Anionic Rearrangement Research Articles

Loss of Chirality through Facile Lewis Base Mediated Aza-enolate Formation in Na and K (S)-N-(α-Methylbenzyl)methallylamides

Metalation of (S)-N-(α-methylbenzyl)methallylamine with nBuM (M = Li, Na, or K) in hexane leads to the allylic metal amides [(S)-PhCH(CH3)N(CH2C{CH3}═CHLi)Li]6, 1, [(S)-PhCH(CH3)N(CH2C{CH3}═CH2)Na]n, and [(S)-PhCH(CH3)N(CH2C{CH3}═CH2)K]n, respectively. The addition of any Lewis base (here THF, TMEDA, or PMDETA) to the Na and K amides promotes rapid anion rearrangement to the aza-enolate complexes [PhC(═CH2)N(CH2CH{CH3}2)Na]∞, 2, [PhC(═CH2)N(CH2CH{CH3}2)Na·TMEDA]n, 3, [PhC(═CH2)N(CH2CH{CH3}2)Na·PMDETA]n, 4, and [PhC(═CH2)N(CH2CH{CH3}2)K]n, 5, resulting in loss of chirality. In contrast, the addition of benzene leads exclusively to the 1-aza-allyl complexes [(S)-PhCH(CH3)N(CH═C{CH3}2)Na]n, 6, and [(S)-PhCH(CH3)N(CH═C{CH3}2)K]n, 7, both of which are not observed in the presence of Lewis donors. Doping a benzene solution of 7 with THF gives the first observation of reorganization to the intermediate 2-aza-allyl anion. All seven complexes have been characterized by NMR spectroscopy, with complexes 1 and 2 also...

Coordination Chemistry and Structural Dynamics of a Long and Flexible Piperazine-Derived Ligand.

A long and highly flexible internally functionalized dipyridyl ligand α,α'-p-xylylenebis(1-(4-pyridylmethylene)-piper-4-azine), L, has been employed in the synthesis of a series of coordination polymer materials with Co(II), Cd(II), and Ag(I) ions. In poly-[Cd(L)(TPA)] 1 and poly-[Co(L)(IPA)], 2, (TPA = terephthalate, IPA = isophthalate) the ligand adopts a similar linear conformation to that seen in the structure of the unbound molecule and provides a long (2.6 nm) metal-metal bridging distance. Due to the mismatch of edge lengths with that provided by the carboxylate coligands, geometric distortions from the regular dia and (4,4) network geometries for 1 and 2, respectively, are observed. In poly-[Ag2(CF3SO3)2(L)], 3, the ligand coordinates through both pyridine groups and two of the four piperazine nitrogen donors, forming a high-connectivity 2-dimensional network. The compound poly-[Ag2(L)](BF4)2·2MeCN, 4, a porous 3-dimensional cds network, undergoes a fascinating and rapid single-crystal-to-single-crystal rearrangement on exchange of the acetonitrile guests for water in ambient air, forming a nonporous hydrated network poly-[Ag2(L)](BF4)2·2H2O, 5, in which the well-ordered guest water molecules mediate the rearrangement of the tetrafluoroborate anions and the framework itself through hydrogen bonding. The dynamics of the system are examined in greater detail through the preparation of a kinetic product, the dioxane-solvated species poly-[Ag2(L)](BF4)2·2C4H8O2, 6, which undergoes a slow conversion to 5 over the course of approximately 16 h, a transition which can be monitored in real time. The reverse transformation can also be observed on immersing the hydrate 5 in dioxane. The structural features and physical properties of each of the materials can be rationalized based on the flexible and multifunctional nature of the ligand molecule, as well as the coordination behavior of the chosen metal ions.

Probing the Self-Assembly Mechanism of Lanthanide-Containing Sandwich-Type Silicotungstates [{Ln(H2O)n}2{Mn4(B-α-SiW9O34)2(H2O)2}](6-) Using Time-Resolved Mass Spectrometry and X-ray Crystallography.

