Oligomérisation anionique de l'ethylène. I. Etude cinétique

A kinetic study of ethylene oligomerization in hexane, in the presence of n-BuLi–TMEDA complexes, allowed us to suggest a new mechanism for anionic ethylene oligomerization. n-BuLi and n-Bu(CH₂CH₂)Li species have the same reactivity. The RLi–TMEDA complex in a 1-to-1 stoichiometry is the active species. The following kinetic equation has been established: It reflects the intervention of associated species (n-BuLi–TMEDA)₂ as well as the influence of the concentration of the complexing agent on the kinetics of oligomerization.     

Formation of mixed aryl–, alkyl–lithium aggregates in the heteroatom assisted lithiation of α,α′-dialkyl substituted 1,3-bis[(dimethylamino)methyl]benzene

The heteroatom assisted lithiation of 1,3-bis[1-(dimethylamino)ethyl]benzene with n-BuLi afforded 2,6-bis[1-(dimethylamino)ethyl]phenyllithium. An X-ray crystal structure determination revealed a dimeric aggregate in which the four benzylic chiral centers are identical, pointing to stereoselective crystallization. In contrast, reaction of 1,3-bis[1-(dimethylamino)propyl]benzene with n-BuLi afforded a dimeric aggregate comprising the parent lithiated compound and n-BuLi in a 1:1 molar ratio. The four Li atoms and the four bridging carbon atoms are arranged in a unique ladder-type C–Li₂–C₂′–Li₂–C framework.     

Oligomérisation anionique de l'ethylène. III. Application à la synthèse d'alcools à longue chaine

Living oligomers of ethylene obtained by n-BuLi complexed with TMEDA have been deactivated by ethylene oxide. The nuclear magnetic resonance study of the product obtained allowed us to follow the influence of TMEDA toward the functionalization. Three products have been characterized: By increasing the ratio [TMEDA]/[n-BuLi] one obtains a decrease of the functionalization reaction.     

Generation and electrophilic substitution reactions of 3-lithio-2-methyleneaziridines

2-Methyleneaziridinyl anions can be produced by selective deprotonation of the parent aziridine at C-3 using sec-BuLi/TMEDA. Subsequent reaction with a wide variety of electrophiles including MeI, ICH₂CH₂CH₂CH₂Cl, PhCH₂Br, allyl bromide, Me₃SiCl, Bu₃SnCl, PhCHO and Ph₂CO provides the corresponding C-3 substituted derivatives in moderate to good yields (43-91%). In the case of homochiral methyleneaziridines bearing an (S)-α-methylbenzyl group on nitrogen, high levels of diastereocontrol (up to 90%de) can be achieved in this lithiation/alkylation sequence.     

Lithiation of 2,5-dimethylazaferrocene

Reaction of 2,5-dimethylazaferrocene with sec-BuLi/TMEDA in THF at −78 °C, followed by quenching with D₂O brought about incorporation of deuterium into the Cp ring (54%), methyl groups (38%) and the pyrrolyl β-position (8%). When benzyl chloride or p-methoxybenzaldehyde was used as quenchers products originated from the lateral lithiation were only formed, accompanied by recovered starting material. For this reaction a radical pathway is suggested.     

A Benzodiphosphaborolediide

The first example of a diphosphaborolediide, the benzo-fused [C₆H₄P₂BPh]²⁻ ( 1²⁻ ), is prepared from ortho-bis(phosphino)benzene (C₆H₄{PH₂}) and dichlorophenylborane, via a sequential lithiation approach. The dilithio-salt can be obtained as an oligomeric THF solvate or discrete TMEDA adduct, both of which are fully characterized, including by X-ray diffraction. Alongside NICS calculations, data strongly suggest some aromaticity within 1²⁻ , which is further supported by preliminary coordination studies that demonstrate η⁵-coordination to a zerovalent molybdenum center, as observed crystallographically for the oligomeric [{Mo(CO)₃(η⁵- 1 )}{μ-η¹-Mo(CO)₃(TMEDA)}₂] ⋅ [μ-Li(THF)][μ-Li(TMEDA)].     

