Reaction of Dichloromethyltris(trimethylsilyl)silane with Organolithium Reagents: Synthesis of an Intramolecularly Donor-Stabilized Silene

Stable Phosphonium Sila-ylide with Reactivity as a Sila-Wittig Reagent

“…This interaction induces an elongation of the Si-C bond (Si1-C5, 1.755 Å) 8,20 and a slight pyramidalization around the silicon center (∑Si R ) 339.3°), which are features that have been reported previously for other silene-Lewis base adducts (silene-THF, 1.747 Å and 348.7°; silene-amine, 1.751 Å and 345.5°). 21,22 In view of the strong oxygen affinity of the Si atom, 23 the lability of P-Si bonds, 15a and the previous report on the reactivity of transient phosphonium sila-ylides II with ketones, 5 the results obtained here are rather surprising and reveal a very different behavior for 2 than for other silylene-Lewis base adducts. 5,10 Although the formation of the cis isomer of 5 was not detected, the stereoselectivity of the sila-Wittig reaction remains obscure because of the presence of the silene-phosphoxide interaction, which could decrease the rotation barrier around the Si-C1 bond, potentially inducing the isomerization reaction.…”

peri-Interactions in Naphthalenes, 14 [1]. Pyramidalization versus Planarization at Nitrogen in 8-Dialkylamino-naphth-1-yl Compounds as a Measure of peri Bond Formation

“…200 -207 pm; these features were ascribed to N→Si interaction; the compounds were called "intramolecularly amine-stabilized silenes" [56] and described by formulae which contain both a Si=C double bond and a Me 2 N→Si dative bond. The meaning of both sym-bols remains somewhat vague: Including the N atom, the Si atom has four nearest neighbours and is therefore tetracoordinate [55,56]. On the other hand, if the dative arrow represents a dative covalent bond, the Si atom would be hypervalent; the Si=C bond would not be the Si analog of a C=C(p-p) π bond, but a Si=C(dp) π bond or some more up-to-date type of hypervalent "double bond".…”

“…Within the realm of the octet rule, formation of a N + -Si bond would require the withdrawal of π-electrons from the Si atom and cause tetrahedralization of the latter. In fact, it deviates considerably from planarity, but is far from perfect tetrahedrality either, whereas the C atom is indeed virtually planar [55,56]. While consistently speaking of "silenes" and almost exclusively using the corresponding formula, Oehme et al concluded that "the structural data... agree with our notion about the ylide-like nature of the two donor-stabilized silenes" [56] for which the pertinent formula (with the Me 2 N + -Si-C − segment containing tetracovalent Si) was used, albeit in a bond/no bond resonance relation with the (dimethylamino)aryl-silaethene formula.…”

The Synthesis oftert-Butyl(dichloromethyl)bis(trimethylsilyl)silane and (Dibromomethyl)ditert-butyl(trimethylsilyl)silane and their Reactions with Organolithium Derivatives

“…But when extremely congested aryllithium compounds, such as 2,4,6-triisopropylphenyllithium or 2-tert-butyl-4,5,6-trimethylphenyllithium, were applied, kinetically stabilized silenes were obtained, which could be characterized by various consecutive reactions [1 b]. Meanwhile, the reaction of (dichloromethyl)oligosilanes with suitably substituted organolithium compounds proved to be a new and versatile route to intramolecularly donor stabilized silenes [2]. Z With the aim of extending the substitution pattern in the starting materials and with the intention to get a better insight into the rearrangements taking place in the course of the reactions mentioned, we synthesized tert-butyl(dichloromethyl)bis(trimethylsilyl)silane (4), ditert-butyl(dichloromethyl)(trimethylsilyl)silane (6) and (dibromomethyl)ditert-butyl(trimethylsilyl)silane (7) and describe in this paper the reaction of these derivatives with organolithium compounds.…”