Synthesis and Reactivity of Tricoordinate Organoberyllium Azides.

A series of terminal mono- and disubstituted beryllium azides of the form [(CAAC)Be(N3)R] (R=CAACH, Dur; CAACH/CAAC=1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-yl/idene, Dur=2,3,5,6-tetramethylphenyl) and [L2Be(N3)2] (L=CAACNH=1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-imine, IiPrMe=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene), respectively, were synthesized and characterized by NMR spectroscopy and X-ray crystallography. Thermolysis and photolysis products of these first examples of tricoordinate azidoberyllium complexes evidence extensive ligand scrambling and the formal insertion of nitrenes into the CAAC-Be bond, generating cyclic alkyl(amino)imine (CAAI) ligands. Furthermore, the reaction with a small N-heterocyclic carbene (NHC) leads to unexpected CAAC-NHC ligand exchange, while the reaction with pentaphenylborole yields the first γ-azide adduct of a borole, long postulated to be the first step in the synthesis of 1,2-azaborinines from boroles and azides.

Ge14Br8-xClx(PEt3)4: Insight into the Reaction Route to Metalloid Clusters of Germanium.

The isolation of the germanium mixed halide cluster Ge14Br8-xClx(PEt3)4 (2) by the reaction of a metastable GeIBr solution (toluene/PEt3) with GeCl2·dioxane provides new insights into the complex formation mechanism of metalloid germanium clusters through the disproportionation reaction of GeIX (X = Cl and Br). It is shown that the GeII halide is involved in at least two steps in the build-up reaction of 2. The molecular structure of 2 is presented together with a plausible reaction mechanism leading to the binary cluster Ge14Br8(PEt3)4 and future aspects of these findings.

Cascade-Reaction Leading to an Intramolecular [2 + 4] Cycloaddition of a Phenyl Group by a Reactive Ge═Si Double Bond.

The reaction of GeCl2·dioxane with 2 equiv of the thiolate LiSHyp [Hyp = Si(SiMe3)3] yields the germanide (12-crown-4)2Li[Ge(SHyp)3] (1). A small structural variation in the substituent leads to a completely different result because the reaction of GeCl2·dioxane with 2 equiv of the thiolate KSHypPh3 [HypPh3 = Si(SiMe3)2(SiPh3)] in toluene yields the unexpected compound [Ph3Si][Me3Si]Ge[{(C6H5)Ph2Si}{SiMe3}2SiS]Si[SSiMe3] (2) in high yield. The reaction cascade to give 2 includes several rearrangement reactions and an intramolecular [2 + 4] cycloaddition of a phenyl ring. The syntheses and molecular structures of both compounds are presented, together with quantum-chemical calculations and NMR measurements, to enlighten the reaction mechanism behind the formation of 2.

Halides of the Heavier Group†14 Homologues Germanium, Tin, and Lead-A Journey through Unusual Compounds and Oxidation States.

Classical halides of the heavier Group 14 homologues germanium, tin, and lead are common precursors for the synthesis of exciting compounds, such as polyhedral clusters. To get access to larger metalloid cluster compounds of Group 14, the disproportionation reaction of metastable monohalide solutions, accessible through a preparative co-condensation reaction, proved to be quite successful. As the identity of the subvalent halides within the metastable solutions were yet unknown the reaction course from a monohalide precursor to a metalloid cluster was mostly unidentified. This might change now, as a first subhalide cluster [Ge14 Br8 (Et3 P)4 ] could be characterized, being the first trapped intermediate of the disproportionation reaction of Group 14 subhalides. All these aspects are included within this Minireview, together with a short historical overview, dealing with the development of the preparative co-condensation technique out of the matrix isolation technique, being the essential first step of the synthesis of metastable monohalide solutions of the heavier Group 14 elements Ge and Sn.

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 .

Ge14 Br8 (PEt3 )4 : A Subhalide Cluster of Germanium.

Heating a metastable solution of GeI Br to room temperature led to the first structurally characterized metalloid subhalide cluster Ge14 Br8 (PEt3 )4 (1). Furthermore 1 can be seen as the first isolated binary halide cluster on the way from GeI Br to elemental germanium, giving insight into the complex reaction mechanism of its disproportionation reaction. Quantum chemical calculations further indicate that a classical bonding situation is realized within 1 and that the last step of the formation of 1 might include the trapping of GeBr2 units.

LiEC(SiMe3)3 (E = Se, Te) as a new donor of chalcogen atoms for the generation of binary [(RxGey)Ez] cage compounds with unique structural features.

The reaction of GeCl2·dioxane with LiEC(SiMe3)3 (E = Se, Te) shows unexpected products different from those of the previously presented reaction system GeCl2·dioxane/LiSC(SiMe3)3. Here, LiEC(SiMe3)3 (E = Se, Te) acts as a chalcogen atom donor and simultaneously as a substituent to give cage compounds of the composition [(RxGey)Ez] with unique structural features of the Ge/E cores. The molecular structures are presented together with a possible formation mechanism of the selenium/germanium cage compound [{((SiMe3)3CGe)2GeSe4}2(µ2-Se)2] supported by quantum chemical calculations.