Kristallstrukturen von TMEDA‐Addukten und Salzen mit protonierten TMEDA‐Molekülen

Crystal Structures of TMEDA Adducts and of Salts with Protonated TMEDA Molecules The reaction of TMEDA with two equivalents of [BH₃(SMe₂)] in toluene at 20 °C gives the adduct [TMEDA(BH₃)₂] ( 1 ). A similar reaction of pyrrolidine with [BH₃(SMe₂)] in a molar ratio of 1:1 leads to the adduct [pyrrolidine(BH₃)] ( 2 ). TMEDA can be introduced into the coordination sphere of In³⁺ by the treatment of InI₃ with TMEDA in toluene to give the complex [InI(TMEDA)] ( 3 ). The salt [HTMEDA]I ( 4 ), containing a mono‐protonated TMEDA molecule, is the result of the reprotonation of [NH₄]I and TMEDA in toluene at 20 °C. The salts [H₂TMEDA]—[InCl₄(TMEDA)]₂ ( 5 ) and [H₂TMEDA][InCl₅(THF)] ( 6 ) are formed in the reaction mixtures TMEDA/toluene/InCl₃/HCl and TMEDA/toluene/THF/InCl₃/HCl, respectively, whereupon 6 was characterized more closely. Crystals of [In₅I₆(OH)(TMEDA)₄]I·2, 5toluene ( 7 ·2.5toluene) can be obtained after treatment of InI₃ with non‐dried TMEDA; 4 was identifed as by‐product. 1 — 7 ·2.5toluene were partially investigated by NMR methods and vibrational spectroscopy. In all cases a characterization by single crystal X‐ray diffraction was performed. According to this, all nitrogen atoms in 1 and 2 are coordinated by BH₃ groups leading to a distorted tetrahedral environment at the nitrogen and the boron atoms. In 3 a distorted trigonal‐bipyramidal coordination sphere at the In³⁺ is present. The apical positions are occupied by I3 and N3. Strong N‐H···N bridges, running along [001] is the feature in 4 ; the ^I—‐Ions are not involved into the system of H‐bridges. A ion triple, [H₂TMEDA][InCl₄(TMEDA)]₂, hold together by bifurcated H‐bridges is the dominating structural motif in 5 , whereas alternation bifurcated and linear H‐bridges, leading zu a zig‐zag chain along [100], is the build‐up principle of 6 . In 7 ·2.5toluene a complex In₅O₈ skeleton was formed, consisting of a virtual corner‐connected doubled heterocubane. At every heterocubane a corner, occupied by a metal ion, is missing. The coordination spheres of the In atoms of the complex cation are completed by TMEDA molecules and iodide ions.     

Temperature dependence of the rate constants of the reactions of oxygen atoms with 1-pentene, 1-hexene,cis-2-pentene,and trans-2-pentene

The kinetics of the reactions of ground state oxygen atoms with 1-pentene, 1-hexene, cis-2-pentene, and trans-2-pentene was investigated in the temperature range 200 to 370 K. In this range the temperature dependences of the rate constants can be represented by k = A′ Tⁿ exp(− E′_a/RT) with A′ = (1.0 ± 0.6) · 10⁻¹⁴ cm³ s⁻¹, n = 1.13 ± 0.02, E′_a = 0.54 ± 0.05 kJ mol⁻¹ for 1-pentene: A′ = (1.3 ± 1.2) · 10⁻¹⁴ cm³ s⁻¹, n = 1.04 ± 0.08, E′_a = 0.2 ± 0.4 kJ mol⁻¹ for 1-hexene; A′ = (0.6 ± 0.6) · 10⁻¹⁴ cm³ s⁻¹, n = 1.12 ± 0.05, E′_a = − 3.8 ± 0.8 kJ mol⁻¹ for cis-2-pentene; and A′ = (0.6 ± 0.8) · 10⁻¹⁴ cm³ s⁻¹, n = 1.14 ± 0.06, E′_a = − 4.3 ± 0.5 kJ mol⁻¹ for trans-2-pentene. The atoms were generated by the H₂-laser photolysis of NO and detected by time resolved chemiluminescence in the presence of NO. The concentrations of the O(³P) atoms were kept so low that secondary reactions with products are unimportant. © 1997 John Wiley & Sons, Inc.     

