A Series of Cyclopentadienyl Lanthanum Complexes with Metalloid Germanium Clusters.

A series of cyclopentadienyllanthanum complexes with the disilylated metalloid germanium cluster [Ge9(Hyp)2]2- [Hyp = Si(SiMe3)3] has been prepared and fully characterized. The synthetic procedure is based on the salt metathesis reaction of two different cyclopentadienyllanthanum diiodides CpLaI2 (Cp: Cp*, pentamethylcyclopentadienyl; Cpttt, 1,2,4-tri-tert-butylcyclopentadienyl) with K2[Ge9(Hyp)2] in tetrahydrofuran (THF) with a subsequent extraction with n-hexane. The composition of the obtained compounds and the mode of coordination of the germanium cluster to the rare-earth metal are strongly influenced by the steric demand of the cyclopentadienyl ligands and the crystallization conditions. The centrosymmetric dimeric compounds with the common formula [CpLa(solv)(η2,3-Ge9(Hyp)2)]2 [1, Cp = Cp*, solv-THF; 2, Cp = Cpttt, solv-NCCH2C(Me)NSiMe3] have been isolated by the slow evaporation of a n-hexane solution, while a mononuclear complex [CptttLa(THF)2(η3-Ge9(Hyp)2)] (4) was found by crystallization from THF. The repeated recrystallization of 1 from n-hexane afforded the asymmetric dimer [Cp*La(THF)(η2,3-Ge9(Hyp)2)][Cp*La(η2,3-Ge9(Hyp)2)] (3) with only one coordinated THF molecule.

Synthesis and Reactivity of Fluorenyl-Based Germanium(II) Compounds.

We present the synthesis of alkyl-substituted germylenes GeFlu2, Ge(FluTMS)2, and FluTMSGeCl (Flu = 9H-fluorenyl, FluTMS = 9-trimethylsilyl-9H-fluorenyl) using bulky fluorenyl ring systems and modifications of that. GeFlu2 can only be crystallized as its three-membered ring trimer, whereby the reaction is accompanied by the formation of several byproducts, such as [Li(THF)4][Ge(Ge3Flu7H)]. These results led to the modification of the fluorenyl framework by substitution the one H atom in the 9-position by a TMS group. With the synthesis of the corresponding Li salt LiFluTMS, Ge(FluTMS)2 could be isolated in good yields in a further reaction. The homoleptic Ge(FluTMS)2 is found in its crystalline form as a monomer and thus belongs to the series of monomeric alkyl-substituted germylenes. Also, the corresponding monoalkyl-substituted halogenido germylene was isolated as a four-membered ring tetramer [FluTMSGeCl]4 during an unselective reaction. However, FluTMSGeCl undergoes significant stabilization through the formation of the monomeric phosphane adduct FluTMSGeCl·PEt3, which greatly increases the selectivity of the reaction. During further reactions of Ge(FluTMS)2 with a GeBr solution (toluol/nPr3P), more impressions of the reactivity of Ge(I)X solutions with germylenes were achieved, showing that those germylenes take part in the disproportionation reaction of metastable Ge(I) solutions to give oxidized Ge(IV) compounds like (FluTMS)2GeBr2.

[(thf)5Ln(Ge9{Si(SiMe3)3}2)] (Ln = Eu, Sm, Yb): Capping Metalloid Germanium Cluster with Lanthanides.

We report the synthesis of three neutral complexes with different coordination modes of a di-silylated metalloid germanium cluster to divalent lanthanides [(thf)5Ln(ηn-Ge9(Hyp)2)] (Ln = Yb (1, n = 1); Eu (2, n = 2, 3), Sm (3, n = 2, 3); Hyp = Si(SiMe3)3) by the salt metathesis of LnI2 with K2[Ge9(Hyp)2] in THF. The complexes were characterized by elemental analysis, nuclear magnetic resonance and UV-vis-NIR spectroscopy, and single-crystal X-ray diffraction. In thf solution, the formation of contact or solvate-separated ion pairs depending on the concentration is assumed. Compound 2 exhibits a blue luminescence typical for Eu2+. The solid-state magnetic measurements of compounds 2 and 3 confirm the presence of divalent europium and samarium, respectively.

Metalloid germanium cluster shears for lanthanide diiodides.

We report the synthesis and characterization of ionic compounds [(thf)4YbI]2[Ge9(Hyp)3]2 (1) and [(thf)5LnI]4[Ge9(Hyp)3]4 (Ln = Eu (2), Sm (3)), (Hyp = Si(SiMe3)3). All compounds were examined by UV-Vis spectroscopy and a blue luminescence of Eu2+ was found. The solid state magnetic measurements of complexes 2 and 3 confirmed the presence of divalent lanthanides.