The reaction of [γ-SiW10O36](8-) with Mn(2+) and Ln(3+) in an aqueous solution led to the isolation of a series of new lanthanide-containing sandwich-type polyoxometalates (POMs) [{Ln(H2O)n}2{Mn4(B-α-SiW9O34)2(H2O)2}](6-) (1-5a) (Ln = La (1), Nd (2), Gd (3), Dy (4), Er (5); n = 5, 6), which crystallize in the space groups C2/c with a = 33.0900(2)-32.9838(15) Å, b = 12.8044(10)-12.7526(6) Å, c = 22.8273(17)-22.6368(11) Å, V = 9669.2(12)-9519.7(8) Å(3), Z = 2 (1, 2); P1̅ with a = 11.9502(4)-11.8447(6) Å, b = 13.2203(4)-13.1164(5) Å, c = 15.8291(5)-15.8524(7) Å, V = 2221.25(13)-2189.95(18) Å(3), Z = 1 (3, 4, 5), respectively. X-ray diffraction analysis reveals that they consist of two-dimensional networks based on a sandwich-type polyanion [Mn4(B-α-SiW9O34)2(H2O)2](12-) (6a, {Mn4(SiW9)2}) and lanthanide cations (Ln(3+)), which are further connected into three-dimensional frameworks by potassium cations for 3, 4, and 5. The unprecedented combination of time-resolved electrospray ionization mass spectrometry (ESI-MS) studies and X-ray crystallography allows us not only to directly observe the in-solution rearrangement of divant anion [γ-SiW10O36](8-) into the sandwich-type POM 6a via an intermediate species [Mn3(B-β-SiW8O30(OH))(B-β-SiW9O33(OH))(H2O)](12-) (7a, {Mn3(SiW8)(SiW9)}) from ESI-MS results, but also to gain the solid-state structures of intermediate and final product isolated from reaction solutions from X-ray crystallography results, from which the self-assembly mechanism of the lanthanide-containing sandwich-type POMs 1-5a was proposed.

Brook/Elimination/Aldol Reaction Sequence for the Direct One‐Pot Preparation of Difluorinated Aldols from (Trifluoromethyl)trimethylsilane and Acylsilanes

AbstractA methodology allowing the one‐pot preparation of difluorinated aldols directly from Ruppert–Prakash reagent, acyltrimethylsilanes and aldehydes is reported. The process, initiated by a catalytic amount of an ammonium salt, involves the addition of (trifluoromethyl)trimethylsilane to the acylsilane, followed by a Brook rearrangement and elimination of a fluoride anion that promotes the subsequent aldol reaction. An efficient racemic reaction catalyzed by tetrabutylammonium difluorotriphenylsilicate is described, as well as our first efforts towards an asymmetric version.magnified image

An Efficient Isoprenylation of Xanthones at the C1 Position by Utilizing Anion-Accelerated Aromatic Oxy-Cope Rearrangement

An effective method for the installation of isoprenyl moiety at the C1 position of xanthone has been developed. Addition of isoprenyl Grignard reagent to 1-fluoroxanthone derivatives proceeded γ-selectively, and the obtained tertiary alcohols underwent aromatic oxy-Cope rearrangement and subsequent elimination of fluoride anion under mild conditions to give 1-isoprenylxanthones in high yields.

The Strange Case of Sodium (S)-N-α-(Methylbenzyl)allylamide: Anion Rearrangement, Decomposition, and a Peculiar Propyl Addition

An unexpected aza-enolate propyl addition complex, [(PhC═CH2)(CH═C(CH2CH2CH3)CH3)NNa·THF]∞ (1), was isolated when (S)-N-α-(methylbenzyl)allylamine reacted in hexane with nBuNa in the presence of THF. Analytical studies revealed a decomposition of the sodium 1-azaallylamide to a sodium enamide and propene, identified by solution studies and a GC-headspace study, respectively. Propene then adds to the carbanion tautomer of the sodium 1-azaallylamide followed by anionic rearrangements to later form the aza-enolate propyl addition complex.

