Showing papers on "Carbon group published in 2006"

Recent developments in the field of organic heterobimetallic compounds of the alkaline-earth metals.

Abstract: Heterobimetallic compounds of the alkaline-earth metals show a wide structural variety with strongly differing reactivity patterns. The combination of magnesium and alkali metal amides yields cyclic molecules with an extreme high reactivity which often are considered as “inverse crowns” with the metal atoms as coordination sites for Lewis bases. In other metallates of the alkaline-earth metals an activation of alkyl groups succeeds. In alkaline-earth metal zincates an inverse coordination of the type M2[(μ-R)2ZnR]2 is observed and the alkyl groups are in bridging positions between zinc and the s-block metals thus forming a very reactive M–C–Zn three-center–two-electron bond. Furthermore, the metals of the carbon group form alkaline-earth metal–silicon, –germanium and –tin bonds or, in the presence of very strong Lewis bases, even solvent-separated ion pairs. For electronegative substituents at tin an inverse coordination mode such as M[(µ-R)2SnR]2 is observed.

P-hydrogen-substituted 1,3,2-diazaphospholenes: molecular hydrides.

Abstract: P-Hydrogen-substituted 1,3,2-diazaphospholenes 1 were prepared by an improved procedure from diazadienes and were characterized by spectroscopy and in one case by X-ray diffraction. A unique hydride-type reactivity of the P-H bonds was documented by extensive reactivity studies. Aldehydes and ketones were readily reduced to diazaphospholene derivatives of the corresponding alcohols, with alkyl-substituted ketones being converted at much lower rates than aldehydes or diaryl ketones. Reactions with the tetrachlorides of group 14 elements proceeded via hydride/chloride metathesis to give either partially chlorinated derivatives EH(n)Cl(4-n) (n = 0-3 for E = C, Si) or HCl and phosphenium salts 16c[ECl3] (for E = Ge, Sn) which were characterized by spectroscopic and X-ray diffraction studies. Tin dichloride was readily reduced to the element. Reactions of 1c with the P-chloro-diazaphospholene 3c and the salt 16c[OTf] allowed the first experimental detection of intermolecular exchange of a hydride, rather than a proton, between phosphine derivatives. Computational studies indicated that the hydride transfer between 1c and the cation 16c involves a transient H-bridged species with bonding properties similar to those of B2H7-. The preference for the formation of these bridged intermediates over P-P bonded phosphenium-phosphine adducts is attributed to the low electrophilicity of the diazaphospholenium cations and characterizes a novel reaction mode for phosphenium ions.

Germanium(II)‐, Zinn(II)‐ und Blei(II)‐Derivate des polycyclischen Alumosiloxans [Ph2SiO]8[Al(O)OH]4

Abstract: Germanium(II)-, Tin(II)- and Lead(II)-Derivatives of the polycyclic Alumosiloxane [Ph2SiO]8[Al(O)OH]4 Five new derivatives of the polycyclic alumosiloxane [Ph2SiO]8[Al(O)OH]4 have been synthesized by replacement of the protic hydrogen atoms on the hydroxy-groups attached to the aluminium atoms by the divalent group 14 elements germanium, tin and lead. The compounds can be divided in those with one metal atom per alumosiloxane moiety, [Ph2SiO]8[Al(O)OH]2[AlO2]M (M=Ge, Sn), and those with complete substitution of the protic hydrogen atoms by metal atoms like [Ph2SiO]8[AlO2]4M2 (M= Sn, Pb). Always one element of the series Ge, Sn, Pb is missing in the two types of compounds. Crystal structure analyses of [Ph2SiO]8[Al(O)OH]2[AlO2]2M · 2 C4H8O2 (M= Ge (1), Sn (2a)), [Ph2SiO]8[Al(O)OH]2[AlO2]2Sn · 2 THF (2b) and [Ph2SiO]8[AlO2]4M2 (M= Sn (3), Pb (4)) have been performed elucidating either polycyclic basket-type (1, 2a, 2b) or closed polyhedral structures (3, 4).

Metallocanes of group 14 elements. 1. Derivatives of silicon and germanium. (Review)

Abstract: Results on the synthesis of silocanes and germocanes, eight-membered heterocycles with the general formula D(CH2CH2Z)2MXY are analyzed and classified The chemical behavior of these compounds and the characteristics of the element-nitrogen transannular bond are studied

Carbocationic cyclopropanation using tin

Abstract: γ-Effects of group 14 elements such as silicon and tin is discussed with the emphasis on the comparison with p-effects. Based on the striking γ-effect of tin, cyclopropantion reactions of alkenes using organotin compounds have been developed. Using allyl group 14 element compounds as alkenes, intramolecular competition between p-elimination and γ-elimination of group 14 elements has been studied. Intermolecular competition has also been examined using the reaction of allyl- and homoallyl group 14 element compounds with electrophiles. As an application of the present method in organic synthesis, intramolecularization of cationic cyclopropanation based on in-situ transacetalization to form unique cyclopropane structures is demonstrated.

Carbon, silicon, germanium, tin and lead

Abstract: This report surveys publications from the calendar year 2011 in the general area of Group 14 chemistry.

Carbocationic Cyclopropanation Using Tin

Abstract: γ-Effects of group 14 elements such as silicon and tin is discussed with the emphasis on the comparison with p-effects. Based on the striking γ-effect of tin, cyclopropantion reactions of alkenes using organotin compounds have been developed. Using allyl group 14 element compounds as alkenes, intramolecular competition between p-elimination and γ-elimination of group 14 elements has been studied. Intermolecular competition has also been examined using the reaction of allyl- and homoallyl group 14 element compounds with electrophiles. As an application of the present method in organic synthesis, intramolecularization of cationic cyclopropanation based on in-situ transacetalization to form unique cyclopropane structures is demonstrated.