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Published August 25, 2021 | Supplemental Material
Journal Article Open

Terminal, Open-Shell Mo Carbide and Carbyne Complexes: Spin Delocalization and Ligand Noninnocence

Abstract

Open-shell compounds bearing metal–carbon triple bonds, such as carbides and carbynes, are of significant interest as plausible intermediates in the reductive catenation of C₁ oxygenates. Despite the abundance of closed-shell carbynes reported, open-shell variants are very limited, and an open-shell carbide has yet to be reported. Herein, we report the synthesis of the first terminal, open-shell carbide complexes, [K][1] and [1][BAr^F₄] (1 = P2Mo(≡C:)(CO), P2 = a terphenyl diphosphine ligand), which differ by two redox states, as well as a series of related open-shell carbyne complexes. The complexes are characterized by single-crystal X-ray diffraction and NMR, EPR, and IR spectroscopies, while the electronic structures are probed by EPR studies and DFT calculations to assess spin delocalization. In the d₁ complexes, the spin is primarily localized on the metal (∼55–77% Mo d_(xy)) with delocalization on the triply bonded carbon of ∼0.05–0.09 e⁻. In the reduced carbide [K][1], a direct metal–arene interaction enables ancillary ligand reduction, resulting in reduced radical character on the terminal carbide (⩽0.02 e⁻). Reactivity studies with [K][1] reveal the formation of mixed-valent C–C coupled products at −40 °C, illustrating how productive reactivity manifolds can be engendered through the manipulation of redox states. Combined, the results inform on the electronic structure and reactivity of a new and underrepresented class of compounds with potential significance to a wide array of reactions involving open-shell species.

Additional Information

© 2021 American Chemical Society. Received 11 April 2021. Published online 11 August 2021. Published in issue 25 August 2021. We thank Lawrence Henling, Michael Takase, and Manar Shoshani for invaluable crystallographic assistance. Lawrence Henling is also thanked for assistance with elemental analysis. G.A.B. is grateful to NSERC of Canada and the Resnick Sustainability Institute at Caltech for fellowship support. J.A.B. is grateful for an NSF graduate research fellowship. We thank the NSF (CHE-1800501), the Dow Next Generation Education Fund (instrumentation), and Caltech for funding. The authors declare no competing financial interest. Accession Codes. CCDC 2076055, 2076057–2076058, and 2076060 contain the supplementary crystallographic data for this paper.

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August 20, 2023
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