The role of π electrons in the formation of benzene-containing lithium-bonded complexes

The intermolecular interactions in C₆H₆???LiX (X=OH, NH₂, F, Cl, Br, NC, CN) complexes are investigated by using second‐order Møller–Plesset perturbation theory (MP2) calculations and quantum theory of “atoms in molecules” (QTAIM) studies, and the role of π electrons is studied in the formation of these benzene‐containing lithium‐bonded complexes. The molecular electrostatic potentials of benzene and LiX determine the geometries of the lithium‐bonded complexes. The electron densities at the lithium bond critical points in the πC₆H₆???LiX complexes are obviously stronger than those in the σC₆H₆???LiX complexes, which indicates that the intermolecular interactions in the C₆H₆???LiX complexes are mainly attributable to π‐type interaction. The topological and energy properties at the lithium bond critical points in both the C₆H₆???LiX and πC₆H₆???LiX complexes are linear with the interaction energies, thereby showing the crucial role of the π electrons in the formation of these complexes. Electron localization function (ELF) analysis indicates that the formation of the lithium bonds leads to the reduction of the ELF π‐electron density and volume, and the reduction of the π‐electron volume is linear with the interaction energies with the correction coefficient 0.9949.     

Lithium-alkyl, -aryl, and -amido ligand-exchange dynamics of dianionic zirconium(IV) complexes with chelating amidophenolate ligands

The synthesis, characterization, and solution behavior of a series of six-coordinate zirconium(IV) dianions [ZrX2(ap)2]2- (ap = 2,4-di-tert-butyl-6-(tert-butylamido)phenolate; X = Ph, 3a; X = p-tolyl, 3b; X = Me, 4; X = NMe2, 5) are described. Complexes 3-5 were prepared by treating the neutral zirconium complex Zr(ap)2(THF)2 (1) with 2 equiv of LiX or by the direct reaction of apLi2 and LiX with ZrCl4. The complexes were isolated as lithium-etherate salts, and they were characterized by NMR spectroscopy and single-crystal X-ray diffraction. In non-coordinating solvents such as benzene-d6, complexes 3-5 are robust in solution, but in coordinating solvents such as THF-d8, dissociation of LiX was observed. The rate of LiX loss was evaluated by exchange reactions; the reaction rate constants span nine orders of magnitude at 298 K, with the slowest reaction being the dissociation of PhLi from 3a (tau1/2 = 4 h) and the fastest reaction being the dissociation of LiNMe2 from 5 (tau1/2 = 53 mus). In the case of LiNMe2 dissociation from 5, activation parameters suggest that the rate-determining step is purely dissociative; however, for diphenyl and dimethyl complexes 3a and 4, respectively, activation parameters suggest a solvent-assisted rate-determining step.     

Multinuclear copper(I) guanidinate complexes

A series of multinuclear Copper(I) guanidinate complexes have been synthesized in a succession of reactions between CuCl and the lithium guanidinate systems Li{L} (L = Me(2)NC((i)PrN)(2) (1a), Me(2)NC(CyN)(2) (1b), Me(2)NC((t)BuN)(2)(1c), and Me(2)NC(DipN)(2) (2d) ((i)Pr = iso-propyl, Cy = cyclohexyl, (t)Bu = tert-butyl, and Dip = 2,6-disopropylphenyl) made in situ, and structurally characterized. The di-copper guanidinates systems with the general formula [Cu(2){L}(2)] (L = {Me(2)NC((i)PrN)(2)} (2a), {Me(2)NC(CyN)(2)} (2b), and {Me(2)NC(DipN)(2)} (2d) differed significantly from related amidinate complexes because of a large torsion of the dimer ring, which in turn is a result of transannular repulsion between adjacent guanidinate substituents. Attempts to synthesis the tert-butyl derivative [Cu(2){Me(2)NC((t)BuN)(2)}(2)] result in the separate formation and isolation of the tri-copper complexes [Cu(3){Me(2)NC((t)BuN)(2)}(2)(μ-NMe(2))] (3c) and [Cu(3){Me(2)NC((t)BuN)(2)}(2)(μ-Cl)] (4c), both of which have been unambiguously characterized by single crystal X-ray diffraction. Closer inspection of the solution state behavior of the lithium salt 1c reveals a previously unobserved equilibrium between 1c and its starting materials, LiNMe(2) and N,N'-di-tert-butyl-carbodiimide, for which activation enthalpy and entropy values of ΔH(?) = 48.2 ± 18 kJ mol(-1) and ΔS(?) = 70.6 ± 6 J/K mol have been calculated using 1D-EXSY NMR spectroscopy to establish temperature dependent rates of exchange between the species in solution. The molecular structures of the lithium complexes 1c and 1d have also been determined and shown to form tetrameric and dimeric complexes respectively held together by Li-N and agostic Li···H-C interactions. The thermal chemistry of the copper complexes have also been assessed by thermogravimetric analysis.     

