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.

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.

[(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.

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.

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.

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.

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.

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 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.

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.

LiGe(SiMe3)3: A New Substituent for the Synthesis of Metalloid Tin Clusters from Metastable Sn(I) Halide Solutions.

The most fruitful synthetic route to metalloid tin clusters applies the disproportionation reaction of metastable Sn(I) halide solutions, whereby Si(SiMe3)3 is mostly used as the stabilizing substituent. Here, we describe the synthesis and application of the slightly modified substituent Ge(SiMe3)3, which can be used for the synthesis of metalloid tin clusters to give the neutral cluster Sn10[Ge(SiMe3)3]6 as well as the charged clusters {Sn10[Ge(SiMe3)3]5}− and {Sn10[Ge(SiMe3)3]4}2−. The obtained metalloid clusters are structurally similar to their Si(SiMe3)3 derivatives. However, differences with respect to the stability in solution are observed. Additionally, a different electronic situation for the tin atoms is realized as shown by 119mSn Mössbauer spectroscopy, giving further insight into the different kinds of tin atoms within the metalloid cluster {Sn10[Ge(SiMe3)3]4}2−. The synthesis of diverse derivatives gives the opportunity to check the influence of the substituent for further investigations of metalloid tin cluster compounds.

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.

{[Si(SiMe3)3]2Ge9-SiMe2-(C6H4)-SiMe2-Ge9[Si(SiMe3)3]2K}-: The Connection of Metalloid Clusters via an Organic Linker.

The reaction of [(Hyp)2Ge9]2- (Hyp = Si(SiMe3)3) with ClSiMe2-C6H4-SiMe2Cl gives [K(THF)][(Hyp)2Ge9-SiMe2-C6H4-SiMe2-Ge9(Hyp)2K] K1 in 45% yield in the form of orange-red crystals. 1 is thereby the first compound where two Ge9(Hyp)2 clusters are bound together via a bridging ligand. 1 is stable in solution but cannot be transferred intact into the gas phase via electrospray ionization indicating a higher reactivity with respect to other metalloid Ge9R3 clusters. The arrangement of the nine germanium atoms within the two Ge9 units in 1 is unique for metalloid Ge9R3 clusters. Quantum chemical calculations further reveal an electronic interaction of the two Ge9 units in 1 via the bridging phenylene group.

Au108 S24 (PPh3 )16 : A Highly Symmetric Nanoscale Gold Cluster Confirms the General Concept of Metalloid Clusters.

The reduction of (Ph3 P)AuCl with NaBH4 in the presence of HSC(SiMe3 )3 , leads to one of the largest metalloid gold clusters: Au108 S24 (PPh3 )16 (1). Within 1 an octahedral Au44 core of gold atoms arranged as in Au metal is surrounded by 48 oxidized Au atoms of an Au48 S24 shell, a novel building block in gold chemistry. The protecting Au48 S24 shell is completed by additional 16 Au(PPh3 ) units, leading to a complete protection of the gold core. Within 1 the Au-Au distances get more molecular on going from the center to the ligand shell. Cluster 1 represents novel structural motives in the field of metalloid gold clusters which also are partly typical for metal atoms in metalloid clusters: Mn Rm (n>m).

Reactivity of [Ge9 {Si(SiMe3 )3 }3 ]- Towards Transition-Metal M2+ Cations: Coordination and Redox Chemistry.

Recently the metalloid cluster compound [Ge9 Hyp3 ]- (1; Hyp=Si(SiMe3 )3 ) was oxidatively coupled by an iron(II) salt to give the largest metalloid Group 14 cluster [Ge18 Hyp6 ]. Such redox chemistry is also possible with different transition metal (TM) salts TM2+ (TM=Fe, Co, Ni) to give the TM+ complexes [Fe(dppe)2 ][Ge9 Hyp3 ] (3; dppe=1,2-bis(diphenylphosphino)ethane), [Co(dppe)2 ][Ge9 Hyp3 ] (4), [Ni(dppe)(Ge9 Hyp3 )] (5) and [Ni(dppe)2 (Ge9 Hyp3 )]+ (6). Such a redox reaction does not proceed for Mn, for which a salt metathesis gives the first open shell [Hyp3 Ge9 -M-Ge9 Hyp3 ] cluster (2; M=Mn). The bonding of the transition metal atom to 1 is also possible for Ni (e.g., compound 6), in which one or even two nickel atoms can bind to 1. In contrast to this in case of the Fe and Co compounds 3 and 4, respectively, the transition-metal atom is not bound to the Ge9 core of 1. The synthesis and the experimentally determined structures of 2-6 are presented. Additionally the bonding within 2-6 is analyzed and discussed with the aid of EPR measurements and quantum chemical calculations.

