The reactions of dialkylgallium hydrides with tert-butylethynylbenzenes--a systematic investigation into the course of hydrogallation reactions

The reactions of bis- and tris(tert-butylethynyl)benzenes with dialkylgallium hydrides afforded two different types of products. 1,4-Di(tert-butylethynyl)benzene and dialkylgallium hydrides R(2)GaH bearing relatively small substituents (R = Et, nPr) gave the expected addition products with each C triple bond C triple bond inserted into a Ga-H bond. The intact GaR(2) groups are attached to those carbon atoms which are in alpha-position to the benzene rings, and intermolecular Ga-C interactions led to the formation of one-dimensional coordination polymers. In contrast secondary reactions with the release of the corresponding trialkylgallium derivatives GaR(3) (R = Et, nPr, iPr, CH(2)tBu, tBu) were observed for all hydrogallation reactions involving the trisalkyne 1,3,5-tris(tert-butylethynyl)benzene. A similar reaction was observed upon treatment of the 1,4-bisalkyne with a dialkylgallium hydride bearing a relatively bulky substituent (R = neopentyl). Cyclophane type molecules are formed in all these cases with two or three gallium atoms in the bridging positions between both benzene rings.     

Oxidation of ethers with dimethyldioxirane

Oxidation of a series of tert-butyl ethers Bu^tOR (R = Me, Et, CH₂CH₂Cl, Prⁱ, Buⁱ), diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, diisobutoxymethane, 1,4-dioxane, and tetrahydrofuran with dimethyldioxirane (DMDO) was studied. The reaction kinetics obeys the second-order equation w = k[DMDO][ether]. The rate constants in a range of 5–50 °C and the activation parameters of the reaction were determined. The solvent effect on the oxidation rate was studied. The oxidation products are the corresponding alcohols and carbonyl compounds. The competition between the nonradical (oxygen insertion) and radical mechanisms of the reaction is discussed. The reactions of the parent dioxirane and DMDO with a series of methyl ethers MeOr’ (r’ = Me, Et, CH₂CH₂F, Prⁱ) were studied by the density functional theory (DFT). The (U)B3LYP-6-311G(d,p) method was employed to calculate the geometry and energies of the reactants and transition states. The data obtained indicate a possible increase in the probability of oxidation via the radical route and an increase in the activation barrier for the substrates containing electron-withdrawing substituents. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2309–2318, October, 2005.     

Modification of aluminium alkoxides with dialkylmalonates

Abstract  

Depending on the reaction conditions, different aluminium dialkylmalonate derivatives were obtained by reaction of aluminium alkoxides Al(OR)₃ (R = Et, iPr, tBu) with dialkylmalonates, viz. Al(malonate)₃ (malonate = dimethyl, diethyl, di-iso-propyl and di-tert-butyl malonate), Al₂(OiPr)₄(malonate)₂ (malonate = di-iso-propyl and di-tert-butyl malonate), Al₂(OiPr)₂(di-iso-propylmalonate)₄ and Al₃(OH)(OEt)₃(diethylmalonate)₅. All compounds were characterized by NMR spectroscopy, and single crystal structure analyses are reported for each type of compound. An Al₂(OiPr)₂(dialkylmalonate)₄ derivative was only obtained by disproportionation of Al₂(OiPr)₄(di-iso-propylmalonate)₂, but not by reaction of Al(OiPr)₃ with dialkylmalonates in the corresponding molar ratio. Reactions of Al(OtBu)₃ only resulted in Al(malonate)₃ derivatives, but no transesterification was observed, contrary to the reaction of Al(OiPr)₃ with dimethyl or diethyl malonate.     

Isolation and Characterization of intermediate in the Synthesis of α-Fluorodiesters

The anion [(EtO)₂P(O)CFCO₂Et]^?Li⁺, pregenerated from its precursor diethyl (carboethoxyfluoromethyl)phosphonate (EtO)₂P(O)CFHCO₂Et and n-butyllithium, was added via syringe to a THF solution of ethyl oxaiyl chloride to yield an acylated phosphonate (EtO)₂P(O)CF(COCO₂Et)CO₂Et. In situ reaction with Grignard reagents RMgX produces the α-fluorodiesters (E,Z)-R(CO₂Et)C=CFCO₂Et in good yields. In contrast, addition of ethyl oxalyl chloride to a THF solution of diethyl (carboethoxyfluoromethyl)phosphonate anion gives an isolated intermediate (EtO)₂P(O)CFCO₂Et(CO₂Et)C=CFCO₂Et. Subsequent reaction of this isolated intermediate with Grignard reagents also affords a one-pot synthesis of the α-fluorodiesters with high E-stereoselectivity. The E-stereoselectivity increases when HMPT or DMPU is used as a cosolvent in the preparation of diethyl 2-fluoro-3-phenylfumarate (E,Z)-Ph(CO₂Et)C=CFCO₂Et.     

Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten

Treatment of pyridine‐stabilized silylene complexes [(η⁵‐C₅Me₄R)(CO)₂(H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe₃)₃) with an N‐heterocyclic carbene ^MeIⁱPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η⁵‐C₅Me₄R)(CO)₂W?SiH(Tsi)][H^MeIⁱPr] (R=Me ( 1‐Me ); R=Et ( 1‐Et )). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η²‐silaaldehydetungsten complexes [(η⁵‐C₅Me₄R)(CO)₂W{η²‐O?SiH(Tsi)}][H^MeIⁱPr] (R=Me ( 2‐Me ); R=Et ( 2‐Et )). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.     

Formation of substituted pyrazolines in the reaction of C,N-diphenylnitrilimine with a zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate

The reaction of C,N-diphenylnitrilimine with a P-zwitterion derived from Prⁱ ₃P and H₂C=C(CN)CO₂Et afforded the first representative of 2-pyrazolines containing the phosphonium group and products of the addition of nitrilimine to Prⁱ ₃P and H₂C=C(CN)CO₂Et. The reaction of the P-zwitterion with C-4-nitrophenyl-N-phenylnitrilimine gave rise to a condensation product of one Prⁱ ₃P molecule and two nitrilimine molecules. The three-dimensional structures of the compounds synthesized were established by X-ray diffraction analysis.     

Synthesis of Cyclopentapeptides with Three to Five Aib Units

Four new Aib‐containing cyclopentapeptides have been synthesized by cyclization of the corresponding linear pentapeptides using the diethyl phosphorocyanidate (DEPC)/EtN(ⁱPr)₂ method. The linear precursors were prepared via the ‘azirine/oxazolone method’, i.e., the Aib units were introduced by the reaction of amino acids or peptide acids with a 2,2‐dimethyl‐2H‐azirin‐3‐amine, followed by selective hydrolysis of the terminal amide function. Most remarkably, cyclo[(Aib)₅] exists in CDCl₃ solution in a symmetrical conformation, i.e., no intramolecular H‐bonds are detectable.     

Synthesis and Structures of New Oxidation/ Cycloaddition Products of λ3‐Cyclodiphosphazanes

Reaction of the cyclodiphosphazane [(OC₄H₈N)P(μ‐N‐t‐Bu)₂P(HN‐t‐Bu)] ( 1 ) with an equimolar quantity of diisopropyl azodicarboxylate afforded the phosphinimine product [(OC₄H₈N)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂ ‐i‐Pr)NHCO₂‐i‐Pr] ( 6 ) having a P^III‐N‐P^V skeleton. Similar products [(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂Et)NHCO₂Et] ( 7 ) and [(CO₂‐i‐Pr)HNN(CO₂‐i‐Pr)](t‐BuN=P(μ‐N‐t‐Bu)₂POCH₂CMe₂CH₂O[P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂‐i‐Pr)NH(CO₂‐i‐Pr)] ( 8 ) were spectroscopically characterized in the reaction of [(t‐BuNH)P‐N‐t‐Bu]₂ ( 2 ) and [(t‐BuNH)P(μ‐N‐t‐Bu)₂POCH₂CMe₂CH₂OP(μ‐N‐t‐Bu)₂P(NH‐t‐Bu)] ( 3 ) with diethyl‐ and diisopropyl azodicarboxylate, respectively. By contrast, the reaction of [(μ‐t‐BuN)P]₂[O‐6‐t‐Bu‐4‐Me‐C₆H₂]₂CH₂ ( 4 ) and [(C₅H₁₀N)P‐μ‐N‐t‐Bu]₂ ( 5 ) with diisopropyl azodicarboxylate afforded the mono‐ and bis‐oxidized compounds [(O)P(μ‐N‐t‐Bu)₂P][O‐6‐t‐Bu‐4‐Me‐C₆H₂]₂CH₂ ( 9 ) and [(C₅H₁₀N)(O)P‐μ‐N‐t‐Bu]₂ ( 10 ), respectively. Oxidative addition of o‐chloranil to 7 and its DIAD analogue [(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂‐i‐Pr)NHCO₂‐i‐Pr] ( 11 ) afforded [(C₆Cl₄‐1, 2‐O₂)(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂R)NHCO₂R] [R = Et ( 12 ) and i‐Pr ( 13 )] containing tetra‐ and pentacoordinate P^V atoms in the cyclodiphosphazane ring. The structures of 6 , 9 , 12 and 13 have been confirmed by X‐ray structure determination. For comparison, the X‐ray structure of the double cycloaddition product [(C₆Cl₄‐1, 2‐O₂)(t‐BuNH)PN‐t‐Bu]₂ ( 14 ), obtained from the reaction of 2 with two mole equivalents of o‐chloranil is also reported.     