Oxidative Coupling of [Ge9(Si(SiMe3)3)2]2- with f Elements.

We report the reactions of K2[Ge9(Hyp)2] (Hyp = Si(SiMe3)3) with (thf)3YbI3, ThI4, and UCl4, leading to the oxidative coupling of the metalloid germanium cluster to form the dimeric dianion [Ge18(Hyp)4]2-. The novel dimerized Ge18-cluster was isolated and characterized by single-crystal X-ray diffraction analysis as a component of ionic compounds [Yb(thf)6][Ge18(Hyp)4] (1) and [K(2.2.2-crypt)]2[Ge18(Hyp)4] (2) with two different counterions. The dihedral angle between two intact Ge9 cages depends on the counterions, which was also studied by quantum-chemical calculations.

Oxidation of [Ge9{Si(SiMe3)3}3]- with LnI3 (Ln = Eu, Sm, Yb): Isomerism of Metalloid Germanium Clusters.

The oxidation of K[Ge9(Hyp)3] (Hyp = Si(SiMe3)3) with lanthanide triiodides LnI3 (Ln = Eu, Sm, Yb) leads to the formation of novel clusters with a Ge18-core isolated as a co-crystallizate of Ge*18(Hyp)6 (1a) and Ge18(Hyp)5(Si(SiMe3)2)(SiMe3) (1b). Clusters 1a and 1b differ distinctly from the known cluster Ge18(Hyp)6 (A), which has been found earlier in the reaction of K[Ge9(Hyp)3] with FeCl2 and now identified as an intermediate product in the production of compounds 1a and 1b. These three compounds A, 1a, and 1b are thus structural isomers being the first example of genuine isomerism in metalloid main-group cluster compounds.

{Ge8[Fe(CO)4]8}7-: an anionic cubic germanium-iron-cluster featuring an unpaired electron.

Within the reaction of a metastable Ge(I)Cl solution and Na2Fe2(CO)8 the anionic cubic cluster compound {(thf)14Na6Ge8[Fe(CO)4]8}- (3) is obtained. The open shell character of 3 is proven by EPR spectroscopy. Quantum chemical calculations furthermore show that also the closed shell systems should be stable, but could not be isolated so far. Additionally, 3 can be seen as an intermediate cluster compound on the formation of metalloid clusters.

Higher stability of metalloid tin clusters obtained via the cation-anion interaction.

The reaction of a metastable SnCl solution with KR (R = Si(SiMe3)2(SitBuMe2) = HyptBuMe2 or Si(SiMe3)2(SiEt3) = HypEt3) gives the metalloid tin cluster [Sn10R4]2- in partly good yields. The tin clusters are in the solid state as well in solution coordinated by a potassium cation, leading first of all to a more static compound and novel coordination polymers in the solid state. Additionally, the coordination of the potassium cation strongly increases the stability of the cluster in solution. This higher stability is thereby an important prerequisite for future investigation of this open shell metalloid tin cluster.

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.

(thf)2Ln(Ge9{Si(SiMe3)3}3)2 (Ln = Eu, Sm): the first coordination of metalloid germanium clusters to lanthanides.

We report the synthesis, structure and magnetic properties of the first rare earth complexes of metalloid group 14 clusters [(thf)2Ln(Ge9Hyp3)2] (Ln = Eu, Sm, Hyp = Si(SiMe3)3). X-Ray crystallographic analysis and DFT calculations reveal a novel η2-coordination mode of the Ge9Hyp3 units and a slight distortion of the Ge9 cage.

A new reductant in gold cluster chemistry gives a superatomic gold gallium cluster.

The low valent gallium(i) compound GaCp was primarily used in gold cluster chemistry to synthesize the superatomic cluster [(PPh3)8Au9GaCl2]2+, complementing the borane-dominated set of reducing agents in gold chemistry, opening a whole new field for further research. Using density functional theory calculations, the cluster can be described by the jellium model as an 8-electron superatom cluster.

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.

Au54(Et3P)18Cl12: a structurally related cluster to Au32(Et3P)12Cl8 gives insight into the formation process.

The reaction of Et3PAuCl with NaBH4 in EtOH leads to the metalloid gold cluster Au32(Et3P)12Cl8 (Au32) or Au54(Et3P)18Cl12 (Au54) depending on the work-up procedure of the reaction mixture. The molecular structure of Au54 is determined by X-ray diffraction and can be described as a fusion of two Au32 clusters showing a similar solubility. The metalloid cluster Au54 can be either described by a shell model or as a combination of tetrahedral Au4X units (X = Cl, Et3P); edge and face sharing, whereas tetrahedral Au4 units are a central motif in gold cluster chemistry. This novel Au54 gold cluster gives another unique insight into the formation or decomposition process of metalloid clusters, indicating that Au32 and Au54 form from a single yet unknown cluster source.