The Largest Metalloid Group†14 Cluster, Ge18[Si(SiMe3)3]6 : An Intermediate on the Way to Elemental Germanium.

The oxidation of [Ge9(Hyp)3](-) (Hyp=Si(SiMe3 )3) with an Fe(II) salt leads to Ge18 (Hyp)6 (1), the largest Group 14 metalloid cluster that has been structurally characterized to date. The arrangement of the 18 germanium atoms in 1 shows similarities to that found in the solid-state structure Ge(cF136). Furthermore, 1 can be described as a macropolyhedral cluster of two Ge9 units. Quantum-chemical calculations further hint at a strained arrangement so that 1 can be considered as a first trapped intermediate on the way from Ge9 units to elemental germanium with the clathrate-II structure (Ge(cF136)).

{Sn10 [Si(SiMe3 )3 ]4 }(2-) : A highly reactive metalloid tin cluster with an open ligand shell.

The reaction of a Sn(I) Cl solution with LiSi(SiMe3 )3 gave the anionic metalloid tin cluster {Sn10 [Si(SiMe3 )3 ]4 }(2-) (7) in good yield. The arrangement of the ten tin atoms in the cluster core can be described as a distorted centaur polyhedron. Quantum chemical calculations suggest that there are 26 bonding electrons in the cluster core, which may be described as an arachno cluster in agreement with Wade's rules. NMR and mass spectrometric investigations showed that 7 is highly reactive, which may be due to the open ligand shell. The easily available tin atoms in 7 thereby open the door to further subsequent reactions, in which 7 may act as a building block to larger cluster aggregates.

Reactions with a Metalloid Tin Cluster {Sn10[Si(SiMe3)3]4}(2-): Ligand Elimination versus Coordination Chemistry.

Chemistry that uses metalloid tin clusters as a starting material is of fundamental interest towards understanding the reactivity of such compounds. Since we identified {Sn10[Si(SiMe3)3]4}(2-) 7 as an ideal candidate for such reactions, we present a further step in the understanding of metalloid tin cluster chemistry. In contrast to germanium chemistry, ligand elimination seems to be a major reaction channel, which leads to the more open metalloid cluster {Sn10[Si(SiMe3)3]3}(-) 9, in which the Sn core is only shielded by three Si(SiMe3)3 ligands. Compound 9 is obtained through different routes and is crystallised together with two different countercations. Besides the structural characterisation of this novel metalloid tin cluster, the electronic structure is analysed by (119)Sn Mössbauer spectroscopy. Additionally, possible reaction pathways are discussed. The presented first step into the chemistry of metalloid tin clusters thus indicates that, with respect to metalloid germanium clusters, more reaction channels are accessible, thereby leading to a more complex reaction system.

{Ge9[Si(SiMe3)2(SiPh3)]3}(-): Ligand Modification in Metalloid Germanium Cluster Chemistry.

The influence of the stabilizing ligand on the physical and chemical properties of a metalloid cluster compound is important for nanotechnology as metalloid clusters are ideal model compounds for metal nanoparticles. Here we present the synthesis of a differently substituted metalloid {Ge9R3}(-) cluster: {Ge9[Si(SiMe3)2(SiPh3)]3}(-) 1, which is obtained in good yield by the reaction of K4Ge9 with ClSi(SiMe3)2(SiPh3). 1 is characterized via NMR and mass spectrometry, but crystallization is hindered. However, the reaction with HgCl2 gives the neutral compound HgGe18[Si(SiMe3)2(SiPh3)]6 2, which can be crystallized and structurally characterized. The presented results are a first step for the investigation of the ligand's influence on the properties of a metalloid germanium cluster compound.