Synthesis and Reactivity of Martin's Spirosilane-Derived Chloromethylsilicate.

Thomas Deis,Jérémy Forte,Gilles Lemière,Louis Fensterbank

doi:10.3390/molecules27061767

Abstract

Pentacoordinate silicon derivatives with a chloromethyl ligand are versatile compounds that are usually obtained from the corresponding tetravalent trialkoxy- or trihalogeno(chloromethyl)silane. We describe herein the synthesis of a chloromethylsilicate bearing two Martin’s ligands readily obtained by addition of in situ generated chloromethyllithium to a spirosilane. The reactivity of this new species was evaluated and it has been established that the chloride is displaced by strong nucleophiles such as alkyllithiums and (hetero)aryllithiums. In Lewis acidic conditions, the pentacoordinate silicon species rearranges through a formal insertion of a methylene into one Si–C bond, to form a new tetravalent spirosilane with a six-membered ring. The same kind of rearrangement can be triggered also by addition of a Lewis base. The mechanism of the rearrangement in both conditions has been studied by means of DFT calculations.

Highlights

To carbon, silicon can reach coordination higher than four [1]
To access chloromethylsilicate 2, we first tried to apply the conditions abovementioned in Scheme 1 for silatrane in the presence of a tris(amino)phosphine, to spirosilane 1
It is well established that alkyllithium reagents can efficiently add to spirosilane 1 at low temperature to afford the corresponding pentacoordinate silicon adducts [18,19]

Summary

Introduction

The stability of the corresponding species depends on the ligands surrounding the silicon atom and to date, an impressive number of various stable pentacoordinate and hexacoordinate silicon(IV) compounds have been reported [2,3] Among these structures, some of them present a chloromethyl ligand that can bring peculiar reactivity and properties to the hypercoordinate system. The direct introduction of the chloromethyl group to the silicon part has been described only once by the group of Lazareva for the formation of chloromethylsilatrane [11]. In this procedure, the chloromethyl group is introduced by mixing bromochloromethylene and a tris(amino)phosphine in the presence of a chlorosilatrane at high temperature (Figure 1)

Methods

Results

Conclusion