Synthesis and Structural Characterization of Novel Silenes Stabilized by Intramolecular Coordination of a Dialkylamino Group

Abstract

Two intramolecularly donor-stabilized silenes, 1-(8-dimethylamino-1-naphthyl)-1,2,2-tris(trimethylsilyl)silene (6a) and 1-(2-dimethylaminomethylphenyl)-1,2,2-tris(trimethylsilyl)silene (6b), were synthesized according to a novel one-step process by the reaction of (dichloromethyl)tris(trimethylsilyl)silane (1) with a twofold molar excess of 8-dimethylamino-1-naphthyllithium or 2-(dimethylaminomethyl)phenyllithium, respectively. Compounds 6a and 6b are thermally stable compounds. X-ray structural analyses of both silenes revealed strong donor-acceptor interactions between the dialkylamino groups and the electrophilic silene silicon atoms (Si-N distances: 6a: 1.751(3) A; 6b: 1.749(3) A) that lead to pyramidalization at the silicon centers. In contrast, the configuration at the silene carbon atoms was found to be planar. The Si=C distances (6a: 1.751(3) A; 6b: 1.749(3) A) fit with literature data of comparable compounds. Addition of water or methanol to the Si=C bonds of 6a,b afforded the silanols 7a,b and the methoxysilanes 8a,b, respectively. The compound 1-(8-dimethylaminomethyl-1-naphthyl)-1,2,2-tris(trimethylsilyl)silene (6c), generated following the same procedure by the reaction of 1 with 8-(dimethylaminomethyl)-1-naphthyllithium (molar ratio 1:2) proved to be unstable at room temperature and underwent rapid insertion of the Si=C group into a methylene C-H bond of the dimethylaminomethylnaphthyl ligand to afford the 1-silaacenaphthene 9.

NHC-Stabilized Silicon–Carbon Mixed Cumulene

“…The silene 2 is very likely to be formed by the base-induced elimination of LiCl from the silylenoid followed by silyl migration from the carbon to the central silicon atom. Compound 2 is a new type of NHC-stabilized silene with a chloride ligand on the silicon atom . Attempts to substitute the chloride with the bulky potassium amide Ar­(Me 3 Si)­NK in toluene at low temperature led to the immediate formation of a deep green solution, from which compound 3 was crystallized as deep green crystals at −40 °C from toluene in high yield with the concomitant formation of ArN­(SiMe 3 ) 2 and KCl.…”

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

“…When aryl was DAN or 2-Me 2 NCH 2 C 6 H 4 , the compounds exhibited an extraordinary stability and N··· Si distances of ca. 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].…”

“…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.…”