Controlled Growth of Dichlorogermanium Oligomers from Lewis Basic Hosts

Activation of Ge-H and Sn-H Bonds with N-Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene

A study of the reactivity of several N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene (cAACMe ) with the group 14 hydrides GeH2 Mes2 and SnH2 Me2 (Me=CH3 , Mes=1,3,5-(CH3 )3 C6 H2 ) is presented. The reaction of GeH2 Mes2 with cAACMe led to the insertion of cAACMe into one Ge-H bond to give cAACMe H-GeHMes2 (1). If 1,3,4,5-tetramethyl-imidazolin-2-ylidene (Me2 ImMe ) was used as the carbene, NHC-mediated dehydrogenative coupling occurred, which led to the NHC-stabilized germylene Me2 ImMe ⋅GeMes2 (2). The reaction of SnH2 Me2 with cAACMe also afforded the insertion product cAACMe H-SnHMe2 (3), and reaction of two equivalents Me2 ImMe with SnH2 Me2 gave the NHC-stabilized stannylene Me2 ImMe ⋅SnMe2 (4). If the sterically more demanding NHCs Me2 ImMe , 1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene (iPr2 ImMe ) and 1,3-bis-(2,6-di-isopropylphenyl)-imidazolin-2-ylidene (Dipp2 Im) were employed, selective formation of cyclic oligomers (SnMe2 )n (5; n=5-8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAACMe H-SnHMe2 (3).

Synthesis of Low-Valent Dinuclear Group 14 Compounds with Element-Element Bonds by Transylidation

Dinuclear low-valent compounds of the heavy main group elements are rare species owing to their intrinsic reactivity. However, they represent desirable target molecules due to their unusual bonding situations as well as applications in bond activations and materials synthesis. The isolation of such compounds usually requires the use of substituents that provide sufficient stability and synthetic access. Herein, we report on the use of strongly donating ylide-substituents to access low-valent dinuclear group 14 compounds. The ylides not only impart steric and electronic stabilization, but also allow facile synthesis via transfer of an ylide from tetrylene precursors of type R Y2 E to ECl2 (E=Ge, Sn; R Y=TolSO2 (PR3 )C with R=Ph, Cy). This method allowed the isolation of dinuclear complexes amongst a germanium analogue of a vinyl cation, [(Ph Y)2 GeGe(Ph Y)]+ with an electronic structure best described as a germylene-stabilized GeII cation and a ylide(chloro)digermene [Cy Y(Cl)GeGe(Cl)Cy Y] with an unusually unsymmetrical structure.

Stable Mesoionic N-Heterocyclic Olefins (mNHOs)

We report a new class of stable mesoionic N-heterocyclic olefins, featuring a highly polarized (strongly ylidic) double bond. The ground-state structure cannot be described through an uncharged mesomeric Lewis-structure, thereby structurally distinguishing them from traditional N-heterocyclic olefins (NHOs). mNHOs can easily be obtained through deprotonation of the corresponding methylated N,N'-diaryl-1,2,3-triazolium and N,N'-diaryl-imidazolium salts, respectively. In their reactivity, they represent strong σ-donor ligands as shown by their coordination complexes of rhodium and boron. Their calculated proton affinities, their experimentally derived basicities (competition experiments), as well as donor abilities (Tolman electronic parameter; TEP) exceed the so far reported class of NHOs.

1,2- and 1,1-Migratory Insertion Reactions of Silylated Germylene Adducts

The reactions of the PMe₃ adduct of the silylated germylene [(Me₃Si)₃Si]₂Ge: with GeCl₂·dioxane were found to yield 1,1-migratory insertion products of GeCl₂ into one or two Ge–Si bonds. In a related reaction, a germylene was inserted with tris(trimethylsilyl)silyl and vinyl substituents into a Ge–Cl bond of GeCl₂. This was followed by intramolecular trimethylsilyl chloride elimination to another cyclic germylene PMe₃ adduct. The reaction of the GeCl₂ mono-insertion product (Me₃Si)₃SiGe:GeCl₂Si(SiMe₃)₃ with Me₃SiC≡CH gave a mixture of alkyne mono- and diinsertion products. While the reaction of a divinylgermylene with GeCl₂·dioxane only results in the exchange of the dioxane of GeCl₂ against the divinylgermylene as base, the reaction of [(Me₃Si)₃Si]₂Ge: with one GeCl₂·dioxane and three phenylacetylenes gives a trivinylated germane with a chlorogermylene attached to one of the vinyl units.