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene.

1,4-Diols resulting from the double addition of ArCCLi (Ar = Ph, substituted phenyl, 2-thienyl) to ortho-C6H4(CHO)2 undergo cascades to tetracenes on simple admixture of LiHDMS, CS2 and MeI. Acene formation proceeds by [3,3]-sigmatropic rearrangement of xanthate anions followed by 6π electrocyclisations. The reactions are terminated by E2 or anionic Chugaev-type eliminations. Structural packing motifs and electronic properties are reported for the tetracenes.

A comparative study of alkylimidazolium room temperature ionic liquids with FSI and TFSI anions near charged electrodes

Electric double layer (EDL) structure and capacitance generated by the two series of room temperature ionic liquids containing alkylimidazolium Cnmim (n=2,4,6,8) cations and bis(fluorosulfonyl) imide (FSO2)2N−, (FSI) or bis(trifluoromethylsulfonyl) imide (CF3SO2)2N− (TFSI) anions were studied on flat (basal plane graphite) and atomically corrugated (prismatic plane graphite) charged electrode surfaces using atomistic molecular dynamics simulations. On atomically flat surface, generated EDLs in all systems produced a weakly changing differential capacitance (DC) as a function of electrode potential. However, on atomically rough surfaces, ionic liquids with FSI and TFSI anions show substantially different EDL structures and DC dependence. Unlike [Cnmim][TFSI], which generated a camel-shape DC regardless of the cation alkyl tail length, the [Cnmim][FSI] showed a transition from a bell-shape to a camel-shape DC upon increase of the cation alkyl tail length. Analysis of contributions from rearrangement and reorientation of cations and anions indicated that the ability of the FSI anion to respond to changes in electrode potential is the primary driving force for such behavior.

Oxidative dehydrogenation of ethane on dynamically rearranging supported chloride catalysts.

Ethane is oxidatively dehydrogenated with a selectivity up to 95% on catalysts comprising a mixed molten alkali chloride supported on a mildly redox-active Dy2O3-doped MgO. The reactive oxyanionic OCl(-) species acting as active sites are catalytically formed by oxidation of Cl(-) at the MgO surface. Under reaction conditions this site is regenerated by O2, dissolving first in the alkali chloride melt, and in the second step dissociating and replenishing the oxygen vacancies on MgO. The oxyanion reactively dehydrogenates ethane at the melt-gas phase interface with nearly ideal selectivity. Thus, the reaction is concluded to proceed via two coupled steps following a Mars-van-Krevelen-mechanism at the solid-liquid and gas-liquid interface. The dissociation of O2 and/or the oxidation of Cl(-) at the melt-solid interface is concluded to have the lowest forward rate constants. The compositions of the oxide core and the molten chloride shell control the catalytic activity via the redox potential of the metal oxide and of the OCl(-). Traces of water may be present in the molten chloride under reaction conditions, but the specific impact of this water is not obvious at present. The spatial separation of oxygen and ethane activation sites and the dynamic rearrangement of the surface anions and cations, preventing the exposure of coordinatively unsaturated cations, are concluded to be the origin of the surprisingly high olefin selectivity.

Pressure-induced phase transitions in rubidium azide: Studied by in-situ x-ray diffraction

We present the in-situ X-ray diffraction studies of RbN3 up to 42.0 GPa at room temperature to supplement the high pressure exploration of alkali azides. Two pressure-induced phase transitions of α-RbN3 → γ-RbN3 → δ-RbN3 were revealed at 6.5 and 16.0 GPa, respectively. During the phase transition of α-RbN3 → γ-RbN3, lattice symmetry decreases from a fourfold to a twofold axis accompanied by a rearrangement of azide anions. The γ-RbN3 was identified to be a monoclinic structure with C2/m space group. Upon further compression, an orthogonal arrangement of azide anions becomes energetically favorable for δ-RbN3. The compressibility of α-RbN3 is anisotropic due to the orientation of azide anions. The bulk modulus of α-RbN3 is 18.4 GPa, quite close to those of KN3 and CsN3. By comparing the phase transition pressures of alkali azides, their ionic character is found to play a key role in pressure-induced phase transitions.

