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Herein, we present the efficient isomerization of epoxides into methyl ketones with a novel pincer‐rhodium complex under very mild conditions. The catalyst system has an excellent functional group tolerance and a wide array of epoxides was tested. The corresponding methyl ketones were obtained in very high yields with excellent chemo‐ and regioselectivity. In addition, we investigated mechanistic details like the isomerization of the catalyst, and we obtained evidence that the catalytic cycle follows a β‐hydride elimination‐reductive elimination pathway after the nucleophilic ring opening of the epoxide.

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The coordination chemistry of an electron-rich macrocyclic CNC pincer-ligand consisting of two pentamethylene tethered N-heterocyclic carbene moieties on a carbazole backbone (bimcaC5) is investigated by mainly NMR spectroscopy and X-ray crystal structure analysis. A bridging coordination mode is found for the lithium complex. With the larger and softer potassium ion, the ligand adopts a facial coordination mode and a polymeric structure by intermolecular potassium nitrogen interactions. The facial coordination is also confirmed at a Cp*Ru fragment, while C-H activation under dehydrogenation at the alkyl chain is observed upon reaction with [Ru(PPh3)3Cl2]. In contrast, Pd(OAc)2 reacts under C-H activation at the central carbon atom of the pentamethylene tether to an alkyl-pincer macrocycle.

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Two methods for the synthesis of the bis­(imidazolin-2-ylidene)­carbazolide cobalt­(I) complex [Co­(bimcaHomo)] (2) have been developed. The first route relies on the direct transmetalation of the in situ generated lithium complex [Li­(bimcaHomo)] with CoCl­(PPh3)3. The second route is a two-step synthesis that consists of the transmetalation of [Li­(bimcaHomo)] with CoCl2 followed by reduction of the Co­(II) complex to yield the desired Co­(I) complex 2. The analogous iridium complex [Ir­(bimcaHomo)] (4) was prepared by transmetalation of [Li­(bimcaHomo)] or [K­(bimcaHomo)] with [Ir­(μ-Cl)­(COD)]2. The catalytic activity of complexes 2 and 4 in the epoxide isomerization was tested in the absence and presence of H2. When [M­(bimcaHomo)] (M = Ir (4), Rh (3)) was exposed to 1 bar of H2 at 80 °C, single crystals formed whose X-ray structure analyses revealed the hydrogenation of the N-homoallyl moieties and formation of the dimeric hydrido complexes [Ir­(bimca n‑Bu)­(H)2]2 (7) and [Rh­(bimca n‑Bu)­(H)2]2 (8).