Origin of the detrimental effect of lithium halides on an enantioselective nucleophilic alkylation of aldehydes

The effect of lithium halides on the enantioselectivity of the addition of methyllithium on o-tolualdehyde, in the presence of chiral lithium amides derived from chiral 3-aminopyrrolidines (3APLi), has been investigated. The enantiomeric excess of the resulting 1-o-tolylethanol was found to drop upon addition of significant amounts of LiCl, introduced before the aldehyde. The competitive affinity between the lithium amide, the methyllithium, and the lithium halides in THF was examined by multinuclear NMR spectroscopy and DFT calculations. The results showed that the original mixed aggregate of the chiral lithium amide and methyllithium is rapidly, totally, and irreversibly replaced by a similar 1:1 complex involving one lithium chloride or bromide and one lithium amide. While the MeLi/LiX substitution occurs with some degree of epimerization at the nitrogen for the endo-MeLi:3APLi complex, it is mostly stereospecific for the exo-type arrangements of the aggregate. The thermodynamic preference for mixed aggregates between 3APLi and LiX was confirmed by static DFT calculations: the data show that the LiCl and LiBr aggregates are more stable than their MeLi counterparts by more than 10 kcal.mol(-1) provided THF is explicitly taken into account. These results suggest that a sequestration of the source of chirality by the lithium halides is at the origin of the detrimental effect of these additives on the ee of the model reaction.     

Expanding the tools available for direct ortho cupration--targeting lithium phosphidocuprates

Reaction of in situ generated lithium phosphides with 0.5 eq. Cu(I) is employed as a means of targeting lithium phosphidocuprates of either Gilman- or Lipshutz-type formulation--e.g., (R(2)P)(2)CuLi·n(LiX) (n = 0, 1). For R = Ph, X = CN in toluene followed by thf or R = Ph, X = I in thf/toluene an unexpected product results. [(Ph(2)P)(6)Cu(4)][Li·4thf](2)1 reveals an ion-separated structure in the solid state, with solvated lithium cations countering the charge on an adamantyl dianion [(Ph(2)P)(6)Cu(4)](2-). Deployment of R = Ph, X = CN in thf affords a novel network based on the dimer of Ph(2)PCu(CN)Li·2thf 2 with trianions based on 6-membered (PCu)(3) rings acting as nodes in the supramolecular array and solvated alkali metal counter-ions completing the linkers. Cy(2)PLi (Cy = cyclohexyl) has been reacted with CuCN in thf/toluene to yield Gilman-type lithium bis(phosphido)cuprate (Cy(2)P)(2)CuLi·2thf 3 by the exclusion of in situ generated LiCN. A polymer is noted in the solid state.     

A computational study of lithium enolate mixed aggregates

Ab initio calculations were performed to examine the formation of mixed dimer and trimer aggregates between the lithium enolate of acetaldehyde (lithium vinyloxide, LiOV) and lithium chloride, lithium bromide, and lithium amides. Gas-phase calculations showed that in the absence of solvation effects, the mixed trimer 2LiOV.LiX is the most favored species. Solvation in ethereal solvents was modeled by a combination of specific coordination of dimethyl ether ligands on each lithium and "dielectric solvation" (DSE, dielectric solvation energies), immersion of each molecule in a cavity within a continuous dielectric having the dielectric constant of THF at room temperature. DSE is less important for aggregates (reduced dipoles or quadrupoles) than monomers (dipoles) and is also reduced for the coordinatively solvated species. Both solvation terms reduce the exothermicity of aggregation. In many cases, lithium salts that are three- rather than four-coordinate have significant populations at room temperature. The strongly basic lithium amides prefer mixed aggregates with weaker bases than homoaggregates. The computational results are consistent with the limited experimental data available.     

