Tetrahydrofuran Activation Assisted Synthesis of Nanosized Lithium Niobate and Lithium Tantalate

Black solid precursors obtained from reactions between MCl₅ (M = Nb, Ta) and alkyllithiums, n‐butyllithium (ⁿBuLi) and ethyllithium (EtLi), in tetrahydrofuran (THF) were heat treated under vacuum at 673–973 K to form nano‐sized particles (20–100 nm in diameter) of lithium niobate (LiNbO₃) and lithium tantalate (LiTaO₃). Stoichiometry of the reactants is critical and affects the phases of the products. Based on the volatile byproducts detected, a reaction pathway involving the activation of THF by alkyllithiums is proposed to be important for the formation of LiNbO₃ and LiTaO₃ precursors.     

A mild and selective synthesis of cyclopropene and cyclopropane derivatives via cycliallylation of alkenyllithiums

Treatment of cis-1-iodo-3-chloro-1-propene derivatives, readily obtainable via trans addition of organometals to propargyl alcohols followed by iodinolysis and chlorination, with alkyllithiums, such as t-BuLi and n-BuLi, can proceed rapidly and cleanly even at ?78°C to give in high yields cyclopropene derivatives, which undergo cis hydrometalation and carbometalation reactions more rapidly than the corresponding alkynes to produce cyclopropane derivatives.     

Access to functionalized cyclopropylcarbinyl compounds from homoallylic ethers via zirconocene intermediates

Cyclopropylcarbinylzirconium complexes were generated from homoallylic ethers and zirconocene (Cp₂ZrCl₂/2n-BuLi). They underwent further in situ transformations that is, bromination-substitution, transmetallation-functionalization and insertion reactions to afford various cyclopropylcarbinyl derivatives. In contrast, ring-opening products could be selectively obtained by treating the zirconium complex with MeLi, prior to functionalization.     

Synthesis of stable 1-ethoxy-2,3-diferrocenylcyclopropenylium tetrafluoroborate and its reactions with lithium reagents

1-Ethoxy-2,3-diferrocenylcyclopropenylium tetrafluoroborate selectively reacts with MeLi, n-BuLi, sec-BuLi with formation of the 3,3-dialkyl-1,2-diferrocenylcyclopropenes, while with tert-BuLi both 2-tert-butyl-1,3-diferrocenylcyclopropene and 1,3-di-tert-butyl-2,3-diferrocenylcyclopropene are obtained. The structures of 3,3-dimethyl-, 3,3-dibutyl-1,2-diferrocenyl and 2-tert-butyl-1,3-diferrocenylcyclopropenes were confirmed by X-ray crystallographic analysis.     

Competing reaction pathways from α-halo-α-protioalkyl aryl sulfoxides initiated by organometallic reagents

The reactions of syn-1-haloethyl p-chlorophenyl sulfoxides (halogen = Cl, Br) with main-group organometallic reagents (n-BuMgCl, MeLi, n-BuLi, s-BuLi, and t-BuLi) in THF and PhMe solvents were examined. Product distributions were analyzed to determine the extent of competing sulfoxide ligand exchange, halogen-metal exchange, and deprotonation reaction pathways. A combination of t-BuLi in PhMe was optimal for initiation of sulfoxide ligand exchange from syn-1-chloroethyl p-chlorophenyl sulfoxide.     

Synthesis of enantiomerically enriched amines by chiral ligand mediated addition of organolithium reagents to imines

The effect of the imine and ligand structure on the enantioselective addition of organolithiums to imines has been studied. Thus, (−)-sparteine-mediated additions of MeLi and/or n-BuLi to p-anisidine derived phenylimine 1a afforded the corresponding amines with modest e.e.s. The use of bulkier or more reactive imines (naphthyl or tosyl imines) resulted in loss of enantioselectivity. The best enantioinduction with this ligand was obtained with enolizable imines 8 and 10. When bis(oxazolidines) were used as chiral ligands, a strong influence of their structure in the enantioselectivity of the addition of MeLi and n-BuLi to phenylimine 1a was observed.     

A novel type of free radical reactions: isomerization of a radical with concerted fragmentation

A comparison of experimental data and results of the rate constant calculations by the method of intersecting parabolas (MIP) showed that abstraction of H atom by a peroxyl radical from the C_α-H bond in hydroperoxide is accompanied by concerted fragmentation of the molecule. The complicated character of the elementary event is due to high exothermicity of the reaction. The kinetic parameters of isomerization with fragmentation of peroxyalkyl, peroxyalkoxyl, and peroxyperoxyl radicals were calculated within the framework of the MIP method. The enthalpies, activation energies, and rate constants for a series of isomerization reactions of peroxyl radicals with concerted fragmentation were also obtained from the MIP calculations. Factors influencing these reactions are analyzed.     

