Article

Synthesis and Structures of [(Trimethylsilyl)methyl]sodium and -potassium with Bi- and Tridentate N-Donor Ligands

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Abstract

[(Trimethylsilyl) methyl] sodium [NaCH(2)SiMe(3)] (1) was prepared by a metathesis reaction of [(trimethylsilyl) methyl] lithium [LiCH(2)SiMe(3)] with sodium tert-butoxide in n-hexane. Polydentate donors such as N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N', N '', N ''-pentamethyldiethylenetriamine (PMDETA) form n-hexane-soluble complexes of 1 and the potassium congener [KCH(2)SiMe(3)] (2). The crystal structures of the polymers [(TMEDA) NaCH(2)SiMe(3)] (1a) and [(PMDETA) KCH(2)SiMe(3)] (2a) were determined as infinite helical chains exhibiting 3(1) or 3(2) screw-axis symmetry. Compound 2b was obtained as the donor-deficient heterocubane pseudotetramer [(TMEDA)(3)(KCH(2)SiMe(3))(4)], with intermolecular interactions of the TMEDA-uncoordinated potassium atom with a peripheral methyl group of a neighbouring tetramer to form infinite chains. The relatively easy accessibility and stability should make these (trimethylsilyl) methyl compounds of sodium and potassium valuable starting points for further exploration of the chemistry of these common-utility heavier alkali metals.

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... The lack of information regarding the use of trimethylsilylmethyl in alkali metal superbases is not to be confused with related reactions producing heavier alkali metal trimethylsilylmethyl congeners of sodium [NaCH 2 SiMe 3 ], [20,21] potassium [KCH 2 SiMe 3 ], [20,22] rubidium [RbCH 2 SiMe 3 ], [23] or cesium [CsCH 2 SiMe 3 ] [23] (Scheme 1). This approach is also applicable to neopentyl compounds of sodium [24] and potassium. ...
... The lack of information regarding the use of trimethylsilylmethyl in alkali metal superbases is not to be confused with related reactions producing heavier alkali metal trimethylsilylmethyl congeners of sodium [NaCH 2 SiMe 3 ], [20,21] potassium [KCH 2 SiMe 3 ], [20,22] rubidium [RbCH 2 SiMe 3 ], [23] or cesium [CsCH 2 SiMe 3 ] [23] (Scheme 1). This approach is also applicable to neopentyl compounds of sodium [24] and potassium. ...
... [44] Earlier attempts to produce CH 3 @1 from sub-ideal ratios of NaR and NaOtBu (e. g., 1/4) regularly led to a second high field CH 3 singlet signal of lower intensity in the 1 H NMR spectrum at À 3.25 ppm in C 6 D 12 or À 3.13 ppm in C 6 D 6 . When present, this signal is accompanied by two other singlets (in C 6 D 12 : À 2.36 ppm and À 0.03 ppm; in C 6 D 6 : À 2.08 ppm and 0.37 ppm), similar to the signals of pure NaR [20] (in C 6 D 12 : CH 2 : À 2.23 ppm, SiMe 3 : 0.05 ppm; in C 6 D 6 : CH 2 : À 2.44 ppm, SiMe 3 : 0.15 ppm). This result is consistent with the replacement of a peripheral OtBu group by a CH 2 SiMe 3 group, associated with a low field shift of the 1 H NMR signal of the central methide anion. ...
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Alkali metal alkoxides are widely used in chemistry due to their Brønsted basic and nucleophilic properties. Potassium alkoxides assist alkyllithium in the metalation of hydrocarbons in Lochmann‐Schlosser‐bases. Both compounds form mixed aggregates, which enhance the thermal stability, solubility, and the basic reactivity of these mixtures. A very unusual spherical mixed alkoxy aggregate was discovered by Grützmacher et al., where a central dihydrogen phosphide anion is surrounded by a highly dynamic shell of thirteen sodium atoms and a hull of twelve tert ‐butoxide groups. This structural motif can be reproduced by a reaction of trimethylsilyl compounds of methane, halogens, or pseudo‐halogens with excess sodium tert ‐butoxide. A nucleophilic substitution releases the corresponding anion, which is then encapsulated by the sodium alkoxide units. The compounds are soluble in hydrocarbon solvents, enabling studies of solutions by high resolution NMR spectroscopy and IR/Raman studies of the crystalline materials.
... Corresponding heavier alkali metal compounds, despite their high reactivity, play a considerable less prominent role. The large majority of these compounds show a poor solubility in some inert solvents and a destructive reactivity in other coordinating solvents [8]. An exemption from this trend can be observed for alkali metal compounds of bis(trimethylsilyl)methane, which allow the formation and isolation of a wide range of organometallic compounds [9]. ...
... The preparation of alkyl compounds of heavier alkali metal compounds often follows a similar protocol. By mixing an alkoxide of the corresponding alkali metal with an alkyllithium compound in n-hexane, the immediately formed insoluble alkyl compound can be isolated by filtration [8]. The preparation for 2 stands out, because no precipitate is formed, and the alkyl sodium compound is isolated by crystallization at −30 °C from hexane [11]. ...
... The preparation of alkyl compounds of heavier alkali metal compounds often follows a similar protocol. By mixing an alkoxide of the corresponding alkali metal with an alkyllithium compound in n-hexane, the immediately formed insoluble alkyl compound can be isolated by filtration [8]. The preparation for 2 stands out, because no precipitate is formed, and the alkyl sodium compound is isolated by crystallization at −30 • C from hexane [11]. ...
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In contrast to alkyl compounds of lithium, which play an important role in organometallic chemistry, the corresponding heavier alkali metal compounds are less investigated. These compounds are mostly insoluble in inert solvents or undergo solvolysis in coordinating solvents due to their high reactivity. An exception from this typical behavior is demonstrated by bis(trimethylsilyl) methylsodium. This study examines alkane solutions of bis(trimethylsilyl)methyllithium and -sodium by NMR spectroscopic and cryoscopic methods. In addition, structural studies by X-ray crystallography of the corresponding compounds coordinated by O- and N- ligands (tetrahydrofuran and tetramethylethylenediamine) present possible structural motifs of the uncoordinated compounds in solution.
... In our own research, we found that mixtures of potassium tert-b utoxide with neopentyllithium [49] [LiCH 2 tBu, LiNp] also produced solid neopentylpotassium [50] [KCH 2 tBu, KNp].T he precipitate was isolated by filtration.H owever,t he yield of isolated KNp was considerably lower comparedt ot he results of similar potassium compounds. [51] In fact, it was possible to isolate ac rystalline solid from the filtrate, which contained all four components expected to be presents in LSBs:Lithium, potassium,a lkyl groups, and alkoxide groups. [52] One reason for the unexpected high solubility of the neopentyl/alkoxide mixed aggregates is the structural similarity between tertbutoxy groups [O-tBu]a nd Np groups [CH 2 -tBu]( Scheme 6). ...
... The fractional ratios shown on the diagram axes are defined by the number n of each component:L i/K: n(K)/[n(Li) + n(K)] and R/OR': n(R)/[n(OR') + n(R)].A ccordingly,t he pure alkyl or alkoxy compounds can be found in the corners of the diagram:l ithium alkoxide LiOR' at the top left, potassium alkoxide KOR' at the top right corner,a lkyllithium LiR and alkylpotassium KR in the bottom left and bottom right corners, respectively.E very mixed aggregate consistingo ft hree or more of these four components (Li, K, R, OR'), independentf rom its existence in solution or solid state, can be placed on the edges (three components) or the area (four components)o ft his diagram. This raw diagram can then be populated with substances relevant for this type of system ( Figure 3): lithium tert-butoxide LiOtBu, whichc an be found both in hexameric [39] [Li 6 (OtBu) 6 ]o r octameric [40] [Li 8 (OtBu) 8 ]f orm;t etrameric potassium tert-butoxide [K 4 (OtBu) 4 ]; [41a] and hexameric butyllithium[ Li 6 (nBu) 6 ]. [55] No relevant alkylpotassium compound is known,b ut examples of alkylsodium [9c] or donor coordinated alkylpotassium [51] hint towards the possible existence of tetrameric units [K 4 R 4 ]. ...
