SiSi Double Bonds: Synthesis of an NHC‐Stabilized Disilavinylidene

An efficient two‐step synthesis of the first NHC‐stabilized disilavinylidene (Z)‐(SIdipp)SiSi(Br)Tbb ( 2 ; SIdipp=C[N(C₆H₃‐2,6‐iPr₂)CH₂]₂, Tbb=C₆H₂‐2,6‐[CH(SiMe₃)₂]₂‐4‐tBu, NHC=N‐heterocyclic carbene) is reported. The first step of the procedure involved a 2:1 reaction of SiBr₂(SIdipp) with the 1,2‐dibromodisilene (E)‐Tbb(Br)SiSi(Br)Tbb at 100 °C, which afforded selectively an unprecedented NHC‐stabilized bromo(silyl)silylene, namely SiBr(SiBr₂Tbb)(SIdipp) ( 1 ). Alternatively, compound 1 could be obtained from the 2:1 reaction of SiBr₂(SIdipp) with LiTbb at low temperature. 1 was then selectively reduced with C₈K to give the NHC‐stabilized disilavinylidene 2 . Both low‐valent silicon compounds were comprehensively characterized by X‐ray diffraction analysis, multinuclear NMR spectroscopy, and elemental analyses. Additionally, the electronic structure of 2 was studied by various quantum‐chemical methods.     

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR,Raman, Mass Spectrometric,and Quantum Chemical Investigation

Polyanionic silicon clusters are provided by the Zintl phases K₄Si₄, comprising [Si₄]⁴⁻ units, and K₁₂Si₁₇, consisting of [Si₄]⁴⁻ and [Si₉]⁴⁻ clusters. A combination of solid‐state MAS‐NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum‐chemical investigations was used to investigate four‐ and nine‐atomic silicon Zintl clusters in neat solids and solution. The results were compared to ²⁹Si isotope‐enriched samples. ²⁹Si‐MAS NMR and Raman shifts of the phase‐pure solids K₄Si₄ and K₁₂Si₁₇ were interpreted by quantum‐chemical calculations. Extraction of [Si₉]⁴⁻ clusters from K₁₂Si₁₇ with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si₉ clusters. This compound was characterized by elemental and EDX analyses and ²⁹Si‐MAS NMR and Raman spectroscopy. Charged Si₉ clusters were detected by ²⁹Si NMR in solution. ²⁹Si and ¹H NMR spectra reveal the presence of the [H₂Si₉]²⁻ cluster anion in solution.     

Preparation and Characterization of Uranium–Iron Triple‐Bonded UFe(CO)3− and OUFe(CO)3− Complexes

We report the preparation of UFe(CO)₃⁻ and OUFe(CO)₃⁻ complexes using a laser‐vaporization supersonic ion source in the gas phase. These compounds were mass‐selected and characterized by infrared photodissociation spectroscopy and state‐of‐the‐art quantum chemical studies. There are unprecedented triple bonds between U 6d/5f and Fe 3d orbitals, featuring one covalent σ bond and two Fe‐to‐U dative π bonds in both complexes. The uranium and iron elements are found to exist in unique formal U(I or III) and Fe(−II) oxidation states, respectively. These findings suggest that there may exist a whole family of stable df–d multiple‐bonded f‐element‐transition‐metal compounds that have not been fully recognized to date.