The functionalization of molecules by cleaving inert carbon–carbon single bonds is regarded as a great synthetic challenge due to their inherent stability. In recent years, significant progress has been made in the activation of small rings relying on the release of strain energy. By contrast, the number of catalytic methodologies for the activation of unstrained carbon–carbon single bonds is still limited. This review focuses on the recent developments in transition-metal-catalyzed cleavage of C–C bonds in unstrained alcohols via β-carbon elimination. Emphasis is placed on the mechanistic aspects of the discussed transformations and their applications to the deconstruction and reorganization of molecules.

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Carbon dioxide (CO2) impacts every aspect of life, and numerous sensing technologies have been established to detect and monitor this ubiquitous molecule. However, its selective sensing at the molecular level remains an unmet challenge, despite the tremendous potential of such an approach for understanding this molecule’s role in complex environments. In this work, we introduce a unique class of selective fluorescent carbon dioxide molecular sensors (CarboSen) that addresses these existing challenges through an activity-based approach. Besides the design, synthesis, and evaluation of these small molecules as CO2 sensors, we demonstrate their utility by tailoring their reactivity and optical properties, allowing their use in a broad spectrum of multidisciplinary applications, including atmospheric sensing, chemical reaction monitoring, enzymology, and live-cell imaging. Collectively, these results showcase the potential of CarboSen sensors as broadly applicable tools to monitor and visualize carbon dioxide across multiple disciplines.

The advent of transfer hydrogenation and borrowing hydrogen reactions paved the way to manipulate simple alcohols in previously unthinkable manners and circumvent the need for hydrogen gas. Analogously, transfer hydrocarbylation could greatly increase the versatility of tertiary alcohols. However, this reaction remains unexplored because of the challenges associated with the catalytic cleavage of unactivated C–C bonds. Herein, we report a rhodium(I)-catalyzed shuttle arylation cleaving the C(sp²)–C(sp³) bond in unstrained triaryl alcohols via a redox-neutral <i>β</i>-carbon elimination mechanism. A selective transfer hydrocarbylation of substituted (hetero)aryl groups from tertiary alcohols to ketones was realized, employing benign alcohols as latent <i>C</i>-nucleophiles. All preliminary mechanistic experiments support a reversible <i>β</i>-carbon elimination/migratory insertion mechanism. In a broader context, this novel reactivity offers a new platform for the manipulation of tertiary alcohols in catalysis.

We report the synthesis of coordinatively unsaturated cationic rhodium complexes bearing the sterically encumbered electron-rich NHC ligand IPr* OMe . The COD (1,5-cyclooctadiene) complex [Rh(IPr* OMe )(COD)]BF 4 adopts a tilted, pseudo-square planar coordination geometry, where bonding to the ipso-carbon of the NHC aryl substituent was observed in the solid state. Hydrogenation of this complex afforded a metastable dihydride complex [Rh(IPr* OMe )(H) 2 ]BF 4 with an unusual internal coordination to an arene of the ligand. In the absence of a hydrogen atmosphere, spontaneous reductive elimination of H 2 afforded a rhodium complex [Rh(IPr* OMe )]BF 4 with a single chelating ligand that stabilizes the highly unsaturated metal by two-fold π-face donation as suggested by NMR spectroscopy and computational studies. This unusual complex might serve as a versatile precatalyst for a variety of transformations.