N‐Heterocyclic Silylene Main Group Element Chemistry: Adduct Formation, Insertion into E−X Bonds and Cyclization of Organoazides

Abstract

Investigations concerning the reactivity of the N‐heterocyclic silylene Dipp2NHSi (1, 1,3‐bis(2,6‐diisopropylphenyl)‐1,3‐diaza‐2‐silacyclopent‐4‐en‐2‐ylidene) towards selected alanes and boranes, elemental halides X2 (X=Br, I), selected halide containing substrates such as tin chlorides and halocarbons, as well as organoazides are presented. The NHSi adducts Dipp2NHSi⋅AlI3 (2), Dipp2NHSi⋅Al(C6F5)3 (3), and Dipp2NHSi⋅B(C6F5)3 (4) were formed by the reaction of Dipp2NHSi with the corresponding Lewis acids AlI3, Al(C6F5)3 and B(C6F5)3. Adducts 3 and 4 were tested with respect to their ability to activate small organic molecules, but no frustrated Lewis pair reactivity was observed. Reactions of Dipp2NHSi with Br2, I2, Ph2SnCl2 and Me3SnCl led to formation of Dipp2NHSiBr2 (5), Dipp2NHSiI2 (6), Dipp2NHSiCl2 (7) and {(Me3Sn)N(Dipp)CH}2 (8), respectively. The reaction with the halocarbons methyl iodide, benzyl chloride, and benzyl bromide afforded the insertion products Dipp2NHSi(I)(CH3) (9), Dipp2NHSi(Cl)(CH2Ph) (10) and Dipp2NHSi(Br)(CH2Ph) (11). Reaction of Dipp2NHSi with the organoazides Ad‐N3 (Ad=adamantyl) and TMS‐N3 (TMS=trimethylsilyl) led to the formation of 1‐Dipp2NHSi‐2,5‐bis(adamantyl)‐tetrazoline (12) and bis(trimethylsilyl)amido azido silane (13), respectively. For 2,6‐(diphenyl)phenyl‐N3 C−H activation occurs and a cyclosilamine 14 was isolated.

N-Heterocyclic silylenes as ambiphilic activators and ligands

“…4 However, this particular silylene, Dipp 2 NHSi, proved to be rather unreactive for small molecule activation. 28 Adduct formation was observed with the Lewis acids AlI 3 , Al(C 6 F 5 ) 3 and B(C 6 F 5 ) 3 which led to isolation of Dipp 2 NHSi•AlI 3 , Dipp 2 NHSi•Al(C 6 F 5 ) 3 and Dipp 2 NHSi•B(C 6 F 5 ) 3 (see Scheme 2). The compound Dipp 2 NHSi•B(C 6 F 5 ) 3 reveals a high thermal stability, which is in contrast to the lability of the literatureknown adduct tBu 2 NHSi•B(C 6 F 5 ) 3 .…”

“…Dipp 2 NHSi is a good halide acceptor and reductant in main group chemistry and may be used for controlled redox reactions. The reaction of 1 with one equivalent of Ph 2 SnCl 2 leads exclusively to the dichlorosilane Dipp 2 NHSiCl 2 and cyclic polystannanes (Ph 2 Sn) n (Scheme 2), owing to the strong bond enthalpy of the Si-Cl bond, 28 which also demonstrates the strong halophilicity of the NHSi when reacted with other element halides. To summarize, Dipp 2 NHSi shows some interesting reactivities to selected substrates, but it currently appears that several other silylenes of different ring size or stable acyclic silylenes outperform the five-membered ring NHSis such as 1 as activators of enthalpically strong bonds.…”

A Monomeric Aluminum Imide (Iminoalane) with Al–N Triple-Bonding: Bonding Analysis and Dispersion Energy Stabilization

“…The reaction of :AlAr i Pr8 with 2 equiv of Me 3 SiN 3 gives the amido- azido-alane 3 (Figure , right) as colorless crystals in which silyl migration from the second equivalent of azide to the nitrogen atom of the transient imide has occurred. Such migrations have been observed in a number of reactions of Me 3 SiN 3 with low valent main group compounds. − …”

A germanimidoyl chloride: synthesis, characterization and reactivity

“…27 Similar five-membered ring compounds were also obtained in the reactions of tetrelenes with organic azides. [28][29][30] In order to test if the chloride in 3 could be replaced by a weakly coordinating anion to give a germanium cation, which might act as a Lewis acid for small molecule activation and catalysis, 31,32 we carried out the reaction of 3 with 1 molar equivalent of NaBAr The molecular structure of 2 was determined by singlecrystal X-ray diffraction (SC-XRD) analysis (Fig. 2).…”

“…27 Similar five-membered ring compounds were also obtained in the reactions of tetrelenes with organic azides. 28–30…”