Cu(0)/Selectfluor system-catalyzed intramolecular Csp2-H/Csp2-H cross-dehydrogenative coupling (CDC)

A Cu(0)/Selectfluor system-catalyzed intramolecular C_sp2-H/C_sp2-H bond cross-dehydrogenative coupling of 2-aryloxybenzaldehydes is described. A variety of substituted xanthone derivatives are synthesized in moderate to excellent yields. Reaction can also be extended to the synthesis of 9H-thioxanthen-9-one 10,10-dioxide and phenanthridin-6(5H)-ones, respectively.     

Facile preparation of aromatic esters from aromatic bromides with ethyl formate or DMF and molecular iodine via aryllithium

Various aromatic bromides were treated with n-BuLi and subsequently with ethyl formate, followed by the reaction with ethanol and molecular iodine in the presence of K₂CO₃ to provide the corresponding aromatic ethyl esters in good yields. Moreover, aromatic bromides could be transformed into the corresponding aromatic methyl esters in good yields by the treatment with n-BuLi and subsequently with DMF, followed by the reaction with methanol, molecular iodine, and K₂CO₃. Some aromatics could be also converted into the corresponding aromatic esters in good yields by the treatment with n-BuLi, and subsequently with ethyl formate or DMF, followed by the reaction with molecular iodine and K₂CO₃. The present reactions offer a novel route for the transition-metal-free, carbon-monoxide-free, and therefore environmentally benign one-pot conversion of aromatic bromides and aromatics into aromatic esters.     

Peculiarities of dissociative ionization of alkylcyclopentadienyl nitrosyl π-complexes of nickel

The decomposition of alkylcyclopentadienyl nitrosyl -complexes of nickel, (C₅H₄R)(NO)Ni (R=H, Et,i-Pr, CH₂Ph), under the action of electron impact has been studied. The nature of the nitrosyl ligand has been shown to be the factor determining the main fragmentation pathway which involves the abstraction of an NO molecule. The effect of the nature of the ligand on the ability of the molecular ion (C₅H₄R)LNi⁺ (L=C₅H₄R, C₅H₅, C₃H₅, NO) to rearrange with hydrogen atom migration from one ligand to another has been considered. The structure of the alkyl group R determines a competing fragmentation pathway involving cleavage of the -C-C bond with respect to the cyclopentadienyl ring in the substituent.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1985–1988, November, 1993.     

Rearrangements Leading to Fragmentations of Hydrocinnamate and Analogous Nitrogen-Containing Anions Upon Collision-Induced Dissociation

Tandem mass spectrometry (MS/MS) confirmed decarboxylation as the major collision-induced dissociation (CID) pathway of deprotonated hydrocinnamic acid (C₆H₅CH₂CH₂CO₂H), N-phenylglycine (C₆H₅NHCH₂CO₂H) and 3-pyridin-2-ylpropanoic acid (C₅H₄NCH₂CH₂CO₂H). The structure and stability of isomeric precursor and product anions were examined using density functional theory and ab initio methods. Geometry optimizations and frequency calculations were performed using the B3LYP/6-31++G(2d,p) level of theory and basis set with additional single point energies calculated at the MP2/6-311++G(2d,p) level. The formation of a delocalized product anion by carboxyl group-mediated migration of a benzylic proton to the ortho position of the ring and subsequent C_α–CO₂ ^– bond cleavage was energetically more favorable than direct decarboxylation and rearrangements of anions within ion-neutral complexes with carbon dioxide. The energy barrier for rearrangement of the delocalized product anion to the more stable benzylic anion was lowest in the fragmentation pathway of 3-pyridin-2-ylpropanoate. More energetically demanding fragmentation processes were indicated by the formation of other product anions at higher collision energy. Computations supported the feasibility of the formation of hydroxycarbonyl, styrene, and phenide ions from the benzylic anion of hydrocinnamate and the corresponding product anions from the nitrogen-containing analogues. The loss of dihydrogen from decarboxylated 3-pyridin-2-ylpropanoate was characterized computationally as hydride abstraction of an aryl proton. Overall, the results highlight the importance of exploring rearrangements in the fragmentation pathways of ions formed by electrospray ionization (ESI).

