Equilibrium Formation of Stable All‐Silicon Versions of 1,3‐Cyclobutanediyl

Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c ‐Si3Tip4 (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c ‐[(CR2CH2)(Nt Bu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c ‐(CH)2(Nt Bu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate

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Bildung Stabiler All‐Silicium Varianten von 1,3‐Cyclobutandiyl im Gleichgewicht

Hauptgruppenanaloga von 1,3‐Cyclobutandiylen faszinieren mit ihrer einzigartigen Reaktivität und ihren elektronischen Eigenschaften. Bisher sind allerdings nur heteronukleare Vertreter isoliert worden. Wir berichten hier über die Isolierung und Charakterisierung von All‐Silicium‐1,3‐Cyclobutandiylen als stabile Singulettspezies mit geschlossenschaliger Konfiguration aus den reversiblen Reaktionen von Cyclotrisilen c ‐Si3Tip4 (Tip=2,4,6‐Triisopropylphenyl) mit den N‐heterocyclischen Silylenen c ‐[(CR2CH2)(Nt Bu)2]Si: (R=H oder Methyl) mit gesättigten Grundgerüsten. Bei erhöhten Temperaturen werden aus diesen Gleichgewichtsmischungen Tetrasilacyclobutene erhalten. Die analoge Reaktion mit dem ungesättigten N‐heterocyclischen Silylen c ‐(CH)2(Nt Bu)2Si: verläuft direkt zum entsprechenden Tetrasilacyclobuten ohne Nachweis des angenommenen 1,3‐Cyclobutandiyl‐Zwischenprodukts

‘Sons of athelings given to the earth’: Infant Mortality within Anglo-Saxon Mortuary Geography

FOR 20 OR MORE YEARS early Anglo-Saxon archaeologists have believed children are underrepresented in the cemetery evidence. They conclude that excavation misses small bones, that previous attitudes to reporting overlook the very young, or that infants and children were buried elsewhere. This is all well and good, but we must be careful of oversimplifying compound social and cultural responses to childhood and infant mortality. Previous approaches have offered methodological quandaries in the face of this under-representation. However, proportionally more infants were placed in large cemeteries and sometimes in specific zones. This trend is statistically significant and is therefore unlikely to result entirely from preservation or excavation problems. Early medieval cemeteries were part of regional mortuary geographies and provided places to stage events that promoted social cohesion across kinship systems extending over tribal territories. This paper argues that patterns in early Anglo-Saxon infant burial were the result of female mobility. Many women probably travelled locally to marry in a union which reinforced existing social networks. For an expectant mother, however, the safest place to give birth was with experience women in her maternal home. Infant identities were affected by personal and legal association with their mother’s parental kindred, so when an infant died in childbirth or months and years later, it was their mother’s identity which dictated burial location. As a result, cemeteries central to tribal identities became places to bury the sons and daughters of a regional tribal aristocracy

A Molecular Complex with a Formally Neutral Iron-germanide Motif (Fe2Ge2)

We report the synthesis and isolation of a stable complex containing the formally neutral Fe2Ge2 motif, which is stabilized by the coordination of an N-heterocyclic carbene to the germanium and carbon monoxide to the iron center. [(NHCiPr2Me2)GeFe(CO)4]2 is obtained by reduction of the NHCiPr2Me2-coordinated dichlorogermylene adduct with Fe(CO)4, which in turn is obtained from reaction of Fe2(CO)9 with GeCl2·NHCiPr2Me2 (NHCiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The solid state structure of the title compound reveals two distinct coordination modes for the Fe(CO)4 fragments: bridging (p-type) and terminal (s-type). In solution, the rapid equilibrium between the two modes was resolved by NMR at −35°C. Reaction with propylene sulfide at room-temperature affords the sulfide-bridged digermanium complex with two terminal Fe(CO)4 moieties.We report the synthesis and isolation of a stable complex containing the formally neutral Fe2Ge2 motif, which is stabilized by the coordination of an N-heterocyclic carbene to the germanium and carbon monoxide to the iron center. [(NHCiPr2Me2)GeFe(CO)4]2 is obtained by reduction of the NHCiPr2Me2-coordinated dichlorogermylene adduct with Fe(CO)4, which in turn is obtained from reaction of Fe2(CO)9 with GeCl2·NHCiPr2Me2 (NHCiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The solid state structure of the title compound reveals two distinct coordination modes for the Fe(CO)4 fragments: bridging (p-type) and terminal (s-type). In solution, the rapid equilibrium between the two modes was resolved by NMR at −35°C. Reaction with propylene sulfide at room-temperature affords the sulfide-bridged digermanium complex with two terminal Fe(CO)4 moieties.We report the synthesis and isolation of a stable complex containing the formally neutral Fe2Ge2 motif, which is stabilized by the coordination of an N-heterocyclic carbene to the germanium and carbon monoxide to the iron center. [(NHCiPr2Me2)GeFe(CO)4]2 is obtained by reduction of the NHCiPr2Me2-coordinated dichlorogermylene adduct with Fe(CO)4, which in turn is obtained from reaction of Fe2(CO)9 with GeCl2·NHCiPr2Me2 (NHCiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The solid state structure of the title compound reveals two distinct coordination modes for the Fe(CO)4 fragments: bridging (p-type) and terminal (s-type). In solution, the rapid equilibrium between the two modes was resolved by NMR at −35°C. Reaction with propylene sulfide at room-temperature affords the sulfide-bridged digermanium complex with two terminal Fe(CO)4 moieties

