Lithium Metal In Tetrahydrofuran Research Articles

Reaktionen von Bis(trimethylsilyl)aminochlorsilanen mit Lithium – N, Si‐Trimethylsilylgruppenwanderung oder Selbstkondensation von Bis(trimethylsilyl)aminosilyllithiumverbindungen

AbstractThe chlorosilanes [(Me3Si)2N]HMeSiCl (1), [(Me3Si)2N]2MeSiCl (2) and [(Me3Si)2N]RPhSiCl (3: R = Me, 4: R = Ph, 5: R = (Me3Si)2N, 6: R = H) were allowed to react with lithium metal in tetrahydrofuran (THF) or in a mixture of THF/Et2O/n‐pentane in the volume ratio 4:1:1 (Trapp mixture). 1 and 2 did not react with lithium in THF at room temperature. A mixture of 1 and Me3SiCl in molar ratio 1:1 reacted with lithium to give [(Me3Si)2N]HMeSi–SiMeH[N(SiMe3)2] (7) and [(Me3Si)2N]HMeSi–SiMe3 (8). The analogous reaction of 2, Me3SiCl and lithium afforded [(Me3Si)2N]2MeSi–SiMe3 (10) only. [(Me3Si)2N]MePhSiLi (11) and [(Me3Si)2N]Ph2SiLi (16) prepared by reaction of 3 and 4 with lithium in THF underwent a partial rearrangement to form the lithium amides [(Li)(Me3Si)N]MePhSi–SiMe3 (12) and [(Li)(Me3Si)N]Ph2Si–SiMe3 (17), respectively, when the temperature raised from –78 °C to room temperature. In the reaction of 5 with lithium in THF at –78 °C, the amide [(Li)(Me3Si)N][(Me3Si)2N]PhSi–SiMe3 (21) was formed. [(Me3Si)2N]2PhSiLi (20) was obtained by reaction of 5 with lithium in the Trapp mixture at –110 °C. The silyllithiums 11, 16, 20 and the lithium amides 12, 17, 21 were trapped with HMe2SiCl resulting in the following products: [(Me3Si)2N]MePhSi–SiMe2H (13), [(Me3Si)2N]Ph2Si–SiMe2H (18), [(Me3Si)2N]2PhSi–SiMe2H (24), [(HMe2Si)(Me3Si)N]MePhSi–SiMe3 (14), [(HMe2Si)(Me3Si)N]Ph2Si–SiMe3 (19), and [(HMe2Si)(Me3Si)N][(Me3Si)2N]PhSi–SiMe3 (22). The silyllithiums 11, 16, and 20 were formed directly by reaction of the corresponding aminochlorosilanes with lithium at –78 °C (11 and 16) and at –110 °C (20), respectively. In the reaction of the aminochlorosilane 6 with lithium in THF at –78 °C a mixture of [(Me3Si)2N]HPhSiLi (25) and [(Me3Si)2N]HPhSi–SiHPhLi (26) was obtained. Compounds 25 and 26 were trapped with HMe2SiCl to give [(Me3Si)2N]HPhSi–SiMe2H (27) and [(Me3Si)2N]HPhSi–SiHPh–SiMe2H (28). The molecular structures of 19, 22 and 24 were determined.

Mediated electron transfer from lithium investigated voltammetrically in tetrahydrofuran: why are some mediators more effective reducing reagents than others?

