A crystalline uranium Fischer-type carbyne

Since their discovery in 1973, transition metal Fischer carbynes have become a foundational class of metal-carbon triple bond in organometallic chemistry. However, even though the uranium Fischer carbyne bonding motif has been a fundamental target in f-element chemistry, its isolation has remained challenging. Here we report the synthesis and characterization of the uranium Fischer-type carbyne complex [N″₃U(μ-CNN)UN″₃] (N″ = N(SiMe₃)₂). Single-crystal X-ray diffraction analysis reveals a uranium-carbyne distance of 2.379(15) Å, and density functional theory calculations combined with experimental quantum crystallography Hirshfeld atom refinement reveal the presence of two-electron C→U σ-donation, weak two-electron C→U π-donations and two orthogonal one-electron U→C π-back-bonds, demonstrating σ²π¹π¹ Fischer-type carbyne bonding overall. This work redefines the range of bonding modes for the diazomethanediide ligand and reveals a uranium-carbon triple-bond interaction that is related, yet distinct from transition metal Fischer carbynes, providing a basis to develop and understand f-element carbyne chemistry.