Early Main Group Metal Catalysts for Imine Hydrosilylation |
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| Authors: | Holger Elsen Christian Fischer Christian Knüpfer Dr Ana Escalona Prof Dr Sjoerd Harder |
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| Institution: | Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany |
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| Abstract: | The efficient catalytic reduction of imines with phenylsilane is achieved by using the potassium, calcium and strontium based catalysts (DMAT)K (THF)]∞, (DMAT)2Ca⋅(THF)2 and (DMAT)2Sr⋅(THF)2 (DMAT=2-dimethylamino-α-trimethylsilylbenzyl). Eight different aldimines and the ketimine Ph2C=NPh could be successfully reduced by PhSiH3 at temperatures between 25–60 °C with catalyst loadings down to 2.5 mol %. Also, simple amides like KN(SiMe3)2 or AeN(SiMe3)2]2 (Ae=Ca, Sr, Ba) catalyze this reaction. Activities increase with metal size. For most substrates the activity increases along the row K<Ca<Sr<Ba. Fastest conversion was found for imines with alkyl substituents at N and aryl rings at C, for example, PhC(H)=NtBu, while tBuC(H)=NtBu or PhC(H)=NPh react much slower. Reasonable functional group tolerance is observed. The proposed metal hydride mechanism is supported by stoichiometric reactions using a catalyst model system, isolation of intermediates and DFT calculations. |
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| Keywords: | alkaline earth metals density functional calculations hydrosilylation imines potassium |
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