AbstractA study of a range of aromatic molecules is investigated electrochemically to determine what makes an effective reducing mediator. With the aim of developing a better understanding of electron transfers (ETs) mediated from lithium in functional group reduction, a series of single ET reactions are reported in this paper. Typical reaction conditions involved the use of aromatic mediators such as naphthalene, anthracene, 4,4′‐di‐tert‐butyl‐1,1′‐biphenyl (DBB) with lithium metal in tetrahydrofuran (THF) at −78 °C. The results of these experiments showed that some mediators were more effective reducing reagents than others. Cryoelectrochemical procedures are used to mimic the conditions of the SET reactions in order to investigate the exact nature and role of the mediator formed upon ET. It is demonstrated that electro‐generated and stabilized radical anions of anthracene at −78 °C mediate the reduction of organic substrates, whereas the more reactive dianion is quickly protonated and therefore unable to act as an ET reagent; direct electrochemical reduction of the sulfide, phenyl 3‐phenylpropylsulfide (RSPh) gives the thiol, thiophenol, and propyl benzene whereas mediated reduction gives the dimer, diphenyl disulfide and propyl benzene. The possibility to selectively reduce a substrate with either a single electron or with two electrons is possible by using either the radical anion (mediated) or via the direct electroreduction. DBB and naphthalene (both single electron accepting species only) have been found to be the most effective reducing reagents in this study. Anthracene and other two‐electron accepting species only showed effective reducing ability when a stoichiometric amount of lithium was used therefore preventing the ‘over‐reduction’ to the dianion. Copyright © 2007 John Wiley & Sons, Ltd.

Aromaticity of the Cyclobutadiene Dianion: Structural Characteristics and Magnetic Properties

The dilithium salts of cyclobutadiene dianions (CBD2-), 1,2-diphenyl-3,4-bis(trimethylsilyl)cyclobutadiene dianion dilithium (3), and 1,3-diphenyl-2,4-bis(trimethylsilyl)cyclobutadiene dianion dilithium (4) have been synthesized by the reaction of the corresponding cyclobutadiene cobalt complexes with lithium metal in tetrahydrofuran (THF). The dilithium salts were isolated as air- and moisture-sensitive crystals, and their molecular structures, containing two molecules of 1,2-dimethoxyethane (DME), were determined by X-ray crystallography. Each of the CBD2- has a monomeric structure and forms contact ion pairs (CIPs) in the crystal. The two Li+ ions are located above and below the plane of the four-membered ring and are bonded to the four quaternary carbon atoms. The cyclobutadienediide ring of the cis-diphenyl CBD2- (3) shows a conspicuous trapezoid structure, whereas that of the trans-diphenyl CBD2- (4) shows a slightly rhomboid structure. The 7Li NMR spectra of the CBD2- indicate that the two lithium ...

Isolation and characterization of the monomeric and dimeric structures of tetrakis(trimethylsilyl)butatriene dianion dilithium

Tetrakis(trimethylsilyl)butatriene reacted with lithium metal in tetrahydrofuran to yield yellow crystals of the monomeric and dimeric molecules of the butatriene dianion dilithium with a lithium doubly bridged bisallylic structure.

Synthesis and Reduction of Silyl-Substituted [5]Radialene. Characterization and Structure of a [5]Radialene Tetraanion with a Ten-Center, Fourteen-Electron π-System

Abstract The reaction of 3,3,6,6,8,8,11,11,14,14,16,16,19,19,21,21-hexadecamethyl-3,6,8,11,14,16,19,21-octasilacyclohenicosa-1,4,9,12,17-pentayne with an excess molar amount of [Mn(CO)3(Me-Cp)] in tetrahydrofuran (THF) under photochemical and refluxing conditions produced 2,2,4,4,9,9,11,11,13,13,15,15,17,17,21,21-hexadecamehyl-2,4,9,11,13,15,17,21-octasilahexacyclo[10.5.3.15,8.06,18.07,20.014,19]henicosa-1(18),5,7,12(20),14(19)-pentaene (2) as silyl-substituted [5]radialene derivative. This was reacted with lithium metal in THF to give dark red crystals of the tetralithium salt (4) of 2. The molecular structure of tetraanion of 2 with a novel ten-center, fourteen-electron π-system was established by X-ray crystallography. The tetralithium salt 4 has a monomeric structure and forms contact ion pairs (tetrakis-CIPs) in the crystals. The structural parameters of 4 are discussed in comparison with those of the neutral starting molecule 2. The structure of 4 in solution is also discussed on the basis of NMR spectroscopic data.

