Unexpected Silaazetidine Formation in the Thermolysis of thf‐Supported Silanimine Et2Si=N–SitBu3·thf

The silyl amide Et₂SiCl‐NLi‐SitBu₃ can be cleanly prepared from precursor silylamine Et₂SiCl‐NH‐SitBu₃ and Li[nBu]. The CF₃SO₃SiMe₃ induced LiCl elimination of Et₂SiCl‐NLi‐SitBu₃ in thf afforded a 2‐silaazetidine derivative by [2+2] cycloaddition of Et₂Si=N–SitBu₃ with Et₂Si(OCH=CH₂)–NH–SitBu₃. X‐ray quality crystals of this 2‐silaazetidine derivative (triclinic, space group P$\bar{1}$ ) were grown from benzene at room temperature. The starting material for this approach, Et₂SiCl–NH–SitBu₃, is water‐sensitive. Hydrolysis of Et₂SiCl‐NH‐SitBu₃ gave [tBu₃SiNH₃]Cl along with (Et₂SiO)_n oligomers. The hydro chloride [tBu₃SiNH₃]Cl could be isolated and was characterized by X‐ray crystallography (trigonal, space group P$\bar{3}$ ).     

Regioselective stannylmetalation of acetylenes in the presence of transition-metal catalyst

The reaction of terminal acetylenes with Bu₃SnMgMe, Bu₃SnA1Et₂, or (Bu₃Sn)₂Zn in the presence of various transition-metal catalysts provides vinylstannanes in good yields. Whereas copper catalysed stannylmagnesation of 4-benzyloxy-1-butyne gives (E)-4-benzyloxy-1-tributylstannyl-1-butene exclusively, palladium catalysed stannylzincation affords 4-benzyloxy-2-tributylstannyl-1-butene preferentially.     

Organoaluminium assisted rearrangements of five-membered ring enol ethers with vinyl substituents

Such organoaluminium reagents as ⁱBu₃A1, PhC=CA1Et₂, and Et₂A1SPh mediate the title reactions in three different directions. (1) [3,3]sigmatropic rearrangement producing 7-membered rings. (2) isomerization to form vinylcyclopropane derivatives and (3) S_N2 type reaction with phenylthio anion via oxolane ring opening.     

Reaction Mechanism of the Hydrogermylation/Hydrostannylation of Unactivated Alkenes with Two‐Coordinate EII Hydrides (E=Ge,Sn): A Theoretical Study

Quantum chemical calculations using density functional theory with the TPSS+D3(BJ) and M06‐2X+D3(ABC) functionals have been carried out to understand the mechanisms of catalyst‐free hydrogermylation/hydrostannylation reactions between the two‐coordinate hydrido‐tetrylenes :E(H)(L⁺) (E=Ge or Sn, L⁺=N(Ar⁺)(SiiPr₃); Ar⁺=C₆H₂{C(H)Ph₂}₂iPr‐2,6,4) and a range of unactivated terminal (C₂H₃R, R=H, Ph, or tBu) and cyclic [(CH)₂(CH₂)₂(CH₂)_n, n=1, 2, or 4] alkenes. The calculations suggest that the addition reactions of the germylenes and stannylenes to the cyclic and acyclic alkenes occur as one‐step processes through formal [2+2] addition of the E?H fragment across the C?C π bond. The reactions have moderate barriers and are weakly exergonic. The steric bulk of the tetrylene amido groups has little influence on the activation barriers and on the reaction energies of the anti‐Markovnikov pathway, but the Markovnikov addition is clearly disfavored by the size of the substituents. The addition of the tetrylenes to the cyclic alkenes is less exergonic than the addition to the terminal alkenes, which agrees with the experimentally observed reversibility of the former reactions. The hydrogermylation reactions have lower activation energies and are more exergonic than the stannylene addition. An energy decomposition analysis of the transition state for the hydrogermylation of cyclohexene shows that the reaction takes place with simultaneous formation of the Ge?C and (Ge)H?C′ bonds. The dominant orbitals of the germylene are the σ‐type lone pair MO of Ge, which serves as a donor orbital, and the vacant p(π) MO of Ge, which acts as acceptor orbital for the π* and π MOs of the olefin. Inspection of the transition states of some selected reactions suggests that the differences between the activation energies come from a delicate balance between the deformation energies of the interacting species and their interaction energies.     

