Triplet carbenes with transition-metal substituents

The extraordinary advances in carbene (R¹–C–R²) chemistry have been fuelled by strategies to stabilize the electronic singlet state via π interactions. In contrast, the lack of similarly efficient approaches to obtain authentic triplet carbenes with appreciable lifetimes beyond cryogenic temperatures hampers their exploitation in synthesis and catalysis. Transition-metal substitution represents a potential strategy, but metallocarbenes (M–C–R) usually represent high-lying excited electronic configurations of the well-established carbyne complexes (M≡C–R). Here we report the synthesis and characterization of triplet metallocarbenes (M–C–SiMe₃, M = Pd^II, Pt^II) that are persistent beyond cryogenic conditions, and their selective reactivity towards carbene C–H insertion and carbonylation. Bond analysis reveals significant stabilization by spin-polarized push–pull interactions along both π-bonding planes, which fundamentally differs from bonding in push–pull singlet carbenes. This bonding model, thus, expands key strategies for stabilizing the open-shell carbene electromers and closes a conceptual gap towards carbyne complexes.