Dataset Information

Molecular Zinc Hydride Cations [ZnH]⁺ : Synthesis, Structure, and CO₂ Hydrosilylation Catalysis.

ABSTRACT: Protonolysis of [ZnH₂ ]_n with the conjugated Brønsted acid of the bidentate diamine TMEDA (N,N,N',N'-tetramethylethane-1,2-diamine) and TEEDA (N,N,N',N'-tetraethylethane-1,2-diamine) gave the zinc hydride cation [(L₂ )ZnH]⁺ , isolable either as the mononuclear THF adduct [(L₂ )ZnH(thf)]⁺ [BAr^F ₄ ]^- (L₂ =TMEDA; BAr^F ₄ ^- =[B(3,5-(CF₃ )₂ -C₆ H₃ )₄ ]^- ) or as the dimer [{(L₂ )Zn)}₂ (?-H)₂ ]²⁺ [BAr^F ₄ ]^- ₂ (L₂ =TEEDA). In contrast to [ZnH₂ ]_n , the cationic zinc hydrides are thermally stable and soluble in THF. [(L₂ )ZnH]⁺ was also shown to form di- and trinuclear adducts of the elusive neutral [(L₂ )ZnH₂ ]. All hydride-containing cations readily inserted CO₂ to give the corresponding formate complexes. [(TMEDA)ZnH]⁺ [BAr^F ₄ ]^- catalyzed the hydrosilylation of CO₂ with tertiary hydrosilanes to give stepwise formoxy silane, methyl formate, and methoxy silane. The unexpected formation of methyl formate was shown to result from the zinc-catalyzed transesterification of methoxy silane with formoxy silane, which was eventually converted into methoxy silane as well.

SUBMITTER: Ritter F

PROVIDER: S-EPMC7756573 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Publications

Molecular Zinc Hydride Cations [ZnH]+ : Synthesis, Structure, and CO2 Hydrosilylation Catalysis.

Ritter Florian F Spaniol Thomas P TP Douair Iskander I Maron Laurent L Okuda Jun J

Angewandte Chemie (International ed. in English) 20201015 51

Protonolysis of [ZnH2 ]n with the conjugated Brønsted acid of the bidentate diamine TMEDA (N,N,N',N'-tetramethylethane-1,2-diamine) and TEEDA (N,N,N',N'-tetraethylethane-1,2-diamine) gave the zinc hydride cation [(L2 )ZnH]+ , isolable either as the mononuclear THF adduct [(L2 )ZnH(thf)]+ [BArF 4 ]- (L2 =TMEDA; BArF 4 - =[B(3,5-(CF3 )2</sub ...[more]

PMID: 32931656

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Project description:The dimeric ?-diketiminato magnesium hydride, [(BDI)MgH]2, reacts at 80 °C with the terminal alkenes, 1-hexene, 1-octene, 3-phenyl-1-propene and 3,3-dimethyl-butene to provide the respective n-hexyl, n-octyl, 3-phenylpropyl and 3,3-dimethyl-butyl magnesium organometallics. The facility for and the regiodiscrimination of these reactions are profoundly affected by the steric demands of the alkene reagent. Reactions with the phenyl-substituted alkenes, styrene and 1,1-diphenylethene, require a more elevated temperature of 100 °C with styrene providing a mixture of the 2-phenylethyl and 1-phenylethyl products over 7 days. Although the reaction with 1,1-diphenylethene yields the magnesium 1,1-diphenylethyl derivative as the sole reaction product, only 64% conversion was achieved over a 21 day timeframe. Reactions with the ?,?-dienes, 1,5-hexadiene and 1,7-octadiene, provided divergent results. The initial 5-alkenyl magnesium reaction product of the shorter chain diene undergoes 5-exo-trig cyclisation via intramolecular carbomagnesiation to provide a cyclopentylmethyl derivative, which was shown by X-ray diffraction analysis to exist as a three-coordinate monomer. In contrast, 1,7-octadiene provided a mixture of two compounds, a magnesium oct-7-en-1-yl derivative and a dimagnesium-octane-1,4-diide, as a result of single or two-fold activation of the terminal C[double bond, length as m-dash]C double bonds. The magnesium hydride was unreactive towards internal alkenes apart from the strained bicycle, norbornene, allowing the characterisation of the resultant three-coordinate magnesium norbornyl derivative by X-ray diffraction analysis. Computational analysis of the reaction between [(BDI)MgH]2 and 1-hexene using density functional theory (DFT) indicated that the initial Mg-H/C[double bond, length as m-dash]C insertion process is rate determining and takes place at the intact magnesium hydride dimer. This exothermic reaction (?H = -14.1 kcal mol-1) traverses a barrier of 18.9 kcal mol-1 and results in the rupture of the dinuclear structure into magnesium alkyl and hydride species. Although the latter three-coordinate hydride derivative may be prone to redimerisation, it can also provide a further pathway to magnesium alkyl species through its direct reaction with a further equivalent of 1-hexene, which occurs via a lower barrier of 15.1 kcal mol-1. This Mg-H/C[double bond, length as m-dash]C insertion reactivity provides the basis for the catalytic hydrosilylation of terminal alkenes with PhSiH3, which proceeds with a preference for the formation of the anti-Markovnikov organosilane product. Further DFT calculations reveal that the catalytic reaction is predicated on a sequence of Mg-H/C[double bond, length as m-dash]C insertion and classical Si-H/Mg-C ?-bond metathesis reactions, the latter of which, with a barrier height of 24.9 kcal mol-1, is found to be rate determining.

Dataset Information

Molecular Zinc Hydride Cations [ZnH]⁺ : Synthesis, Structure, and CO₂ Hydrosilylation Catalysis.

Publications

Molecular Zinc Hydride Cations [ZnH]<sup>+</sup> : Synthesis, Structure, and CO<sub>2</sub> Hydrosilylation Catalysis.

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