[GeRu6(CO)18HI]: A Germanium-Centered Ruthenium Carbonyl Cluster with Aromatic Ring Current.

The carbonyl cluster compound [GeRu6(CO)18HI] is unique in regard to its structure and bonding with a GeRu6 cluster core, a planar GeRu4HI unit, extensive multi-center bonding, and an aromatic ring current similar to benzene (9-10 nA T-1). The open-shell cluster core is a Ge-centered five-membered Ru4(Ru2) ring with CO ligands and an additional H and I atom, each bridging two Ru atoms on opposite sides of the cluster core. The compound is prepared at 130 °C in a weakly-coordinating ionic liquid.

Molecular cyclo-P3 complexes of the rare-earth elements via a one-pot reaction and selective reduction.

Synthesis of new organo-lanthanide polyphosphides with an aromatic cyclo-[P4]2- moiety and a cyclo-[P3]3- moiety is presented. For this purpose, the divalent LnII-complexes [(NON)LnII(thf)2] (Ln = Sm, Yb) ((NON)2- = 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene) and trivalent LnIII-complexes [(NON)LnIIIBH4(thf)2] (Ln = Y, Sm, Dy) were used as precursors in the reduction process of white phosphorus. While using [(NON)LnII(thf)2] as a one-electron reducing agent the formation of organo-lanthanide polyphosphides with a cyclo-[P4]2- Zintl anion was observed. For comparison, we investigated a multi-electron reduction of P4 by a one-pot reaction of [(NON)LnIIIBH4(thf)2] with elemental potassium. As products molecular polyphosphides with a cyclo-[P3]3- moiety were isolated. The same compound could also be obtained by reducing the cyclo-[P4]2- Zintl anion within the coordination sphere of SmIII in [{(NON)SmIII(thf)2}2(µ-η4:η4-P4)]. Reduction of a polyphosphide within the coordination sphere of a lanthanide complex is unprecedented. Additionally, the magnetic properties of the dinuclear DyIII-compound bearing a bridging cyclo-[P3]3- moiety were investigated.

Tin Bromido Aluminate Networks with Bright Luminescence.

The novel tin bromido aluminates [Sn3 (AlBr4 )6 ](Al2 Br6 ) (1), Sn(AlBr4 )2 (2), [EMIm][Sn(AlBr4 )3 ] (3) and [BMPyr][Sn(AlBr4 )3 ] (4) ([EMIm]: 1-ethyl-3-methylimidazolium, [BMPyr]: 1-butyl-1-methyl-pyrrolidinium), are obtained from a ionic-liquid-based reaction of AlBr3 and SnCl2 or SnBr2 , resulting in colorless and transparent crystals. 1 contains a neutral, inorganic ∞ 3 [Sn3 (AlBr4 )6 ] network filled with intercalated Al2 Br6 molecules. 2 represents a 3D structure isotypic to Pb(AlCl4 )2 or α-Sr[GaCl4 ]2 . 3 and 4 exhibit infinite ∞ 1 [Sn(AlBr4 )3 ]n- chains that are separated by the voluminous [EMIm]+ /[BMPyr]+ cations. All title compounds contain Sn2+ coordinated by AlBr4 tetrahedra, resulting in chains or 3D networks. Moreover, all title compounds show photoluminescence due to Br- →Al3+ ligand-to-metal charge-transfer excitation, followed by 5s2 p0 ←5s1 p1 emission on Sn2+ . Most surprisingly, the luminescence is highly efficient (quantum yield >50 %). Specifically, 3 and 4 exhibit outstanding quantum yields of 98 and 99 %, which are the highest values observed for Sn2+ -based luminescence so far. The title compounds have been characterized by single-crystal structure analysis, elemental analysis, energy-dispersive X-ray analysis, thermogravimetry, infrared and Raman spectroscopy, UV-Vis and photoluminescence spectroscopy.

Molecular Lanthanide Switches for Magnetism and Photoluminescence.

