Mononuclear (O,O′ or N,N′) and Heterodinuclear (O,O′ and N,N′) Transition-Metal Complexes of ortho-Quinoid Bis(pyrazol-1-yl)methane Ligands

Abstract

The ortho-hydroquinone-substituted bis(3,5-dimethylpyrazol-1-yl)methane ligand (HO)2C6H3–C(H)(pzMe,Me)2 (7) has been synthesized and fully characterized. Together with its bis(3-tert-butylpyrazol-1-yl)methane congener (HO)2C6H3–C(H)(pztBu)2 (6), 7 was employed in oxidation and complexation studies. 6 has been oxidized with 2,3-dichloro-5,6-dicyano-para-benzoquinone to the corresponding ortho-benzoquinone form 9 on a preparative scale. Pure samples of 9 are stable for several hours in solution and for approximately one day in the solid state. Attempts at a N,N′ coordination of [PdCl2] to 6 led to decomposition of the −C(H)(pztBu)2 moiety, whereas an introduction of [PdCl2] exclusively at the N,N′ site was possible in high yield for ligand 7. A selectively O,O′-chelated [(p-cym)Ru]2+ complex was accessible for ligand 6, but not for 7. In contrast, [(ppy)2Ir]+ and [(Cp*)Ir]2+ gave O,O′ complexes with both donors 6 and 7 (Hppy = 2-phenylpyridine; HCp* = pentamethylcyclopentadiene). The heterodinuclear complex...