Michael Veith

Mitochondrial sequence analysis of Salamandra taxa suggests old splits of major lineages and postglacial recolonizations of Central Europe from distinct source populations of Salamandra salamandra

Representatives of the genus Salamandra occur in Europe, Northern Africa and the Near East. Many local variants are known but species and subspecies status of these is still a matter of dispute. We have analysed samples from locations covering the whole expansion range of Salamandra by sequence analysis of mitochondrial D‐loop regions. In addition, we have calibrated the rate of divergence of the D‐loop on the basis of geologically dated splits of the closely related genus Euproctus. Phylogenetic analysis of the sequences suggests that six major monophyletic groups exist (S. salamandra, S. algira, S. infraimmaculata, S. corsica, S. atra and S. lanzai) which have split between 5 and 13 million years ago (Ma). We find that each of the Salamandra species occupies a distinct geographical area, with the exception of S. salamandra. This species occurs all over Europe from Spain to Greece, suggesting that it was the only species that has recolonized Central Europe after the last glaciation. The occurrence of specific east and west European haplotypes, as well as allozyme alleles in the S. salamandra populations suggests that this recolonization has started from at least two source populations, possibly originating in the Iberian peninsula and the Balkans. Two subpopulations of S. salamandra were found that are genetically very distinct from the other populations. One lives in northern Spain (S. s. bernardezi) and one in southern Italy (S. s. gigliolii). Surprisingly, the mitochondrial lineages of these subpopulations group closer together than the remainder S. salamandra lineages. We suggest that these populations are remnants of a large homogeneous population that had colonized Central Europe in a previous interglacial period, approximately 500 000 years ago. Animals from these populations were apparently not successful in later recolonizations. Still, they have maintained their separate genetic identity in their areas, although they are not separated by geographical barriers from very closely related neighbouring populations.

Lithiumsalze des Tris(trimethylsilylamino)silans

Amides, which result from the reaction of tris(trimethylsilylamino)silane (Me3SiNH)3SiH (1) with n-butyllithium in the molar ratio 1:1 and 1:2 in nonpolar solvents, form a system in which the aminosilane 1, the monoamide (Me3SiNLi)(Me3-SiNH)2SiH (2a), the diamide (Me3SiNLi)2(Me3SiNH)SiH (3), and the triamide (Me3SiNLi)3SiH (4) are in equilibrium. When the monoamide 2a is dissolved in THF only the dimeric monolithiated THF adduct 2b is obtained. An X-ray structure analysis of the lithium silylamide 2b reveals that in the dimeric unit one of the lithium atoms is coordinated by THF, the two lithium atoms thus differing in coordination number (3 versus 4). An X-ray study of the triamide 4 reveals a centrosymmetric polycycle. Multipole interactions are formed between the lithium and the nitrogen atoms. The reaction of the diamide 3 with chlorotrimethylsilane in boiling THF yields the cis isomer of the cyclic diamide [(Me3SiNLi)(Me3-SiNH)SiN(SiMe3)]2.2 THF (5) as a byproduct. According to an X-ray structure analysis of 5 the lithium centers are coordinated by one oxygen and three nitrogen atoms, which form a strongly distorted tetrahedron. The interactions between lithium and nitrogen atoms N(1) and N(2), which are part of the four-membered Si2N2 cycle, have to be considered as weak on the basis of the remarkably long Li-N distances (233 and 243 pm).

Zur Reaktion eines Bis(amino)germylens mit Germaniumazeden

Das cyclische Bis(amino)germylen 1 wurde mit verschiedenen Germaniumaziden Me2Si(NtBu)2GeR(N3) (R = Me (2), tBu (3), N(SiMe3)2 (4), N3 (5)) umgesetzt. Auser 4 reagieren alle Azide mit dem Germylen 1 unter Distickstoffentwicklung und gleichzeitigem Angriff des GeII-Zentrums auf den -Stickstoff einer Azidgruppe. Das sich offenbar zwischenzeitlich bildende Germaimin (bzw. Germanitrid) wird durch weitere Reaktion mit der Azidkomponente (2 und 5) bzw. mit dem Losungsmittel Pyridin abgefangen. Im Falle der Reaktion mit 2 bildet sich ein Germatetrazol [Me2Si(NtBu)2]GeN4[Ge(Me)(NtBu)2SiMe2]2 (6), dessen Stickstoffatome ausschlieslich durch Germaniumatome substituiert sind (Punktsymmetrie Cs(m)). Bei der Reaktion mit 5 entsteht ein Tris(germa)amin [Me2Si(NtBu)2Ge(N3)]3N (7), das an jedem Germaniumatom noch jeweils eine Azidgruppe gebunden hat. Nach Rontgenstrukturanalyse befinden sich neben der trigonal planaren Ge3N-Einheit noch die 9 Stickstoffatome der Azidgruppen in der Molekulebene (kristallographische 3/m Symmetrie). Besonders uberraschend ist die Reaktion von 1 mit 3 in Pyridin: im Produkt Me2Si(NtBu)2Ge(C5H4N)N(H)Ge(tBu)(NtBu)2SiMe2 (8) ist der Pyridinrest uber das -Kohlenstoffatom an das Germanium gebunden, wahrend das verbleibende Wasserstoffatom sich an den Nitrid-Stickstoff addiert hat. 6 kristallisiert monoklin in C2/m mit a = 24,306(9), b = 10,933(6), c = 19,420(9) A, = 91,81(2)° mit Z = 4, 7 kristallisiert hexagonal in P63/m mit a = b = 16,73(1), c = 11,006(6) A, = 120° mit Z = 2, und 8 kristallisiert monoklin in P21/n mit a = 11,341(6), b = 26,086(9), c = 13,244(7) A, = 98,12(2)° mit Z = 4.