... Ad ecreasei nc oncentrationr esulted in the formation of al ighter,m ore mobile neopentyl-containing species. The formation of ah exameric form cannotb er uled out,b ut the preference of potassium alkoxide [41a, 42] and alkylpotassium [13,51] for the formation of tetramers makes this unlikely. The example of this dimerization might also hint to what happenst om ore neopentyl-rich hetero-tetramers. ...
Article
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Lochmann-Schlosser superbases (LSB) are a standard reagent in synthetic chemistry to achieve an exchange of a proton on an organic framework with an alkali metal cation, which in turn can be replaced by a wide range of electrophilic groups. In standard examples, the deprotonating reagent consists of an equimolar mixture of n-butyllithium and potassium t-butoxide. However, the nature of the reactive species could not be pinned down either for this composition or for similar mixtures with comparable high reactivity. Despite the poor solubility and the fierce reactivity, some insights into this mixture were achieved by some indirect results, comparison with chemically related systems, or skillful deductions. Recent results, mainly based on new soluble compounds, delivered structural evidence. These new insights lead to advanced and more detailed conclusions about the interplay of the involved components.
... To facilitate the formation of mixed aggregates of the composition of Li x K y R z (OtBu) x+yÀz by overcoming the obstacle of low solubility of alkylpotassium in alkanes, [25,26] we turned to the neopentyl group (CH 2 tBu, Np). It promises better solubility and higher stability compared to n-butyl, aconsequence of the absence of b-hydrogen atoms.Therefore we carried out areaction between neopentyllithium, [27] LiNp, and KOtBu [4] in n-hexane.T he precipitate formed was collected by filtration, washed with n-hexane,a nd dried in vacuum. ...
... ppm (compared to LiNp with d = À0.62 ppm in the same solvent). [28] Encouraged by the low yields of precipitated 2 of only 24 %(compared to [KCH(SiMe 3 ) 2 ]a nd [KCH 2 SiMe 3 ]w ith 80-90 %), [25,26] we started to examine the filtrate for potassium compounds. ...
Article
Mixtures of alkyllithium and heavier alkali-metal alkoxides are often used to form alkyl compounds of heavier alkali metals, but these mixtures are also known for their high reactivity in deprotonative metalation reactions. These organometallic mixtures are often called LiC-KOR superbases, but despite many efforts their constitution remains unknown. Herein we present mixed alkali-metal alkyl/alkoxy compounds produced by reaction of neopentyllithium with potassium tert-butoxide. The key to success was the good solubility and temperature-stability of neopentyl alkali-metal compounds, leading to hexane-soluble mixtures, which allowed handling at ambient temperatures and isolation by crystallization. The compounds in solid state and in solution were identified by X-ray crystallography and NMR spectroscopy as mixtures of lithium/potassium neopentyl/tert-butoxy aggregates of varying compositions Lix Ky Npz (OtBu)x+y-z .
... Nevertheless, the closest potassium-cluster contact was found to be 3.586(1)Å, which signicantly exceeds the range for K-C bonds reported in the literature (2.75(3) to 3.247(3)Å). [42][43][44] The determination of this structure along with 13 C NMR spectroscopy data led us to believe that the complete ion separation is possible for the metalated carborane cluster, and that the discrete deprotonated carborane anion can be isolated and properly characterized if its symmetry were lowered to prevent crystallographic disorder. Thus, we utilized 9-iodo-ortho-carborane that contains one iodine atom attached to a boron atom of the cluster on the side that is opposite to carbon atoms. ...
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Gemische aus Alkyllithium und Alkoxiden der schweren Alkalimetalle eignen sich zur Herstellung der entsprechenden Alkylverbindungen. Sie zeichnen sich ebenfalls durch ihre Reaktivität bei Metallierungsreaktionen aus. Diese metallorganischen Mischungen werden oft als LiC-KOR-Superbasen bezeichnet, doch trotz vieler Bemühungen ist nur wenig über ihren Aufbau bekannt. Hier werden dimetallische Alkalimetall-Alkyl/Alkoxy-Verbindungen vorgestellt, die durch die Reaktion von Neopentyllithium und Kalium-tert-butoxid gebildet werden. Dank guter Löslichkeit in Alkanen und Temperaturbeständigkeit der Neopentylverbindungen konnten die Lösungen in n-Hexan bei Umgebungstemperatur gehandhabt werden und ermöglichten die Isolierung durch Kristallisation. Die Verbindungen konnten durch Röntgendiffraktometrie und NMR-Spektroskopie sowohl in fester Form als auch in Lösung als Li/K-Neopentyl/tert-Butoxy-Aggregate mit veränderlicher Zusammensetzung LixKyNpz(OtBu)x+y−z identifiziert werden.
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While Li/Cl carbenoids are versatile reagents in organic synthesis, the controlled handling of the extremely reactive and labile M/F carbenoids remains a challenge. We now show that even these compounds can be stabilized and isolated in solid state as well as in solution. Particularly the sodium and potassium com¬pounds exhibit a remarkable stability, thus allowing the first isolation of a room temperature stable fluorine carbenoid. Spectro¬scopic as well as DFT studies confirm the pronounced carbenoid character, showing M-F-C interactions with elongated C-F bonds. The different stabilities of the carbenoids was found to originate from the different strength of the M-F interaction. Hence, the lithium compounds are considerably more reactive than their heavier congeners. Reactivity studies show that the nature of the metal also influences the reactivity, resulting in different selectivities in the addition to thioketones.
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Advancing the applications of s‐block heterobimetallic complexes in catalysis, we report the use of potassium magnesiate (PMDETA)2K2Mg(CH2SiMe3)4 [PMDETA=N,N,N’,N’,N’’‐pentamethyldiethylenetriamine] for the catalytic hydrophosphinylation of styrenes under mild conditions. Exploiting chemical cooperation, this bimetallic approach offers greater catalytic activity and chemoselectivity than the single‐metal components KCH2SiMe3 and Mg(CH2SiMe3)2. Stoichiometric studies between (PMDETA)2K2Mg(CH2SiMe3)4 and Ph2P(O)H help to elucidate the constitution of the active catalytic species, and illustrate the influence of donors on the potassium cation coordination, and how this may impact catalytic activity. Mechanistic investigations support that the rate determining step is the insertion of the olefinic substrate. s‐Block heterobimetallic catalysts: Exploiting s‐block cooperativity, the use of a heterobimetallic potassium magnesiate for the catalytic hydrophosphinylation of styrenes has been developed.
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Lochmann‒Schlosser superbases are formed by mixing alkyllithium with potassium alkoxides. These reagents could prove their synthetic usefulness and reliability in many reactions over five decades. However, despite many efforts the real source of the exceptional reactivity remained a secret. The seemingly manageable system of four components (lithium, potassium atoms, alkyl groups, and alkoxy groups) and their interaction is obscured by poor solubility and fierce reactivity. Recent progress was achieved by using neopentyllithium, leading to alkane soluble-aggregates with varying lithium/potassium content and a flexible alkyl/alkoxy ratio. In this work we isolated two new alkane-soluble alkyl/alkoxy mixed aggregates, [Li4KNp2(OtBu)3] and [K4Np(OtAm)3]. The latter compound is a thermally-stable three-component potassium alkyl/alkoxy base with well-defined stoichiometry in contrast to lithium-containing Lochmann-Schlosser bases with variable metal and alkyl/alkoxy content. In a simple protocol this potassium base produced tetrametalated ferrocene which was converted into 1,1',3,3'-ferrocenetetracarboxylic acid by reaction with CO2. A subsequent conversion into the methyl ester allowed its separation from accompanying di- and tri-substituted ferrocenes.