Synthesis and Molecular Structure of a Dilithium Salt of the cis-Diphenylcyclobutadiene Dianion

Abstract The cis-diphenyl-substituted cyclobutadiene cobalt complex (1), prepared from the reaction of 1,8-diphenyl-3,6-disila-1,7-octadiyne with CpCo(CO)2, reacted with lithium metal in tetrahydrofuran (THF) to yield pale orange crystals of the dilithium salt of the cis-diphenylcyclobutadiene dianion (2). The structure was determined by spectroscopic methods and X-ray crystallography to reveal the aromatic character of the doubly-charged four-membered ring system.

Reaktionen von Trimethylsiloxychlorsilanen (Me3SiO)Me2−nPhnSiCl (n=0,1,2) mit Lithium—Bildung von Trimethylsiloxy-substituierten Silyl- und Disilanyllithiumver- bindungen sowie Di- und Trisilanen

Abstract The trimethylsiloxychlorosilanes (Me 3 SiO)Me 2− n Ph n SiCl ( 1 : n = 0; 2 : n = 1; 3 : n = 2) were allowed to react with lithium metal in tetrahydrofuran (THF) and in a mixture of THF–diethylether– n -pentane in volume ratio 4:1:1 (Trapp mixture). The reaction of 1 with lithium metal in THF under refluxing leads to the homo-coupling product [(Me 3 SiO)Me 2 Si] 2 ( 4 ). A mixture of 1 and Me 3 SiCl in molar ratio 1:2 reacts with lithium metal in THF to give 4 and the cross-coupling product (Me 3 SiO)Me 2 SiSiMe 3 ( 7 ). The silyllithium derivatives Me 3 SiO(SiMePh) n Li ( 8 : n = 1; 9 : n = 2; 10 : n = 3) and Me 3 SiSiMePhLi ( 11 ) are formed in the reaction of 2 with lithium metal in THF at −78°C and in the Trapp mixture at −110°C. Main product in both cases is 9 . 8 – 11 are trapped by Me 3 SiCl and HMe 2 SiCl. The trapping products (Me 3 SiO)SiMePhSiMe 3 ( 13a ), Me 3 SiO(SiMePh) 2 SiMe 2 R ( 14a , 14b ; a : R=Me, b : R=H), Me 3 SiO(SiMePh) 3 SiMe 2 R ( 15a , 15b ) and Me 3 SiSiMePhSiMe 2 R ( 16a , 16b ) are obtained. The reaction of 3 with lithium metal like 2 produces the silyllithium derivatives Me 3 SiO(SiPh 2 ) n Li ( 18 : n = 1, 19 : n = 2) and Me 3 SiSiPh 2 Li ( 20 ), wich are trapped by Me 3 SiCl and HMe 2 SiCl to give the corresponding disilanes (Me 3 SiO)SiPh 2 SiMe 2 R ( 23a , 23b ) and trisilanes Me 3 SiO(SiPh 2 ) 2 SiMe 2 R ( 24a , 24b ) as well as Me 3 SiSiPh 2 SiMe 2 R ( 25a , 25b ). In addition to 18 , 19 and 20 LiSiPh 2 SiPh 2 Li ( 21 ) is formed in a small amount in the reaction of 3 with lithium metal at −78°C to afford tetrasilanes [RMe 2 SiPh 2 Si] 2 ( 26a , 26b ) after trapping by Me 3 SiCl and HMe 2 SiCl. The disilane (Me 3 SiO)SiMeR′SiMe 3 ( 17 ) (R′=3,4,5,6-tetrakis(trimethylsilyl)cyclohex-1-enyl) is produced by reaction of a mixture of 2 and Me 3 SiCl in molar ratio 1:6 with 6 equivalents of lithium at −78°C in THF. The reaction of a mixture of 3 and Me 3 SiCl in the molar ratio 1:10 with 11 equivalents of lithium under the same conditions gives (Me 3 SiO)SiR′ 2 SiMe 3 ( 27 ).