Reactions of tBu2P–PLi–PtBu2 with [(Et3P)2MCl2] (M = Ni,Pd, Pt). Synthesis and Properties of [(1,2‐η‐tBu2P=P–PtBu2)M(PEt3)Cl] (M=Ni,Pd)

^tBu₂P–PLi–P^tBu₂·2THF reacts with [cis‐(Et₃P)₂MCl₂] (M = Ni, Pd) yielding [(1,2‐η‐^tBu₂P=P–P^tBu₂)Ni(PEt₃)Cl] and [(1,2‐η‐^tBu₂P=P–P^tBu2)Pd(PEt₃)Cl], respectively. ^tBu₂P– PLi–P^tBu₂ undergoes an oxidation process and the ^tBu₂P–P–P^tBu₂ ligand adopts in the products the structure of a side‐on bonded 1,1‐di‐tert‐butyl‐2‐(di‐tert‐butylphosphino)diphosphenium cation with a short P–P bond. Surprisingly, the reaction of ^tBu₂P–PLi–P^tBu₂·2THF with [cis‐(Et₃P)₂PtCl₂] does not yield [(1,2‐η‐^tBu₂P=P–P^tBu₂)Pt(PEt₃)Cl].     

Reaktionen von tBu2P–P=P(Me)tBu2 mit (Et3P)2NiCl2 und [{η2‐C2H4}Ni(PEt3)2]

Coordination Chemistry of P‐rich Phosphanes and Silylphosphanes. XXIII. Reactions of ^tBu₂P–P=P(Me)^tBu₂ with (Et₃P)₂NiCl₂ and [{η²‐C₂H₄}Ni(PEt₃)₂] ^tBu₂P–P=P(Me)^tBu₂ ( 1 ) forms with (Et₃P)₂NiCl₂ ( 2 ) and Na(Nph) the [μ‐(1,3 : 2,3‐η‐^tBu₂P₄^tBu₂){Ni(PEt₃)Cl}₂] ( 3 ) as main product. Using Na/Hg instead as reducing agent the Ni⁰ compounds [{η²‐^tBu₂P–P}Ni(PEt₃)₂] ( 4 ), [{η²‐^tBu₂P–P=P–P^tBu₂}Ni(PEt₃)₂] ( 5 ) and [(Et₃P)Ni(μ‐P^tBu₂)]₂ ( 6 ) with four‐membered Ni₂P₂ ring result. [{η²‐C₂H₄}Ni(PEt₃)₂] yields with 1 also 4 . The compounds were characterized by ¹H and ³¹P{¹H} NMR investigations and 3 also by a single crystal X‐ray analysis. It crystallizes triclinic in the space group P 1 with a = 1129.4(2), b = 1256.8(3), c = 1569.5(3) pm, α = 72.44(3)°, β = 70.52(3)° and γ = 74.20(3)°.     

Radical Silyl- and Germylzincation of Propargylic Alcohols

The silyl- and germylzincation of terminal or internal propargylic alcohols by reaction with (Me₃Si)₃SiH/Et₂Zn, [(Me₃Si)₃Si]₂Zn/Et₂Zn or Ph₃GeH/Et₂Zn is examined. These reactions proceed through the addition of silicon- or germanium-centered radicals across the carbon≡carbon triple bond followed by the trapping by diethylzinc of the produced vinyl radical through homolytic substitution at the zinc atom. The influence of the hydroxy unit on the regio- and stereoselectivity of these reactions is discussed and compared to its role played in radical hydrosilylation and hydrogermylation reactions. Protocols developed to achieve the β-regioselective silylzincation of propargyl alcohol and the α-regioselective germylzincation of internal propargylic alcohols are particularly important, as they occur with trans stereoselectivity. For both procedures the C(sp²)−Zn bond remains available for subsequent in-situ electrophilic substitution leading overall to net alkyne trans difunctionalization.     