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Expanding the scope and applications of anionic N‐heterocyclic carbenes (NCHs), a novel series of magnesium NHC complexes is reported using a mixed‐sodium‐magnesium approach. Sequential reactivity of classical imidazol‐2‐ylidene carbene IPr with NaR and MgR2 (R= CH2SiMe3) affords [(THF)3Na(μ‐IPr─)MgR2(THF)] (2) [IPr─ = :C{[N(2,6‐iPr2C6H3)]2CHC] containing an anionic NHC ligand, whereas surprisingly sodium magnesiate [NaMgR3] fails to deprotonate IPr affording instead the redistribution coordination adduct [IPr2Na2MgR4] (1). Compound 2 undergoes selective C2‐methylation when treated with MeOTf furnishing novel abnormal NHC complex [{aIPrMeMgR2}2] (3). Dissolving 3 in THF led to the dissociation of this complex into MgR2 and aIPrMe with the latter isomerizing to the olefinic NHC IPr=CH2. The ability of 2 and 3 to transfer their anionic and abnormal NHC ligands respectively to Au(I) metal fragments has been investigated allowing the isolation and structural characterization of [RAu(μ‐IPr─)MgR(THF)2] (4) and [aIPrMeAuR] (5) respectively. In both cases transfer of an alkyl R group is observed. However while 3 can also transfer its abnormal NHC ligand to give 5, in 4 the anionic NHC still remains coordinated to Mg via its C4 position, whereas the {AuR} fragment occupies the C2 position previously filled by a donor‐solvated {Na(THF)3}+ cation.
Article
The series of alkali metal (Li – Cs) alkoxides of tert-pentanol (1,1-dimethylpropan-1-ol) has been prepared by reaction of the corresponding metal with the alcohol in n-hexane or n-heptane. The compounds were purified by vacuum sublimation and cystallised in n-hexane to produce crystals suitable for single-crystal X-ray diffraction studies. The structures of the potassium, rubidium, and cesium compounds revealed tetrameric units with additional intra- and intermolecular interactions between the metal atom and alkoxide methyl groups increasing with the size of the involved metal.
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Despite their ubiquitous presence in synthesis, the use of polar organolithium reagents under environmentally benign conditions constitutes one of the greatest challenges in sustainable chemistry. Their high reactivity imposes the use of severely restrictive protocols (e.g., moisture‐ and oxygen‐free toxic organic solvents, inert atmospheres, low temperatures, etc.). Making inroads towards meeting this challenge, here we establish a new air‐ and moisture‐compatible organolithium‐mediated methodology for the anionic polymerization of different olefins (like styrenes and vinylpyridines) by pioneering the use of Deep Eutectic Solvents (DESs) as an eco‐friendly reaction media in this type of transformations. Fine‐tuning of the conditions (sonication of the reaction mixture at 40 ºC in the absence of protecting atmosphere) along with the careful choice of the components of the DES employed [choline chloride (ChCl) and glycerol (Gly) in a 1:2 ratio], furnish the desired organic polymers (homopolymers and random copolymers) in excellent yields (up to 90%) and low polydispersities (IPD 1.1‐1.3). Remarkably, the in‐situ formed polystyril lithium exhibits a great resistance to hydrolysis in the eutectic mixture 1ChCl/2Gly (up to 1.5 h) hinting at an unexpected high stability. This unique stability can be exploited to create well defined di‐block copolymers.
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Through mixed metal cooperativity, alkali metal magnesiates efficiently catalyse the cyclisation of alkynols.
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The 60-year history of sodium diisopropylamide (NaDA) is described herein. We review various preparations, solvent-dependent stabilities, and solution structures. Synthetic applications of NaDA reported to date are framed by a mechanism-driven approach, emphasizing selectivities when appropriate. We conclude with examples beyond metalation in which NaDA plays a central role and with a few thoughts on where future applications could be focused. 1 Introduction 2 Preparation and Physical Properties 3 Solution Structures 4 Reactivity and Mechanism 4.1 Solvent Decomposition 4.2 Alkene and Diene Metalation 4.3 Arene Metalations 4.4 Dehydrohalogenations 5 Selectivity and Applications in Synthesis 5.1 Picoline Metalations 5.2 C–H Metalation 5.3 Dehydrohalogenations 5.4 Triflate Alkylation 5.5 Allyl Ether Isomerizations 5.6 Cyclic Allene Synthesis 5.7 Epoxide Elimination 5.8 Enolization 5.9 Orthometalation 6 Flow 7 Catalysis 8 Organosodium Salts and Secondary Applications 9 Conclusion
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A complex of a metal in its zero oxidation state can be considered a stabilized, but highly reactive, form of a single metal atom. Such complexes are common for the more noble transition metals. Although rare examples are known for electronegative late-main-group p-block metals or semimetals1–6, it is a challenge to isolate early-main-group s-block metals in their zero oxidation state7–11. This is directly related to their very low electronegativity and strong tendency to oxidize. Here we present examples of zero-oxidation-state magnesium (that is, magnesium(0)) complexes that are stabilized by superbulky, monoanionic, β-diketiminate ligands. Whereas the reactivity of an organomagnesium compound is typically defined by the nucleophilicity of its organic groups and the electrophilicity of Mg²⁺ cations, the Mg⁰ complexes reported here feature electron-rich Mg centres that are nucleophilic and strongly reducing. The latter property is exemplified by the ability to reduce Na⁺ to Na⁰. We also present a complex with a linear Mg3 core that formally could be described as a MgI–Mg⁰–MgI unit. Such multinuclear mixed-valence Mgn clusters are discussed as fleeting intermediates during the early stages of Grignard reagent formation. Their remarkably strong reducing power implies a rich reactivity and application as specialized reducing agents.
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The incorporation of heavy alkali metals into substrates is both challenging and essential for many reactions. Here, we report the formation of thf‐solvated alkali metal benzyl compounds [PhCH 2 M(thf) n ] ( M = Na, Rb, Cs). The synthesis was carried out by deprotonation of toluene with the bimetallic mixture n‐butyllithium/alkali metal tert‐butoxide and selective crystallization from thf of the defined benzyl compounds. Insights into the molecular structure in the solid as well as in solution state are gained by single crystal X‐ray experiments and NMR spectroscopic studies. The compounds could be successfully used as alkali metal mediating reagents. The example of caesium showed the convenient use by deprotonating acidic C–H as well as N–H compounds to gain insight into the aminometalation using these reagents.
Article
While 1,4-disubstituted 1,2,3-triazoles can be readily prepared by copper(I) alkyne/azide cycloaddition, the methods available to access the alternative 1,5-disubstituted isomers have been significantly less well developed. Exploiting chemical cooperativity, here we report the first examples of s-block bimetallic catalysis using a sodium magnesiate precatalyst as an efficient and versatile new method to synthesize 1,5-disubstituted triazoles via azide/alkyne ligation. Showing an excellent substrate scope and selectivity under mild reaction conditions, this bimetallic approach has also been successfully applied to access symmetrical and non-symmetrical di-triazoles. Mechanistic insights on how the Na/Mg cooperative partnership is established are also provided, supporting a stepwise process where initial deprotonation of the alkyne renders a highly nucleophilic tetra-alkynyl sodium magnesiate to which the azide can coordinate, facilitating its insertion into an Mg-C bond and subsequent cyclization, which is favored by π-coordination of Na to the alkyne C≡C triple bond.
