Ligand- and Metal-Based Reactivity of a Neutral Ruthenium Diolefin Diazadiene Complex: The Innocent, the Guilty and the Suspicious

Coordination of the diazadiene diolefin ligand (trop₂dad) to ruthenium leads to various complexes of composition [Ru(trop₂dad)(L)]. DFT studies indicate that the closed‐shell singlet (CSS), open‐shell singlet (OSS), and triplet electronic structures of this species are close in energy, with the OSS spin configuration being the lowest in energy for all tested functionals. Singlet‐state CASSCF calculations revealed a significant multireference character for these complexes. The closed‐shell singlet wavefunction dominates, but these complexes have a significant (≈8–16 %) open‐shell singlet [d⁷‐Ru^I(L)(trop₂dad^.−)] contribution mixed into the ground state. In agreement with their ambivalent electronic structure, these complexes reveal both metal‐ and ligand‐centered reactivity. Most notable are the reactions with AdN₃, diazomethane, and a phosphaalkyne leading to scission of the C−C bond of the diazadiene (dad) moiety of the trop₂dad ligand, resulting in net (formal) nitrene, carbene, or P≡C insertion in the dad C−C bond, respectively. Supporting DFT studies revealed that several of the ligand‐based reactions proceed via low‐barrier radical‐type pathways, involving the dad^.− ligand radical character of the OSS or triplet species.