Reaktionen von Bis(trimethylsilyl)amino-substituierten Chlorsilanen [(Me 3Si) 2N]Me 2− nPh nSiCl ( n=0, 1, 2) mit Lithium—Darstellung von Bis(trimethylsilyl)amino-substituierten Silyllithiumverbindungen und Disilanen

The bis(trimethylsilyl)amino-substituted chlorosilanes [(Me 3Si) 2N]Me 2− n Ph n SiCl ( 1: n=0, 2: n=1, 3: n=2) were allowed to react with lithium metal in tetrahydrofuran. 1 slowly reacts at room temperature to the homocoupling product {[(Me 3Si) 2N]Me 2Si} 2 ( 4). An equimolar mixture of 1 and Me 3SiCl gives 4 and the cross-coupling product [(Me 3Si) 2N]Me 2Si–SiMe 3 ( 5). The reaction of 2 at −78°C leads to formation of bis(trimethylsilyl)aminosilyllithium [(Me 3Si) 2N]MePhSiLi ( 6), which reacts with Me 3SiCl and 2 resp. to the corresponding disilanes [(Me 3Si) 2N]MePhSi–SiMe 3 ( 7) and {[(Me 3Si) 2N]MePhSi} 2 ( 8). 6 undergoes partially self-condensation at −40 and 0°C and the disilanyllithium [(Me 3Si) 2N]MePhSi–SiMePhLi ( 9) is formed. 3 reacts rapidly at 0 and −20°C to give the silyllithium [(Me 3Si) 2N]Ph 2SiLi ( 12). Treatment of 12 with Me 3SiCl and 3 resp. affords the disilanes [(Me 3Si) 2N]Ph 2Si–SiMe 3 ( 13) and {[(Me 3Si) 2N]Ph 2Si} 2 ( 14). The disilane R[(Me 3Si) 2NMeSi–SiMe 3 ( 11) (R=3,4,5,6-tetrakis(trimethylsilyl)cyclohex-1-enyl) is obtained by reaction of a mixture of 2 and Me 3SiCl in molar ratio 1:5 with 6 equivalents of lithium in THF. The crystal structure of 11 is reported. Zusammenfassung Die bis(trimethylsilyl)amino-substituierten Chlorsilane [(Me 3Si) 2N]Me 2− n Ph n SiCl ( 1: n=0, 2: n=1, 3: n=2) wurden mit Lithium in Tetrahydrofuran umgesetzt. 1 reagiert langsam bei Raumtemperatur zum Homokupplungsprodukt {[(Me 3Si) 2N]Me 2Si} 2 ( 4). Ein äquimolares Gemisch von 1 und Me 3SiCl ergibt neben 4 auch das Kreuzkupplungs-produkt [(Me 3Si) 2N]Me 2Si–SiMe 3 ( 5). Die Reaktion von 2 bei −78°C führt zum Bis(trimethylsilyl)aminosilyllithium [(Me 3Si) 2N]MePhSiLi ( 6), bei dessen Umsetzung mit Me 3SiCl bzw. 2 die entsprechenden Disilane [(Me 3Si) 2N]MePhSi–SiMe 3 ( 7) und {[(Me 3Si) 2N]MePhSi} 2 ( 8) entstehen. Bei −40 und 0°C unterliegt 6 partiell einer Eigenkondensation, und das Disilanyllithium [(Me 3Si) 2N]MePhSi–SiMePhLi ( 9) wird gebildet. 3 reagiert bei 0 und −20°C schnell zum Silyllithium [(Me 3Si) 2N]Ph 2SiLi ( 12). Die Reaktion von 12 mit Me 3SiCl bzw. 3 ergibt die entsprechenden Disilane [(Me 3Si) 2N]Ph 2Si–SiMe 3 ( 13) und {[(Me 3Si) 2N]Ph 2Si} 2 ( 14). Bei der Reaktion eines Gemisches von 2 und Me 3SiCl im Molverhältnis 1:5 mit 6 Äquivalen-ten Lithium in THF entsteht das Disilan-R[(Me 3Si) 2NMeSi–SiMe 3 ( 11) (R=3,4,5,6-Tetrakis(trimethylsilyl)cyclohex-1-enyl). Die Kristallstruktur von 11 ist beschrieben.

