Synthese und Struktur gemischt‐substituierter Dialane Al2X2{Si(SiMe3)3}2 · 2 THF (X = Cl,Br)

Synthesis and Structure of two Mixed Substituted Dialanes Al₂X₂{Si(SiMe₃)₃}₂ · 2 THF (X = Cl, Br) The syntheses of tris(trimethylsilyl)silyl (hypersilyl) and halide substituted dialanes Al₂X₂{Si(SiMe₃)₃}₂ · 2 THF (X = Cl, Br) are presented. The results of the X‐ray diffraction experiments are presented and discussed in comparison to the Al^III compounds AlBr₂Si(SiMe₃)₃ · THF and AlBr₃ · OPh₂.     

[Ga6R8]2– (R = SiPh2Me): Eine metalloide Clusterverbindung mit einem unerwarteten Ga6‐Gerüst

[Ga₆R₈]^2– (R = SiPh₂Me): A Metalloid Cluster Compound with an Unexpected Ga₆‐Frame The reaction of a metastable solution of GaBr with a solution of LiSiPh₂Me in a toluene/THF mixture results in orange coloured crystals of [Ga₆(SiPh₂Me)₈]^2– · 2 [Li(THF)₄]⁺ ( 1 ). The unexpected structure of the planar Ga₆ frame (C_2h) could also be realized with the help of DFT calculation. DFT calculations furthermore show that 1 is energetically favoured against an octahedral Ga₆R₆^2– species and R₂. In contrast calculations for the similar Al and B species show that in these cases the octahedral entities are favoured. These results demonstrate that even for similar compounds of B, Al, and Ga Wade rules are too general and that they cannot predict the correct structure. Moreover the atomic arrangement within 1 shows that a structure is preferred which is also present in allotropic β‐Ga and that therefore clusters of this type should be called metalloid or more general elementoid.     

Si@Al14(N(Dipp)SiMe3)6: Ein Si‐zentrierter metalloider Aluminiumcluster und ergänzende Untersuchungen zur Strukturproblematik des Si@Al14Cp*6‐Clusters

The preparation and X‐ray structure of Si@Al₁₄R₆ (R = Cp*, N(Dipp)SiMe₃; Dipp = 2,6‐iPr₂–C₆H₃) are described via the disproportionation and substitution reaction of a metastable AlCl solution. One silicon atom occupies the center of an Al₈ cube. This central unit is stabilized through capping of six AlR moieties above the faces of the cube. These findings open the door for a reinvestigation of Si@Al₁₄Cp*₆ through MALDI, DFT and X‐ray investigations: Caused by the preparation procedure a small part of the Si@Al₁₄Cp*₆ clusters are partially oxidized by chlorine and one of the eight aluminum atoms of the cube is substituted by a Si atom: Thus, within the crystal about ¹/₃ of the SiAl₁₄Cp*₆ clusters are Si₂Al₁₃Cp*₆Cl species causing a more unsymmetrical arrangement of all cluster species than those observed in crystalline SiAl₁₄(N(Dipp)SiMe₃)₆. The serious problems during the solution of the crystal structure of Si@Al₁₄Cp*₆ caused by only slightly modified cluster species may be a strong hint at being careful with the interpretation of any nanoscale species: Even very small modifications (e.g. a single silicon atom i.e. neighbor element of aluminum containing only one more electron and proton substitutes one aluminum atom) cause drastical structural changes and consequently also different e.g. electric properties can be expected.     

Diastereoselective synthesis of highly functionalized tetrahydroxanthenols--unprecedented access to privileged structural motifs

Tetrahydroxanthenones, which can be easily prepared by a domino oxa-Michael aldol condensation, offer various possibilities for diastereoselective functionalization, giving access to the stereocontrolled synthesis of stereochemical triades or tetrades, which represent privileged structural motifs. In most cases, the relative stereochemistry was unequivocally established by crystal structure analysis.