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This chapter provides a non-critical overview of research advances involving the elements of Groups 1 and 2 during the calendar year 2009. As was the case in previous years, coverage will concentrate upon topics centred around the synthesis, structures and applications of coordination compounds of these elements. This self-imposed restriction will necessarily result in the omission of numerous advances in other branches of chemistry and, for this, the author wishes to apologise in advance.
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Deprotonation of alkyl and vinyl carbon-hydrogen bonds for synthetic purposes is often hindered not merely by the need for an exceptionally strong base, but by the inherent instability of the resultant anion. Metalation of cyclic ethers adjacent to oxygen, for example, has invariably initiated a ring-opening decomposition pathway. Here, we show that the use of a bimetallic base can overcome such instability through a cooperative combination of zinc-carbon and sodium-oxygen bonding. Both tetrahydrofuran and tetrahydropyran reacted cleanly over days at room temperature to yield alpha-zinc-substituted products that were sufficiently stable to be isolated and crystallographically characterized. A related zincation-anion trapping strategy, with sodium replaced by potassium, induced clean deprotonation of ethene to yield a stable product. Preliminary electrophilic quenching experiments with the alpha-zinc-substituted cyclic ethers and benzoyl chloride gave satisfactory yields of the tetrahydrofuran-derived ketone but only trace amounts of the tetrahydropyran-derived ketone.
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The syntheses of a number of alkali metal compounds MC(SiMe3)3-n(SiMe2Ph)n, are described (n = 1, M = Li(TMEDA) (3a), Li(Et2O) (3b), or Na(TMEDA) (Bc); n = 2, M = Li(THF)2 (6a), Li(TMEDA) (6b), Na(TMEDA) (6c), or K (6d); n = 3, M = Rb (7d) or Cs (7e); THF = tetrahydrofuran, TMEDA= tetramethylethylenediamine). The compounds 3b, 3c, and 6c adopt molecular structures with intramolecular metal-phenyl interactions. The lithium compound LiCH(SiMe2Ph)2, 5, is dimeric with electron-deficient μ-Li bridges and intramolecular metal-phenyl interactions. The compounds MC(SiMe2Ph)S, M = Na (7b), K (7c), Rb (7d), or Cs (7e), form polymeric chains in the solid state with both intra- and intermolecular metal-phenyl interactions. For the lighter alkali metals the interaction is unsymmetrical and mainly with the ipso and ortho carbon atoms, but for the heavier metals there are almost equal metal-carbon distances to all six atoms of the phenyl ring. The long M-C and short Si-C bond lengths and the wide Si-C-Si angles indicate that the structures are highly ionic. The presence of ionic species in solution is revealed by multinuclear NMR data, in particular by the low frequency shifts associated with the central carbon atoms, by the high carbon-silicon coupling constants, and by the low barriers to inversion compared with those in the trisilylmethanes from which the carbanions are derived.
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The reduction of the ketone to a secondary alcohol that accompanies addition in reactions of ketones and dialkylmagnesium compounds can be lessened by first adding an appropriate salt to the dialkylmagnesium compound. With favorable salts and reactant stoichiometries, reduction is eliminated in reactions of dipropylmagnesium with diisopropyl ketone or di-tert-butyl ketone. In reactions of di-tert-butylmagnesium and di-tert-butyl ketone, reduction always predominates, although some addition does occur. Salts observed to have significant effects are potassium methoxide, (Me2NCH2)2CHOK, sodium methoxide, lithium methoxide, lithium tert-butoxide, tetrabutylammonium bromide, and benzyltriethylammonium chloride. Stoichiometry has significant effects on product composition, the least reduction product generally resulting when the ratio of salt to diorganomagnesium compound is at least one. The fundamental significance of the effects of stoichiometry and of the relative effects caused by different salts is obscured, however, by the heterogeneity of many of the systems. Magnesiate ions, such as (R2MgOMe)22-, are thought to be the organomagnesium species responsible for reactions that proceed without reduction.
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Over the last several decades, research directed at optimization of reactions involving organolithium reagents has led to the recognition that a variety of experimental parameters may affect the outcome and viability of such reactions. Investigation of the factors that influence organolithium-mediated reactions on a large scale is a requirement for development of a feasible and practical process. This contribution critically reviews selected examples, taken from the literature, in which adjustment of the reaction medium, order of addition, temperature, the presence of additives, and judicious choice of base, substrate and/or electrophile resulted in optimization of processes involving organolithium reactions.
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The investigation of the reactivity and structure of organometallic compounds of alkali metals has experienced a blustering development in the last decades. This class includes compounds that are especially important for our understanding of chemical bonding and also quite simple, for example methyl alkali metal complexes, whose structures have been unequivocally determined. Organometallic compounds of alkali metals (and also magnesium) generally exist as ion aggregates whose properties can be significantly modified through solvation by, for example, ether or amines. Important advances in the synthesis of new compounds, especially those of the heavier alkali metals, have been based on these results. It was long believed that the alkali metals had little tendency to undergo coordination and that their coordination chemistry would offer few surprises. This picture has now changed completely. Results from crystal structure investigations have revealed a variety of often surprising structure types (rings, heterocubanes, chains, layers, etc.) not only with the organometallic compounds but also with the amides, imides, alkoxides, phenoxides, enolates, and even halides. A comparison reveals interesting similarities between compounds that appear to be so different and leads to a general classification of the structure types possible with C, N, O, and halo ligands.
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The series [MOBut·ButOH]∞ (M = K, Rb and Cs) have been prepared by the reaction of M with ButOH in THF. Single-crystal X-ray diffraction studies revealed for M = K or Rb that [MOBut·ButOH]∞ crystallizes from tetrahydrofuran-n-pentane at −20°C in the triclinic space group P, with unit cell dimensions [K, Rb]: a = 9.862(3), 9.886(2) Å; b = 9.929(4), 9.914(2) Å; c = 6.330(2), 6.640(1) Å; β = 90.66(2), 90.46(1)° and Z = 2, as a one-dimensional chain linked by hydrogen-bonding. The strong hydrogen-bonding within the chain O(2)O(7) (2.46, 2.44 Å) also results in a near linear O(7)HO(2) angle (167.4, 172.61°) with the hydrogen atom closer to O(7) (1.22, 1.18 Å), than O(2) (1.24, 1.27 Å). These alcohol adducts may be readily converted into the compounds [MOBut]4 (M = K, Rb and Cs) by sublimation. Single-crystal X-ray diffraction studies reveal for M = K or Rb, that [MOBut]4 crystallizes from toluene at −20°C in the cubic space group P3M; with unit cell dimensions [K, Rb]; a = 8.372(1), 8.514(1) Å, and Z = 4, as cubane structures. Within the cubane-like structures the OMO angles are found to deviate only slightly from 90°, with OMO (90.18, 89.11°) and MOM (89.82, 90.89°) for M = K and Rb, respectively. The alcohol adducts undergo an alkoxide ligand exchange process that is rapid on the 1H NMR time scale at room temperature.