Synthetic and Mechanistic Investigations of Trimethylsilyl-Substituted Triamidoamine Complexes of Tantalum That Contain Metal−Ligand Multiple Bonds

[N3N]TaPPh ([N3N]3- = [(Me3SiNCH2CH2)3N]3-) reacts with excess lithium metal in tetrahydrofuran to give “[N3N]TaPLi”, as judged by NMR studies and by reactions with RX at −35 °C to afford the phosphinidene complexes [N3N]TaPR (R = Me, n-Bu, SiMe3, SiMe2Ph). [N3N]TaCl2 reacts with 2 equiv of LiN(H)R (R = H, CMe3, Ph) to produce 1 equiv of RNH2 and imido complexes [N3N]TaNR and with 2 equiv of benzylmagnesium chloride or ((trimethylsilyl)methyl)lithium to afford the alkylidene complexes [N3N]TaCHR (R = Ph or SiMe3). The ethylene complex [N3N]Ta(C2H4) is formed quantitatively upon addition of 2 equiv of ethylmagnesium chloride to [N3N]TaCl2. [N3N]Ta(C2H4) decomposes in a first-order manner in solution over a period of days at room temperature to give a complex in which a C−N bond in the TREN backbone has been cleaved. Alkylation of [N3N]TaCl2 with 2 equiv of RCH2CH2MgX (R = CH3, CH2CH3, CH(CH3)2, C(CH3)3; X = Cl or Br) produces a mixture of alkylidene and products derived from decomposition of the incipient ...

Synthesis, resolution and reactions of (±)-1-(dimethylarsino)-2-(methylphenylphosphino)benzene. Crystal and molecular structure of [(S), (S)]-(+)589-{2-[1-(dimethylamino)ethyl]phenyl-C1,N}[1-(dimethylarsino)-2-(methylphenylphosphino)benzene-As,P]palladium(II) hexafluorophosphate

Asymmetric bidentate (±)-1-(dimethylarsino)-2-(methylphenylphosphino)benzene has been prepared by the reaction of sodium dimethylarsenide with (±)-1-chloro-2-(methylphenylphosphino)benzene in tetrahydrofuran. Its resolution has been achieved by the separation by fractional crystallisation of a pair of internally diastereomeric palladium(II) complexes containing the racemic ligand and orthometallated (S)-dimethyl(1-phenylethyl)amine. The optically pure antipodes have α±32°(589 nm, dichloromethane). The absolute configuration of the R enantiomer of the ligand has been assigned by a crystal-structure determination of the least-soluble diastereomeric complex [(S),(S)]-(+)589-{2-[1-(dimethylamino)ethyl]phenyl-C1, N}[1-(dimethylarsino)-2-(methylphenylphosphino)benzene-As,P]palladium(II) hexafluorophosphate. Chemoselective cleavage of the dimethylarsino moiety of the free benzene derivative occurs in the presence of lithium metal in tetrahydrofuran.

Synthesis of 2-cumyladamantan-2-ol by the catalytic use of 4,4′-di-t-butylbiphenyl as an electron-transfer agent with lithium in a Barbier-type reaction of adamantanone and cumyl chloride

A Barbier-type condensation between adamantanone and cumyl chloride to produce the strained product 2-cumyladamantan-2-ol (1) has been effected using lithium metal in tetrahydrofuran (THF) with a catalytic amount of 4,4′-di-t-butylbiphenyl as an electron-transfer regent; (1) is characterised by X-ray analysis.

Application of microelectrodes to the study of the Li|Li+ couple in ether solvents. Part 2.—Temperature dependence

Cyclic voltammetry and potential step experiments at microelectrodes have been used to probe the influence of temperature (over the range 253–333 K) on the deposition and dissolution of lithium metal in tetrahydrofuran containing lithium hexafluoroarsonate. The temperature strongly influences both the kinetics of nucleation of the lithium phase on other conducting materials (Ni, Cu, C) and of the Li|Li+ couple after the new phase is formed. The exchange current density for the Li|Li+ couple at 293 K is found to be 4 mA cm–2 for a solution containing 0.84 mol dm–3 Li+, a much higher value than previously reported in the literature, suggesting that these earlier data were adversely affected by experimental problems, surface films and/or IR drop. The energy of activation for the couple was determined to be 56 kJ mol–1. The temperature dependence of the LiAl|Li+ couple is also discussed.

