Higher-Nuclearity Group 14 Metalloid Clusters: [Sn9{Sn(NRR′)}6]

Disproportionation of Sn(II){CH(SiMe3)2}2 to ˙Sn(III){CH(SiMe3)2}3 and ˙Sn(I){CH(SiMe3)2}: characterization of the Sn(I) product

Half a century after the photolytic disproportionation of Lappert's dialkyl stannylene SnR₂, R = CH(SiMe₃)₂ (1) gave the persistent trivalent radical [˙SnR₃], the characterization of the corresponding Sn(I) product, ˙SnR is now described. It was isolated as the hexastannaprismane Sn₆R₆ (2), from the reduction of 1 by the Mg(I)-reagent, Mg(BDI^Dip)₂ (BDI = (DipNCMe)₂CH, Dip = 2,6-diisopropylphenyl).

Higher stability of metalloid tin clusters obtained via the cation-anion interaction

The reaction of a metastable SnCl solution with KR (R = Si(SiMe₃)₂(SitBuMe₂) = Hyp^tBuMe₂ or Si(SiMe₃)₂(SiEt₃) = Hyp^Et₃) gives the metalloid tin cluster [Sn₁₀R₄]^2- in partly good yields. The tin clusters are in the solid state as well in solution coordinated by a potassium cation, leading first of all to a more static compound and novel coordination polymers in the solid state. Additionally, the coordination of the potassium cation strongly increases the stability of the cluster in solution. This higher stability is thereby an important prerequisite for future investigation of this open shell metalloid tin cluster.

Synthesis and Reactivity Studies of Amido-Substituted Germanium(I)/Tin(I) Dimers and Clusters

Three amide ligands of varying steric bulk and electronic properties were utilized to prepare a series of amido-germanium(II)/tin(II) halide compounds, (LEX)_n , (L= -N{B(DipNCH)₂ }(SiMe₃ ), ^TBo L; -N{B(DipNCH)₂ }(SiPh₃ ), ^PhBo L; -N(Dip)(tBu), ^DBu L; Dip=C₆ H₃ iPr₂ -2,6; E=Ge or Sn; X=Cl or Br; n=1 or 2). Reductions of these with a magnesium(I) dimer, {(^Mes Nacnac)Mg}₂ (^Mes Nacnac=[(MesNCMe)₂ CH]^- , Mes=mesityl), afforded singly bonded amido-digermynes (^TBo LGe-Ge^TBo L and ^PhBo LGe-Ge^PhBo L), and an amido-distannyne (^PhBo LSn-Sn^PhBo L), in addition to several low-valent, amido stabilized tetrel-tetrel bonded cluster compounds, (^DBu LGe)₄ , (^DBu LSn)₆ and Sn₅ (^TBo L)₄ . The nature of the products resulting from these reactions was largely dependent on the steric bulk of the amide ligand employed. Cluster (^DBu LGe)₄ possessed an unusual folded butterfly structure, the bonding and electronic of which were examined using DFT calculations. Reactions of the amido-germanium(I) compounds with H₂ were explored, and gave rise to the amido-digermene, ^TBo L(H)Ge=Ge(H)^TBo L and the cyclotetragermane, {^DBu L(H)Ge}₄ . Reactions of (^DBu LGe)₄ with a series of unsaturated small molecule substrates yielded ^DBu LGeOGe^DBu L, ^DBu LGe(μ-C₂ H₄ )₂ Ge^DBu L and ^DBu LGe(μ-1,4-C₆ H₈ )(μ-1,2-C₆ H₈ )Ge^DBu L. The latter results imply that (^DBu LGe)₄ can act as a masked source of the digermyne ^DBu LGeGe^DBu L in these reactions. All further reactivity studies indicated that the germanium(I) compounds exhibit a "transition-metal-like" behavior, which is closely related to that previously described for bulky digermynes and related compounds.

Reductive Elimination of Hydrogen from Bis(trimethylsilyl)methyltin Trihydride and Mesityltin Trihydride

Alkyltin trihydride [(Me₃ Si)₂ CHSnH₃ ] was synthesized and the reductive elimination of hydrogen from this species was investigated. A methyl-substituted N-heterocyclic carbene reacts with the organotrihydride in dependence on stoichiometry and solvent to give a series of products of the reductive elimination and dehydrogenative tin-tin bond formation. Besides characterization of the carbene adduct of the alkyltin(II) hydride, a Sn₄ chain was also isolated, encompassing two stannyl-stannylene sites, which are stabilized each as NHC-adducts. Complete dehydrogenation resulted to give either a carbene-stabilized distannyne or a metalloid Sn₉ -cluster salt. Reductive elimination of hydrogen was also achieved with an excess of diethylmethylamine to give the alkyltin(II) hydride as a Lewis base free tetramer [(RSnH)₄ ]. The method of cluster formation at low temperatures by hydrogen elimination was also transferred to the mesityl-substituted tin trihydride MesSnH₃ . In this case [(MesSn)₁₀ ], showing a [5]prismane structure, was isolated in good yield and characterized. NMR spectroscopic features of the propellane-type cluster [Trip₆ Sn₆ ] are reported.