Article
Solvates of triphenylmethyl potassium have been prepared with three different Lewis bases and their crystal structures determined by X-ray diffraction methods. In [KCPh3(PMDTA)] (bd1) (PMDTA  N,N,N′,N″,N″-pentamethyl-diethylenetriamine) discrete molecules are observed whereas the solvates with DIGLYME (MeOCH2CH20CH2CH2OMe) and THF are polymeric in the crystal: [KCPh3(DIGLYME)]n (32, zigzag-chain structure) [KCPh3(THF)]n (3, sheet structure).ZusammenfassungSolvate von Triphenylmethylkalium wurden mit drei verschiedenen Lewis-Basen dargestellt and ihre Strukturen röntgenographisch bestimmt. In [KCPh3(PMDTA)] (1) (PMDTA  N,N,N′,N″,N″-Pentamethylentriamin) liegen Einzelmoleküle vor, wogegen die Solvate mit DIGLYM (MeOCH2CH 2OCH2OMe) und THF im Kristall polymer sind: [KCPh3(DIGLYME)]n (2, Zickzack-Kette, [KCPh3(THF)]n (3, Schichtstruktur).
Article
Several organosodium compounds with the carbanions benzyl (phenylmethadine), diphenylmethyl (diphenylmethadine), o-xylyl (o-methylphenylmethadine) and 1-phenyllethyl (1-phenylethadine) have been synthesized as base adducts with TMEDA (tetramethylethylenediamine) or PMDTA (pentamethyldiethylenetriamine) and studied by X-ray diffraction methods. Their structures are the result of ionic interactions between solvated Na ions and carbanions in combination with steric effects. Always a maximum number of shorter (ca. 260 pm) and longer (up to 300 pm) NaC contacts is achieved, often by formation of cyclic tetramers or polymer chains. The following compounds have been investigated in detail: [benzylsodium(PMDTA)]n (3), [o-xylysodium(TMEDA)]4 (4), [diphenylmethylsodium(TMEDA)]4, (5), diphenylmethylsodium(PMDTA) (monomer) (6) and [1-phenylethylsodium(TMEDA)]4 (7).ZusammenfassungEs wurden verschiedene organonatrium-Verbindungen mit den Carbanionen Benzyl (Phenylmethanid), Diphenylmethyl (Diphenylmethanid), o-Xylyl (o-Methylphenylmethanid) und 1-Phenylethyl (1-Phenylethanid) als Basenaddukte mit TMEDA (Tetramethylethylendiamin) oder PMDTA (Pentamethyldiethylentriamin) synthetisiert und röntgenographisch untersucht. Ihre Strukturen sind das Ergebnis von ionischen Wechselwirkungen zwischen den solvatisierten Na-Ionen und Carbanionen in Kombination mit sterischen Effekten. Stets bildet sich eine maximale Anzahl von kürzeren (ca. 260 pm) und längeren (bis 300 pm) NaC-Kontakten aus, wodurch vielfach cyclische Tetramere oder Polymerketten ten entstehen. Im Einzelnen wurden untersucht: [Benzylnatrium-(PMDTA)]n (3), [o-Xylynatrium-(TMEDA)]4 (4), [Diphenylmethylnatrium(TMEDA)]4 (5), Diphenylmethylnatrium(PMDTA) (monomer) (6) und [1-Phenylethylnatrium(TMEDA)]n (7).
Article
The solid state structure of trimethylsilylmethyllithium has been determined by single crystal X-ray diffraction techniques. The compound crystallizes in the monoclinic system, space group P21/n. Cell dimensions were determined as follows: a 10.931(3), b 18.397(6), c 21.490(8) Å, β 96.0(2)°, V 4298(2) Å3, Z = 4, and a final Rf 5.1% based on 2203 data with σ(I) ≥ 2.5σ(I). The compound is formed by hexameric units, {LiCH2Si(CH3)3}6, with two distinct classes of LiLi distances of 2.46 and 3.18 Å. There are also two LiC distances av 2.20 and 2.27 Å. The LiH distances to the methylene H atoms have been determined and are short varying between 2.0 and 2.3 Å to the closest lithium atom. The structure, including possible LiH interactions, is discussed and compared with the other known hexameric aggregates.
Article
The crystalline, hexane-soluble metal alkyls [Na(µ-R)∞1, [KR(pmedta)]m, and [Rb(µ-R)(pmdeta)]22[R = CH(SiMe3)2, pmdeta =(Me2NCH2CH2)2NMe] have been prepared from LiR with equimolar portions of NaOBut, KOBut+ pmdeta, and Rb(OC6H2But2-2,6-Me-4)+ pmdeta, respectively; 1has chains of alternating cations and planar R– anions which are approximately orthogonal to the chains, (Na–C)av 2.555(10)Å, (Na–C–H)av 76(3) and (Na–C–Na)av 152(1)°, whereas 2 consists of discrete dimers, (Rb–C)av 3.412(9)Å, Rb–C–Rb 75.3(2) and C–Rb–C 104.7(2)°.
Article
An die Kette gelegt: Die Einführung von Methoxygruppen in (Me3Si)4Si und Umsetzung mit einem Alkalimetallalkoxid führt zu bisher unbekannten zwitterionischen Alkalimetallsilaniden [(MeOMe2Si)3SiM] mit Bicyclooctan- (Li, Na) oder Heterocubanstruktur (K). Die Lithium- und Natriumverbindungen bilden im festen Zustand polymere Ketten (siehe z. B. das Li-Derivat; blau Si, rot O, grün Li, grau C) und dissoziieren in THF-Lösungen zu zwitterionischen Monomeren.
Article
Die Erforschung der Reaktivität und Struktur alkalimetallorganischer Verbindungen hat in den letzten Jahrzehnten eine geradezu stürmische Entwicklung durchlaufen. Zu diesen Verbindungen gehören einige für das Verständnis der chemischen Bindung besonders wichtige und auch einfache wie die Methylverbindungen der Alkalimetalle, deren Strukturen nun vollständig aufgeklärt sind. Ganz allgemein erwiesen sich die organischen Verbindungen der Alkalimetalle und auch des Magnesiums als Ionenaggregate, deren Eigenschaften sich durch Solvatisierung, z.B. durch Ether und Amine, stark verändern lassen. Auf diesen Erkenntnissen beruhen auch wichtige Fortschritte bei der Synthese vor allem von Verbindungen der schwereren Alkalimetalle. Lange galten die Alkalimetalle als wenig koordinationsfreundlich, und ihre Komplexchemie bot kaum Überraschungen. Dieses Bild hat sich völlig gewandelt. Kristallstrukturuntersuchungen erbrachten eine Fülle von oft überraschenden Strukturtypen (Ringe, Heterocubane, Ketten, Stapel etc.), nicht nur bei ihren organischen Verbindungen, sondern auch bei ihren Amiden, Imiden, Alkoxiden, Phenoxiden, Enolaten und sogar Halogeniden. Ein Vergleich läßt interessante Gemeinsamkeiten der scheinbar so verschiedenen Verbindungen erkennen und führt zu einer allgemeineren Klassifizierung derartiger Strukturtypen mit C‐, N‐, O‐ und Halogeno‐Liganden.
Article
The reactions of 1,3,5-trimethyl-1,3,5-triazacyclohexane, TMTAC, with methyllithium (MeLi) in the absence or presence of the Lewis acid trimethylaluminum (AlMe3) give different kinds of adducts but do not lead to deprotonation of the heterocycle. With MeLi, an aggregation motif of endless linear chains of MeLi tetramers is obtained, in which the three nonconnected lithium atoms are saturated by binding to only one of the three nitrogen atoms of the tridentate terminal TMTAC ligands; in contrast, in the presence of AlMe3, methyllithium is completely disaggregated to give a [Li(TMTAC)2][AlMe4] salt with six-coordinated lithium atoms.