Zur Synthese von Tris(diorganylphosphino)phosphanen mit Substituenten geringen Raumbedarfs

Synthesis of Tris(diorganylphosphino)phosphines with Substituents of Low Steric Hindrance The reaction of M^IP(SiMe₃)₂ (M^I = Li, Na, K) with diorganylchlorophosphines forms tris(diorganylphosphino)phosphines P(PR₂)₃ (R = Cy, Ph, i-Pr, n-Pr, Et, Me). In all cases, the stepwise formation reaction proceeds via di- and triphosphines resulting in iso-tetraphosphines which are stable in solution. Only the compounds with bulky substituents (R = Cy, Ph) can be isolated. By using quantumchemical procedures it is possible to get information about the pyramidal structure and the reaction behaviour. In agreement with these results orbitally controlled reactions occur where nucleophiles attack the central phosphorus atom.     

Two Different Structural Motifs Observed for Dimeric Dialkylaluminum and Dialkylgallium Alkynides [R2E‐C≡C‐C6H5]2

The dialkylaluminum and dialkylgallium alkynides [R₂E‐C≡C‐R′]₂ (R = Me, CMe₃; E = Al, Ga; R′ = Ph) containing C≡C triple bonds attached to their central aluminum or gallium atoms are easily obtained by the reactions of dialkylelement chlorides with lithium alkynides or by treatment of the corresponding alkyne R‐C≡C‐H with dialkylaluminum or dialkylgallium hydrides. The first reaction is favored by the precipitation of LiCl, the second one by the formation of elemental hydrogen. All products form dimers in which the carbanionic carbon atoms of the alkynido groups adopt bridging positions, but, interestingly, different types of molecular structures were observed depending on the steric demand of the substituents terminally attached to the aluminum or gallium atoms. The small methyl substituents gave structures in which the aluminum or gallium atoms seemed to be side‐on coordinated by the C≡C triple bonds of almost linear E‐C≡C groups. In contrast, the more bulky tert‐butyl groups forced an arrangement in which the C≡C triple bonds were perpendicular to the E‐E axis of the molecules. Different bonding modes result, which were analyzed by quantum‐chemical calculations.     

P(RNCH2CH2)3N: AN EFFICIENT PROMOTER FOR THE SYNTHESIS OF 3-SUBSTITUTED COUMARINS

ABSTRACT

The title compounds wherein R = Me or i-Pr function as efficient promoters for the formation of coumarins in good to excellent yields (80–95%) from salicylaldehydes and di-activated methylene compounds of the type R′CH₂CO₂Et (R′ = CO₂Et, COMe, CN). Although the yields are not generally superior to those reported in the literature, our methodology is more convenient in that milder conditions and shorter reaction times are facilitated by the use of the aforementioned commercially available catalysts.     