Solvation of [(CNT)Ln(η8 -COT)] (Ln=La, Ce, Nd, Tb, Er; CNT=cyclononatetraenyl, i.e., C9 H9 - ; COT=cyclooctatetraendiid, i.e., C8 H8 2- ) complexes with tetrahydrofuran (THF) gives rise to neutral [(η4 -CNT)Ln(thf)2 (η8 -COT)] (Ln=La, Ce) and ionic [Ln(thf)x (η8 -COT)][CNT] (x=4 (Ce, Nd, Tb), 3 (Er)) species in a solid-to-solid transformation. Due to the severe distortion of the ligand sphere upon solvation, these species act as switchable luminophores and single-molecule magnets. The desolvation of the coordinated solvents can be triggered by applying a dynamic vacuum, as well as a temperature gradient stimulus. Raman spectroscopic investigations revealed fast and fully reversible solvation and desolvation processes. Moreover, we also show that a Nd:YAG laser can induce the necessary temperature gradient for a self-sufficient switching process of the Ce(III) analogue in a spatially resolved manner.

Stimuli Responsive Silylene: Electromerism Induced Reversible Switching Between Mono- and Bis-Silylene.

Electromerism is a very well-known phenomenon in transition metal chemistry. In main group chemistry, this concept has only started getting attention recently. We report stimuli responsive low-valent silicon compounds exhibiting electromerism. A mixed-valent silaiminyl-silylene 1, [LSi-Si(NDipp)L] (L=PhC(Nt Bu)2 ), was synthesized in a single step from amidinate-chlorosilylene. Compound 1 has two interconnected Si atoms in formally +I and +III oxidation states. Upon treatment with Lewis acidic CuI X (X=mesityl, Cl, Br, I), electron redistribution occurs resulting in the formation of [{LSi(NDipp)Si(L)}-CuX], in which both silicon atoms are in the +II formal oxidation state. Removal of the copper center from [{LSi(NDipp)Si(L)}-CuX] by using a Lewis basic carbene led to reformation of the precursor [LSi-Si(NDipp)L]. Thus, the process is fully reversible. This showcases the first example of Lewis acid/base-induced reversible electromerism in silicon chemistry.

Luminescent early-late-hetero-tetranuclear group IV - Au(I) bisamidinate complexes.

The versatile metalloligand [{HCCC(NDipp)2}2Au2] (dipp = 2,6-diisopropylphenyl) was converted into early-late heterotetrametallic complexes [{ClCp2MCCC(NDipp)2}2Au2] (M = Ti, Zr). These compounds show photoluminescence with either remarkably different (Ti) or similar (Zr) features as compared to related solely coinage metal containing acetylide amidinate complexes.

Room-Temperature Synthesis of [BMIm][Sn5O2Cl7] with ∞1(Sn2OCl2) Strands in a Saline [BMIm][SnCl3] Matrix.

The novel tin(II) oxychloride [BMIm][Sn5O2Cl7] (BMIm = 1-butyl-3-methylimidazolium) is obtained by the room-temperature reaction (25 °C) of black SnO and SnCl2 in [BMIm]Cl/SnCl2 as an ionic liquid. The title compound can be described as composed of noncharged, infinite ∞1(Sn2OCl2) strands that are embedded in a saline matrix of [BMIm]+ and [SnCl3]-. The ∞1(Sn2OCl2) strands consist of a backbone of edge-sharing OSn4/2 tetrahedra, which represent one-dimensional (1D) strands cut out of the layer-type structure of SnO. In [BMIm][Sn5O2Cl7], the ∞1(Sn2OCl2) strands, which mimic a 1D semiconductor, are terminated by chlorine atoms, whereas they are interconnected by oxygen atoms in the 2D semiconductor SnO. The view of the noncharged ∞1(Sn2OCl2) strands in a saline [BMIm][SnCl3] matrix is validated by dissolution experiments. Thus, electron microscopy and Raman spectroscopy show a deconstruction of [BMIm][Sn5O2Cl7] single crystals after treatment with chloroform with a dissolution of [BMIm][SnCl3], the formation of SnCl2 needles, and tin oxide as a solid remain.