Anionic access to silylated and germylated binuclear heterocycles.

A simple access to silylated and germylated binuclear heterocycles, based on an original anionic rearrangement, is described. A set of electron-rich and electron-poor silylated aromatic and heteroaromatic substrates were tested to understand the mechanism and the factors controlling this rearrangement, in particular its regioselectivity. This parameter was shown to follow the rules proposed before from a few examples. Then, the effect of the substituents borne by the silicon itself, in particular the selectivity of the ligand transfer, was studied. Additionally, this chemistry was extended to germylated substrates. A hypervalent germanium species, comparable to the putative intermediate proposed with silicon, seems to be involved. However, a pathway implicating the elimination of LiCH2Cl was observed for the first time with this element, leading to unexpected products of the benzo-oxa (or benzo-aza) germol-type.

The electrochemical and local structural analysis of the mesoporous Li4Ti5O12 anode

Mesoporous lithium titanate microsphere anodes have been made by hydrothermal synthesis. Layered hydrous lithium titanate was obtained after hydrothermal reaction and Li4Ti5O12 microspheres assembled from nanosheets were subsequently formed by thermal treatment. This results in improved voltage profiles and charge/discharge dynamics. Mesoporous lithium titanate microspheres showed stable cycling performances, with high capacity retention (140 mAh g−1) even after 4000 cycles. In order to understand the functioning of this promising anode material at the molecular level, we used in-situ X-ray absorption spectroscopy (XAS). The XAS results verify the Ti conversion between Ti4+ and Ti3+ during charge/discharge cycling and demonstrate that this reduction is accompanied by small changes Ti–O distance but no detectable change in Ti–Ti distance. This anion re-arrangement suggests a structural explanation for the fact that this material is electrochemically very stable even under higher current density cycling.

Complex thermal expansion properties in a molecular honeycomb lattice.

[FeL3][BF4]2·xH2O (L = 3-(pyrazinyl)-1H-pyrazole) shows negative thermal expansion between 150-240 K but positive thermal expansion at 240-300 K, linked to rearrangement of anions and water molecules within pores in the lattice.

Theoretical study of the mechanism of formation of 4-aminoisoxazoles. 2*. An unusual rearrangement of oximinonitriles

The base-catalyzed cyclization of oximinonitriles in the presence of lithium ions leads to 4-aminoisoxazoles and, sometimes, to 5-aminooxazoles. Modeling using the density functional theory and the HF and MP2 methods indicated that both 4-aminoisoxazoles and 5-aminooxazoles are formed from the anion of one of the oximinonitrile lithium complexes. The formation of 5-aminooxazoles proceeds through an unusual anion rearrangement. The thermodynamic parameters of the transition states were calculated to explain the predominant formation of 4-aminoisoxazoles.

The Intramolecular Rearrangement of Phosphinohydrazides [R′2P–NR–NR–M] → [RN═PR′2–NR–M]: General Rules and Exceptions. Transformations of Bulky Phosphinohydrazines (R–NH–N(PPh2)2, R =tBu, Ph2P)