Article
The reaction of LuCl3(THF)3 with 2 equiv of LiCH2SiMe3 and 1 equiv of KCHPh2 (1) affords Lu(CH2SiMe3)2(CHPh2)(THF)2 (2). X-ray structural analyses show the benzhydryl unit to be planar in 1, but bent in 2.
Article
The syntheses of a number of alkali metal compounds MC(SiMe3)3-n(SiMe2Ph)n, are described (n = 1, M = Li(TMEDA) (3a), Li(Et2O) (3b), or Na(TMEDA) (3c); n = 2, M = Li(THF)2 (6a), Li(TMEDA) (6b), Na(TMEDA) (6c), or K (6d); n = 3, M = Rb (7d) or Cs (7e); THF = tetrahydrofuran, TMEDA= tetramethylethylenediamine). The compounds 3b, 3c, and 6c adopt molecular structures with intramolecular metal−phenyl interactions. The lithium compound LiCH(SiMe2Ph)2, 5, is dimeric with electron-deficient μ-Li bridges and intramolecular metal−phenyl interactions. The compounds MC(SiMe2Ph)3, M = Na (7b), K (7c), Rb (7d), or Cs (7e), form polymeric chains in the solid state with both intra- and intermolecular metal−phenyl interactions. For the lighter alkali metals the interaction is unsymmetrical and mainly with the ipso and ortho carbon atoms, but for the heavier metals there are almost equal metal−carbon distances to all six atoms of the phenyl ring. The long M−C and short Si−C bond lengths and the wide Si−C−Si angles indicate that the structures are highly ionic. The presence of ionic species in solution is revealed by multinuclear NMR data, in particular by the low frequency shifts associated with the central carbon atoms, by the high carbon−silicon coupling constants, and by the low barriers to inversion compared with those in the trisilylmethanes from which the carbanions are derived.
Methylkalium konnte sowohl aus (CH3)2Hg und einer K/Na-Legierung als auch durch doppelte Umsetzung von CH3Li mit Kalium-tert.-butylat hergestellt werden. Die röntgenographische Untersuchung des Kristallpulvers ergab eine hexagonale Struktur vom NiAs-Typ für die K-Ionen und CH3-Gruppen (a = 4.278, c = 8.283 Å, 2 Formeleinheiten, Dichte 1.37 g/cm3).CH3 K ist die erste Methylmetall-Verbindung mit im Gitter isolierten Methyl-Carbanionen. Jede CH3-Gruppe ist trigonal-prismatisch von 6 K-Ionen koordiniert. Die H-Lagen ließen sich aus den experimentellen Daten nur angenähert bestimmen. Nach dem IR-Spektrum besitzt die CH3-Gruppe C3v-Symmetrie.Metal Alkyl Compounds, XI *) Preparation and Crystal Structure of Methyl PotassiumMethyl potassium could be prepared from (CH3)2Hg and a K/Na-alloy as well as by a metathetical reaction between CH3Li and potassium tert-butoxide. From an X-ray investigation of the crystal powder a hexagonal structure (NiAs-type) was derived for the K-ions and CH3-groups (a = 4.278, c = 8.283 Å, 2 formula units, density 1.37 g/cm3). CH3K is the first methyl metal compound with isolated methyl carbanions in the lattice. Each CH3-group is coordinated by 6 K-ions in a trigonal-prismatic array. Approximate H-positions could be derived from the experimental data. The i. r. spectrum shows that the CH3-group has C3v-symmetry.
Article
Lithium and potassium silyloxide complexes [Li(OSiPh3)]n (1), [K(thf)0.2 (OSiPh3)]n (3) and [K(OSiMe2(t)Bu)]n (6) were prepared by deprotonation of HOSiPh3 or HOSiMe2(t)Bu with [Li((n)Bu)] in hexane or KH in THF, respectively. Crystalline DME adducts [Li(mu-OSiPh3)(eta(2)-DME)]2 (2) and [K4(mu(3)OSiPh3)3(mu(3)OSiPh2(eta(1)Ph))(eta(2)DME)]2 (mu-DME) (4) were prepared by dissolving 1 or 3, respectively, in dimethoxyethane followed by precipitation with alkane. The potassium-sequestered complexes [K(18-crown-6) (OSiPh3)]2 (5) and [K(18-crown-6)(OSiMe2(t)Bu)]n (7) were prepared from 3 or 5, respectively, and one equiv. of 18-crown-6 ether. The complexes were characterized by single-crystal X-ray diffraction: [Li(mu-OSiPh3)(eta(2)-DME)]2 (2): a dimer featuring tetrahedral lithium centres linked by bridging-OSiPh3 ligands. [Crystal data (-156-degrees-C): space group P1BAR, a = 14.238(6), b = 15.182(7), c = 11.796(5) angstrom, alpha = 110.57(2), beta = 112.02(2), gamma = 63.02(1) angstrom, V = 2055.33 angstrom 3, Z = 2.] [K4(mu(3)-OSiPh3)3{mu(3)-OSiPh2(eta(1)-Ph)}(eta(2)-DME)]2(mu-DME) (4): (1) two cubanes each having every potassium vertex chemically distinct; (2) one chelating DME ligand, one DME ligand bridging between two cubanes; and (3) a K-ipso-phenyl carbon contact. [Crystal data (- 133-degrees-C): a = 14.246(4), b = 30.939(9), c = 17.981(5) angstrom, beta = 112.33(1)-degrees with Z = 2 in space group P2(1)/c.] [K(18-crown-6)OSiPh3]2 (5): A dimer with slipped face-to-face stacking of the quasi-planar K(18-crown-6)+ part of the two Ph3SiOK(18-crown-6) molecules; these are linked by a dative bond from one ether oxygen of a given crown to potassium contained in the other crown. [Crystal data (- 155-degrees-C): a = 9.324(2), b = 17.640(5), c = 18.148(15) angstrom, beta = 91.60(1)-degrees with Z = 4 in space group P2(1)/c.]
Article
Crystalline [K(μ-R)(thf)]∞ (1) was obtained from equivalent portions of n-butyllithium in hexane, bis(trimethylsilyl)methane (RH) and potassium t-butoxide in thf, removal of volatiles and extraction with hexane. Desolvation of 1 in a vacuum led to KR. The first three-coordinate metallate(II) alkyls [K(MR3)]∞ [M=Ca (2), M=Yb (3)] of calcium and ytterbium(II) were prepared from the appropriate metal(II) iodide and three equivalents of KR in benzene. Mixing LiR, YbI2 and two equivalents of KR in a mixture of diethyl ether and small amount of thf yielded the red (like 3) [Li(thf)4][YbR3] (4). Each of 1–4 was obtained in good yield and was characterised by multinuclear NMR spectra in C6D6 and single crystal X-ray diffraction. The central metal is in a trigonal planar 1 or pyramidal 2–4 environment and the average MC bond lengths are 2.98 (1), 2.50 (2), 2.52 (3 and 4) Å. Crystalline 2 and 3 are isomorphous and consist of double chains of [MR3]− anions linked by K+ cations along the a axis, whereas complex 4 has an ionic structure with isolated [Li(thf)4]+ cation and [YbR3]− anion.
Article
The preparation of organoalkali-metal compounds by reaction of organic halides with alkali metals and with organoalkali-metal compounds was discussed. The attempts by J. A. Wanklyn to prepare sodium alkyls were described, which involved the use of the metal displacement reaction for the first time, but the sodium alkyl, a strong, highly polar nucleophile and base, reacted with the excess of diethylzinc, a Lewis acid, to give an adduct, the zincate complex NaZn(C 2H 5) 3. George Bowdler Buckton, an organometallic chemist, reported his preparations of ethyl derivatives of mercury, tin, and lead by the action of diethylzinc on halides of these metals. Later on, Schorigin extended the side-chain metalation reaction to the preparation of m-tolylacetic acid from m-xylene, of o-tolylacetic acid from o-xylene, of p-tolylacetic acid from p-methyltoluene. Wilhelm Schlenk's pioneering work in organoalkali-metal chemistry opened the door to studies of trivalent carbon, and led to the formation of products formed by the action of alkali metals on dirayl ketones.
