Tetrylene-Functionalized Si7-Siliconoids.

The core expansion of metallic or metalloid clusters by the addition of further homo- or heteronuclear vertices is pivotal to the nucleation and growth of particles. The exohedral grafting of a low-valent functionality followed by endohedral incorporation have been identified as key steps. Following previous work on the Si6 series, we now report the synthesis and full characterization of the amidinatotetrylene-functionalized seven-vertex siliconoids Si7R5[E(NtBu)2CPh] (E = Si, Ge, Sn). In the case of the silylene derivative, the solid-state structure was determined by single crystal X-ray diffraction.

Stable Silapyramidanes.

Starting from tetrakis(trimethylsilyl)cyclobutadiene and an amidinate-supported silylene of the Roesky-type, a sequence of addition and reduction cleanly gives the elusive silapyramidane via an isolable cyclobutene intermediate with an exocyclic Si═C bond. The silapyramidane features an unusually shielded 29Si NMR resonance at -448.3 ppm for the apex silicon atom. Treatment with Fe2(CO)9 results in the formation of the corresponding silapyramidane-iron complex. Silapyramidane also reacts with the cyclobutadiene starting material to cleanly afford a fluorescent spirobis(silole).

Low-Valent Mx Al3 Cluster Salts with Tetrahedral [SiAl3 ]+ and Trigonal-Bipyramidal [M2 Al3 ]2+ Cores (M=Si/Ge).

Schnöckel's [(AlCp*)4 ] and Jutzi's [SiCp*][B(C6 F5 )4 ] (Cp*=C5 Me5 ) are landmarks in modern main-group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]+ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)3 ][WCA] ([WCA]- =[Al(ORF )4 ]- and [F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ). The tetrahedral [SiAl3 ]+ core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also-due to its facile accessibility and high stability-provides a convenient preparative entry towards low-valent Si-Al clusters in general. For example, an elusive binuclear [Si2 (AlCp*)5 ]2+ with extremely short Al-Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge2 (AlCp*)5 ]2+ dication were also obtained and represent the first mixed Al-Ge cluster.

A Striking Mode of Activation of Carbon Disulfide with a Cooperative Bis(silylene).

The reactivity of the 1,4-substituted bis(silylenyl)terphenylene 1, 1,4-[ortho-(LSi)C6 H4 ]2 C6 H4 , (L=RC(NtBu)2 , R=Ph, Mes) towards CS2 is reported. It results in a dearomatization of the phenylene ring, affording the 1,3-substituted cyclohexadiene derivative 2. According to DFT calculations, a transient silene containing a Si=C bond capable of π(C=C) addition at the aromatic phenylene ring is a key intermediate. In contrast, addition of CS2 to the biphenyl-substituted mono-silylene ortho-(LSi)C6 H4 -C6 H5 3 leaves the aromatic π-system intact and forms, in a [1+2] cycloaddition reaction, the corresponding thiasilirane 4 with a three-membered SiSC ring. Further experimental studies led to the isolation of the novel mesoionic five-membered Si2 S2 C heterocycle 6, which reacts with CS2 under C-C bond formation. All isolated new compounds were fully characterized and their molecular structures determined by single-crystal X-ray diffraction analyses.

Indirect and Direct Grafting of Transition Metals to Siliconoids.

Unsaturated charge-neutral silicon clusters (siliconoids) are important as gas-phase intermediates between molecules and the elemental bulk. With stable zirconocene- and hafnocene-substituted derivatives, we here report the first examples containing directly bonded transition-metal fragments that are readily accessible from the ligato-lithiated Si6 siliconoid (1Li) and Cp2 MCl2 (M=Zr, Hf). Charge-neutral siliconoid ligands with pending tetrylene functionality were prepared by the reaction of amidinato chloro tetrylenes [PhC(NtBu)2 ]ECl (E=Si, Ge, Sn) with 1Li, thus confirming the principal compatibility of such low-valent functionalities with the unsaturated Si6 cluster scaffold. The pronounced donor properties of the tetrylene/siliconoid hybrids allow for their coordination to the Fe(CO)4 fragment.

Exohedral functionalization vs. core expansion of siliconoids with Group 9 metals: catalytic activity in alkene isomerization.

Taking advantage of pendant tetrylene side-arms, stable unsaturated Si6 silicon clusters (siliconoids) with the benzpolarene motif (the energetic counterpart of benzene in silicon chemistry) are successfully employed as ligands towards Group 9 metals. The pronounced σ-donating properties of the tetrylene moieties allow for sequential oxidative addition and reductive elimination events without complete dissociation of the ligand at any stage. In this manner, either covalently linked or core-expanded metallasiliconoids are obtained. [Rh(CO)2Cl]2 inserts into an endohedral Si-Si bond of the silylene-functionalized hexasilabenzpolarene leading to an unprecedented coordination sphere of the Rh centre with five silicon atoms in the initial product, which is subsequentially converted to a simpler derivative under reconstruction of the Si6 benzpolarene motif. In the case of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) a similar Si-Si insertion leads to the contraction of the Si6 cluster core with concomitant transfer of a chlorine atom to a silicon vertex generating an exohedral chlorosilyl group. Metallasiliconoids are employed in the isomerization of terminal alkenes to 2-alkenes as a catalytic benchmark reaction, which proceeds with competitive selectivities and reaction rates in the case of iridium complexes.