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.

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 $^3\Delta_1$, $v^+=0$, $J^+=1$. 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$^{-1}$) of ThF using both Laser Induced Fluorescence (LIF) and $1+1'$ 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 $\Omega = 3/2$ [32.85] intermediate state. In addition, we propose a method to increase the aforementioned efficiency to $\sim$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

Multimetallic lithium complexes derived from the acids Ph₂C(X)CO₂H (X = OH, NH₂) : 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

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.

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.

In vivo testing of crosslinked polyethers. II. Weight loss, IR analysis, and swelling behavior after implantation

As reported in Part I (In vivo testing of crosslinked polyethers. I. Tissue reactions and biodegradation, J. Biomed. Mater. Res., this issue, pp. 307-320), microscopical evaluation after implantation of crosslinked (co)polyethers in rats showed differences in the rate of biodegradation, depending on the presence of tertiary hydrogen atoms in the main chain and the hydrophilicity of the polyether system. In this article (Part II) the biostability will be discussed in terms of weight loss, the swelling behavior, and changes in the chemical structure of the crosslinked polyethers after implantation. The biostability increased in the order poly(POx) < poly(THF-co-OX) < poly(THF) for the relatively hydrophobic polyethers. This confirmed our hypothesis that the absence of tertiary hydrogen atoms would improve the biostability. On the other hand, signs of biodegradation were observed for all polyether system studied. Infrared surface analysis showed that biodegradation was triggered by oxidative attack on the polymeric chain, leading to the formation of carboxylic ester and acid groups. It also was found that in the THF-based (co)polyethers, α-methylene groups were more sensitive than β-methylene groups. For a hydrophilic poly(THF)/PEO blend, an increase in surface PEO content was found, which might be due to preferential degradation of the PEO domains

Hydrophobic Polyelectrolytes in Better Polar Solvent. Structure and Chain Conformation as seen by Saxs and Sans

We demonstrate in this paper the influence of solvent quality on the structure of the semi-dilute solution of a hydrophobic polyelectrolyte, partially sulfonated Poly-Styrene Sulfonate. Two solvents are used: (i) one mixture of water and an organic solvent: THF, which is also slightly polar; (ii) DMSO, a polar organic solvent. In case (i), it is shown by SAXS study that the structure - namely the scattering from all chains, characterised by a maximum ("polyelectrolyte peak"), of the aqueous hydrophobic polyelectrolyte solutions (PSS) depends on the solvent quality through the added amount of organic solvent THF. This dependence is more pronounced when the sulfonation rate is low (more hydrophobic polyelectrolyte). It is proposed that when THF is added, the chain conformation evolves from the pearl necklace shape already reported in pure water, towards the conformation in pure water for fully sulfonated PSS, which is string-like as also reported previously. On the contrary, for a hydrophilic polyelectrolyte, AMAMPS, no evolution occurs with added THF in the aqueous solution. In case (ii), it is shown directly by SANS study that PSS can behave as a classical solvophilic polyelectrolyte when dissolved in an organic polar solvent such as DMSO: the structure (total scattering) as well as the form factor (single chain scattering measured by SANS using the Zero Average Contrast method) of the PSS chains is independent of the charge content in agreement with Manning condensation, and identical to the one of a fully charged PSS chain in pure water, which has a classical polyelectrolyte behaviour in the semi-dilute regime

Koordinationschemie -gebundener Cyclopentadienyl-Chalkogeno-Ether

Coordination Chemistry of rr-Bonded Cyclopentadienyl Chalcogeno Ethers, I. - Chelate Complexes of Pentakis(methylthio)cymantrene with Metal Carbonyls [C5(SMe)5]Mn(CO)3 (1) reacts with W(CO)5(THF), Mo(CO)4(C7H8), Cr(CO)3(NCMe)3, and Re(CO)4(-C3H5)/HBF4 to yield the monochelate complexes [[C5(SMe)5]Mn(C0)3][M(CO)4] (M = W: 2; M = Mo: 3) and the dichelate complexes [[C5(SMe)5]Mn(CO)3][M(C0)4]2 (M = W: 4; M = Cr: 5; M = Re BFF4 : 6). The reaction with Mo(CO)3(p-xylene) in THF leads via unstable intermediates, which contain coordinated THF, to a mixture of 3 and [[C5(SMe)5]Mn(CO)3][Mo(CO)4]2 (7). The structures of 3 and 4 in the crystal have been determined by X-ray diffraction methods

