Synthesis and Characterization of Gold Silyl Compounds with Different Phosphine or Phosphite Groups for Reduction Reactions

A first glance into mixed phosphine-stibine moieties as protecting ligands for gold clusters

Atomically precise gold clusters have attracted considerable research interest as their tunable structure-property relationships have resulted in widespread applications, from sensing and biomedicine to energetic materials and catalysis. In this article, the synthesis and optical properties of a novel [Au₆(SbP₃)₂][PF₆]₂ cluster are reported. Despite the lack of spherical symmetry in the core, the cluster shows exceptional thermal and chemical stability. Detailed structural attributes and optical properties are evaluated experimentally and theoretically. This, to the best of our knowledge, is the first report of a gold cluster protected via synergistic multidentate coordination of stibine (Sb) and phosphine moieties (P). To further show that the latter moieties give a set of unique properties that differs from monodentate phosphine-protected [Au₆(PPh₃)₆]²⁺, geometric structure, electronic structure, and optical properties are analyzed theoretically. In addition, this report also demonstrates the critical role of overall-ligand architecture in stabilizing mixed ligand-protected gold clusters.

Au20 (t Bu3 P)8 : A Highly Symmetric Metalloid Gold Cluster in Oxidation State 0

Metalloid gold clusters have unique properties with respect to size and structure and are key intermediates in studying transitions between molecular compounds and the bulk phase of the respective metal. In the following, the synthesis of the all-phosphine protected metalloid cluster Au20 (t Bu3 P)8 , solely built from gold atoms in the oxidation state of 0 is reported. Single-crystal X-ray analysis revealed a highly symmetric hollow cube-octahedral arrangement of the gold atoms, resembling gold bulk structure. Quantum-chemical calculations illustrated the cluster can be described as a 20-electron superatom. Optical properties of the compound have shown molecular-like behavior.

Luminescent Pyrrole‐Based Phosphaphenalene Gold Complexes: Versatile Anticancer Tools with Wide Applicability

Brain cancer, one of the most lethal diseases, urgently requires the discovery of novel theranostic agents. In this context, molecules based on six‐membered phosphorus heterocycles – phosphaphenalenes – are especially attractive; they possess unique characteristics that allow precise chemical engineering. Herein, we demonstrate that subtle structural modifications of the phosphaphenalene‐based gold(I) complexes lead to modify their electronic distribution, endow them with marked photophysical properties and enhance their efficacy against cancer. In particular, phosphaphenalene‐based gold(I) complexes containing a pyrrole ring show antiproliferative properties in 14 cell lines including glioblastomas, brain metastases, meningiomas, IDH‐mutant gliomas and head and neck cancers, reaching IC₅₀ values as low as 0.73 μM. The bioactivity of this new family of drugs in combination with their photophysical properties thus offer new research possibilities for both the fundamental investigation and treatment of brain cancer.

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

The isolation of the germanium mixed halide cluster Ge₁₄Br_8-xCl_x(PEt₃)₄ (2) by the reaction of a metastable Ge^IBr solution (toluene/PEt₃) with GeCl₂·dioxane provides new insights into the complex formation mechanism of metalloid germanium clusters through the disproportionation reaction of Ge^IX (X = Cl and Br). It is shown that the Ge^II 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.

Metalloid gold clusters - past, current and future aspects

Gold chemistry and the synthesis of colloidal gold have always caught the attention of scientists. While Faraday was investigating the physical properties of colloidal gold in 1857 without probably knowing anything about the exact structure of the molecules, 150 years later the working group of Kornberg synthesized the first structurally characterized multi-shell metalloid gold cluster with more than 100 Au atoms, Au102(SR)44. After this ground-breaking result, many smaller and bigger metalloid gold clusters have been discovered to gain a better understanding of the formation process and the physical properties. In this review, first of all, a general overview of past investigations is given, leading to metalloid gold clusters with staple motifs in the ligand shell, highlighting structural differences in the cores of these clusters. Afterwards, the influence of the synthetic procedure on the outcome of the reactions is discussed, focusing on recent results from our group. Thereby, newly found structural motifs are taken into account and compared to the existing ones. Finally, a short outlook on possible subsequent reactions of these metalloid gold clusters is given.

A Series of Homoleptic Linear Trimethylsilylchalcogenido Cuprates, Argentates and Aurates Cat[Me3SiE-M-ESiMe3] (M = Cu, Ag, Au; E = S, Se)

The syntheses and XRD molecular structures of a complete series of silylsulfido metalates Cat[M(SSiMe₃)₂] (M = Cu, Ag, Au) and corresponding silylselenido metalates Cat[M(SeSiMe₃)₂] (M = Cu, Ag, Au) comprising lattice stabilizing organic cations (Cat = Ph₄P⁺ or PPN⁺) are reported. Much to our surprise these homoleptic cuprates, argentates, and aurates are stable enough to be isolated even in the absence of any strongly binding phosphines or N-heterocyclic carbenes as coligands. Their metal atoms are coordinated by two silylchalcogenido ligands in a linear fashion. The silyl moieties of all anions show an unexpected gauche conformation of the silyl substituents with respect to the central axis Si-[E-M-E]-Si in the solid state. The energetic preference for the gauche conformation is confirmed by quantum chemical calculations and amounts to about 2-6 kJ/mol, thus revealing a rather shallow potential mainly depending on electronic effects of the metal. Furthermore, 2D HMQC methods were applied to detect the otherwise nonobservable NMR shifts of the ²⁹Si and ⁷⁷Se nuclei of the silylselenido compounds. Preliminary investigations reveal that these thermally and protolytically labile chalcogenido metalates are valuable precursors for the precipitation of binary coinage metal chalcogenide nanoparticles from organic solution and for coinage metal cluster syntheses.

Gold(i) complexes based on six-membered phosphorus heterocycles as bio-active molecules against brain cancer

π-Systems based on six-membered phosphorus heterocycles possess structural and electronic characteristics that clearly distinguish them from the rest of the organophosphorus molecules. However, their use in cancer therapy has been uninvestigated. In particular, glioblastoma is one of the most lethal brain tumors. The development of novel and more efficient drugs for the treatment of glioblastoma is thus crucial to battle this aggressive disease. Herein, we report a new family of gold(i) complexes based on six-membered phosphorus heterocycles as a promising tool to investigate brain cancer. We discovered that the latter complexes inhibit the proliferation, sensitize to apoptosis and hamper the migration of not only conventional but also stem-like glioblastoma cells. Our results unveil thus new research opportunities for the treatment of glioblastoma.

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.

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 .