Triplet Metallovinylidenes of Palladium and Platinum Based on a Chelating P/Diazoalkene Ligand

Abstract Triplet carbenes featuring a metal adjacent to the carbene center (metallocarbenes; R─C─M) are an emerging class of diradicals within the field of reactive intermediates. Here, we report the synthesis of the first spectroscopically characterized triplet metallovinylidenes (R─C→M; M = Pt, Pd). The synthetic access is based on a rigid P/C chelating diazoalkene ligand and its coordination to Pt and Pd. The C/P chelating ligand geometrically constrains the R─C→M angle and inhibits free bending. Irradiation of the free diazoalkene ligand generates a triplet vinylidene, characterized by Q‐band electron paramagnetic resonance (EPR) spectroscopy. Irradiation of the metal coordination complexes (Pt and Pd) affords triplet metallovinylidenes, which were characterized at low temperatures including photochemically triggered in crystallo X‐ray diffraction. Combined FD‐FT THz‐EPR spectroscopy and SQUID measurements allowed the determination of the large triplet zero‐field splitting (ZFS) with D values of 124.5 cm −1 (Pt) and 8.0 cm −1 (Pd) in excellent agreement with the electronic structure obtained by high‐level quantum chemical calculations.