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: M_n R_m (n>m).

Synthesis and solid state structure of a metalloid tin cluster [Sn10(trip8)]

The Mg(i) compound (LMg)₂ reacts with (trip₂Sn)₂ with formation of the metalloid Sn₁₀trip₈ cluster 1, which contains Sn atoms in the formal oxidations states 0, +I and +II, while the stronger Mg(i) reductant (L′Mg)₂ yielded elemental tin. The reaction demonstrates the promising potential of Mg(i) compounds to serve as soluble reductants for cluster synthesis.

{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.

{Sn9[Si(SiMe3)3]3}− and {Sn8Si[Si(SiMe3)3]3}−: variations of the E9 cage of metalloid group 14 clusters

The disproportionation reaction of the subvalent metastable halide SnBr proved to be a powerful synthetic method for the synthesis of metalloid cluster compounds of tin. Hence, the neutral metalloid cluster compound Sn(10)[Si(SiMe(3))(3)](6) (3) was synthesized from the reaction of SnBr with LiSi(SiMe(3))(3). In the course of the reaction anionic clusters might also be present, and we now present the first anionic cluster compound {Sn(8)E[Si(SiMe(3))(3)](3)}(-) (E = Si, Sn), where one position in the cluster core is occupied by a silicon or a tin atom, giving further insight into structural variations of E(9) cages in metalloid group 14 cluster compounds.

Thiostannate tin-tin bond formation in solution: in situ generation of the mixed-valent, functionalized complex [{(RSn(IV))2(mu-S)2}3Sn(III)2S6]

In broad daylight: The double-decker thiostannate [(RSn(IV))(4)S(6)] (1, R = CMe(2)CH(2)COMe) condenses to form [{(RSn(IV))(2)(mu-S)(2)}(3)Sn(III)(2)S(6)] (2; see picture). This mixed-valent complex, which formally contains both Sn(III) and Sn(IV) atoms as confirmed by Mössbauer spectroscopy and DFT calculations, forms by a complicated, concerted mechanism. Additionally, 2 provides six carbonyl groups for further derivatization.

[Si(SiMe(3))(3)](6)Ge(18)M (M = Cu, Ag, Au): metalloid cluster compounds as unusual building blocks for a supramolecular chemistry

Very recently it was shown that the metalloid cluster compound {Ge(9)[Si(SiMe(3))(3)](3)}(-) can be used for subsequent reactions as the shielding of the cluster core is rather incomplete. Here further reactions of with M(+) sources of group 11 metals are described, leading to metalloid cluster compounds of the formula {MGe(18)[Si(SiMe(3))(3)](6)}(-) (M = Ag, Cu). These reactions can be seen as first steps into a supramolecular chemistry with metalloid cluster compounds. Beside this feature, the structural properties as well as the bonding situations in these cluster compounds are discussed.

Discussion on the Formation and Bonding in Three [Ga8R10] Compounds: The Diversity in Classical GaGa Bonds

Herein we describe three Ga(8) compounds that feature gallium atoms in an oxidation state of 1.25 with normal valent 2e-2c bonding. Their structures and the influence of their ligands (phosphorus and nitrogen atoms directly bonded to the Ga(8) moieties) are discussed on the basis of DFT calculations, providing an insight into a probable mechanism for insertion reactions between GaX and GaX(3) species that lead to a reaction cascade via halides like Ga(2)X(4) and Ga(5)X(7) to Ga(8)X(10) and Ga(8)X(12) (2-), respectively. Finally, the Ga(8) cores of the three title compounds were compared with the topology of carbon atoms in C(8) alkanes.

{Ge10Si[Si(SiMe3)3]4(SiMe3)2Me}−: A Ge10Si framework reveals a structural transition onto elemental germanium

The reaction of the metastable high temperature molecule GeCl synthesized via a co-condensation technique with LiSi(SiMe(3))3 leads to a metalloid Ge(10)Si cluster compound, in which the arrangement of the germanium atoms can be seen as a cutout from the structure of elemental germanium.

Metalloid group 14 cluster compounds: an introduction and perspectives to this novel group of cluster compounds

Metalloid cluster compounds of group 14 of the general formulae E(n)R(m) with n > m (E = Si, Ge, Sn and Pb, tetrel elements; R = ligand), where "naked" tetrel atoms are present as well as ligand-bound tetrel atoms, represent a novel class of cluster compounds in group 14 chemistry. Since the "naked" tetrel atoms in these clusters exhibit an oxidation state of 0, the average oxidation state of the tetrel atoms in such metalloid group 14 cluster compounds is between 0 and 1. Thus, these cluster compounds may be seen as intermediates on the way to the elemental state. Therefore, interesting properties maybe expected for these compounds which might complement results from nanotechnology. During the last years many different syntheses of such novel cluster compounds have been introduced, leading to several metalloid group 14 cluster compounds which exhibit new and unusual structure and bonding properties. In this tutorial review an account is given of the first steps in this novel field of group 14 chemistry. Special attention is focused on structural features and bonding properties.