Reaktionen von tBu2P?PP(Br)tBu2 mit Phosphanen. Ein Weg zu unterschiedlich substituierten Phosphinophosphiniden-Phosphoranen

Reactions of ^tBu₂P? P?P(Br)^tBu₂ with Phosphanes A Route to Variously Substituted Phosphinophosphinidene-phosphoranes ^tBu₂P? P?P(Br)^tBu₂ 1 reacts with PR₃ [R₃ = Et₃, ^tBu₃, Ph₃, (NMe₂)₃, (NEt₂)₃, (NEt₂)₂Me, Me₂SiMe₃] according to ^tBu₂P? P?P(Br)^tBu₂ + PR₃ → ^tBu₂P? P?PR₃ + ^tBu₂PBr While 1 decomposes above ?30°C yielding ^tBu₂PBr and the cyclophosphanes (^tBu₂P)₃P₃ and (^tBu₂P)₄P₄, there is no condensation to give any cyclophosphanes from the intermediately formed ^tBu₂P? P in the presence of PR₃. The chlorophosphanes ^tBu₂PCl, ^tBuPPhCl, (Et₂N)₂PCl and Ph₂PCl as well as (CF₃)₂PBr react quite analogously to the above equation yielding ^tBu₂P? P?P(Cl)^tBu₂, ^tBu₂P? P?P^tBuPhCl, ^tBu₂P? P?P(NEt₂)₂Cl and ^tBu₂P? P?P(NEt₂)₂Br.     

Hydrogermylation of silyl-substituted ethylenes with trimethylgermane and trichlorogermane etherate

Investigation of the reaction of some vinylsilanes of the general formula Cl_3?n (CH₃) _n SiCH=CH₂ (n = 0,1,2,3) and 1,2-bis(trimethylsilyl)ethylene with trimethylgermane and trichlorogermane etherate was carried out. It was established that hydrogermylation only at the use of HGeCl₃·2Et₂O was sensitive to the nature of the substituting silyl groups in vinylsilanes. Nucleophilic mechanism of the reaction of trichlorogermane etherate with vinylsilanes is suggested.     

Asymmetric alkylation of aromatic aldehydes with dialkylzinc catalyzed by novel amino derivatives of hydroxytetrahydropyran

Novel, specially prepared, tetrahydropyran‐based γ‐amino alcohols (S)‐2‐(aminomethyl)‐3‐hydroxy‐6‐ethoxy(phenoxy)‐tetrahydropyrans ( I ) (amino = n‐Bu₂N, piperidinyl, pyrrolidinyl, azetidinyl) were tested as catalysts in the asymmetric addition of Et₂Zn and n‐Bu₂Zn to (hetero)aromatic aldehydes. In most cases the phenoxy derivatives of I acted more enantioselectively than the ethoxy ones. The dibutylamino derivaties showed the least enantioselectivity; the pyrrolidinyl derivatives were more active as catalysts than piperidinyl and azetidinyl compounds. The highest enantioselectivity was observed in the addition of Et₂Zn to benzaldehyde in the presence of (S)‐2‐(N‐pyrrolidinylmethyl)‐3‐hydroxy‐6‐phenoxytetrahydropyran. The corresponding alcohol was prepared with 72% ee (R‐configuration). The addition of dibutylzinc proceeded slowly and less selectively. The alkylation of (hetero)aromatic aldehydes with Et₂Zn and n‐Bu₂Zn was also studied in the presence of the known optical inductor (1S,2R)‐N,N‐dibutylnorephedrine. Some chiral aromatic secondary alcohols were synthesized in high chemical yields and up to 93% ee enantioselectivity. Copyright © 1999 John Wiley & Sons, Ltd.     

