A 1,5-Oligosilanylene Dianion as Building Block for Oligosiloxane Containing Cages, Ferrocenophanes, and Cyclic Germylenes and Stannylenes

The First Planar, Not Twisted, Distannene - A Structural Alkene Analog. Synthesis, Isolation and X-ray Crystallography Characterization

The tetrasilyl-substituted distannene, (tBu2 HSi)2 Sn=Sn(SiHtBu2 )2 6, was synthesized by mild thermolysis (70 °C in hexane) of tris(di-tert-butyl-hydridosilyl)stannane 4. The X-ray crystallography structure of 6 reveals the following unusual structural properties: a planar geometry around both Sn atoms (Σ∡Sn=359.87°), a non-twisted Sn=Sn double bond, and the shortest Sn=Sn double bond of 2.599 Å among all acyclic distannenes. Thus, compound 6 is the first reported distannene having a structure closely analogous to a classic alkene. Reactions of 6 with CCl4 or with 2,3-dimethylbuta-1,3-diene to produce 1,2-dichlorodistannane 9 and the [2+4] cycloadduct 10, respectively, are characteristic for a Sn=Sn double bond.

Metallacyclosilanes of Calcium, Yttrium, and Iron

Utilizing a choice of α,ω-oligosilanylene diides, it is possible to synthesize a number of heterocyclosilanes with heteroelements of calcium, yttrium, and iron by metathesis reactions with respective metal halides CaI₂, YCl₃, and FeBr₂. ²⁹Si NMR spectroscopic analysis of the calcacyclosilanes suggests that these compounds retain a strong oligosilanylene dianion character, which is more pronounced than in the analogous magnesacyclosilanes. As the electronegativity of calcium lies between potassium and magnesium, silyl calcium reagents should be considered as building blocks with an attractive reactivity profile. Reaction of a 1,4-oligosilanylene diide with YCl₃ gave the five-membered yttracyclosilane as an ate-complex with two chlorides still attached to the yttrium atom. Reaction of the obtained compound with two equivalents of NaCp led to another five-membered yttracyclosilane ate-complex with an yttracene fragment. When using a dianionic oligosilanylene ligand containing a siloxane unit, the siloxane oxygen acted as an additional coordination site for Ca and Y. When the same ligand was used to prepare a cyclic 1-ferra-4-oxatetrasilacyclohexane, an analogous transannular interaction between the iron and oxygen atoms is missing.

Reactions of some α,ω-oligosilanylene diides with CaI₂, YCl₃, and FeBr₂ allow convenient access to metallocyclosilanes with Ca, Y, and Fe as heteroatoms. The calcium and yttrium compounds resemble previously prepared magnesacyclosilanes, retaining a strong silanide character. The only related compounds to the described ferracyclosilanes are acyclic examples.