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. 2025 Apr 24;16(21):9406-9412.
doi: 10.1039/d5sc01576f. eCollection 2025 May 28.

Post-coordination of Ru(ii) controlled regioselective B(4)-H acylmethylation of o-carboranes with sulfoxonium ylides

Hou-Ji Cao  1 , Jia-Xin Li  1 , Jia-Hui Yan  1 , Miao-Xin Liu  1 , Qianyi Zhao  1 , Jie Zhang  1 , Ju Zhang  1 , Hong Yan  2
Affiliations

Post-coordination of Ru(ii) controlled regioselective B(4)-H acylmethylation of o-carboranes with sulfoxonium ylides

Hou-Ji Cao et al. Chem Sci. .

Abstract

Despite significant progress in the B-H functionalization of carboranes, the development of cost-effective catalytic systems devoid of noble metals, coupled with mechanistic validation of regioselectivity control, remains a formidable challenge. Herein, we disclose an Ag salt-free, redox-neutral, and inexpensive ruthenium(ii)-catalyzed protocol that enables exclusive B(4)-H acylmethylation of o-carboranes through a novel post-coordination strategy. By exploiting weakly coordinating carboxylic acid as a traceless directing group, this method achieves excellent mono-site selectivity for B-C(sp3) bond formation using diverse sulfoxonium ylides, demonstrating both functional group tolerance and synthetic scalability. This work not only establishes a practical synthetic platform but also addresses critical mechanistic questions unresolved in prior analogous studies. Through deuterium labeling, in situ high-resolution mass spectrometry (HRMS) tracking, and single-crystal X-ray analysis of critical Ru intermediates, we unequivocally demonstrate that the mono-site selectivity originates from a unique post-coordination mode of Ru(ii). The Ru catalyst simultaneously engages both the carboxylic acid and the enolizable acylmethyl moiety in the mono-acylated intermediate, thereby dictating the B(4)-H activation trajectory. Our findings establish a generalizable platform for regiocontrolled carborane functionalization while defining mechanistic paradigms in transition metal-mediated B-H activation chemistry.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. Transition metal-catalyzed cage B–H alkylation of o-carboranes.
Scheme 2
Scheme 2. Scope of sulfoxonium ylides. aReaction conditions: 1a (0.1 mmol), 2 (1.5 equiv.), [Ru(benzene)Cl2]2 (2.5 mol%), HFIP (1.0 mL), 60 °C, 3 h, N2 atmosphere. bIsolated yield. c1 mmol scale. d2J was used as a racemic mixture. eNo d.r. was determined. fEnantiopure 2K was used.
Scheme 3
Scheme 3. Scope of carboranyl acids. Reaction conditions: 1 (0.1 mmol), 2a (1.5 equiv.), [Ru(benzene)Cl2]2 (2.5 mol%), HFIP (1.0 mL), 60 °C, 3 h, N2 atmosphere. bIsolated yield.
Scheme 4
Scheme 4. Synthetic applications.
Scheme 5
Scheme 5. Control experiments.
Scheme 6
Scheme 6. Proposed reaction cycle for Ru(ii)-catalyzed B(4)–H alkylation of o-carboranyl acid (a) and illustration of the post-coordination step (b).
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