Copper Complexes with a Hybrid Scorpionate Ligand Containing Pyridazine‐3‐thione

A new scorpionate ligand, Na[HB(mim)2(PntBu)] (Na[PnBm]), with one pyridazinyl-3-thione and two methimazolyl (mim) substituents was prepared by mixing 6-tert-butylpyridazine-3-thione (HPntBu) and sodium dihydridobis(methimazolyl)borate (Na[Bm]) in boiling xylene. Addition of CuCl to a solution of Na[PnBm] in methanol in the presence of PR3 gave the monomeric copper(I) complexes [Cu{PnBm}(PR3)] (R = cyclohexyl 1, phenyl 2) in good yields. They were characterized by NMR spectroscopy and in the case of 2 also by single-crystal X-ray diffraction analysis. The latter revealed a compound in which the ligand is coordinated in a ?3-S,S,H fashion, exhibiting a 3-center-2-electron BH...Cu interaction. Reaction of the ligand Na[PnBm] with CuCl in the absence of phosphane yielded a copper(I) complex, which was determined to be [Cu{PnBm}] (3). Variable-temperature 1H NMR spectroscopy points to the occurrence of two dimeric isomers in solution, which interconvert in a fluxional behavior at room temperature. DFT calculations show that two isomers with a ?3-Smim,Smim,H or a ?3-Hmim,SPn,H coordination mode have very similar energies with a low energy barrier (25.4 kJ/mol) for their interconversion.