Synthese von Magnesium-bis[N,N′-bis(trimethylsilyl)benzamidinat] als Bis(THF)- und Benzonitril-Addukt

Synthesis of Magnesium Bis[N,N′ -bis(trimethylsilyl)benzamidinate] as both Bis(THF) and Benzonitrile Adduct Magnesium bis[bis(trimethylsilyl)amide] 1 , reacts with benzonitrile in toluene at room temperature to yield magnesium bis[N,N′-bis(trimethylsilyl)benzamidinate]-benzonitrile(1/1) 2 . Addition of THF leads to a quantitative substitution of the benzonitrile ligand by two THF molecules. The performance of the addition reaction in THF yields magnesium bis[N,N′-bis(trimethylsilyl)benzamidinate] · THF(1/2) 3 . The upper benzonitrile complex 2 , crystallizes in the orthorhombic space group Pbcn with {a = 1383.2(2); b = 2589.1(4); c = 1133.7(1) pm; Z = 4}. The magnesium atom is coordinated distorted trigonal-bipyramidal, where the benzonitrile ligand lies within the equatorial plane. The axial bound nitrogen atom of the benzamidinate substitution shows with a value of 213 pm a slightly longer bond distance to the metal center than the one in the equatorial plane (210 pm). The steric strain within the benzamidinate ligand leads to an elongation of the silicon atoms out of the 1,3-diazaallylic moiety under an enlargement of the C? N? Si angle to 131°.     

4,5-Dihydro-1H-azepine aus aktivierten Cyclobutenen und 1,3-Dipolen

Cycloaddition of diphenylnitrile ylide to dicyanocyclobutene and of a mesoionic oxazolium-5-olate to isopropylidenecyclobutenone yields dihydroazepine derivatives by cleavage of the strained internal σ-bonds in the primarily formed bicyclic adducts.     

Application of force field calculations—III: Conformational isomerism and dynamic gearing in ethanes with many alkyl substituents. EFF calculations and dynamic NMR measurements

Force-field calculations and dynamic NMR measurements of symmetrical 1,2-dialkyl-1,1,2,2-tetramethylethanes where the alkyl group is methyl, ethyl, isobutyl, neopentyl, isopropyl, cyclohexyl, or t-butyl are reported. There is usually slightly less than one third of the population in the anti-conformation, slightly more than two thirds in gauche conformations but the t-butyl compound adopts only the anti-conformation. Barriers to rotation vary markedly between 8.1 and 13.8kcal/mol, being lower for secondary alkyl groups than for primary alkyl groups. Calculations suggest that rotation about the central bond and rotation of the secondary alkyl group, by taking place in a concerted fashion, produce several rotational itineraries of similar energies. The low barrier is thus due to a favourable entropy effect.     

On the consistency strength of ‘Accessible’ Jonsson Cardinals and of the Weak Chang Conjecture

Using the core model K we determine better lower bounds for the consistency strength of some combinatorial principles:I. Assume that λ is a Jonsson cardinal which is ‘accessible’ in the sense that at least one of (1)-(4) holds: (1) λ is a successor cardinal; (2) λ = ω_ξ and ξ<λ; (3) λ is singular of uncountable cofinality; (4) λ is a regular but not weakly hyper-Mahlo. Then 0² exists.II. For λ = ?⁺ a successor cardinal we consider the weak Chang Conjecture, wCC(λ), which is a consequence of the Chang transfer property (λ⁺, λ)?(λ, ?).III. If λ = ?⁺?ω₂, then wCC(λ) implies the existence of 0².IV. We can determine the consistency strenght of wCC(ω₁). We include a relatively simple definition of the core model which together with the results of Dodd and Jensen suffices for our proofs.