Kinetic resolution of P-stereogenic phosphine boranes via deprotonation using s-butyllithium/(−)-sparteine

The attempted kinetic resolution of racemic secondary phosphine boranes [t-BuPhP(BH₃)H and t-BuMeP(BH₃)H] by P–H deprotonation using 0.5 equiv of s-BuLi and (?)-sparteine was unsuccessful and generated racemic benzyl bromide-trapped adducts in 42–49% yield. In contrast, an efficient kinetic resolution was observed with racemic tertiary phosphine boranes [t-BuPhP(BH₃)Me and t-BuEtP(BH₃)Me] by C–H deprotonation on the P–Me group using 0.5 or 0.6 equiv of s-BuLi and (?)-sparteine. For example, the use of 0.6 equiv of s-BuLi/(?)-sparteine with t-BuEtP(BH₃)Me and trapping with DMF gave the (R)-aldehyde adduct in 37% yield and 83:17 er together with recovered (R)-t-BuEtP(BH₃)Me in 44% yield and 74:26 er. These are the first examples of kinetic resolution of P-stereogenic phosphine boranes via deprotonation using s-BuLi/(?)-sparteine.     

Lithium-silylindolide als Precursor für 1,2-, 1,3-Bis(silyl)indole und Bis(indol-1,3-yl)silane

Lithium-silylindolide as Precursor of 1,2-, 1,3-Bis(silyl)indoles and Bis(indole-1,3-yl)silane Lithium-indolide reacts with difluorosilanes (F₂SiR₂: R = CHMe₂ ( 1 ); CMe₃ ( 2 )) in a molar ratio 2 : 1 with formation of bis(indole-1-yl)silanes. The 1-(di-tert-butylfluorosilyl)-3-(fluorodiisopropylsilyl)indole ( 3 ) is obtained in the reaction 1-(di-tert-butylfluorosilyl)-3-lithium-indolide and F₂Si(CHMe₂)₂. In a molar ratio 2 : 1 the bis(1-di-tert-butylfluorosilyl-indole-3-yl)diisopropylsilane 4 is formed. As a byproduct bis(1-di-tert-butylfluorosilyl-indole-3-yl)dimethylmethane ( 5 ) is isolated. A cleavage of THF and the formation of (indole-1-yl)diisopropylvinyloxysilan ( 6 ) occurs in the reaction of 1-diisopropylfluorosilylindole with t-BuLi in THF. 1-(di-tert-butylfluorosilyl)indole reacts with n-BuLi/TMEDA accompanied by an 1,2-anionic silyl group migration to give the 2-(di-tert-butylfluorosilyl)-1-lithiumindolide 7 . Hydrolysis of 7 gives the 2-(di-tert-butylfluorosilyl)indole ( 8 ). In the reaction of 7 with F₂Si(CHMe₂)₂ the 1-(diisopropylfluorosilyl)-2-(di-tert-butylfluorosilyl)indole 9 is obtained. 1-n-Butyl-diisopropylsilylindole ( 10 ) is the product of the reaction of F₂Si(CHMe₂)₂, n-BuLi/TMEDA and indole at –70 °C. Lithium-indolide reacts with 3 to give the 1-(di-tert-butylfluorosilyl)indole-3-yl)(indole-1-yl)-diisopropylsilane ( 11 ), the first example of this class of substances. In the reaction of 1 , F₂SiMe₂, and t-BuLi in THF the 1-(diisopropyl(indole-1-yl)silyl)-3-dimethyl-(3.3-dimethylbutylsilyl)indole 12 is isolated. The crystal structures of 2 , 5 and 9 are discussed.     

Formal and improved synthesis of enantiopure chiral methanol

[D₂]Methanol was converted to the carbamate derived from 2,2,6,6-tetramethylpiperidine. It was metalated with s-BuLi/TMEDA at −78 °C with a high primary kinetic isotope effect to give an α-oxymethyllithium, which was silylated with chlorodimethylphenylsilane. The silylmethyl carbamate formed was lithiated and borylated with the borate derived from tert-butanol and (R,R)-1,2-dicyclohexylethane-1,2-diol to give diastereomeric boronates, which were separated by preparative HPLC and can in principle be converted to enantiopure chiral methanols. Thus, both enantiomers are easily accessible in nine linear steps.     

