support
reversible Mg deposition and as such we provide insights in how to design other
electrolytes for Mg plating and stripping. The active depositing species are
identified to be (MgCl) monomers coordinated by THF, which exhibit
preferential adsorption on Mg compared to possible passivating species (such as
THF solvent or neutral MgCl complexes). Upon deposition, the energy to
desolvate these adsorbed complexes and facilitate charge-transfer is shown to
be small ( 61 46.2 kJ mol to remove 3 THF from the strongest
adsorbing complex), and the stable orientations of the adsorbed but desolvated
(MgCl) complexes appear favorable for charge-transfer. Finally,
observations of Mg-Cl dissociation at the Mg surface at very low THF
coordinations (0 and 1) suggest that deleterious Cl incorporation in the anode
may occur upon plating. In the stripping process, this is beneficial by further
facilitating the Mg removal reaction
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