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Leveraging Chelating Amido Ligands to Support Metal-Metal Bonding in Dinuclear Cr(II) Complexes
Janadhi L Ananda Nakath Durage1, Joan Cardona1,2, Soumen Sinhababu3
1Department of Chemistry, The University of Iowa, Iowa City, Iowa 52442, United States.
Abstract:
Herein, we report a series of Cr(II) complexes containing triaryl, tetradentate ligands derived from o-phenylenediamide that illuminate how rigid, chelating amido ligands facilitate Cr-Cr bonding. The aminolysis reaction of Cr[N(SiMe3)2]2(thf)2 with H2(L1)─a protonated N4 proligand containing flanking NMe2 groups─yielded square planar and mononuclear Cr(L1) (1), whereas the same reaction with N2S2 and N2O2 proligands with flanking SMe and OMe groups yielded dinuclear [Cr(L2)]2 (2) and [Cr(L3)]2 (3). The structures of 2 and 3 revealed Cr-Cr distances of 2.3356(6) and 2.3481(5) Å, consistent with metal-metal bonding, which was confirmed by the complete active space methods. The theoretical results suggest that Cr-Cr bonding is assisted by the chelating nature of the bridging amido ligands, which fold the dinuclear structure and orient the metals so that side-on overlap of Cr 3d orbitals can occur. Variable-temperature SQUID magnetometry and spectroscopic data (e.g., UV-vis-NIR, Raman, and IR) reported for 1-3 show differences indicative of the change in nuclearity and electronic structure. Collectively, these results reveal bridging amido ligand characteristics that support metal-metal bonding with Cr(II), and they help account for the wide range of metal-metal distances observed in dinuclear (or binuclear) Cr(II) complexes containing Cr2N2 cores.
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