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

Mirjam J Krahfuss,Udo Radius

doi:10.1002/ejic.202000942

Mirjam J Krahfuss, Udo Radius

Open Access

https://doi.org/10.1002/ejic.202000942

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Abstract

AbstractInvestigations 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.

Highlights

Which have a rather small HOMO-LUMO gap compared to NHCs and N-heterocyclic silylenes (NHSis), e. g. 3.1 eV for cAACMe with a HOMO of σ-symmetry at 4.43 eV and the LUMO of π-symmetry at 1.33 eV
We have demonstrated earlier that these differences in the electronic features of NHSis lead to interesting differences in the transition metal coordination chemistry of
As silylene 1 is sterically demanding,[5] using an alane or borane with steric bulk could favor the formation of frustrated Lewis pairs (FLP)

Summary

Introduction

The LUMO of Dipp2NHSi, which is of π-character, lies at 0.87 eV, much lower than the LUMO of Dipp2Im, and leads to an energy gap of 4.61 eV Another commonly used important class of ligands in both transition metal and main group element chemistry are cyclic (alkyl)(amino)carbenes (cAAC),[6]. (X = Br, I), selected halide containing substrates, selected alanes and boranes as well as selected azides Since their first synthesis in 1994,[1] N-heterocyclic silylenes (NHSis) were established as useful ligands for transition metal complexes.[2] In the following decades, the properties of Arduengo-type NHCs[3] and of NHSis[4] towards main group element compounds were examined.

Results and Discussion

Conclusion

Conflict of Interest