Reactions of diphosphinohydrazines R-NH-N(PPh(2))(2) (R = tBu (1), Ph(2)P (3)) with some metalation reagents (Co[N(SiMe(3))(2)](2), LiN(SiMe(3))(2), La[N(SiMe(3))(2)](3), nBuLi, MeLi) were performed. Compound 1 was synthesized by the reaction of Ph(2)PCl with tert-butylhydrazine hydrochloride in 83% yield. This compound reveals temperature-dependent (31)P NMR spectra due to hindered rotation about the P-N bonds. Complicated redox reaction of 1 with Co[N(SiMe(3))(2)](2) proceeds with cleavage of the P-N and N-N bonds to form a binuclear cobalt complex [Co{HN(PPh(2))(2)-κ(2)P,P'}(2)(μ-PPh(2))](2) (2) demonstrating a short Co···Co distance of 2.3857(5) Å, which implies a formal double bond between the Co atoms. Strong nucleophiles (nBuLi, MeLi) cause fragmentation of the molecules 1 and 3, while reactions of 3 with lithium and lanthanum silylamides give products of the NNP → NPN rearrangement [Li{Ph(2)P(NPPh(2))(2)-κ(2)N,N'}(THF)(2)] (4) and [La{Ph(2)P(NPPh(2))(2)-κ(2)N,N'}{N(SiMe(3))(2)}(2)] (5), respectively. These complexes represent the first examples of a κ(2)N,N' bonding mode for the triphosphazenide ligand [(Ph(2)PN)(2)PPh(2)](-). DFT calculations showed large energy gain (52.1 kcal/mol) of the [NNP](-) to [NPN](-) anion rearrangement.

Cyclization Reactions of 3,4-Diazaheptatrienyl Metal Compounds. Pyridines from an Anionic Analogue of the Fischer Indole Synthesis: Experiment and Theory

Unsymmetrical N,N'-bisalkylidene hydrazines 7a,b, 10a-c and 13, which are accessible in good to excellent yields from hydrazones 6, 9, and 12 and commercially available α,β-unsaturated carbonyl compounds, are converted into 3,4-diazaheptatrienyl anions 14a,b, 16a-c, and 18 by treatment with KO-t-Bu as base. These anionic species form pyridines 15a,b, 5,6-dihydrobenzo[h]quinolones 17a-c, and bipyridine 19 in moderate yields. We interpret thermodynamics and kinetics of these reactions by quantum chemical calculations and discuss this multistep anionic rearrangement, based on an electrocyclic ring formation with a Möbius aromatic transition structure 22, the N-N bond fission (25), and the 6-exo-trig cyclization (27) as key steps, considering the results of NICS and NBO-charge calculations. This novel anionic reaction sequence bears an interesting analogy to the mechanism of the (cationic) Fischer indole synthesis. Precursor 10c and product 16c could be characterized by X-ray diffraction.

Activation of the Si−B Linkage: Copper-Catalyzed Addition of Nucleophilic Silicon to Imines

Activation of the Si-B bond through copper-catalyzed transmetalation quickly developed into a practical method to generate Cu-Si reagents. These silicon nucleophiles cleanly add to aldehyde-derived imine electrophiles to form α-silylated amines in protic media, and no carbon-to-nitrogen Brook-type rearrangement of the intermediate anion is observed. Aside from electron-withdrawing groups at the imine nitrogen atom, for example, SO(2)Tol and P(O)Ph(2), previously delicate nitrogen substituents such as phenyl or benzhydryl are tolerated. The same protocol also allows the unprecedented addition to representative ketone-derived imines.

Pyridine‐Directed Organolithium Addition to an Enol Ether

AbstractA previously reported anionic rearrangement of benzyl 2‐pyridyl ethers can now be accessed by a distinct and unusual mechanism: addition of alkyllithium reagents to α‐(2‐pyridyloxy)‐styrene triggers an anionic rearrangement to afford tertiary pyridyl carbinols. The process is explained by invoking a contra‐electronic, pyridine‐directed carbolithiation of the enol ether π‐system.

ChemInform Abstract: A Complex-Induced Proximity Effect in the Anionic Fries Rearrangement of o-Iodophenyl Benzoates: Synthesis of Dihydro-O- methylsterigmatocystin and Other Xanthones.

The success of an anionic Fries rearrangement, used to synthesise dihydro-O-methylsterigmatocystin and other xanthones, is dependent on the presence of a remote methoxyl substituent

ChemInform Abstract: Anionic Rearrangement in the Gas Phase. The Collision-Induced Loss of Carbon Monoxide from Deprotonated Pyruvates and Hydroxyacetates.

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