Verbindungen des Formeltyps M2El2(OtBu)8

By simple salt-exchange processes the starting materials Na2El2(OtBu)6 (El = Ge, Sn, Pb) can be transformed to germanates, stannates and plumbates of divalent magnesium and divalent transition metals. Two types of compounds are formed in these reactions: MEl2(OtBU)6 [El = Ge, M = Mg (1A), Cr (1B), Mn (1C), Zn (1 F); El = Pb, M Mn (3C), M = Zn (3 F)] and M2El2(OtBu)8 [El = Ge, M = Co (1d), Ni (1e); El = Sn, M = Mg (2a), Cr (2b), Mn (2c), Co (2d), Ni (2e); El = Pb, M = Co (3d)]. Single-crystal X-ray diffraction studies have been performed on 1C, 1d, 2a, 2b, 2c, 2d, and 2e, and the structures have been solved. In 1C the Mn atom occupies the center of an elongated O6 octahedron, the germanium(II) atoms displaying pyramidal coordination by three oxygen atoms. The central molecular cage can be described as two MnO3Ge trigonal bipyramids sharing the common central Mn atom and being wrapped by tert-butyl groups linked to the oxygen atoms. The other compounds of the MEl2(OtBU)6 formula seem to be isostructural with the exception of 3F, which displays a H-1-NMR spectrum which is not compatible with this structure. All X-ray structures of the compounds M2El2(OtBu)8 show the same feature: to a central M2(OtBU)2 four-membered ring are spirocyclically connected two M(OtBu)2El rings through the common metal atoms M. The structure is completed by the coordination of an exocyclic tert-butoxy group to the terminal El atoms. The metal atoms M are therefore quasi tetrahedrally coordinated while the Ge and Sn atoms are in pyramidal three-fold oxygen atom environments. All molecules display an El...M...M...El one-dimensional arrangement. From susceptibility measurements it is apparent, that in the compounds MEl2(OtBu)6 and M2El2(OtBu)8 the transition metal atoms are in high-spin configurations, which is also supported by the UV spectra. Analysis of the structural data of the series 2a-2e reveal important contributions of the electronic environments of the transition metal atoms to the M...M and M...Sn distances. A qualitative MO description is used to explain these features. Again it has been shown that the geometrical softness of Ge(OtBu)3 and Pb(OtBu)3 is greater than of Sn(OtBu)3, as the former two can accomodate Cr2+ and Mn2+ in a sixfold coordination site by two units, while Sn(OtBu)3 coordinates Cr2+ and Mn2+ with only two alkoxy groups. when 1C and 2d are allowed to react with nonacarbonyldiiron Mn-Ge2(OtBu)6 . 2 Fe(CO)4 (4) and Co2Sn2(OtBu)8 . 2 Fe(CO)4 (5), respectively, are formed. Compound 4 displays presumably five metal atoms in a linear arrangement while 5 has six metallic elements arranged in one dimension. The latter fact has been unambigously proved by an X-ray structure determination.

Polycyclische Silylamide mit lambda 3-Li und lambda 3-Tl

1,3-Di-tert-butyl-2,4-bis(tert-butylamino)-2,4-dimethyl-1,3,2,4-diazadisiletidin kann in zwei stereochemisch unterschiedlichen Formen erhalten werden: in der cis-Verbindung 3a stehen die Methyl- bzw. tert-Butylaminosubstituenten am Silicium auf derselben Seite des zentralen Si2N2-Vierringes, wahrend sie in der trans-Verbindung 3b entgegengesetzte Positionen einnehmen. Die Wasserstoffatome an den Stickstoffatomen lassen sich durch einwertige Metalle wie Lithium oder Thallium(I) ersetzen. Geht man dabei von der cis-Verbindung 3a aus, so entsteht ein molekularer Polycyclus mit einem cubanartigen Si2N4M2-Gerust, was durch Rontgenstrukturanalysen nachgewiesen werden kann. Sowohl im Lithiumderivat 5a als auch in der Thallium-Verbindung 6 sind die beiden im Polycyclus befindlichen Metallatome jeweils von 3 Stickstoffatomen pyramidal koordiniert. Wahrend fur das Thalliumatom eine formale Edelgaskonfiguration entsteht, sind die 3-Li-Atome elektronisch und koordinativ ungesattigt: im Festkorper wirkt sich diese Tatsache in einer Dimerisierung der Molekule 5a aus, wobei CHLi-Kontakte zustande kommen. Das trans-konfigurierte Isomer 3b reagiert mit Butyllithium zu einem tricyclischen System 5b, in dem die Lithiumatome durch ein zusatzliches Ethermolekul koordiniert werden. Die Koordinationszahl an den Lithiumatomen ist ebenso 3, aber die Figur ist trigonal planar. Besonders auffallend ist der kurze LiN(2)-Abstand mit 188(3) pm, was mit der sp2-Hybridisierung am Metallatom zu erklaren ist.

ESR spectra of radical anions of aliphatic azo compounds

Compound ( I ) is not the sole product; about 70% of the reactants undergo an obscure reaction leading to nitrogen and an oil containing boron-nitrogen compounds of unknown composition. The diimine ( I ) is polymeric, insoluble in the usual solvents, and extremely unreactive; thermal decomposition occurs only slowly above 400OC. with loss of all the nitrogen. The compound is stable towards acids, but decomposes in the basic pyridine, giving up half its nitrogen. Two structural formulas ( la) and (Ib) (Ph = C6H5) require consideration: