- LITHIUM-POTASSIUM EXCHANGE IN ALKYLLITHIUM/POTASSIUM t-PENTOXIDE SYSTEMS XIV. INTERACTIONS OF ALKOXIDES
-
Benzylpotassium containing only traces of lithium compounds is formed in the reaction of alkyllithium, potassium alkoxide and toluene over broad ranges of molar ratios of the reaction components and reaction times.This confirms that metal-metal exchange is occurring under the conditions used.The potassium alkoxide is used in stoichiometric amount for the metallation of toluene and is not only a catalyst.Use of a larger excess of potassium alkoxide leads to formation of its adduct with benzylpotassium.Various mechanisms for the above reaction are considered and formation of lithium alkoxide is assumed to help drive the equilibria towards the observed products.
- Lochmann, L.,Trekoval, J.
-
-
Read Online
- Comparison of Two Phosphinidenes Binding to Silicon(IV)dichloride as well as to Silylene
-
The cyclic alkyl(amino) carbene (cAAC) anchored silylene with two phosphinidenes was isolated as (cAAC)Si{P(cAAC)}2 (3) at room temperature, which was synthesized from the reduction of (Cl2)Si{P(cAAC)}2 (2) using 2 equiv of KC8. Compound 2 resulted from the reaction of 2 equiv of (cAAC)PK (1) with 1 equiv of SiCl4. Compounds 2 and 3 are the first examples where two terminal phosphinidenes are binding each to a silicon center characterized by single crystal X-ray structural analysis. Furthermore, the structure and bonding of compounds 2 and 3 have been investigated by theoretical methods for comparison.
- Kundu, Subrata,Sinhababu, Soumen,Siddiqui, Mujahuddin M.,Luebben, Anna V.,Dittrich, Birger,Yang, Tao,Frenking, Gernot,Roesky, Herbert W.
-
-
Read Online
- Reversible Formation of a Cerium-Bound Terminal Hydride: Ce(C5Me4SiMe3)2(H)(thf)
-
The use of the bulky cyclopentadienyl ligand Cp′ (Cp′ = C5Me4SiMe3) to stabilize cerium hydrides has resulted in the preparation of two novel tuck-in complexes with C–H activated SiMe3groups. Subsequent reaction
- Summerscales, Owen T.,Batista, Enrique R.,Scott, Brian L.,Wilkerson, Marianne P.,Sutton, Andrew D.
-
-
Read Online
- CO Displacement in an Oxidative Addition of Primary Silanes to Rhodium(I)
-
The rhodium dicarbonyl {PhB(Ox Me2)2ImMes}Rh(CO)2 (1) and primary silanes react by oxidative addition of a nonpolar Si-H bond and, uniquely, a thermal dissociation of CO. These reactions are reversible, and kinetic measurements model the approach to equilibrium. Thus, 1 and RSiH3 react by oxidative addition at room temperature in the dark, even in CO-Saturated solutions. The oxidative addition reaction is first-Order in both 1 and RSiH3, with rate constants for oxidative addition of PhSiH3 and PhSiD3 revealing kH/kD a 1. The reverse reaction, reductive elimination of Si-H from {PhB(Ox Me2)2ImMes}RhH(SiH2R)CO (2), is also first-Order in [2] and depends on [CO]. The equilibrium concentrations, determined over a 30 °C temperature range, provide ?"H° = a'5.5 ± 0.2 kcal/mol and ?"S° = a'16 ± 1 cal·mol-1K-1 (for 1 a?., 2). The rate laws and activation parameters for oxidative addition (?"Ha§§ = 11 ± 1 kcal·mol-1 and ?"Sa§§ = a'26 ± 3 cal·mol-1·K-1) and reductive elimination (?"Ha§§ = 17 ± 1 kcal·mol-1 and ?"Sa§§ = a'10 ± 3 cal·mol-1K-1), particularly the negative activation entropy for both forward and reverse reactions, suggest the transition state of the rate-Determining step contains {PhB(Ox Me2)2ImMes}Rh(CO)2 and RSiH3. Comparison of a series of primary silanes reveals that oxidative addition of arylsilanes is ca. 5× faster than alkylsilanes, whereas reductive elimination of Rh-Si/Rh-H from alkylsilyl and arylsilyl rhodium(III) occurs with similar rate constants. Thus, the equilibrium constant Ke for oxidative addition of arylsilanes is >1, whereas reductive elimination is favored for alkylsilanes.