A square planar silylene nickel four-membered ring.

Herein the new nickel silylene [PhC(NtBu)2SiNi(C5Me5)]2, which features a square planar central ring motif consisting of two silicon and two nickel atoms is presented. The title compound was obtained by an insertion of the Ni(0) precursor [Ni(cod)2] (cod = 1,5-cyclooctadiene) in the Si-C bond of the silylene [PhC(NtBu)2Si(C5Me5)]. Analytic characterisation including mass spectrometry as well as IR and Raman spectroscopies was combined with quantum chemical calculations to get an insight on the bonding situation within the four-membered Si-Ni-ring.

Application of the Redox-Transmetalation Procedure to Access Divalent Lanthanide and Alkaline-Earth NHC Complexes*.

Divalent lanthanide and alkaline-earth complexes supported by N-heterocyclic carbene (NHC) ligands have been accessed by redox-transmetalation between air-stable NHC-AgI complexes and the corresponding metals. By using the small ligand 1,3-dimethylimidazol-2-ylidene (IMe), two series of isostructural complexes were obtained: the tetra-NHC complexes [LnI2 (IMe)4 ] (Ln=Eu and Sm) and the bis-NHC complexes [MI2 (IMe)2 (THF)2 ] (M=Yb, Ca and Sr). In the former, distortions in the NHC coordination were found to originate from intermolecular repulsions in the solid state. Application of the redox-transmetalation strategy with the bulkier 1,3-dimesitylimidazol-2-ylidene (IMes) ligand yielded [SrI2 (IMes)(THF)3 ], while using a similar procedure with Ca metal led to [CaI2 (THF)4 ] and uncoordinated IMes. DFT calculations were performed to rationalise the selective formation of the bis-NHC adduct in [SrI2 (IMe)2 (THF)2 ] and the tetra-NHC adduct in [SmI2 (IMe)4 ]. Since the results in the gas phase point towards preferential formation of the tetra-NHC complexes for both metal centres, the differences between both arrangements are a result of solid-state effects such as slightly different packing forces.

Enantiopure Calcium Iminophosphonamide Complexes: Synthesis, Photoluminescence, and Catalysis.

The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L-H (L=[Ph2 P{N(R)CH(CH3 )Ph}2 ]), L'-H (L'=[Ph2 P{NDipp}{N(R)CH(CH3 )Ph}]), (Dipp=2,6-i Pr2 C6 H3 ), and L''-H (L''=[Ph2 P{N(R)CH(CH3 )naph}2 ]), (naph=naphthyl) is presented. The resulting structures [L2 Ca], [L'2 Ca], and [L''2 Ca] represent the first examples of enantiopure homoleptic calcium complexes based on this type of ligands. The calcium complexes show blue-green photoluminescence (PL) in the solid state, which is especially bright at low temperatures. Whereas the emission of [L''2 Ca] is assigned to the fluorescence of naphthyl groups, the PL of [L2 Ca] and [L'2 Ca] is contributed by long-lived phosphorescence and thermally activated delayed fluorescence (TADF), with a strong variation of the PL lifetimes over the temperature range of 5-295 K. Furthermore, an excellent catalytic activity was found for these complexes in hydroboration of ketones at room temperature, although no enantioselectivity was achieved.

Synthesis of Unprecedented 4d/4f-Polypnictogens.

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cpt Mo(CO)2 }2 (µ,η2:2 -E2 )] (E=As, Sb; Cpt =tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*2 Sm] and [(CpMe4nPr )2 Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As2 2- anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.

Regioselective Insertion of Aluminum(I) in the cyclo-P5 Ring of Pentaphosphaferrocene.