A base-coordinated multiply functionalized Ge(II) compound and its reversible dimerization to the corresponding digermene

Stable compounds with Ge=Ge bond are usually prepared under relatively harsh reaction conditions that are incompatible with many functional groups. In particular, unsaturated functionalities are not tolerated due to their facile reaction with low-coordinate germanium compounds. We now report the synthesis of an imino-functionalized germanium(II) species stabilized by coordination of an N-heterocyclic carbene (NHC), which is obtained by reaction of an isonitrile with a heavier NHC-coordinated vinylidene. Removal of the NHC by a Lewis-acid results in dimerization to give the corresponding digermene with Ge=Ge double bond. The reversibility of this process is demonstrated by addition of two equivalents of NHC to the isolated digermene.Stable compounds with Ge=Ge bond are usually prepared under relatively harsh reaction conditions that are incompatible with many functional groups. In particular, unsaturated functionalities are not tolerated due to their facile reaction with low-coordinate germanium compounds. We now report the synthesis of an imino-functionalized germanium(II) species stabilized by coordination of an N-heterocyclic carbene (NHC), which is obtained by reaction of an isonitrile with a heavier NHC-coordinated vinylidene. Removal of the NHC by a Lewis-acid results in dimerization to give the corresponding digermene with Ge=Ge double bond. The reversibility of this process is demonstrated by addition of two equivalents of NHC to the isolated digermene.Stable compounds with Ge=Ge bond are usually prepared under relatively harsh reaction conditions that are incompatible with many functional groups. In particular, unsaturated functionalities are not tolerated due to their facile reaction with low-coordinate germanium compounds. We now report the synthesis of an imino-functionalized germanium(II) species stabilized by coordination of an N-heterocyclic carbene (NHC), which is obtained by reaction of an isonitrile with a heavier NHC-coordinated vinylidene. Removal of the NHC by a Lewis-acid results in dimerization to give the corresponding digermene with Ge=Ge double bond. The reversibility of this process is demonstrated by addition of two equivalents of NHC to the isolated digermene

Singlet diradicals: from transition states to crystalline compounds

Scheschkewitz D, Amii H, Gornitzka H, Schoeller W, Bourissou D, Bertrand G. Singlet diradicals: from transition states to crystalline compounds. SCIENCE. 2002;295(5561):1880-1881.Singlet diradicals are usually not energy minima. As observed by femtosecond spectroscopy, they readily couple to form sigma bonds. Substituent effects allow lifetimes to increase into the microsecond range. Taking advantage of the properties of hetero-elements, a diradical has been prepared that is indefinitely stable at room temperature. The availability of diradicals that can be handled under standard laboratory conditions wilt lead to further insight into their chemical and physical properties, raising the likelihood of practical applications, especially in the field of molecular materials such as electrical conductors and ferromagnets

alpha-bond stretching: A static approach for dynamic process

Scheschkewitz D, Amii H, Gornitzka H, Schoeller W, Bourissou D, Bertrand G. alpha-bond stretching: A static approach for dynamic process. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 2004;43(5):585-587

Neutral and Cationic NHC-Coordinated Heavier Cyclopropylidenes

Cyclopropylidene as the smallest cyclic carbene with saturated backbone is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group 14 elements into the cyclopropylidene scaffold has so far been restricted to the replacement of the carbenic carbon atom by a intramolecularly base-coordinated silicon(II) center. Here we report the synthesis and characterization of NHC-coordinated heavier cyclopropylidenes (Si2GeR3X, and Si3R3Br; X = Cl, Mes; R = Tip = 2,4,6-iPr3C6H2) in which the three-membered cyclic scaffold is exclusively formed of silicon and germanium. In case of the chloro-substituted Si2Ge-cyclopropylidene, a stable heavier cycloprop-1-yl-2-ylidene cation is obtained by NHC-induced chloride dissociation.Cyclopropylidene as the smallest cyclic carbene with saturated backbone is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group 14 elements into the cyclopropylidene scaffold has so far been restricted to the replacement of the carbenic carbon atom by a intramolecularly base-coordinated silicon(II) center. Here we report the synthesis and characterization of NHC-coordinated heavier cyclopropylidenes (Si2GeR3X, and Si3R3Br; X = Cl, Mes; R = Tip = 2,4,6-iPr3C6H2) in which the three-membered cyclic scaffold is exclusively formed of silicon and germanium. In case of the chloro-substituted Si2Ge-cyclopropylidene, a stable heavier cycloprop-1-yl-2-ylidene cation is obtained by NHC-induced chloride dissociation.Cyclopropylidene as the smallest cyclic carbene with saturated backbone is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group 14 elements into the cyclopropylidene scaffold has so far been restricted to the replacement of the carbenic carbon atom by a intramolecularly base-coordinated silicon(II) center. Here we report the synthesis and characterization of NHC-coordinated heavier cyclopropylidenes (Si2GeR3X, and Si3R3Br; X = Cl, Mes; R = Tip = 2,4,6-iPr3C6H2) in which the three-membered cyclic scaffold is exclusively formed of silicon and germanium. In case of the chloro-substituted Si2Ge-cyclopropylidene, a stable heavier cycloprop-1-yl-2-ylidene cation is obtained by NHC-induced chloride dissociation