Synthesis and Characterization of the Highly Unstable Metalloid Cluster Ag64 (Pn Bu3 )16 Cl6.

The reduction of (n Bu3 P)AgCl with LiBH(s Bu)3 in toluene gives the metalloid silver cluster Ag64 (Pn Bu3 )16 Cl6 (1) as dark red, temperature- and light-sensitive single crystals in high yield. 1 is the largest structurally characterized metalloid silver cluster exhibiting chlorine and phosphine substituents only. The silver atoms in 1 show an overall brick-shape arrangement, where structural resemblance to the close-packed fcc and hcp structures is realized. Within 1 a 58 electron closed shell system is present. The light sensitivity renders 1 as a model compound for the primary seeds of the photo process, whereby this sensitivity, together with the high-yield synthesis show that 1 is a perfect starting compound for further investigations like silver-plating processes.

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.

Sn20(SitBu3)10Cl2 - the largest metalloid group 14 cluster shows a raspberry-like arrangement of smaller units.

The reaction of a metastable Sn(i)Cl solution with NaSitBu3 leads to the largest metalloid group 14 cluster Sn20(SitBu3)10Cl2, in which the arrangement of the tin atoms in the cluster can be seen as a raspberry-like cluster of cluster arrangement, giving further insight into the process of the formation of a metalloid tin cluster from molecular precursors. Quantum chemical calculations further indicate that the arrangement of the tin atoms in the cluster core can be highly flexible, leading to the decomposition of the Sn20 cluster into smaller Sn10 units when the right substituent is applied.

Synthesis and Photodimerization of 2- and 2,3-Disubstituted Anthracenes: Influence of Steric Interactions and London Dispersion on Diastereoselectivity.

There is increased evidence that the effect of bulky groups in organic, organometallic, and inorganic chemistry is not only repulsive but can be attractive because of London dispersion interactions. The influence of the size of primary alkyl substituents in 2- and 2,3-positions of anthracenes on the diastereoselectivity (anti vs syn dimer) of the [π4s + π4s] photoinduced dimerization is investigated. The synthesis of the anthracene derivatives was achieved by Suzuki-Miyaura reaction of 2,3-dibromoanthracene with alkylboronic acids as well as by reduction of anthraquinones that were obtained from 2,3-disubstituted 1,3-butadienes and naphthoquinone followed by dehydrogenation. The mixtures of dianthracene isomers were analyzed with respect to the anti/syn-ratio of the products by X-ray crystallography and nuclear Overhauser effect spectroscopy. While for the 2,3-dimethylanthracene the anti and syn isomers were formed in equal amounts, the anti dimers are the major products in all other cases. A linear correlation (R2 = 0.98) between the steric size (Charton parameter) and the isomeric ratio suggests that the selectivity is dominated by classical repulsive steric effects. An exception is the iso-butyl substituent that produces an increased amount of the syn isomer. It is suggested that this is due to an exalted effect of London dispersion interactions.

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 .

Synthesis and Characterization of Three Multi-Shell Metalloid Gold Clusters Au32 (R3 P)12 Cl8.

Three multi-shell metalloid gold clusters of the composition Au32 (R3 P)12 Cl8 (R=Et, n Pr, n Bu) were synthesized in a straightforward fashion by reducing R3 PAuCl with NaBH4 in ethanol. The Au32 core comprises two shells, with the inner one constituting a tilted icosahedron and the outer one showing a distorted dodecahedral arrangement. The outer shell is completed by eight chloride atoms and twelve R3 P groups. The inner icosahedron shows bond lengths typical for elemental gold while the distances of the gold atoms in the dodecahedral arrangement are in the region of aurophilic interactions. Quantum-chemical calculations illustrate that the Jahn-Teller effect observed within the cluster core can be attributed to the electronic shell filling. The easily reproducible synthesis, good solubility, and high yields of these clusters render them perfect starting points for further research.

On the reaction of GeCl2·dioxane with KFeCp(CO)2: isolation and characterization of novel bimetallic clusters.

The reaction of GeCl2·dioxane with KFeCp(CO)2 gives the polyhedral cluster compounds Ge6[FeCp(CO)2]61, Ge6[FeCp(CO)2]6Cl23 and Ge6[FeCp(CO)2]4[Fe2Cp2(CO)3]25. Quantum chemical calculations indicate that the substitution of a halide substituent in GeCl2 by FeCp(CO)2 favours the formation of oligomers with Ge-Ge bonds, giving access to polyhedral cluster compounds from easily accessible starting materials.