A Triplet Iron Carbyne Complex.

Tuning the spin state of metal carbynes, which have broad applications in organic synthesis and material science, presents a formidable challenge for modern chemists as the strong field nature of carbyne ligands dictates low-spin ground spin states ( S = 0 or 1/2) for known metal carbynes. Through the oxidative addition reaction of a low-coordinate iron(0) N -heterocyclic carbene complex with the C-S bond of a thioazole-2-ylidene, we synthesized the first triplet ( S = 1) metal terminal carbyne, an iron cyclic carbyne complex. Different from the classical metal carbynes, the triplet complex features an LXZ -type carbyne ligand and a weak Fe≡C triple bond, which endow it with the unique reactivity pattern of facile carbyne coupling, weak affinity toward nucleophiles, and facial addition reactions with electrophiles.