Reactivity of a trans-[H-Mo≣Mo-H] Unit Towards Alkenes and Alkynes. Bimetallic Migratory Insertion, H-Elimination and Other Reactions

Complex [Mo2(H)2{μ-HC(NDipp)2}2(THF)2], (1·THF), reacts with C2H4 and PhCH[double bond, length as m-dash]CH2 to afford hydrido-hydrocarbyl and bis(hydrocarbyl) derivatives of the Mo[quadruple bond, length as m-dash]Mo bond. Reversible migratory insertion and β-hydrogen elimination, as well as reductive elimination and other reactions, have been uncovered. PhC[triple bond, length as m-dash]CH behaves instead as a Brönsted–Lowry acid towards the strongly basic Mo–H bonds of 1·THF.Ministerio de Economía y Competitividad CTQ2016-75193-PEuropean Research Council 75657

Vanadium(V) tetra-phenolate complexes: synthesis, structural studies and ethylene homo-(co-)polymerization capability

Reaction of α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xylene (p-L¹H₄) with two equivalents of [VO(OR)₃] (R = nPr, tBu) in refluxing toluene afforded, after work-up, the complexes {[VO(OnPr)(THF)]₂ (μ-p-L¹)}·2(THF) (1·2(THF)) or {[VO(OtBu)]₂ (μ-p-L¹)}·2MeCN (2·2MeCN), respectively in moderate to good yield. A similar reaction using the meta pro-ligand, namely α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-m-xylene (m-L²H₄) afforded the complex {[VO(OnPr)(THF)]₂ (μ-p-L²)} (3). Use of [V(Np-R¹C₆H₄)(tBuO)₃] (R¹ = Me, CF₃) with p-L¹H₄ led to the isolation of the oxo–imido complexes {[VO(tBuO)][V(Np-R¹C₆H₄) (tBuO)](μ-p-L¹)} (R¹ = Me, 4·CH2Cl₂; CF₃, 5·CH2Cl₂), whereas use of [V(Np-R¹C₆H₄)CL³] (R¹ = Me, CF₃) in combination with Et₃N/p-L¹H₄ or p-L¹Na₄ afforded the diimido complexes {[V(Np-MeC₆H₄)(THF)Cl]₂ (μ-p-L¹)}·4toluene (6·4toluene) or {[V(Np-CF₃C₆H₄)(THF)Cl]₂ (μ-p-L¹)} (7). For comparative studies, the complex [(VO)(μ-OnPr)L³]₂ (8) has also been prepared via the interaction of [VO(nPrO)₃] and 2-(α-(2-hydroxy-3,5-di-tert-butylphenyl)benzyl)-4,6-di-tert-butylphenol (L³H2). The crystal structures of 1·2THF, 2·2MeCN, 3, 4·CH2Cl₂, 5·CH2Cl₂, 6·4toluene·THF, 7 and 8 have been determined. Complexes 1–3 and 5–8 have been screened as pre-catalysts for the polymerization of ethylene in the presence of a variety of co-catalysts (with and without a re-activator), including DMAC (dimethylaluminium chloride), DEAC (diethylaluminium chloride), EADC (ethylaluminium dichloride) and EASC (ethylaluminium sesquichloride) at various temperatures and for the co-polymerization of ethylene with propylene; results are compared versus the benchmark catalyst [VO(OEt)Cl₂]. In some cases, activities as high as 243 400 g mmol⁻¹ V⁻¹ h⁻¹ (30.43 kgPE mmol V⁻¹ h⁻¹ bar⁻¹) were achievable, whilst it also proved possible to obtain higher molecular weight polymers (in comparable yields to the use of [VO(OEt)Cl₂]). In all cases with dimethylaluminium chloride (DMAC)/ethyltrichloroacetate (ETA) activation, the activities achieved surpassed those of the benchmark catalyst. In the case of the co-polymerization of ethylene with propylene, complexes 1–3 and 5–8 showed comparable or higher molecular weight than [VO(OEt)Cl₂] with comparable catalytic activities or higher in the case of the imido complexes 6 and 7