The synthesis of diene and vinyl copolymers containing predetermined quantities of polynuclear hydrocarbon or heterocyclic adducts—VII: Copolymers formed from butadiene, a heterocyclic compound and some linking or terminating agents

The reaction of butadiene (M) and a suitable heterocyclic molecule (A) (acridine, quinoline or puridine) with lithium metal in tetrahydrofuran (THF) produced polymeric adducts of structure − A— M n — A − where the negative charges are located on the nitrogen atoms. Similar products (mono or difunctional) may be produced by reacting living polybutadiene directly with these heterocyclic molecules. In the case of acridine, proton termination produced oligomers terminated with dihydroacridine groups; polymeric species containing amide linkages can be produced by titration with adipoyl chloride and, although this reaction is in itself efficient, the product easily re-aromatizes. With quinoline and pyridine, the dihydroadducts become progressively less stable, showing strong tendencies to re-aromatise and crosslink. It is shown that the anionic pyridine adduct of polybutadiene may be cleanly re-aromatised to produce pyridine-terminated polymers which are stable. These pyridine groups can be reacted with benzyl halides to produce pyridinium salts; the presence of these ionic groups has a profound effect on the physical properties of the product. Reaction with p-xylylene dibromide converts low molecular weight difunctional pyridine-terminated polybutadiene from a mobile liquid to a rubbery solid; the material remains soluble and so is free from chemical crosslinks.

Preparation of vinyllithium

A thorough investigation of the effect of reaction conditions on the direct formation of vinyllithium from vinyl chloride and lithium metal in tetrahydrofuran is reported. Under optimum conditions yields of 69 to 79% were dependably obtained.

Cleavage of 12-alkylbenzo[a]phenothiazines with lithium in tetrahydrofuran: a dealkylation–desulphurization reaction

A study of the cleavage of 12-methyl- and 12-ethyl-benzo[a]phenothiazine with lithium in tetrahydrofuran is reported. A novel dealkylation–desulphurization reaction was observed in the case of the 12-methyl derivative to yield benzo[a]carbazole, whereas the 12-ethyl derivative gave a complex mixture from which no identifiable material was isolated. However, t.l.c. indicated that the ethyl derivative had undergone dealkylation–desulphurization to a limited extent. The particle size of the lithium used appears to be critical in the cleavage. No cleavage was observed when lithium aluminium hydride or lithium aluminium hydride and lithium metal in tetrahydrofuran was employed.

Bora-aromatic systems I. Competition between haloboration and phenylboration in the attempted synthesis of triphenylboracyclopropene

A possible tactical approach to the synthesis of triphenylboracyclopropene (triphenylborirene) is described as involving: ( a) the addition of phenylboron dibromide to the triple bond of diphenylacetylene; and ( b) the interaction of the resulting ( cis-2-bromo-1,2-diphenylvinyl)phenylboron bromide with lithium metal in tetrahydrofuran at −77°. Factors determining the competition between BBr bond addition in step “a” and the slower BC 6H 5 bond addition to the triple bond are analyzed. By treatment of aliquots of the reaction product of steps “a” and “b” with alkyl halides, with carbon dioxide and with O-deuterioacetic acid, it is concluded that a stilbene derivative with vicinal cis-carbon-boron bonds has been formed. The nature of the organoborane precursor of cis-stilbene is discussed in terms of structural alternatives, such as triphenylborirene, hexaphenyl-1,4-diboracyclohexadiene or a polymer.

Lithium cleavage of unsaturated vicinal di- tert-phosphines

Lithium metal in tetrahydrofuran has been found to react with ethynylenebis(diphenylphosphine) and cis- or trans-1,2-vinylenebis(diphenylphosphine) to produce lithium diphenylphosphide in high yield. Possible mechanistic paths are discussed. In this connection the reactions of the vinylenebis- and ethynylenebis(diphenylphosphines) with lithium diphenylphosphide have been examined and the results are discussed.