Highly conductive oriented PEO-based polymer electrolytes

This contribution presents an overview of the study of the effect of stretching on semicrystalline and amorphous complexes of poly(ethylene oxide) (PEO) with different salts, such as lithium iodide, lithium trifluoromethane-sulfonate, lithium hexafluoroarsenate, lithium bis(oxalato)borate and lithium trifluoromethanesulfonimide. In spite of the conventional belief that ion transport in polymer electrolytes (PE) is mediated primarily by polymer segmental motion, we suggest that ion transport occurs preferentially along the PEO helical axis, at least in the crystalline phase. It was found that the more amorphous the PE, the less its lengthwise conductivity is influenced by stretching. It is suggested that the rate-determining step of ion conduction in semicrystalline LiX:P(EO)₂₀, polymer electrolytes below the melting point (T_m) is “interchain” hopping.     

Novel synthesis of 3-halogenobenzo[b]tellurophene-derivatives

Several substituted benzo[b]tellurophenes were prepared from phenylacetylenes and TeO₂ in the presence of a lithium halide, LiX.     

两种有机磺酸配合物的合成、表征及与DNA键合性质

合成了2个新型有机磺酸配合物,[Cd(phen)₂(ans)₂]·H₂O (1)和[Pb(phen)₂(ans)₂]·H₂O (2) (phen=1,10-邻菲咯啉,ans=4-氨基-1-萘磺酸根),通过元素分析、红外光谱等对配合物进了表征,用X-射线单晶衍射方法测定了配合物的单晶结构。应用紫外-可见吸收光谱、荧光光谱及粘度测定方法研究了配合物与ctDNA的作用,发现2个配合物均以插入和氢键两种模式与ctDNA发生作用。     

Two dinuclear iron(II) complexes K[Fe2(L1)(SCN)4]·2(C3H8O) and [Fe2(L1)(SeCN)3(C5H5N)]·H2O are stabilised in the '[HS-LS]' state by a bis-tetradentate pyrazolate-based ligand

Two air-sensitive dinuclear iron(II) complexes, K[Fe(II)(2)(L(1))(SCN)(4)]·2(C(3)H(8)O) (1) and [Fe(II)(2)(L(1))(SeCN)(3)(C(5)H(5)N)]·H(2)O (2), of 3,5-bis[N,N-bis(2-pyridylmethyl)aminomethyl]-1H-pyrazolate [(L(1))(-)] have been prepared. Interestingly, complex 1 is anionic, featuring four coordinated SCN(-) anions and a potassium counterion whereas complex 2 is neutral, containing a coordinated pyridine molecule and only three coordinated SeCN(-) anions. These are the first iron complexes reported for this type of ligand. Magnetic measurements and M?ssbauer spectra show that both 1 and 2 are in a '[HS-LS]' mixed spin state between 300 and 2 K.     