Article
Various syntheses were carried out for the conversion of organic halides to organoalkali-metal compounds. James Alfred Wanklyn's synthesis of alkylsodium and potassium complexes was carried out in 1858. In 1931, a breakthrough was made when it was found that phenylsodium could be prepared by reaction of sodium wire with chlorobenzene in benzene or benzene/ligroin solution in the absence of atmospheric moisture at temperatures of 15-03°C. In 1950, it was found that the alkyllithiums, except for methyllithium, are soluble in alkanes and benzene and aryllithiums in diethyl ether. It is also observed that 1H, 13C, and 6Li NMR spectroscopy would help to determine the structures of organolithium compounds in solution.
Article
The crystalline hexane-soluble metal alkyls [Na(μ-R)]∞ (1), [K(μ-R){O(Me)But}]∞ (2), [(pmdeta)K(μ-R)K(μ-R)2K(μ-R)(pmdeta)] (3), [Rb(μ-R)(pmdeta)]2 (4), [Cs(μ-R){O(Me)But}2]∞ (5), and Cs(μ-R)(tmeda)]∞ (6) (R = CH(SiMe3)2, pmdeta = (Me2NCH2CH2)2NMe, tmeda = Me2NCH2CH2NMe2) have been prepared from LiR with an equimolar portion of NaOBut, KOBut, RbOC6H2But2-2,6-Me-4, or CsOCH2CH(Et)Bun and for 2−6 the appropriate neutral ligand. X-ray crystal structures of the metal alkyls 2, 3, and 6 are presented; 1 and 4 were described in an earlier communication. Treatment of 5 with ButCN afforded the cesium 1-azaallyl Cs{N(R)C(But)C(H)R} (7).
Article
Crystals of (RMe2Si)3CK (R = Me, 1; R = Ph, 2), obtained from MeK and (RMe2Si)3CH, contain linear chains of alternate potassium cations and planar [(RMe2Si)3C]- anions, with weak interactions between chains; in 1 the central carbon atoms of the anions are midway between the potassium cations, but in 2 cation-anion pairs are linked by eta6 coordination of phenyl groups.
Article
The reduction of the ketone to a secondary alcohol that accompanies addition in reactions of ketones and dialkylmagnesium compounds can be lessened by first adding an appropriate salt to the dialkylmagnesium compound. With favorable salts and reactant stoichiometries, reduction is eliminated in reactions of dipropylmagnesium with diisopropyl ketone or di-tert-butyl ketone. In reactions of di-tert-butylmagnesium and di-tert-butyl ketone, reduction always predominates, although some addition does occur. Salts observed to have significant effects are potassium methoxide, (Me 2 NCH 2 ) 2 CHOK, sodium methoxide, lithium methoxide, lithium tert-butoxide, tetrabutylammonium bromide, and benzyltriethylammonium chloride
Article
It has been found that solutions of cis-α-stilbenyllihium (cis-I) and of cis- and trans-2-p-chlorophenyl-1,2-diphenylvinyllithium (cis- and trans-V) in hydrocarbon solvents have very much greater stereochemical stability than in diethyl ether. Tetrahydrofuran is still much more effective than ether in promoting the isomerization of cis- to trans-1. It has been found further that optically active sec-butyllithium in the absence of ether can be prepared and carbonated with at least 83% retention of configuration. Again the isomerization (racemization in this case) is greatly accelerated even by small amounts of added diethyl ether. It has been found that t-butyllithium can be conveniently prepared from lithium metal containing only 0.2% sodium if the surface is coated with copper powder before reaction.
Article
Reaction of(C6H5)(3)PbCl with 1 equiv of (THF)(2.5)LiGe(SiMe(3))(3) in ether afforded (C6H5)(3)PbGe(SiMe(3))(3) in 25% yield. An attempt to prepare (C6H5)(2)Pb(Ge(SiMe(3))(3))(2) by the reaction of 2 equiv of (THF)(2.5)LiGe(SiMe(3))(3) with Ph(2)PbCl(2) gave a mixture of the expected product as a yellow solid and a red-orange solid identified as the diplumbane, [(C6H5)(2)Pb (Ge(SiMe(3))(3)](2). The mono- and diplumbanes were separated by fractional crystallization from pentane and characterized by their elemental analyses, NMR spectra (H-1 and C-13) and infrared and UV-visible spectra. An X-ray structure determination on [(C6H5)(2)Pb(Ge(SiMe(3))(3)](2) was not completed due to decomposition of the crystal but showed it to be isomorphous with [(C6H5)(2)Pb(Si(SiMe(3))(3)](2), which is known to have a Pb-Pb bond. A low temperature X-ray structure determination on (C6H5)(2)Pb(Ge(SiMe(3))(3))(2) revealed it to be orthorhombic, Pnn2, with a = 13.999(5) Angstrom, b = 17.443(5) Angstrom, c = 10.404(2), V = 2541 Angstrom(3), and Z = 2. The molecular structure exhibited marked distortion of the coordination geometry around Pb with angle Ge-Pb-Ge = 135.0(1)degrees and angle C-Pb-C = 99.8(7)degrees. NMR studies of the two products found that the monoplumbane was stable for 20 h in ether but that the diplumbane experienced marked decomposition, during the same period.
Article
The alkalimetal phosphoraneiminates [KNPCy3]4, (1) [KNPCy3]4·2OPCy3 (2) and [CsNPCy3]4·4OPCy3 (3) (Cy = cyclohexyl) which are obtainable by the reaction of pottassium amide or cesium amide with Cy3PI2 or Cy3PBr2 in liquid ammonia, as well as the lithium derivative [Li4(NPPh3)(OSiMe2NPPh3)3(DME)] (4) have been characterized by crystal structure determinations. 4 has been formed by the insertion reaction of silicon greaze (-OSiMe2)n into the LiN bonds of [LiNPPh3]6 in DME solution (DME = 1, 2-dimethoxyethane). 1: Space group P&1macr;, Z = 2, lattice dimensions at 193 K: a = 1389.8(1); b = 1408.1(1); c = 2205.2(2) pm; α = 78.952(10)?; β = 81.215(10)?; γ = 66.232(8)?; R1 = 0.0418. 2: Space group Pbcn, Z = 4, lattice constants at 193 K: a = 2943.6(2); b = 2048.2(1); c = 1893.8(1) pm; R1 = 0.0428. 3: Space group Cmc21, Z = 4, lattice dimensions at 193 K: a = 2881.6(2); b = 2990.2(2); c = 1883.7(2) pm; R1 = 0.0586. 4·1/2DME: Space group R&3macr;c, Z = 12, lattice dimensions at 193 K: a = b = 1583.5(1); c = 11755.3(5) pm; R1 = 0.0495. All complexes have heterocubane structures. In 1-3 they are formed by four alkali metal atoms and by the nitrogen atoms of the (μ3-NPCy3-) groups, whereas 4 forms a "heteroleptic" Li4NO3 heterocubane.