Reactions of trialkylalanes with cyclic acetals and orthoformates in CH2Cl2 and ClCH2CH2Cl as solvents

Under mild conditions, trialkylalanes (Et₃Al and Buⁱ ₃Al) in chlorine-containing solvents (CH₂Cl₂ or ClCH₂CH₂Cl) react with cyclic acetals and orthoformates to form glycol monoethers and dialkylacetals, respectively, in high yields. The ¹H NMR spectroscopic data demonstrate that CH₂Cl₂ or ClCH₂CH₂Cl interacts with Buⁱ ₃Al.     

Reactions of silylium ions with nucleophiles

Transformation of the diethylsilylium cation Et₂Si⁺H into ethyl-and dimethylsilylium ions EtSi⁺H₂ and Me₂Si⁺H in reactions with nucleophiles is induced by electron-donor compounds. Their activity increases in the order Bu₂O < BuOH < (Me₃Si)₂O < C₆H₆ and is determined by the structure of the intermediate adduct and electron density distribution in it. Qualitative estimation shows that the affinity of the tritiated diethylsilylium cation Et₂Si⁺T for a nucleophile increases in the order C₆H₆ < BuOH < Bu₂O < (Me₃Si)₂O. The higher affinity of the Et₂Si⁺H cation for hexamethyldisiloxane compared to dibutyl ether, at similar basicity of the nucleophiles, is attributable to the higher charge of the oxygen atom in (Me₂Si)₂O.     

Organic base catalyzed carbonyl allylation of methyl trifluoropyruvate with activated alkenes

The carbonyl allylation of methyl trifluoropyruvate (MeTFP) with activated alkenes has been investigated in detail using organic bases as catalysts. Organic bases, such as DMAP, Et₃N, DABCO, NMM, Et₂NH, and quinine, could deprotonate the allylic hydrogen of activated alkenes and furnish nucleophilic species to undergo the addition reaction with methyl trifluoropyruvate and afford versatile homoallylic alcohols with CF₃ group in excellent yields. The ¹⁹F NMR monitoring indicated that the isomerization induced by base gave two separable diastereoisomers in an equilibrium ratio of 1:3. The relative configuration of hydroxy and the neighboring alkyl group in the major diastereoisomer was determined as syn-configuration by X-ray diffraction analysis.     

Zur Reaktion von Trifluorhalomethanen mit Phosphanen

On the Reaction of Trifluorohalomethanes with Phosphanes The reactions of trifluorohalomethanes CF₃X (X = Cl, Br, I) with Ph₃P, Bu₃P, (Me₂N)₃P, and (Et₂N)₃P were investigated. CClF₃ does not react. In the reactions of CBrF₃ and CF₃I with Bu₃P in acetonitrile trifluorophosphonium salts, [Bu₃PCF₃]X (X = Br, I), are formed, whereas gaseous CF₃I and Bu₃P yield Bu₂PCF₃. Depending on the reaction conditions the aminophosphanes form either [(R₂N)₃PX]X (R = Me, Et; X = Br, I) and CF₃H or [(R₂N)₃PCF₃]X.     

Dihexylmagnesium promoted carboalumination of silylacetylenes

The bimetallic species, ⁿBu₂Mg·2Et₃A1 has been found to be effective for the carboalumination of silylacetylenes.     

Neue viergliedrige GaE‐ und InE‐Ringverbindungen: Synthese und Kristallstruktur von [Et2InE(SiMe3)2]2 und [GaCl(PtBu2Me)E(SiMe3)]2 (E = P,As)

New GaE and InE Four Membered Ring Compounds: Syntheses and Crystal Structures of [Et₂InE(SiMe₃)₂]₂ and [GaCl(P t Bu₂Me)E(SiMe₃)]₂ (E = P, As) Et₃In · PR₃ (R = Et, iPr) reacts with H₂ESiMe₃ under liberation of C₂H₆ and EH₃ to form the cyclic compounds [Et₂InE(SiMe₃)₂]₂ ( 1 a : E = P, 1 b : E = As). 1 consists of a planar four membered In₂E₂ ring in which the indium and phosphorus or arsenic atoms are four coordinated. In contrast, the phosphorus/arsenic atoms in [GaCl(PtBu₂Me)E(SiMe₃)]₂ ( 2 a : E = P, 2 b : E = As) only have the coordination number three. 2 results from the reaction of GaCl₃ · PtBu₂Me with As(SiMe₃)₃ or Li₂PSiMe₃ respectively, and displays a folded four membered Ga₂E₂ ring as central structural motif. 1 and 2 have been characterised by single crystal X‐ray diffraction analysis as well as ¹H and ³¹P{¹H} NMR spectroscopy.     