The relation between ion pair structures and reactivities of lithium cuprates

From Li+ well-solvating solvents or complex ligands such as THF, [12]crown-4, amines etc., lithium cuprates R2CuLi(*LiX) crystallise in a solvent-separated ion pair (SSIP) structural type (e.g. 10). In contrast, solvents with little donor qualities for Li+ such as diethyl ether or dimethyl sulfide lead to solid-state structures of the contact ion pair (CIP) type (e.g. 11). 1H,6Li HOESY NMR investigations in solutions of R2CuLi(*LiX) (15, 16) are in agreement with these findings: in THF the SSIP 18 is strongly favoured in the equilibrium with the CIP 17, and in diethyl ether one observes essentially only the CIP 17. Salts LiX (X=CN, Cl, Br, I, SPh) have only a minor effect on the ion pair equilibrium. These structural investigations correspond perfectly with Bertz's logarithmic reactivity profiles (LRPs) of reactions of R2CuLi with enones in diethyl ether and THF: the faster reaction in diethyl ether is due to the predominance of the CIP 17 in this solvent, which is the reacting species; in THF only little CIP 17 is present in a fast equilibrium with the SSIP 18. A kinetic analysis of the LRPs quantifies these findings. Recent quantum-chemical studies are also in agreement with the CIP 17 being the reacting species. Thus a uniform picture of structure and reactivity of lithium cuprates emerges.     

Reactivity of ether- and amine-complexed dimers and tetramers of alkyllithiums towards triphenylmethane

Kinetics of Lewis base (LB) complexed primary and secondary sigma-alkyllithiums (RLi) with triphenylmethane (TPMH) are reported. RLis in which one or two LB groups (-OMe, -NMe, -NMeR) are part of the molecule form, in benzene, intramolecularly complexed tetramers, for example, 2(4), or dimers, for example, 4(2). They are used as models for their intermolecular congeners R4Li4 x 4LB and R2Li2 x 4LB (LB = NR'3, OR'2). Nonunity reaction orders in [RLi] are in line with reactions via as yet unidentified 1:1 complexes formed in an equilibrium (K(stat. corr.) approximately = 1) between aggregated RLi and TPMH. In some cases, a tetramer/dimer equilibrium mixture undergoes complexation/reaction. Reaction rates correlate linearly with calculated concentrations of the complexes. Relative rates of complexes range from 1 [prim-R4Li4 x 3LB x TPMH (presumed)] to 4250 [sec-R2Li2 x 3LB x TPMH (presumed)]. A major role in the reactivity enhancement owing to LB-induced conversion of tetramers into dimers is ascribed to increased LB participation in LB-richer dimer transition states. Amine and ether complexes have practically equal reactivities. Lithiation of TPMH by dimeric RCH2Li is retarded by a factor of 24000 if a silyl group is linked to the alpha-carbon.     

A chemosensor for dihydrogenphosphate based on an oxoazamacrocycle possessing three thiourea arms

We report a new H-bond macrocyclic chromogenic chemosensor in organic media, H(3)L, which displayed drastic changes in its UV-vis spectra revealing selectivity for dihydrogenphosphate over other inorganic anions, such as acetate or fluoride. The X-ray crystal structures of the [H(4)L···NO(3)]·(CH(3)CN)(4) and [H(4)L···CF(3)CO(2)]·(CH(3)CN)(2) salt complexes are also reported.     

Synthesis, structures and reactivity of ruthenium nitrosyl complexes containing Kläui's oxygen tripodal ligand

Ruthenium nitrosyl complexes containing the Kl?ui's oxgyen tripodal ligand L(OEt)(-) ([CpCo{P(O)(OEt)(2)}(3)](-) where Cp = η(5)-C(5)H(5)) were synthesized and their photolysis studied. The treatment of [Ru(N^N)(NO)Cl(3)] with [AgL(OEt)] and Ag(OTf) afforded [L(OEt)Ru(N^N)(NO)][OTf](2) where N^N = 4,4'-di-tert-butyl-2,2'-bipyridyl (dtbpy) (2·[OTf](2)), 2,2'-bipyridyl (bpy) (3·[OTf](2)), N,N,N'N'-tetramethylethylenediamine (4·[OTf](2)). Anion metathesis of 3·[OTf](2) with HPF(6) and HBF(4) gave 3·[PF(6)](2) and 3·[BF(4)](2), respectively. Similarly, the PF(6)(-) salt 4·[PF(6)](2) was prepared by the reaction of 4·[OTf](2) with HPF(6). The irradiation of [L(OEt)Ru(NO)Cl(2)] (1) with UV light in CH(2)Cl(2)-MeCN and tetrahydrofuran (thf)-H(2)O afforded [L(OEt)RuCl(2)(MeCN)] (5) and the chloro-bridged dimer [L(OEt)RuCl](2)(μ-Cl)(2) (6), respectively. The photolysis of complex [2][OTf](2) in MeCN gave [L(OEt)Ru(dtbpy)(MeCN)][OTf](2) (7). Refluxing complex 5 with RNH(2) in thf gave [L(OEt)RuCl(2)(NH(2)R)] (R = tBu (8), p-tol (9), Ph (10)). The oxidation of complex 6 with PhICl(2) gave [L(OEt)RuCl(3)] (11), whereas the reduction of complex 6 with Zn and NH(4)PF(6) in MeCN yielded [L(OEt)Ru(MeCN)(3)][PF(6)] (12). The reaction of 3·[BF(4)](2) with benzylamine afforded the μ-dinitrogen complex [{L(OEt)Ru(bpy)}(2)(μ-N(2))][BF(4)](2) (13) that was oxidized by [Cp(2)Fe]PF(6) to a mixed valence Ru(II,III) species. The formal potentials of the RuL(OEt) complexes have been determined by cyclic voltammetry. The structures of complexes 5,6,10,11 and 13 have been established by X-ray crystallography.     