Article
Polyamine donor bases such as N,N,N′,N′-tetramethylethylenediamine (TMEDA), (–)-sparteine and N,N,N′,N″,N″-pentamethyldiethylentriamine (PMDETA) have been employed to deaggregate parent trimethylsilylmethyllithium (1). The crystal structures of the dimers [(TMEDA)·LiCH2SiMe3]2 (2) and [{(–)-sparteine}·LiCH2SiMe3]2 (3) were determined and reveal a four-membered ring as the central structural motif. The two lithium atoms are each coordinated by the chelating ligands and the carbanions. The Li–C contacts show alternating bond lengths. The monomer [(PMDETA)·LiCH2SiMe3] (4) has the shortest Li–C contact of the aggregates discussed, and the Me3Si group points toward the central nitrogen atom of the PMDETA ligand, even if this alignment seems unfavourable for steric reasons. The bond lengths and angles of compounds 2–4 are discussed in relation to the orientation of the lone pair at the carbanion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Article
Reaction of the chiral amine (S)-N-(α-methylbenzyl)allylamine with n-BuLi in hexane and the subsequent addition of the thus formed lithium amide to n-BuK followed by thf results in the formation and crystallisation of the cyclic heterobimetallic tetramer, {[(S)-α-(PhC(H)Me)(CH2CHCHK)N]Li · (thf)}4 (1), containing the C-metallated and N-metallated dianion of the chiral amine. The structure reveals a degree of asymmetry derived from competitive binding of K+ cations to available thf molecules, π(arene) electrons, and deprotonated allylamine moieties. Solution studies indicate very strong agostic interactions with C–H bonds in the allylamine group and retention of the terminal vinylic anion rather than delocalisation.
Article
1H,23Na, and7Li NMR spectra of 2-ethyl hexylsodiurn, 2-ethylhexyllithium, and isobutyllithium obtained in the reaction of the corresponding alkyl chlorides and metals have been recorded. The1H N MR signal for the protons of the CH2Na group is shifted upheld compared with that for the protons of the CH2Li group (doublets at -0.88 and -0.83, respectively). The composition of the products of reaction of 2-ethylhexyl chloride with sodium depends on the form of the metal reagent employed. The use of sodium balls with diameter up to 2 mm results in the formation of products containing ionic chlorine (30–50 % with respect to Na); the reaction with the dispersion proceeds faster and the reaction product is chlorine-free. The23Na NMR spectra of these substances are also different, which is explained by the formation of 2-ethylhexylsodium complexes with NaCl in the former case.
Article
Exploring the reactivity of mixed-metal synergic bases, it is found that the lithium TMP aluminate iBu3Al(TMP)Li functions as a dual TMP/alkyl base, exhibiting 2-foldAMMAl (alkali-metal-mediated alumination) toward TMEDA to yield the heterobimetallic bis-(deprotonated TMEDA) derivative [Li{Me2NCH2CH2N(Me)CH2}2Al(iBu)2] (2). In contrast, the amide enriched aluminate iBu2Al- (TMP)2Li acts as only a single-fold amido base toward TMEDA or PMDETA to afford the aminedeprotonated derivatives [Li{Me2NCH2CH2N(Me)CH2}(TMP)Al(iBu)2] (4) and [Li{Me2NCH2- CH2N(Me)CH2CH2N(Me)CH2}(TMP)Al(iBu)2] (5), respectively. On their own, the aluminum compounds iBu3Al or iBu2Al(TMP) are not sufficiently strong bases tometalateTMEDAorPMDETA, so in 2, 4, and 5, the R-deprotonations of TMEDA and PMDETA are synergic in origin, as the intramolecular communication between Li and Al appears to activate the TMP and iBu bases. This special behavior can be attributed to intramolecular proximity effects between the active base component (TMP or iBu) and the ligating TMEDA or PMDETA molecule. X-ray crystallography studies reveal 2 is a contacted ion-pair ate containing twoR-aluminatedTMEDAligands,which chelate the lithium cation which is linked to the distorted tetrahedral Al center by two N bridges from the metalated junction of theTMEDAmolecules. In contrast, 4 and 5 have amixed NCH2-TMPbridging ligand set, completed by two terminal iBu ligands on Al and a chelating metalated TMEDA or PMDETA ligand attached to Li, respectively. In addition, the 1H, 7Li, and 13C{1H} spectra of 2 (recorded in C6D6 solutions), 4, and 5 (recorded in cyclohexane solutions-d12) are disclosed.
Article
Two heavy alkali-metal salts of the sterically demanding amine, 2,2,6,6-tetramethylpiperidine (TMPH), have been prepared using different methodologies. Complex 1, [((tmeda)Na(tmp))2] (TMEDA=N,N, N',N'-tetramethylethylenediamine), can be synthesized by a deprotonative route. This is achieved by reacting butylsodium with TMPH in the presence of excess TMEDA in hexane. The potassium congener [((tmeda)K(tmp))2] (2), can be prepared by treating KTMP (made using a metathesis reaction between LiTMP and potassium tert-butoxide) with an excess of TMEDA in hexane. In the solid state, 1 and 2 are essentially isostructural. They are discretely dimeric and their framework consists of a four-membered M-N-M-N ring (M=Na or K, N=TMP). Due to the high steric demand of the TMP ligand, the TMEDA molecules bind to the metal centers in an asymmetric manner. In 2, each of the coordination spheres of the metals is completed by an agostic K...CH3(TMP) interaction. DFT calculations at the B3 LYP/6-311G** level give an insight into why 1 and 2 adopt dramatically different structures from their previously reported, "open-dimeric", lithium counterpart. The theoretical work also focuses on the TMEDA-free parent amide complexes and reveals that the energy difference for the formation of [(M(tmp))x] (in which, M=Li or Na, x=3 or 4; and M=K, x=2, 3 or 4) are small.
Article
The study of co-complexation reactions between NaCH(2)SiMe(3) and Mg(CH(2)SiMe(3))(2) has allowed the isolation and structural elucidation of the first solvent-free alkali-metal alkylmagnesiate [{NaMg(CH(2)SiMe(3))(3)}(∞)] (1) as well as the related solvent-free sodium alkyl [{(NaCH(2)SiMe(3))(4)}(∞)] (3).
Article
The first benzylcalcium complex, (α,α-bis(trimethylsilyl)benzyl)2calcium·(THF)2, has been prepared by reacting CaI2 with α,α-bis(trimethylsilyl)benzylpotassium in THF. The solid state structure of the K precursor shows an interesting Lewis base-free coordination polymer in which the coordination sphere of K is additionally saturated by agostic Si-Me···K interactions. The crystal structure of the Ca product displays a THF-solvated monomeric compound, which shows considerably less delocalization of negative charge into the phenyl ring than the corresponding K compound. NMR investigations as well as ab initio calculations show that the TMS substituents at the benzylic carbon have a charge-localizing influence. Only the more ionic K precursor shows activity in initiating the polymerization of styrene.
Article
The donor-free trimethylsilylmethyllithium [LiCH(2)SiMe(3)](6) hexameric aggregate is for the first time broken up by simple ether donors such as diethyl ether (Et(2)O) and tert-butylmethyl ether ((t)BuOMe) to give the unprecedented asymmetric tetramers while the chelating dimethoxyethane (DME) gives the expected dimer.
Article
Keywords: Synthesis (a manual on organometallics in synthesis); Organometallic compounds Role: RCT (Reactant) ; RACT (Reactant or reagent) (a manual on organometallics in synthesis) ; book organometallic compd synthesis Note: CAN 122:56197 29-1 Organometallic and Organometalloidal Compounds UK. Book written in English. Reference LSCO-BOOK-1994-001 Record created on 2006-03-03, modified on 2016-08-08
Article
At temps. between -100 and -40 Deg, lithium salt-free butylpotassium (prepd. from dibutylmercury) readily metalates satd. ethers such as Me2O or THF. [on SciFinder (R)]