Pyridazine-Based N‑Heterocyclic Carbene Complexes and Ruthenium-Catalyzed Oxidation Reaction of Alkenes

[Ru2Cl­(L)­(CH3CN)4]­(PF6)3 (1, L = 3,6-bis­(N-(pyridylmethyl)­imidazolylidenyl)­pyridazine), [Cu3La3]­(PF6)3 (2,
La = 3-(N-(pyridylmethyl)­imidazolylidenyl)-6-(N-(pyridylmethyl)­imidazolylonyl)­pyridazine), [Pd2(allyl)2L]­(PF6)2 (3), [Pd2(allyl)2Lb2]­(PF6)2 (4, Lb = N-pyridylmethylimidazole), and [NiLc2]­(PF6)2 (5, Lc = 3-(N-(pyridylmethyl)­imidazolylidenyl)-6-methoxylpyridazine)
have been synthesized and fully characterized by NMR spectroscopy,
elemental analysis, and X-ray diffraction analysis. In complex 1, ligand L binds to two Ru­(II) centers, forming a well-behaved
Ru2(L)Cl plane with a five-membered metallocyclic ring.
Complex 2 is trinuclear, containing a triangular Cu3 unit bonded together by three 3-(N-(pyridylmethyl)­imidazolylidenyl)-6-(N-(pyridylmethyl)­imidazolylonyl)­pyridazine, where one imidazolylidene
was oxidized into imidazolone. Deprotonation reaction with Ag2O in CH3CN and CH3OH resulted in C–N
cleavage of the imidazolium salt, and subsequent reaction with [Pd­(allyl)­Cl]2 and Ni­(PPh3)2Cl2 gave 4 and 5, respectively. Dinuclear Ru­(II)-NHC complex 1 exhibits excellent catalytic activity for the oxidation
of alkenes into diketones.