Diradikaloid oder zwitterionischer Charakter: die ungesättigte Verbindung [Si₄{N(SiMe₃)Dipp}₄] mit gefaltetem Si₄‐Strukturmotiv

Abstract

Reduktion des Tribromoamidosilans {N(SiMe 3 )-Dipp}SiBr 3 mit Kaliumgraphit oder Magnesium führte zur Bildung eines Bicyclo[1.1.0]tetrasilatetraamids [Si 4 {N(SiMe 3 )-Dipp} 4 ]( 1). Das Si 4 -Motiv in 1 weist keine tetraedrische Struktur auf und hat zwei dreifach-und zwei vierfach-koordinierte Siliciumatome.D ie dreifach-koordinierten Siliciumatome sind positiv und negativ polarisiert, was durch Messungen der magnetischen Suszeptibilität, EPR-Messungen, DFT-Rechnungen, 29 Si-CP-MAS-NMR-und multinukleare NMR-Spektroskopie in Lçsung herausgefunden wurde.U ntersuchungen der Reaktivitätvon 1 mit Radikalfängern waren nicht erfolgreich und bestätigen somit die partiellen Polarisierungen der Verbindung. 1 reagiert mit Schwefel zu einer neuartigen Si-S-Käfigverbindung [Si 4 S 3 {N(SiMe 3 )Dipp} 4 ]( 2), die von Amidosubstituenten stabilisiert wird.

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

“…Interestingly, the Ge−Ge separations involving trigonal planar Ge(2) [i.e., 2.4354(7) Å and 2.3621(8) Å] are in the normal single‐bond range [mean for Ge 3‐coord −Ge=2.532(5) Å], whereas those encompassing pyramidal Ge(4) are considerably longer [2.5780(8) Å and 2.6740(9) Å], though this might be an artefact of Ge site disorder that was modelled within the Ge 4 core. The structure of 9 is very similar to that of a close silicon analogue, [Si{N(SiMe 3 )(Dip)}] 4 , recently reported by Lips and co‐workers . As was proposed for that compound, 9 can be formulated as being zwitterionic, with a lone pair of electrons at the pyramidal Ge center, and an empty p‐orbital at the trigonal planar germanium.…”

“…That is, this method locates a bond critical point and corresponding bond path running between the bridgehead Ge(1) and Ge(3) atoms (and two ring critical points), which is consistent with the low, yet significant, WBI computed for such a weak interaction. These findings, together with the inspection of the molecular orbitals (MOs) of 9 (see HOMO−1 in Figure below), suggest that a 1,3‐bonding interaction between Ge(1) and Ge(3) can be assumed, a situation which is analogous to that found in its silicon counterpart [Si{N(SiMe 3 )(Dip)}] 4 …”

“…The compound can alternatively be prepared on a larger scale, and in good isolated yield, by treating the alkoxy/amido‐germylene DBu LGeO t Bu with HBpin in a σ‐bond metathesis reaction. It is worth noting that similar attempts to hydrogenate the closely related silicon(I) cluster, [Si{N(SiMe 3 )(Dip)}] 4 , were not successful, as the reaction did not proceed, even when it was carried out at 60 °C under 9 bar of H 2 …”

“…The structure of 9 is very similar to that of ac lose silicon analogue, [Si{N(Si-Me 3 )(Dip)}] 4 ,r ecently reportedb yL ips and co-workers. [26] As was proposed for that compound, 9 can be formulated as being zwitterionic, with al one pair of electrons at the pyramidal Ge center,a nd an empty p-orbital at the trigonal planar germanium.D espite numerous germanium clusters that have appeared in the literature, [27] such as tructuralm otif is unknownf or tetranuclear germanium(I) examples, the only other representatives of which are atetragermatetrahedrane, [28] atet- (6), Ge(1)ÀN(1) 1.865(3), Ge(2)ÀN(4) 1.861 (3), N(1)ÀGe(1)ÀGe(2) 103.09(9), N(4)ÀGe(2)ÀGe(1) 102.43(9). Selectedb ond lengths ()and angles (8)f or 8:Ge(1)ÀGe(2) 2.6022(10), Ge(1)ÀN(3) 1.886 (2),G e(2)ÀN(6) 1.889(3), N(3)ÀGe(1)ÀGe(2) 107.62 (8), N(6)ÀGe(2)ÀGe(1) 108.11 (8).…”

Facile Access to an NHC‐Coordinated Silicon Ring Compound with a Si=N Group and a Two‐Coordinate Silicon Atom

“…We recently reported on a bicyclic silicon ring compound Si 4 {N(SiMe 3 )Dipp} 4 1 with two three‐coordinate Si atoms and zwitterionic character . Herein, we describe the reaction of 1 with 1,3,4,5‐tetramethylimidazol‐2‐ylidene (NHC Me4 ).…”