Mechanical Bond Enhanced Lithium Halide Ion-Pair Binding by Halogen Bonding Heteroditopic Rotaxanes**

A family of novel halogen bonding (XB) and hydrogen bonding (HB) heteroditopic [2]rotaxane host systems constructed by active metal template (AMT) methodology, were studied for their ability to cooperatively recognise lithium halide (LiX) ion-pairs. ¹H NMR ion-pair titration experiments in CD₃CN:CDCl₃ solvent mixtures revealed a notable “switch-on“ of halide anion binding in the presence of a co-bound lithium cation, with rotaxane hosts demonstrating selectivity for LiBr over LiI. The strength of halide binding was shown to greatly increase with increasing number of halogen bond donors integrated into the interlocked cavity, where an all-XB rotaxane was found to be the most potent host for LiBr. DFT calculations corroborated these findings, determining the mode of LiX ion-pair binding. Notably, ion-pair binding was not observed with the corresponding XB/HB macrocycles alone, highlighting the cooperative, heteroditopic, rotaxane axle-macrocycle component mechanical bond effect as an efficient strategy for ion-pair recognition in general.     

A comparative study of lithium,sodium and hydrogen bonds formed by 1:1 interaction of electron donor molecules with lithium,sodium and hydrogen halides

Dissociation energies of 1:1 complexes of hydrogen, lithium and sodium halides with water, methanol and ammonia vary in the order LiX > NaX > HX, the dissociation energy in the case of lithium bonds being of the order of 200 kJ mol^?1 or more. The dissociation energy of sodium bonds lies in the range 80–120 kJ mol^?1. The magnitude of charge transfer, Δq, between the donor and acceptor molecules is also highest in the case of lithium bonds. The dissociation energies and Δq have been related with various properties of the complexes.     

A practical non-cryogenic process for the selective functionalization of bromoaryls

A selective and practical bromine-metal exchange process under non-cryogenic conditions was developed by a simple modification of an existing protocol. By directly adding an alkyl lithium RLi reagent to a solution of a bromoaryl substrate ArBr and an alkylmagnesium reagent RMgX, a lithium triarylmagnesiate Ar₃MgLi complex formed that allowed for various types of functionalization and more elaborate cross-coupling reactions. The simplicity and improved safety of the method represent a significant improvement over current state of the art that uses lithium trialkylmagnesiate R₃MgLi complexes, and is especially advantageous for large-scale synthesis.     