Intramolecular Ring-Expansion Reaction (RER) and Intermolecular Coordination of In Situ Generated Cyclic (Amino)(aryl)carbenes (cAArCs)

Cyclic (amino)(aryl)carbenes (cAArCs) based on the isoindoline core were successfully generated in situ by α-elimination of 3-alkoxyisoindolines at high temperatures or by deprotonation of isoindol-2-ium chlorides with sodium or copper(I) acetates at low temperatures. 3-Alkoxy-isoindolines 2 a , b-OR (R=Me, Et, iPr) have been prepared in high yields by the addition of a solution of 2-aryl-1,1-diphenylisoindol-2-ium triflate ( 1 a , b-OTf ; a : aryl=Dipp=2,6-diisopropylphenyl; b : Mesityl-, Mes=2,4,6-trimethylphenyl) to the corresponding alcohol (ROH) with NEt₃ at room temperature. Furthermore, the reaction of 2 a , b-OMe in diethyl ether with a tenfold excess of hydrochloric acid led to the isolation of the isoindol-2-ium chlorides 1 a , b-Cl in high yields. The thermally generated cAArC reacts with sulfur to form the thioamide 3 a . Without any additional trapping reagent, in situ generation of 1,1-diphenylisoidolin-3-ylidenes does not lead to the isolation of these compounds, but to the reaction products of the insertion of the carbene carbon atom into an ortho C−H bond of a phenyl substituent, followed by ring-expansion reaction; namely, anthracene derivatives 9-N(H)aryl-10-Ph-C₁₄H₈ 4 a , b ( a : Dipp; b : Mes). These compounds are conveniently synthesized by deprotonation of the isoindol-2-ium chlorides with sodium acetate in high yields. Deprotonation of 1 a-Cl with copper(I) acetate at low temperatures afforded a mixture of 4 a and the corresponding cAArC copper(I) chloride 5 a , and allowed the isolation and structural characterization of the first example of a cAArC copper complex of general formula [(cAArC)CuCl].     

Conformational analysis and simulation of the structures of diisobutylsilanediol and dihydroxytetraalkyldisiloxanes and their analogs [R2(HO)Si]2X (X = CH2, S), precursors of liquid-crystalline phases

Molecular mechanics studies of structure formation in condensed phases of [R₂(HO)Si]₂X (X = CH₂ (dihydroxydicarbosilanes) and X = S (dihydroxydisilthians)) compounds have been performed and the results have been compared with those obtained for previously known columnar mesophases of [R₂(HO)Si]₂O (R = Et and Pr) (dihydroxydisiloxanes). Conformational analysis demonstrates the similarity in structure and cross-linking of dihydroxydisiloxanes and dihydroxydicarbosilanes and the difference between these compounds and dihydroxydisilthians. This allows the conclusion that for dihydroxydicarbosilanes the columnar mesophase formed by H-associates can occur. Simulation of dimeric and trimeric H-associates for (Buⁱ)₂Si(OH)₂, which belong to the same class of mesophases, has been performed.Deceased in August, 1995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1711–1715, September, 1995.This work is supported by the International Science Foundation (Grant MP5 000).     

Synthesis of volatile alkoxygallium hydrides and study of their thermostability

A method for the synthesis of alkoxygallium hydrides (ROGaH₂ and (RO)₂GaH, where R=Prⁱ, Buⁱ) was proposed. The method is based on the reaction of gallane GaH₃ with one or two equivalents of the corresponding alcohol. Thermolysis of these compounds was studied by differential thermogravimetry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1655–1657, August, 1998.     

Combining Neopentyllithium with Potassium tert‐Butoxide: Formation of an Alkane‐Soluble Lochmann–Schlosser Superbase

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 Li_xK_yNp_z(OtBu)_x+y?z.     

Einfache Synthese von Alkylaluminium‐ und Alkylgalliumhydriden – Kristallstrukturen von [(Me3C)2GaH]3 und den neuartigen Sesquihydriden [(Me3C)2EH]2[EH2CMe3]2 (E = Al,Ga)

Facile Syntheses of Alkylaluminium and Alkylgallium Hydrides – Crystal Structures of [(Me₃C)₂GaH]₃ and the Novel Sesquihydrides [(Me₃C)₂EH]₂[EH₂CMe₃]₂ (E = Al, Ga) The facile syntheses of some important, sterically highly shielded dialkylaluminium hydrides R₂AlH [R = CMe₃, CH(SiMe₃)₂] succeeded by the reaction of the corresponding trialkylaluminium compounds with the alane adduct AlH₃ × NMe₂Et in a 2 to 1 molar ratio. This route is not suitable for the synthesis of monoalkylaluminium dihydrides. An excess of AlH₃ yielded the novel sesquihydride [(Me₃C)₂AlH]₂[AlH₂CMe₃]₂ ( 3 ) as the hydride richest compound which possesses an unprecedented heterocycle comprising four aluminium and four hydrogen atoms in the solid state. The dialkylgallium hydride (Me₃C)₂GaH ( 4 ) was formed on a similar route by the treatment of tri(tert‐butyl)gallane with the adduct GaH₃ · NMe₂Et. As shown by a crystal structure determination, compound 4 is a trimer in the solid state possessing a Ga₃H₃ heterocycle. A gallium sesquihydride analogous to compound 3 , [(Me₃C)₂GaH]₂[GaH₂CMe₃]₂ ( 5 ), was formed on employing an excess of GaH₃.     