Metalations in hydrocarbon solvents; media effects on n-BuLi reactivity

The relative basicities of solutions of n-BuLi in cyclohexane as a function of the addition of increasing increments of THF or TMEDA (designer media) have been assessed. As the chloro DMG is incapable of complexing to n-BuLi, it can neither affect the n-BuLi oligomeric equilibrium nor exhibit a DoM mechanistic component involving prior-coordination (CIPE). Accordingly, by measuring the rates of loss of chlorobenzene in the varied media as well as by certain ⁷Li NMR studies, a gradual, controlled increase in the basicity of n-BuLi in cyclohexane with increasing increments of THF or TMEDA was observed. Relationships of the basicity in the varied media to the three oligomeric forms of n-BuLi are proposed.     

Carbamate-stabilized anions of 2-azabicyclo[2.1.1]hexanes

The regiochemical outcomes for s-BuLi/TMEDA deprotonations of N-Boc-2-azabicyclo[2.1.1]hexanes had been shown to be temperature dependent. Computational methods have been applied to advance understanding of the complexes that the reagents form, the character of the deprotonations, and hence the experimentally observed regiochemical biases. The tertiary anion is formed more readily than the secondary anion and is also the more stable anion. Computations for the enthalpy of proton abstraction from the analogous N-methoxycarbonyl structure also indicate greater stability for the tertiary carbamate anion.     

New initiator system for the anionic polymerization of (meth)acrylates in toluene. IV. Random copolymerization of (meth)acrylates in toluene initiated by s-BuLi ligated by lithium silanolates

Copolymerization of binary mixtures of alkyl (meth)acrylates has been initiated in toluene by a mixed complex of lithium silanolate  (s-BuMe₂SiOLi) and s-BuLi (molar ratio > 21) formed in situ by reaction of s-BuLi with hexamethylcyclotrisiloxane (D₃). Fully acrylate and methacrylate copolymers, i.e., poly(methyl acrylate-co-n-butyl acrylate), poly(methyl methacrylate-co-ethyl methacrylate), poly(methyl methacrylate-co-n-butyl methacrylate), poly(methyl methacrylate-co-n-butyl methacrylate), poly(isobornyl methacrylate-co-n-butyl methacrylate), poly(isobornyl methacrylate-co-n-butyl methacrylate) of a rather narrow molecular weight distribution have been synthesized. However, copolymerization of alkyl acrylate and methyl methacrylate pairs has completely failed, leading to the selective formation of homopoly(acrylate). As result of the isotactic stereoregulation of the alkyl methacrylate polymerization by the s-BuLi/s-BuMe₂SiOLi initiator, highly isotactic random and block copolymers of (alkyl) methacrylates have been prepared and their thermal behavior analyzed. The structure of isotactic poly(ethyl methacrylate-co-methyl methacrylate) copolymers has been analyzed in more detail by Nuclear Magnetic Resonance (NMR). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2525–2535, 1999     

Darstellung und Charakterisierung von Organodilithiumphosphiden. Die Kristallstruktur von [Li(THF)(TMEDA)P(H)Mes]

Synthesis and Characterization of Organodilithium Phosphides. The Crystal Structure of [Li(THF)(TMEDA)P(H)Mes] t-BuPH₂ and MesPH₂ can be reacted with two equivalents n-BuLi at R. T. in Et₂O/n-hexane to yield the corresponding organodilithium phosphides t-BuPLi₂ ( 1 ) and MesPLi₂ ( 2 ). 1 and 2 can be isolated solvent-free as bright orange-yellow solids. 1 and 2 were characterized by NMR, IR, and RE spectra. When MesPH₂ is treated with one equivalent of n-BuLi, MesP(H)Li is crystallizing as [Li(THF)(TMEDA)P(H)Mes] ( 3 ) from THF/TMEDA/n-pentane in the space group P2₁/n with a = 893.41(6), b = 1 734.7(1), c = 1 391.1(1) pm and β = 90.613(6)°.     