A route to directly access mixed Al-Fe polyphosphide complexes was developed. The reactivity of pentaphosphaferrocene, [Cp*Fe(η5 -P5 )] (Cp*=C5 Me5 ), with two different low-valent aluminum compounds was investigated. The steric and electronic environment around the [AlI ] centre are found to be crucial for the formation of the resulting Al-Fe polyphosphides. Reaction with the sterically demanding [Dipp-BDIAlI ] (Dipp-BDI={[2,6-i Pr2 C6 H3 NCMe]2 CH}- ) resulted in the first Al-based neutral triple-decker type polyphosphide complex. For [(Cp*AlI )4 ], an unprecedented regioselective insertion of three [Cp*AlIII ]2+ moieties into two adjacent P-P bonds of the cyclo-P5 ring of [Cp*Fe(η5 -P5 )] was observed. The regioselectivity of the insertion reaction could be rationalized by isolating an analogue of the reaction intermediate stabilized by a strong σ-donor carbene.

A cyclopentadienyl functionalized silylene - a flexible ligand for Si- and C-coordination.

The synthesis of a 1,2,3,4-tetramethylcyclopentadienyl (Cp4) substituted four-membered N-heterocyclic silylene [{PhC(NtBu)2}Si(C5Me4H)] is reported first. Then, selected reactions with transition metal and a calcium precursor are shown. The proton of the Cp4-unit is labile. This results in two different reaction pathways: (1) deprotonation and (2) rearrangement reactions. Deprotonation was achieved by the reaction of [{PhC(NtBu)2}Si(C5Me4H)] with suitable zinc precursors. Rearrangement to [{PhC(NtBu)2}(C5Me4)SiH], featuring a formally tetravalent silicon R2C[double bond, length as m-dash]Si(R')-H unit, was observed when the proton of the Cp4 ring was shifted from the Cp4-ring to the silylene in the presence of a Lewis acid. This allows for the coordination of the Cp4-ring to a calcium compound. Furthermore, upon reaction with transition metal dimers [MCl(cod)]2 (M = Rh, Ir; cod = 1,5-cyclooctadiene) the proton stays at the Cp4-ring and the silylene reacts as a sigma donor, which breaks the dimeric structure of the precursors.

Highly Selective Substitution and Insertion Reactions of Silylenes in a Metal-Coordinated Polyphosphide.

Selective substitution and insertion reactions of silylenes into the cyclo-P5 ring of [Cp*Fe(η5-P5)] are reported. The selective substitution of one P atom by an isoelectronic [LSi] fragment (L = PhC(NtBu)2) leads to [(η4-P4SiL)FeCp*] and [LSi(Cl)═P-SiL(Cl)2]. To elucidate the reaction mechanism, [{LSi(N(SiMe3)2)}{(η4-P5)FeCp*}], in which the silicon atom binds to the cyclo-P5 ring, was synthesized as a model compound for the reaction intermediate. The insertion of [LSi-SiL] into the cyclo-P5 ring of [Cp*Fe(η5-P5)] resulted in [{η4-P5(SiL)2}FeCp*] featuring a cyclo-P5(SiL)2 ring, which corresponds to the largest silicon-polyphosphorus ring known in a complex.

[SnI8 {Fe(CO)4 }4 ]2+ : Highly Coordinated Sn+II I8 Subunit with Fragile Carbonyl Clips.

[SnI8 {Fe(CO)4 }4 ][Al2 Cl7 ]2 contains the [SnI8 {Fe(CO)4 }4 ]2+ cation with an unprecedented highly coordinated, bicapped SnI8 prism. Given the eightfold coordination with the most voluminous stable halide, it is all the more surprising that this SnI8 arrangement is surrounded only by fragile Fe(CO)4 groups in a clip-like fashion. Inspite of a predominantly ionic bonding situation in [SnI8 {Fe(CO)4 }4 ]2+ , the I- ⋅⋅⋅I- distances are considerably shortened (down to 371 pm) and significantly less than the van der Waals distance (420 pm). The title compound is characterized by single-crystal structure analysis, spectroscopic methods (EDXS, FTIR, Raman, UV/Vis, Mössbauer), thermogravimetry, and density functional theory methods.

A Stable Aromatic Tetrasilacyclobutadiene Dication.