Reactions of GeCl2 with the Thiolate LiSC(SiMe3 )3 : From thf Activation to Insertion of GeCl2 Molecules into C-S Bonds

The reaction system GeCl₂ ⋅dioxane/LiSTsi (Tsi=C(SiMe₃ )₃ ) opens a fruitful area in germanium chemistry, depending on the stoichiometry and solvent used during the reaction. For example, the reaction of GeCl₂ ⋅dioxane in toluene with two equivalents of the thiolate gives the expected germylene Ge(STsi)₂ in excellent yield. This germylene readily reacts with hydrogen and acetylene, however, in a non-selective way. By using an excess amount of the thiolate and toluene as the solvent, the germanide [Ge(STsi)₃ ][Li(thf)] is obtained. Performing the same reaction in thf leads to a C-H activation of thf to give (H₇ C₄ O)Ge[STsi](μ² -S)₂ Ge[STsi]₂ , in which the thf molecule is still intact. Using a sub-stoichiometric amount of the thiolate leads to the heteroleptic compound [ClGe(STsi)]₂ and to the insertion product (thf)Ge[S-GeCl₂ -Tsi]₂ , in which additional GeCl₂ molecules insert into the C-S bonds of Ge(STsi)₂ . The synthesis and the experimentally determined structures of all compounds are presented together with first reactivity studies of Ge(STsi)₂ .

Using N-Heterocyclic Vinyl Ligands to Access Stable Divinylgermylenes and a Germylium Cation

Two efficient methods are presented to install σ- and π-electron-donating N-heterocyclic vinyl groups onto main-group elements (E): halosilane elimination and base-induced E-C bond formation. Placement of two NHC=CH^- ligands (NHC=N-heterocyclic carbene) onto a Ge^II center affords a two-coordinate germylene, a heavy congener of the elusive divinyl carbenes. The π-donating ability of this vinylic ligand scaffold was further demonstrated by the synthesis of a three-coordinate germylium cation R₃ Ge⁺ .

A Bis(silylenyl)pyridine Zero-Valent Germanium Complex and Its Remarkable Reactivity

The synthesis, reactivity, and electronic structure of the unique germylone iron carbonyl complex [SiNSi]Ge⁰ →Fe(CO)₄ is reported. The compound was obtained in 49 % yield from the reaction of the bis(N-heterocyclic silylenyl)pyridine pincer ligand SiNSi (1,6-C₅ NH₃ -[EtNSi(N^t Bu)₂ CPh]₂ ) with GeCl₂ ⋅(dioxane) to give the corresponding chlorogermyliumylidene chloride precursor [SiNSi]Ge^II Cl⁺  Cl^- , which was further reduced with K₂ Fe(CO)₄ . Single-crystal X-ray diffraction analysis of [SiNSi]Ge→Fe(CO)₄ revealed that the Ge⁰ center adopts a trigonal-pyramidal geometry with a Si-Ge-Si angle of 95.66(2)°. Remarkably, one of the Si^II donor atoms in the complex is five-coordinated because of additional (pyridine)N→Si coordination. Unexpectedly, the reaction of [SiNSi]Ge→Fe(CO)₄ with GeCl₂ ⋅(dioxane) (one molar equivalent) yielded the first push-pull germylone-germylene donor-acceptor complex, [SiNSi]Ge→GeCl₂ →Fe(CO)₄ through the insertion of GeCl₂ into the dative Ge⁰ →Fe bond. The electronic features of the new compounds were investigated by DFT calculations.

Single-step conversion of silathiogermylene to germaacid anhydrides: unusual reactivity

Single-step conversion of germylene (2) to germaacid anhydrides (3 and 4) is achieved through oxidative-addition with S/Se that involves condensation for the first time.