Anion binding by metallo-receptors of 5,5'-dicarbamate-2,2'-bipyridine ligands

Three 5,5'-dicarbamate-2,2'-bipyridine ligands (L = L(1)-L(3)) bearing ethyl, isopropyl or tert-butyl terminals, respectively, on the carbamate substituents were synthesized. Reaction of the ligands L with the transition metal ions M = Fe(2+), Cu(2+), Zn(2+) or Ru(2+) gave the complexes ML(n)X(2)·xG (1-12, n = 1-3; X = Cl, NO(3), ClO(4), BF(4), PF(6), ?SO(4); G = Et(2)O, DMSO, CH(3)OH, H(2)O), of which [Fe(L(2))(3)???SO(4)]·8.5H(2)O (2), [Fe(L(1))(3)???(BF(4))(2)]·2CH(3)OH (7), [Fe(L(2))(3)???(Et(2)O)(2)](BF(4))(2)·2CH(3)OH (8), [ZnCl(2)(L(1))][ZnCl(2)(L(1))(DMSO)]·2DMSO (9), [Zn(L(1))(3)???(NO(3))(2)]·2H(2)O (10), [Zn(L(2))(3)???(ClO(4))(Et(2)O)]ClO(4)·Et(2)O·2CH(3)OH·1.5H(2)O (11), and [Cu(L(1))(2)(DMSO)](ClO(4))(2)·2DMSO (12) were elucidated by single-crystal X-ray crystallography. In the complexes ML(n)X(2)·xG the metal ion is coordinated by n = 1, 2 or 3 chelating bipyridine moieties (with other anionic or solvent ligands for n = 1 and 2) depending on the transition metal and reaction conditions. Interestingly, the carbamate functionalities are involved in hydrogen bonding with various guests (anions or solvents), especially in the tris(chelate) complexes which feature the well-organized C(3)-clefts for effective guest inclusion. Moreover, the anion binding behavior of the pre-organized tris(chelate) complexes was investigated in solution by fluorescence titration using the emissive [RuL(3)](2+) moiety as a probe. The results show that fluorescent recognition of anion in solution can be achieved by the Ru(II) complexes which exhibit good selectivities for SO(4)(2-).     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 47. Zur Reaktion von Hexachloroceraten(IV) mit Lithiumorganylen

Contributions to the Chemistry of Organo-Transition Metal Compounds. 47. Reactions of Hexachlorocerates(IV) with Organolithium Compounds Pyridinium hexachlorocerate(IV) reacts with lithium organyls RLi RLi (R = 1-Nor, (CH₃)₂NCH₂CH₂CH₂, n-C₄H₉) in the molar ratio 1:2 with formation of Li₂[CeCl₆] · 2 NC₅H₅. A further mol RLi effects a reduction to Li₃[CeCl₆] · 2 NC₅H₅. With an excess of RLi amidocerium(III) complexes of the typ Li₄ are formed. Li₂[CeCl₆] is formed also at reactions of quartery ammonium salts, e. g. [C₆H₅CH₂N(C₂H₅)₃]₂[CeCl₆], with RLi (R = 1-Nor, Me₂₂NCH₂CH₂CH₂) followed by an reduction to Li₃[CeCl₆]. An excess of the lithium organyl effects the formation Li₄[RCeCl₆] complexes. The yielded compounds were characterized by elementary analysis, the hydrolysis and deuterolysis products, magnetic moments, and IR-spectra.     

50 years of superbases made from organolithium compounds and heavier alkali metal alkoxides

A review of reactions of organolithium compounds (RLi) with alkali metal alkoxides is presented. On the one hand, simple lithium alkoxides form adducts with RLi the reactivity of which differs only slightly from that of RLi. On the other hand, after mixing heavier alkali metal alkoxides (R’OM, M = Na, K, Rb, Cs) with RLi, a new system is formed, which has reactivity that dramatically exceeds that of the parent RLi. A metal interchange, according to the equation RLi + R’OM = RM + R’OLi, occurs in this system, giving rise to a superbase. This reaction is frequently used for the preparation of heavier alkali metal organometallic compounds. Similar metal interchange takes place between R’OM and compounds such as lithium amides and lithium enolates of ketones or esters, thus demonstrating the general nature of this procedure. Superbases react easily with many types of organic compounds (substrates), resulting in the formation of a heavier alkali metal derivative of the substrate (metalation). The metalated substrate can react in situ with an electrophile to yield the substituted substrate, a procedure that is frequently used in synthetic and polymer chemistry. An improved mechanism of metal interchange and reaction of superbases with substrates is proposed.