The isolation and characterization of the first silicon analogue of the aromatic cyclobutadiene dication is reported. The aromatic 2π-electron tetrasilacyclobutadiene dication in [(LPhSi)4](BPh4)2 (LPh = PhC(NtBu)2) has been obtained in a simple and straightforward synthesis, from [LPhSiCl], [LPhSiSiLPh] and NaBPh4, and fully characterized. The molecular structure reveals a four-membered Si4-dication in an almost perfect square-planar geometry. Theoretical calculations support the interpretation of the title compound as a classical 2π-aromatic species with a singlet ground state.

Reaction of an arsinoamide with chloro tetrylenes: substitution and As-N bond insertion.

Reaction of the arsinoamide [(Mes2AsNPh){Li(OEt2)2}] with the low-valent group 14 compounds, [{PhC(tBuN)2}ECl] (E = Si, Ge) and GeCl2·dioxane, resulted in two different reaction pathways: simple substitution or substitution accompanied by an insertion step. As a result, either insertion products with an As-Si[double bond, length as m-dash]N unit and an As-Ge bond, or substitution products, in which the intact arsinoamide binds to the group 14 elements via the N atom, were obtained.

Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence.

The enantiomerically pure ligand P,P-diphenyl-N,N'-bis((R)-1-phenylethyl)phosphinimidic amide (1; (R)-HPEPIA) was synthesized and subsequently deprotonated with alkali metal precursors to yield dimeric complexes [M2{(R)-PEPIA}2] (M = Li (2), Na (3), K (4), Rb (5)). The cesium compound [M{(R)-PEPIA}] (6) crystallized as a cocrystal composed of dimeric ([Cs2{(R)-PEPIA}2] (6d ) and 1D-polymeric ([Cs{(R)-PEPIA}] n ) (6p ) species in a 1 : 1 ratio. The coordination polymer 6p features a unique sinus-shaped configuration of repeating -Cs-N-P-N-Cs-N-P-N- units. Unusual photoluminescence (PL) properties were found for solid 1-6: in contrast to the fluorescent ligand 1, the alkali metal complexes show phosphorescence at low temperatures (<100 K) and thermally activated delayed fluorescence (TADF) above ∼150 K. The latter provides for PL quantum yields up to 36% (3) at ambient temperature. DFT calculations support that both 1 and 2-6d have similar singlet and triplet excited states with energy separations of a few tens of meV. The strongly enhanced intersystem crossing (ISC) in the metal complexes, resulting in TADF, is attributed to their dimeric structure. This suggests that the fluorophore dimerization may serve as a tool to effect ISC for the design of TADF emitters.

Rhenium is different: CO tetramerization induced by a divalent lanthanide complex in rhenium carbonyls.

The reduction of M2(CO)10 (M = Mn, Re) with different divalent lanthanide (Ln = Sm, Yb) compounds was investigated. Depending on the steric demand of the ligand, either unusual CO tetramerization or formation of a new Re carbonyl anion occurred in the case of Re. Theoretical calculations were performed for a better understanding of the nature of bonding in the newly formed species.

Intensely Photoluminescent Diamidophosphines of the Alkaline-Earth Metals, Aluminum, and Zinc.

The positively charged and weakly polarizable s-block metals commonly do not usually have phosphine ligands in molecular complexes. Herein, we report mono- and dinuclear small diamidophosphine complexes of the alkaline-earth metals Mg, Ca, and Sr, which were prepared from simple precursors and a phosphine-functionalized diamine ligand N,N-bis(2-(diphenyl-phosphino)phenyl)ethane-1,2-diamine (PNHNHP). The alkaline-earth metal based complexes [(PNNP)Mg]2 and [(PNNP)M(thf)3 ] (M=Ca, Sr), exhibit unusual coordination spheres and show bright fluorescence, both in the solid state and in solution. For comparison, the even stronger luminescent Al and Zn complexes [(PNNP)Zn]2 and [(PNNP)AlCl] were prepared. Emission lifetimes in the nanosecond range and high photoluminescence quantum yields up to 93 % are observed at room temperature.