One-Pot Synthesis of Heavier Group 14 N-Heterocyclic Carbene Using Organosilicon Reductant

Ravindra Raut,Vikas Kumar,Moumita Majumdar,Padmini Sahoo,Sheikh Amin

doi:10.3390/inorganics6030069

Ravindra Raut, Vikas Kumar + Show 3 more

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https://doi.org/10.3390/inorganics6030069

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Abstract

Syntheses of heavier Group 14 analogues of “Arduengo-type” N-heterocyclic carbene majorly involved the use of conventional alkali metal-based reducing agents under harsh reaction conditions. The accompanied reductant-derived metal salts and chances of over-reduced impurities often led to isolation difficulties in this multi-step process. In order to overcome these shortcomings, we have used 1,4-bis-(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene as a milder reducing agent for the preparation of N-heterocyclic germylenes (NHGe) and stannylenes (NHSn). The reaction occurs in a single step with moderate yields from the mixture of N-substituted 1,4-diaza-1,3-butadiene, E(II) (E(II) = GeCl2·dioxane, SnCl2) and the organosilicon reductant. The volatile byproducts trimethylsilyl chloride and pyrazine could be removed readily under vacuum. No significant over reduction was observed in this process. However, N-heterocyclic silylene (NHSi) could not be synthesized using an even stronger organosilicon reductant under thermal and photochemical conditions.

Highlights

Carbene chemistry kick-started with the ground-breaking discovery of the bottle-ableN-heterocyclic carbene (NHC) by Arduengo in 1991 [1]
The heavier analogues possess distinct electronic features compared to the NHCs, and exhibit different reactivities [3,4]
We have developed a simple one-pot synthetic route milder conditions toInsynthesize

Summary

Introduction

Carbene chemistry kick-started with the ground-breaking discovery of the bottle-able. N-heterocyclic carbene (NHC) by Arduengo in 1991 [1]. Since this seminal work, the versatile NHCs have replaced the classical phosphine-based ligands for transition-metal catalysts [2]. The isolation of heavier Group 14 analogues of ‘Arduengo type’ carbene NHE (E = Si, Ge, and Sn) have been the subject of intense study, both for fundamental interests and potential applications in transition metal catalysis, similar to the NHCs. To date, a handful of NHEs have been synthesized and structurally characterized [3,4]. While N-heterocyclic silylenes (NHSi) have been engaged as ancillary ligands in numerous homogeneous catalysis [5,6,7], N-heterocyclic germylenes (NHGe) serve as a precursor for polymerization chemistry [8,9,10] and for chemical vapour depositions [11]

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