Flipping Motion of the Alkylene Bridge in cis-[N,N'Pentamethylenebis(iminomethylazolato)]M(II) Complexes (M = Pt, Pd) with Hydrogen-Bond-like MH–C Interactions by Soichiro Kawamorita Mitsuhiro Nishino Ngoc Ha-Thu Le Kazuki Nakamura & Takeshi Naota

Author:Soichiro Kawamorita, Mitsuhiro Nishino, Ngoc Ha-Thu Le, Kazuki Nakamura & Takeshi Naota
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Tags: Hydrogen-bond-like MH–C interactions in square-planar d8 metal complexes have recently gained attention as structure-directing elements and design motifs in asymmetric catalysis. In this study, we explore these weak interactions not as static features, but as key modulators of molecular motion. We synthesized four cis-[N,N'pentamethylenebis(iminom ethylazolato)]M(II) (M = Pt, Pd), including iminomethyl-2-imidazole, iminomethyl-5-imidazole, and iminomethylpyrrolato Pt(II) complexes and an iminomethylpyrrolato Pd(II) analog. All complexes display reversible flipping of the alkylene bridge across the coordination plane, with the MH–C interaction alternately engaging from above or below. This dynamic motion was characterized by variable-temperature 1H NMR spectroscopy, revealing activation parameters for the flipping process. X-ray crystallography confirmed geometries consistent with hydrogen-bond-like interactions, while NBO analysis based on DFT calculations provided insight into their electronic nature. Interestingly, although Pt and Pd display comparable MH–C distances, solvent effects dominate the flipping kinetics over metal identity. These findings highlight the role of hydrogen-bond-like MH–C interactions not only in structural stabilization, but also in regulating conformational dynamics., molecular motion; platinum complex; palladium complex; hydrogen-bond-like MH–C interaction; anagostic interaction


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