PdCl2 and NiCl2-catalyzed hydrogen–halogen exchange for the convenient preparation of bromo- and iodosilanes and germanes

doi:10.1016/S0022-328X(02)02147-2

Journal of Organometallic Chemistry

Volume 667, Issues 1–2, 3 February 2003, Pages 90-95

https://doi.org/10.1016/S0022-328X(02)02147-2 Get rights and content

Abstract

Bromination and iodination of hydrosilanes and germanes were studied. Treatment of hydrosilanes with an excess of ethyl, propyl, or allyl bromide in the presence of a catalytic amount of PdCl₂ or NiCl₂ gave bromosilanes in good to high yield by hydrogen–halogen exchange. By using methyl, propyl, or allyl iodide as the iodine source, similar iodination of hydrosilanes was readily performed. Halogenation of hydrogermanes also proceeded by similar treatment.

Treatment of hydrosilanes with an excess of alkyl bromides in the presence of a PdCl₂ or NiCl₂ catalyst gave bromosilanes in good to high yield. Using propyl iodide as the iodine source, similar iodination of hydrosilanes occurred. Halogenation of hydrogermanes also proceeded by similar treatment with PdCl₂ as the catalyst.

Introduction

Halosilanes and germanes are of important reagents as the building units for a variety of organosilicon and germanium compounds. In addition, bromo- and iodosilanes exhibit high Lewis-acidity to permit the interaction with CO and CO bonds, unlike fluoro- and chlorosilanes [1], [1](a), [1](b), [1](c), [1](d). Examples include the reactions of ethers and esters with iodo- and bromosilanes, which afford silyl ethers and esters, respectively, together with halides arising from CO bond cleavage, in good yield [2], [2](a), [2](b), [2](c), [2](d), [2](e), [2](f), [3]. It is also known that aldehydes react with iodosilanes to give silyl α-iodoalkyl ether, by iodosilylation of the carbonyl bond [4], [5].

Conventional methods to prepare bromo- and iodosilanes [1], [1](a), [1](b), [1](c), [1](d) and germanes [6], [6](a), [6](b) involve the cleavage of MM, MH, M–allyl, and M–aryl bonds (M=Si, Ge) with X₂ (X=Br, I), reactions of MH with HX (X=Br, I) and NBS, and halogen exchange of MCl with inorganic halides. Reactions of an MOM bond with HX in the presence (M=Si) or absence (M=Ge) of a Lewis-acid also produce an MX bond. Cleavage of an alkyl-Ge bond with X₂ and Lewis-acid-catalyzed redistribution reactions of R₄Ge and GeBr₄ are also often used for the formation of a GeX bond. However, most of these methods involve the use or by-production of unpleasant HX or X₂. Furthermore, traces of HX and X₂ may contaminate the resulting halosilanes and germanes.

Previously, we have found that the reactions of mono- and dihydrosilanes with alkyl iodides in the presence of a catalytic amount of PdCl₂ afford mono- and diiodosilanes in high yield [7]. We have also reported the CuI-catalyzed bromination of hydrosilanes with CuBr₂ [8], in which an SiH bond is replaced with an SiBr group with the use of two equivalents of CuBr₂. However, there may be a limitation that this method can not be applied to the preparation of tribromosilanes, and treatment of trihydrosilanes with six equivalents of the reagent gives dibromohydrosilanes as the sole isolable products. In this paper, we report a versatile method to prepare bromo- and iodosilanes, including tribromo- and triiodosilanes from PdCl₂- or NiCl₂-catalyzed hydrogen–halogen exchange reactions of hydrosilanes with alkyl bromides and iodides, respectively. Similar halogenation of hydrogermanes is also described.

Section snippets

Bromination of hydrosilanes

The reactions of hydrosilanes with alkyl or allyl bromides in the presence of a catalytic amount of PdCl₂ or NiCl₂ proceeded with the liberation of alkanes to give brominated products in good to high yields (Table 1 and Scheme 1). As can be seen in Table 1, the reactions proceeded more rapidly when allyl bromide, rather than ethyl and propyl bromide, was used as the halide. Typically, PdCl₂-catalyzed bromination of PhMe₂SiH with EtBr or PrBr completed by refluxing the mixture without solvent

Conclusions

In conclusion, we studied the PdCl₂- and NiCl₂-catalyzed hydrogen–halogen exchange of hydrosilanes and germanes with alkyl halides. The reactions proceeded more readily with the PdCl₂ catalyst, but more economic NiCl₂ also can be used as the catalyst for the preparation of halosilanes. This provides a versatile synthetic method leading to a variety of bromo- and iodosilanes and germanes, which would be expected as useful synthetic tools for various organosilicon and germanium compounds.

General

All reactions were carried out under an inert atmosphere. NMR spectra were recorded on JEOL Model JNM-EX 270 and JEOL Model JNM-LA 400 spectrometers. Mass spectra were measured with a Hitachi M80B spectrometer.

Materials

Alkyl halides and allyl halides were distilled from P₂O₅ and stored over molecular sieves in dark until use. The starting hydrosilanes [7], [11] and germanes [7], [10] were prepared by the reactions of the respective chlorides with lithium aluminum hydride.

Halogenation of hydrosilanes and germanes

An illustrative procedure is as

Acknowledgements

We thank Sankyo Kasei Co. Ltd and Sumitomo Electric Industry for financial support, and Shin-Etsu Chemical Co. Ltd for gifts of chlorosilanes.

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PdCl2 and NiCl2-catalyzed hydrogen–halogen exchange for the convenient preparation of bromo- and iodosilanes and germanes

Abstract

Introduction

Section snippets

Bromination of hydrosilanes

Conclusions

General

Materials

Halogenation of hydrosilanes and germanes

Acknowledgements

Organometallics

Silicon in Organic and Organometallic, and Polymer Chemistry

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Organomet. Chem.

Tetrahedron Lett.

Angew. Chem. Int. Ed. Engl.

Chem. Ber.

Tetrahedron Lett.

Organometallics

PdCl₂ and NiCl₂-catalyzed hydrogen–halogen exchange for the convenient preparation of bromo- and iodosilanes and germanes