- Biswas, Abhranil,Ellern, Arkady,Sadow, Aaron D.
-
-
- Metalation of toluene and cumene with alkali metal-crown ether complexes
-
Metalation of toluene and isopropylbenzene with alkali metal-crown ether complexes led to the corresponding α-metalated alkylbenzenes. Treatment of the latter in succession with solid carbon dioxide, water, and hydrochloric acid gave carboxylic or dicarboxylic acids in 65-78% yield. Metalation of isopropylbenzene with sodium or potassium crown ether complexes above 90°C was accompanied by cleavage of the polyether ring with formation of organometallic compounds which then reacted with isopropylbenzene to produce 2-sodio(potassio)-2-phenylpropane and open-chain oligoether.
- Shabanov,Seidov,Gasanova,Kakhramanova,Gasanova
-
experimental part
p. 26 - 29
(2009/06/28)
-
- Process
-
A process for the preparation of an olefin homopolymer or copolymer comprising polymerising at least one C2-20-α-olefin in slurry phase in the presence of 1) a metallocene compound of formula I: (Cp) (Cp″) RnMX2 (I) wherei
- -
-
Page/Page column 5
(2010/11/25)
-
- BESTIMMUNG DER IONENPAAR-BASIZITAT VON LITHIUM- UND KALIUMAMIDEN
-
Ion pair basicities of lithio and potassio salts of some secondary amines were determined by equilibration with benzyl compounds.With these bases it is possible to span a range of about 19 pK-units from pK = 27 up to 46.The structural dependence of thermodynamic as well as kinetic basicity is discussed.Some new effective amide bases for preparative purposes are recommended.For the first time the pK-value of toluene has been determined by direct equilibration.It amounts to 40.7 in tetrahydrofuran.
- Ahlbrecht, Hubertus,Schneider, Gunther
-
p. 4729 - 4742
(2007/10/02)
-
- Dissociation Behavior of Benzylalkali Compounds in Tetrahydrofuran: Effect of Countercation, Aromatic Methoxy Substitution, and α-Alkyl Substitution
-
Conductometric measurements are carried out on different benzylalkali compounds (benzylcesium, -potassium, -sodium, and -lithium, and their o-CH3O and p-CH3O derivatives) in tetrahydrofuran at various temperatures, in order to get information on their dissociative behavior and on the influence of the alkali cation, aromatic methoxy substitution, and α-alkyl substitution on the carbon-metal bond strength.The dissociation constants of the organometallic compounds are determined by using the Kraus and Bray equation, the Fuoss equation, the Wooster equation, or by curve fitting depending on which species are involved in the solution conductance.Temperature variation of Kd is used to determine the enthalpy and entropy of dissociation.The information previously acquired by quantum chemical calculations and NMR measurements on the electronic structure of benzyl-type carbanions and the corresponding organometallic compounds appears to be of great value in interpreting the dissociation behavior of the benzyl- and styrylalkali compounds (which are also included in the study).The resonance saturation phenomenon encountered in the quantum chemical and NMR study turns out to be an important factor in the dissociative behavior of p-CH3O compounds, as compared to the unsubstituted cases.The smaller dissociation costants of the o-CH3O compounds also parallel the results of the quantum chemical calculations, showing an additional interaction between the cation and the CH3O group.The weakening of the carbon-metal bond upon α-alkyl substitution parallels the increase of dissociation capability when alkyl or polymer chain substituents are present on the α-carbon atom.
- Vanermen, G.,Beylen, M. Van,Geerlings, P.
-
p. 603 - 607
(2007/10/02)
-