Synthesis of spiro[4.5]decane and bicyclo[4.3.0]nonane ring systems by self-cyclization of (Z)- and (E)-2-(trimethylsilylmethyl)pentadienal derivative

The two title carbon frameworks were synthesized utilizing a new type of iron-induced cyclization reaction of 2-(trimethylsilylmethyl)pentadienal. 2-Methylspiro[4.5]dec-2-en-1-one was obtained from (Z)- and (E)-4-cyclohexylidene-2-(trimethylsilylmethyl)but-2-enal. It was found that the (Z)-substrate isomerized to (E)-intermediate followed by cyclization to afford the initial product, 2-methylenespiro[4.5]dec-3-en-1-ol, which was isomerized to the above product. The cyclization of 4-(4-alkyl)cyclohexylidene-2-(trimethylsilylmethyl)but-2-enal proceeded stereoselectively. While, (E)-3-(cyclohex-1-en-1-yl)-2-(trimethylsilylmethyl)prop-2-en-1-al cyclized immediately affording 8-methylenebicyclo[4.3.0]non-9-en-7-ol. The corresponding (Z)-isomer gave several cyclization products as a complex mixture.     

Rate constants for the reactions of OH radicals with alkyl substituted olefins

Relative rate constants for the reactions of hydroxyl radicals with a series of alkyl substituted olefins were measured by competitive reactions between pairs of olefins at 298 ± 2 K and 1 atmospheric pressure. Hydroxyl radicals were produced by the photolysis of H₂O₂ with 254-nm irradiation. The obtained rate constants were (× 10^?11 cm³ molecule^?1 s^?1): 2.53 ± 0.06, propylene; 5.49 ± 0.17, cis-2-butene; 5.47 ± 0.1, isobutene; 6.46 ± 0.13, 2-methyl-1-butene; 6.37 ± 0.16, cis-2-pentene; 6.23 ± 0.1, 2-methyl-1-pentene; 8.76 ± 0.14, 2-methyl-2-pentene; 6.24 ± 0.08, trans-4-methyl-2-pentene; 10.3 ± 0.1, 2,3-dimethyl-2-butene; 9.94 ± 0.1, 2,3-dimethyl-2-pentene; 5.59 ± 0.07, trans-4,4-dimethyl-2-pentene. A trend in alkyl substituent effect on the rate constant was found, which is useful to predict k_OH on the basis of the number of alkyl substituents on the double bond.     

Reaktionen des Gallium‐haltigen Heterocyclus [Me2Ga{HNC(Me)}2CCN]

Reactions of the Gallium‐containing Heterocycle [Me₂Ga{HNC(Me)}₂CCN] The reaction of [Me₂Ga{HNC(Me)}₂CCN] ( 1 ) with fac‐[Mo(CO)₃(MeCN)₃] leads after addition of TMEDA to the molybdenum complex fac‐[Mo(CO)₃( 1 )(TMEDA)] ( 2 ). Under identical reaction conditions with fac‐[W(CO)₃(MeCN)₃] only the tetracarbonyle complex [W(CO)₄(TMEDA)] ( 3 ) could be isolated. Treatment of dilithiated 1 with Me₂SiCl₂ or InCl₃ initiate a fragmentation of the skeleton in 1 . Obtained were the salt [Me₂Ga(TMEDA)][Me₂GaCl₂] ( 4 ) and the indium complex [Me₂InCl(TMEDA)] ( 5 ), respectively. 2 — 5 were investigated by spectroscopical and spectrometrical methods as well as by X‐ray structure determinations. According to these 1 occupies a facial site in 2 by donation of the N‐Atom from the NC group in 1 . The molecules 2 are forming a network of hydrogen bonds. In 3 , the TMEDA ligand acts as an intramolecular chelate ligand. In the salt 4 , the cation as well as the anion are coordinated in a distorted tetrahedral environment, while in 5 a distorded trigonal‐bipyramidal coordination‐sphere is present, leading to a elongated In1‐Cl1 distance of 261.74(9) pm.     

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl₄), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were ≥2 at two different temperatures and in different solvents. The square-root dependence of R_p on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.     

Facile Synthesis of Benzotriazines and Indoles by Ring-Scissions of α-Benzotriazol-1-yl Hydrazones

Abstract: α-(Benzotriazol-1-yl)hydrazones 2a-d and 13a-c were prepared by refluxing the corresponding α-(benzotriazol-1-yl)ketones with p-tosyl hydrazide or benzenesulfonyl hydrazide. Treatment of 2a-b with n-butyllithium in the presence of TMEDA gave benzotriazines 6a-b, while lithiation of 13a-c resulted in indole derivatives 16a-c, depending on the structure of the hydrazones.