π‐Excess Aromatic σ2P Ligands: Formation of a Heterocyclic 1,2‐Diphosphine by the Addition of tBuLi and Subsequent Inverse Addition of the Product at the P=C Bonds of Two Molecules of 1‐Neopentyl‐1,3‐benzazaphosphole

The reactivity of tBuLi (pentane) toward the N‐neopentyl‐substituted π‐excess P=CH–N heterocycle 1 depends on the solvent (tetrahydrofuran, diethyl ether, hexane, and toluene) and reaction conditions. Trapping of the resulting organolithium compounds with CO₂/ClSiMe₃, ClSiMe₃, or EtI led to various products indicating CH lithiation ( 1a , b ), normal addition of tBuLi at the P=C bond (E/Z ‐2a , b ), inverse addition of the primary addition product 2_Li at the P=C bond of a second molecule 1 , affording 3‐tert‐butyl‐2,2’‐bis(1,3‐benzazaphospholines) 3 , or inverse addition of tBuLi ( 4b,c ). The formation of 3 demonstrates a novel route to asymmetric heterocyclic 1,2‐diphosphine ligands. The structure elucidation of the new compounds is based on their ³¹P and ¹³C NMR data with conclusive chemical shifts and P–C coupling constants, that of the isolated PH‐functionalized diphosphine 3 on crystal structure analysis.     

Synthesis and Crystal Structures of Copper Zinc Phenylthiolate and the First Copper Zinc Selenolate and Tellurolate Complexes

Five copper zinc phenylchalcogenolate complexes [(iPr₃PCu)₃(ZnMe₂)₂(SPh)₃] ( 1 ), [(iPr₃PCu)₂(ZnPh)₄(SPh)₆] ( 2 ), [(iPr₃PCu)₂(ZnEt)₄(SPh)₆] ( 3 ), [(iPr₃PCu)₃(ZnEt)(SePh)₄] ( 4 ), and [(iPr₃PCu)₃Cu(iPr₃PZn)(TePh)₆] ( 5 ) were synthesized by the reaction of phosphine stabilized copper phenylchalcogenolate complexes with ZnR₂ (R = Me, Et, Ph) with and without additional chalcogenol. The novel mixed metal compounds were characterized by single‐crystal X‐ray structure analysis and NMR spectroscopy. 4 and 5 are the first examples of compounds with a Zn–Se–Cu or a Zn–Te–Cu linkage, respectively.     

Synthesis of Aluminum N,N-Dialkylcarbamates by Insertion of CO2 into Al−N Bonds

Despite decades of research on various carbamates and their important applications, only one aluminum N,N-dialkylcarbamate (ADC) with an aluminum:carbamate ratio of 1 : 3 has been structurally described and comprehensively studied so far, namely tris(diisopropyl)carbamate. The reasons for this situation include problems with the used synthetic routes. The process of CO₂ insertion into Al−N bonds of tris(dialkylamido)alanes resolved these difficulties. Using this advantageous synthetic route, the dimethyl and diethyl, as well as the pyrrolidino, piperidino, and N-methylpiperazino derivatives were now successfully prepared. These ADCs were investigated by solid-state NMR spectroscopy, where line-shape analyses of the ²⁷Al NMR spectra allowed conclusions with respect to the determination of the quadrupole coupling parameters. Furthermore, data of an intermediate during the CO₂ insertion into tris(diisopropylamido)alane were obtained by in-situ IR spectroscopy, which were complemented by NMR measurements of samples periodically taken during the reaction. Partial hydrolysis of tris(pyrrolidino)carbamate revealed a complex Al₃(μ₃-O) cluster structure, which was elucidated by single crystal X-ray diffraction.