Further development and optimization of a quartz tube atomizer for a gas chromatography — atomic absorption spectrometer system

A new quartz T-tube furnace design based on commercial heater modules was evaluated for the determination of organolead and organotin compounds. Furnace operating conditions for both packed and capillary column operation were optimized by multivariate analysis. Response reproducibility ranged from 1.8 to 3.9% relative standard deviation. Calculated limits of detection were 1.4–2.0 pg for Et₄Pb (as Pb) and 2.2–5.5 pg for Bu₄Sn (as Sn). The limits of detection after application of Savitsky-Golay smoothing were 1.1–1.2 pg for Et₄Pb (as Pb) and 2–3.7 pg for Bu₄Sn (as Sn).     

Novel Stibano Amines: Synthesis and Reactivity towards Group 13 Element Organics

In this paper, the syntheses of antimony and nitrogen containing interpnictogen compounds are described. Using tBu₂SbCl as reagent, a tert‐butyl‐substituted stibano amine tBu₂SbN(H)tBu ( 1 ), an isopropyl‐substituted interpnictogen tBu₂SbN(H)iPr ( 2 ), and a primary stibano amine tBu₂SbNH₂ ( 3 ) are obtained. Condensation of compound 3 leads to compound (tBu₂Sb)₂NH ( 4 ) with elimination of ammonia. All compounds were characterized by ¹H, ¹³C, ¹⁵N NMR spectroscopy, mass spectrometry, and IR spectroscopy. These interpnictogens represent a new class of single‐source precursors for MOVPE process. The primary amine 3 reacts with AlEt₃ and GaEt₃ to form previously unknown stibane‐substituted [tBu₂SbN(H)MEt₂]₂ ring compounds [M = Al ( 5 ), M = Ga ( 6 )], which were characterized by different spectroscopic methods. Moreover, compounds 4 and 6 could be analyzed by X‐ray diffraction.     

Cu(OTf)2/Et3N-promoted cyclocondensation of activated α-methylene alkenes and nitroolefins: a novel one-pot synthesis of polysubstituted benzenes

A simple and efficient one-pot synthesis of polyfunctionalized benzenes has been developed via cyclocondensation of activated α-methylene alkenes such as vinyl malononitriles and ethyl vinyl cyanoacetates with nitroolefins using Cu(OTf)₂/Et₃N as a novel catalytic system.     

Regiospecific substitution of carbonyl by phosphine ligands in hydrocarbyl-substituted carbonyl clusters. Synthesis and spectroscopic characterization of Fe3(CO)8(PPh3)(μ3-η2- ⊥ -EtC2Et) and (η5-C5H5)NiFe2(CO)5(PPh3)(η3-η2- ⊥-C2But)

The complexes Fe₃(CO)₈(PPh₃)(μ₃-η²- ⊥ -EtC₂Et) and (η⁵-C₅H₅)NiFe₂(CO)₅(PPh₃)(η₃-η²- ⊥-C₂Bu^t) have been obtained by treating Fe₃(CO)₉(C₂Et₂) or (Cp)NiFe₂(CO)₆(C₂Bu^t) with PPh₃ under mild conditions; the substituted clustes have been characterized spectroscopically. Structures are proposed in which the phosphine is on the unique metalatom σ-bonded to the alkyne or acetylide moiety. Replacement of CO by PPh₃ ligands rather than by addition, is observed for the formally unsaturated Fe₃(CO)₉(C₂Et₂). Reorientation of the acetylide was expected for (Cp)NiFe₂(CO)₆(C₂Bu^t) upon substitution, but was not observed.