Volume 64, Issue 28 e202424273
Research Article

Silylchromium-Catalyzed Selective Semihydrogenation of Undirected Allenes by Sila-Metalation and β-Silyl Elimination

Zheng Luo

Zheng Luo

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064 China

Both authors contributed equally to this work.

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Linhong Long

Linhong Long

Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190 China

Both authors contributed equally to this work.

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Shuaiyong Zhao

Shuaiyong Zhao

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064 China

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Xiaoyu Zhang

Xiaoyu Zhang

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064 China

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Yong Peng

Yong Peng

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064 China

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Prof. Dr. Meiming Luo

Prof. Dr. Meiming Luo

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064 China

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Prof. Dr. Hui Chen

Corresponding Author

Prof. Dr. Hui Chen

Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190 China

E-mail: [email protected]; [email protected]

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Prof. Dr. Xiaoming Zeng

Corresponding Author

Prof. Dr. Xiaoming Zeng

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064 China

E-mail: [email protected]; [email protected]

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First published: 07 May 2025

Graphical Abstract

Substituted allenes without a directing group underwent chromium-catalyzed chemo-, stereo-, and regioselective semihydrogenation with an (alkyl)(amino)carbene-phosphine ligand and a chlorosilane additive. The silylchromium complex formed in situ promotes semihydrogenation through a pathway involving sila-metalation of the allene and β-silyl elimination, with the silyl group acting as a noninnocent ligand to give E-alkene products selectively.

Abstract

The semihydrogenation of simple allenes remains an issue because of the difficulty in controlling of selectivity without coordination assistance from directing groups, wherein over-hydrogenated alkanes and E/Z-mixed stereo- and regio-isomers can be potentially formed. We report here an electron-rich cyclic (alkyl)(amino)carbene (CAAC)-phosphine-ligated chromium(III) complex serving as precatalyst in promoting the selective semihydrogenation of undirected allenes by forming active silylchromium species. The semihydrogenation allows the selective addition of H2 to the less substituted and electron-rich alkyl-substituted C═C bonds of allenes while enabling the suppression of competitive over-hydrogenation, proving generally to form trisubstituted E-alkenes in high chemo-, regio-, and stereoselectivity. By this CAAC-phosphine-Cr-catalyzed selective semihydrogenation, unsaturated nitro, nitrile, alkenyl, and hydrogenation-sensitive bromide, chloride, and fluoride were compatible with various substitution environments. The in situ forming silylchromium as active catalyst by reaction of low-valent chromium complex with chlorosilane was established by studying the catalytic and stoichiometric reactivity of this species in the semihydrogenation. Deuterium labeling experiments, HRMS, XPS, EPR, and magnetic susceptibility analysis of the related intermediates and theoretical studies support a pathway involving sila-metalation of allene and β-silyl elimination processes with silyl as noninnocent ligand, leading to the E-alkene products.

Conflict of Interests

The authors declare no conflict of interest.

Data Availability Statement

The data that support the findings of this study are available in the Supporting Information of this article.

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