Fusing low-valent Germanium with Silicon : from double bonds to polymers and clusters

Low-valent species of silicon and germanium play a pivotal role in the chemical vapor deposition of the bulk elements and their alloys for semiconductor applications. The transition from molecular intermediates to extended unsaturated cluster motifs incorporated into the bulk is of particular interest and stable model compounds for these species are intensively sought. This thesis investigates the structural behavior of such low-valent germanium and germanium-silicon compounds in comparison to their well-established silicon congeners. An anionic Si4Ge2 siliconoid is synthesized by reduction of a Si4Ge2 benzene and the position of the germanium atoms in the scaffold allows mechanistic insight in E6-cluster rearrangements in general (E = Group 14 element). The first examples of heavy germanium-containing Group 14 allyl chlorides and α,β-unsaturated ketones are now accessible from a lithium digermenide and show extraordinary resilience against cyclization, a rearrangement mode commonly observed for the analogue silicon compounds. The same digermenide is used for synthesis of targeted designed asymmetric digermenes, able to undergo heavy olefin metathesis by a dissociation-association rearrangement. Two symmetric digermenes are synthesized that way and the lack of demand for any catalyst is a first in olefin metathesis in general. Extension of the concept now allows Heavy Acyclic Metathesis (HADMET) polymerization of a α,ω-bis(digermene) to the first example of a poly(digermene).Niedervalente Silizium- und Germaniumspezies spielen eine entscheidende Rolle in der chemischen Gasphasenabscheidung beider Elemente für Halbleiteranwendungen. Der Übergang von molekularen Intermediaten zu ungesättigten Cluster-Motiven, die im Festkörper verbleiben, ist von besonderem Interesse und stabile Modellverbindungen dieser Spezies werden intensiv gesucht. Die vorliegende Arbeit untersucht das strukturelle Verhalten solcher niedervalenter Ge- und Si/Ge-Verbindungen im Vergleich zu ihren wohlbekannten Si-analoga. Ein anionisches Si4Ge2 Silicoid wird durch Reduktion eines Si4Ge2 Benzols hergestellt und die Position der Ge-Atome im Gerüst gibt mechanistische Einblicke in E6-Cluster Umlagerungen im Allgemeinen (E= Gruppe 14 Element). Die ersten Beispiele für schwere Ge-haltige Gruppe-14 Allylchloride sowie α,β-ungesättigte Ketone sind nun von einem Lithiumdigermenid aus zugänglich und zeigen erstaunliche Resilienz gegen Cyclisierung, eine Umlagerungsart, die häufig bei den analogen Si-verbindungen auftritt. Dasselbe Digermenid wird für die Synthese zielgerichtet gestalteter, asymmetrischer Digermene verwendet, die durch eine Dissoziations-Assoziations-Umlagerung eine schwere Olefin Metathese durchzumachen. Zwei symmetrische Digermene wurden so hergestellt und der mangelnde Bedarf an Katalysator ist eine Premiere für Olefin-Metathesen. Erweiterung des Konzepts erlaubt nun Schwere Acylische Dien Metathese (HADMET) Polymerisierung von α,ω-Bis(digermenen) zum Poly(digermen)

Persistent Digermenes with Acyl and α‐Chlorosilyl Functionalities

We report the preparation of α-chlorosilyl- and acyl-substituted digermenes. Unlike the corresponding transient disilenes, these species with a Ge=Ge double bond show an unexpectedly low tendency for cyclization, but in turn are prone to thermal Ge=Ge bond cleavage. Triphenylsilyldigermene has been isolated as a crystalline model compound, and is the first fully characterized example of a neutral digermene with an A2 GeGeAB substitution pattern. Spectroscopic and computational evidence prove the constitution of 1-adamantoyldigermene as a first persistent species with a heavy double bond conjugated with a carbonyl moiety

Isolation and Reactivity of a Digerma Analogue of Vinyllithiums: a Lithium Digermenide

The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the SiSi moiety. The corresponding germanium analogue, digermenide Tip₂GeGe­(Tip)­Li·dme₂ (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip₂GeCl₂ with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at −70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the GeGe motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip₂GeGe­(Tip)­SiR₃

Isolation and Reactivity of a Digerma Analogue of Vinyllithiums: a Lithium Digermenide

The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the SiSi moiety. The corresponding germanium analogue, digermenide Tip₂GeGe­(Tip)­Li·dme₂ (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip₂GeCl₂ with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at −70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the GeGe motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip₂GeGe­(Tip)­SiR₃