Nucleophilic Attack on an Electronically Unsaturated Triosmium Cluster Complex of 2-Methylbenzoxazole: An Unusual Oxidative Ring Opening

In the course of our studies of nucleophilic attack on electronically unsaturated benzoheterocycle triosmium clusters we have studied the reaction of the 2-methylbenzoxazole complex (μ-H)Os₃(CO)₉(μ₃-η²-2-CH₃–C₇H₃NO) (1) with hydride followed by protonation with acid. In sharp contrast to our previous studies with related benzoheterocycle triosmium clusters, where the nature of the heterocycle controls the regiochemistry of nucleophilic attack, we observe here an unusual ring opening of the heterocyclic ring, coupled with rearrangement of the carbocyclic ring to a 2-imino-ethyl-phenol complex (μ-H)Os₃(CO)₉(μ₃-η³-N=CHCH₃–C₆H₃(OH)) (2). Deuterium labeling experiments verify initial attack by hydride at the 2-position followed by protonation at oxygen. Reaction of 1 with two equivalents of hydride followed by two equivalents of acid results in reduction of the C=N bond in 2 and on standing in air, oxidation of the carbocyclic ring occurs to give the 2-ethyl-amino hydroquinolyl derivative (μ-H)Os₃(CO)₉(μ₃-η³-NHCH₂CH₃–C₆H₃(2-O)(5-OH)) (3). The solid-state structure of 3 is reported and a plausible mechanism, supported by deuterium labeling experiments, is presented, for the formation of 2 and 3.     

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.     

Reactions of alanes and aluminates with tri-substituted epoxides. Development of a stereospecific alkynylation at the more hindered carbon

The addition of 4 equiv of phenyl ethynyl dimethyl alane (formed by treatment of phenyl acetylene with n-BuLi followed by Me₂AlCl) to 2,3-epoxy geraniol results in the formation of the C-3 alkynyl addition product and the Yamamoto rearrangement/addition product, in 53 and 18% yield, respectively. Replacing the alane reagent with an aluminate (formed by treatment of phenyl acetylene with n-BuLi followed by Me₃Al) and adding BF₃·OEt₂ result in formation of the C-3 addition product in 73% yield.     

Kinetic study of nucleophilic addition to the cycloheptatriene ring in [(C7H8)Fe(Cp)]PF6

Tri-n-butylphosphine, tri-n-butylphosphite, and imidazole add to the cycloheptatriene ring in (C₇H₈)FeCp)⁺ (I) to give cycloheptadienyl adducts (II). The second order rate constants (M^?1 s^?1) in acetone at 25°C are: P(OBu)₃, 0.50; PBu₃, 2250; HIm, 67. The relative nucleophilic reactivities are the same as that found with other coordinated cyclic π-hydrocarbons and with free carbocations. This further supports the recent suggestion [1] that a Ritchie type correlation holds for attack on all complexes of the form (ring)ML_n. The Fe(Cp)⁺ moiety is 11,000 times weaker than Mn(CO)₃⁺ in activating coordinated cycloheptatriene. NaBH₄, MeLi, and NaCH(CO₂Et)₂ also add to the ring in I, indicating that I may have synthetic utility.     

Nucleophilic Addition Reactions of Tricarbonyl [η5-1-(Phenylthio)Cyclohexadienyl]Iron(I) Complex

Hydride abstraction of tricarbonyl[η⁴phenylthio)-l,3-cyclohexadiene]iron(0) complex 2 with Ph₃C⁺PF₆^? regiospecifically provided the title compound 3 in excellent yield. Cationic complex 3 could react with a variety of nucleophiles in good yield. Hard nucleophiles prefer to attack at the C-l position, whereas soft and hindered nucleophiles favor attack at the C-5 position. Some synthetic applications were also studied.     

Mass spectrometry of systems containing a group IVB—transition metal bond : I. The phenyl- and pentafluorophenyl- silicon, -germanium and -tin derivatives of pentacarbonylmanganese

The 70 eV mass spectra of the series Ph_3?n(C₆F₅)_nMMn(CO)₅ (n = 0 to 3 and M = Si, Ge or Sn) and Ph₃PbMn(CO)₅ have been examined and the proposed fragmentation schemes are supported by the observance of the appropriate metastable ions. Most of the total ion current is carried by metal-containing ions, particularly those containing just a Group IV metal. In all cases the initial fragmentation is by the loss of one or more carbonyl groups from the molecular ion, followed, except in the case of the fully fluorinated silicon derivatives, by the cleavage of the metal—metal bond. The fragmentation of the remainder of the molecule is then controlled by the nature of M and the number of pentafluorophenyl groups, the silicon derivatives showing a greater abundance of ions formed by the cleavage of the CC, CH or CF bonds in the aromatic ring, in contrast to the tin and lead derivatives which fragment almost exclusively by the cleavage of the metal—carbon bond. The formation of metal fluoride species plays an important part in the fragmentation of the pentafluorophenyl derivatives and becomes more important as the Group IV metal becomes heavier, while except for Ph₃PbMn(CO)₅ the abundances of the ions resulting from the migration of a complete aromatic ring from one metal to the other remain essentially constant. However, some of the observed changes in the fragmentation modes are not readily predicted on the basis of the expected variation in the relative metal—carbon or metal—metal bond strengths since these appear to be more dependent on the stabilities of the radical species or on the ion species formed. The tin—metal molecular bond dissociation energies in Ph₃SnMn(CO)₅ and Ph₃SnFe(CO)₂Cp were found to be 61 ± 8 and 54 ± 9 kcal mol^?1, respectively.     

Practical resolution of an atropoisomeric α,α-disubstituted glycine with l-phenylalanine cyclohexylamide as chiral auxiliary

l-Phenylalanine cyclohexylamide has been used as a chiral auxiliary for the medium-scale resolution of 2′,1′:1,2;1″,2″:3,4-dinaphthcyclohepta-1,3-diene-6-amino-6-carboxylic acid (Bin), an α,α-disubstituted glycine with only axial dissymmetry. Coupling of X–Bin–OH (X=Ac; Bz) with H–(l)-Phe–NH–C₆H₁₁ by the EDC/HOBt method gave the dipeptide diastereoisomers X–(R)-Bin–(l)-Phe–NH–C₆H₁₁ and X–(S)-Bin–(l)-Phe–NH–C₆H₁₁, which were separated by crystallization (X=Bz) and/or chromatography. Extensive acidic hydrolysis, followed by esterification of the resulting free amino acid enantiomers, led to enantiomerically pure (−)-(R)-H–Bin–OMe and (+)-(S)-H–Bin–OMe with high yields.     

Stoichiometric vs Catalytic MeLi Reaction with the Mixture of (ẽ5‐C5H5)Fe(CO)2l and P(OR)3: Nucleophilic Methylation vs Arbuzov‐Like Dealkylation

The reaction of stoichiometric MeLi with the 1:1 mixture of (?⁵‐C₅H₅)Fe(CO)₂I/P(OR)₃ (R = Me, Et, and Ph) at ?78°C changes the bonding mode between metal and ring from (?⁵‐C₅H₅) to (?⁴‐exo‐MeC₅H₅) and the oxidation state of metal from Fe(II) to Fe(O), the novel complexes (?⁴‐exo‐MeC₅H₅)Fe(CO)₂P(C)R)₃ being obtained in 45‐57% yields. The reaction of trace MeLi with the 1:1 mixture of (?⁵‐C₅H₅)Fe(CO)₂I/P(OMe)₃ at ?78°C results in 70% yield of the phosphonate complex (?⁵‐C₅H₅)Fe(CO)₂P(O)(OMe)₂ which is an Arbuzov‐like dealkylation product from the cationic intermediate [(?⁵‐C₅H₅)Fe(CO)₂P(OMe)₃⁺] and the iodide. The amines could assist the Arbuzov‐like dealkylation of [(?⁵‐C₅H₅)Fe(CO)₂P(OMe)₃⁺] [PF₆^?] where iron‐carbamoyl intermediates are likely involved in the case of primary amines.     

Effect of solvent on reactions of Cp2Zr{(μ-H)2BHR}2 and Cp2ZrH{(μ-H)2BHR} (R = CH3, Ph) with B(C6F5)3

The effect that a solvent has on reactions of Cp₂Zr{(μ-H)₂BHR}₂ and Cp₂ZrH{(μ-H)₂BHR} (R = CH₃, Ph) with B(C₆F₅)₃ has been studied. From the reaction in benzene the metathesis product Cp₂Zr{(μ-H)₂B(C₆F₅)₂}₂, 2, was isolated. In the case of diethyl ether, different hydride abstraction products, including [Cp₂Zr(OEt₂){(μ-H)₂BHPh}][HB(C₆F₅)₃], 3, [Cp₂Zr(OEt₂){(μ-H)₂BHCH₃}][HB(C₆F₅)₃], 4, [Cp₂Zr(OEt₂){(μ-H)₂BH₂}][HB(C₆F₅)₃], 5, and [Cp₂Zr(OEt)(OEt₂)][HB(C₆F₅)₃], 6, were isolated depending on the starting zirconocene complex. The diethyl ether molecules of 3-6 are weakly coordinated to Zr and displaced in THF solution. Isolation of 3 and 4 is attributed to their fast precipitation from the reaction mixture, which prevented further reactions from occurring. In addition to the hydride abstraction, a hydride metathesis was also involved in the formation of 5. Time-elapsed ¹¹B NMR studies indicate that 3 and 4 are the intermediates on the pathway to 5 and 6. The molecular structures of 2-6 were determined by single-crystal X-ray diffraction.