Metal-metal cooperativity boosts Lewis basicity and reduction properties of the bis(gallanediyl) CyL2Ga2.

The interplay of two proximate gallium centres equips the bimetallic complex CyL2Ga2 (1, CyL2 = 1,2-trans-Cy[NC(Me)C(H)C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) with increased Lewis basicity and higher reducing power compared to the monometallic gallanediyl LGa (2, L = HC[MeCN(Dip)]2) as evidenced by cross-over experiments. Quantum chemical calculations were employed to support the experimental findings.

A Planar Five-Membered Aromatic Ring Stabilized by Only Two π-Electrons.

Many chemicals known today are partially or fully aromatic, since a ring framework experiences additional stabilization through the delocalization of π-electrons. While aromatic rings with equal numbers of π-electrons and ring atoms such as benzene are particularly stable, those with the minimally required two π-electrons are very rare and yet remain limited to three- and four-membered rings if not stabilized in the coordination sphere of heavy metals. Here we report the facile synthesis of a dipotassium cyclopentagallene, a unique example of a five-membered aromatic ring stabilized by only two π-electrons. Single-crystal X-ray diffraction revealed a planar Ga5 ring with almost equal gallium-gallium bond lengths, which together with computational and spectroscopic data confirm its aromatic character. Our results prove that aromatic stabilization goes far beyond what has previously been assumed as minimum π-electron count in a five-atom ring fragment.

Cooperative Bond Activation by a Bimetallic Main-Group Complex.

Inspired by natural metalloenzymes that efficiently catalyze a variety of transformations, chemists have developed large numbers of dinuclear transition-metal complexes with extraordinary properties and reactivity patterns. For main-group element compounds, however, metal-metal cooperativity is much less explored. Here we present the synthesis and characterization of a room-temperature-stable compound with two separated two-coordinated gallium(I) centers possessing both a lone pair of electrons and a vacant orbital, reminiscent of singlet carbenes. This species displays enhanced reactivity compared to its mononuclear counterpart due to bimetallic cooperativity that allows for the facile activation of strong C-F bonds across the gallium-gallium bond. Two mechanistic scenarios of the cooperative bond activation have been identified by DFT and DLPNO-CCSD(T) calculations.

Salt metathesis as an alternative approach to access aluminium(i) and gallium(i) ß-diketiminates.

Salt metathesis, i.e. the reaction of sodium ß-diketiminate with (AlCp*)4 and GaCp*, respectively, is a valuable pathway to access the respective aluminium(i) and gallium(i) ß-diketiminates I and II. The protocol gives better yields compared to the established procedures and avoids the use of strong reducing agents such as metallic potassium. Furthermore, the aluminium(i) ß-diketiminate I was found to react with itself and yields upon C-N bond cleavage and hydrogen-atom transfer the asymmetric dinuclear aluminium(iii) complex V that is readily separated from I by crystallisation. The reaction mechanism has been probed by means of DFT and DLPNO-CCSD(T) calculations and the computational findings are in good agreement with the experimental observations.

C-F bond activation by pentamethylcyclopentadienyl-aluminium(i): a combined experimental/computational exercise.

The reaction of (Cp*Al)4 with a series of fluoro(hetero)arenes has been investigated and C-F bond activation was observed with perfluorotoluene, pentafluoropyridine as well as 1,2,3,4-tetrafluoro-, pentafluoro- and hexafluorobenzene. The reaction mechanism has been probed by means of DFT calculations and the computational findings are in good agreement with the experimental observations.

[PtZn2Ge18(Hyp)8] (Hyp = Si(SiMe3)3): A Neutral Polynuclear Chain Compound with Ge9(Hyp)3 Units.

The reaction of [ZnGe18(Hyp)6] (Hyp = Si(SiMe3)3) with Pt(PPh3)4 gives the neutral polynuclear complex of Ge9(Hyp)3 units [HypZn-Ge9(Hyp)3-Pt-Ge9(Hyp)3-ZnHyp], 1. Within 1, the central Pt atom is bound η3 to both Ge9(Hyp)3 units to which further ZnHyp units are bound again, symmetric η3, to the other side of the Ge9(Hyp)3 units, leading to the longest chain compound exhibiting Ge9(Hyp)3 units that is known to date. Dissolved crystals of 1 give a violet solution, showing an absorption maximum around 543 nm. Further UV-vis investigations on different M xGe9(Hyp)3 compounds show that the absorption maximum depends on the number of transition metal atoms bound to the Ge9(Hyp)3 unit, which is supported by TD-DFT calculations.

{[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.

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)).

{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.

Polytellurides of Mn, Fe, and Zn from mild solvothermal reactions in liquid ammonia.

The reaction of elemental Mn, Fe, and Zn with Te in liquid ammonia at 50 °C leads to the polytellurides [Mn(NH3)6]Te4 (1), [Fe(NH3)6]Te4·NH3 (2), and [Zn(NH3)4]2Te15 (3) in quantitative yield for 1 and 3, and in 30-50% yield for 2. The compounds form black crystals, which are air sensitive and easily lose ammonia without a protective atmosphere of NH3. Compound 3 is semiconducting with a thermal activation energy of 1.2 eV. In the crystal structures of 1 and 2, tetratelluride anions Te4(2-) in gauche conformation with dihedral angles around 90° are present, which are linked to form infinite spiral chains. Compound 3 contains an unusual Te15(4-) polyanion in the form of a bent chain Te7-Te-Te7. The connection between the Te4 groups in 1 and 2 and the two Te7 groups in 3 is achieved via linear Te3 entities, which are strongly asymmetric in 1, almost symmetric in 2, and symmetric in 3 (for 1, Te-Te···Te 174.0°, d1 = 2.87, d2 = 3.25 Å; for 2, Te-Te-Te 178.8°, d1 = 3.01, d2 = 3.09 Å; for 3, Te-Te-Te 180°, d1 = d2 = 3.06 Å). Periodic DFT calculations show that interaction between the Te4(2-) units is negligible in 1 and weak but undoubtedly present in 2. The overlap population amounts to 0.09 in the linear Te3 group of 3. The band structure calculation of 3 gives semiconducting behavior with a band gap of 1.5 eV in fair agreement with experimental data.