Bimetallic Complexes Supported by a Redox-Active Ligand with Fused Pincer-Type Coordination Sites

Authors

Denan Wang, Marquette University
Sergey Lindeman, Marquette UniversityFollow
Adam T. Fiedler, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

2015

Publisher

American Chemical Society

Source Publication

Inorganic Chemistry

Source ISSN

1520-510x

Original Item ID

DOI: 10.1021/acs.inorgchem.5b01380

Abstract

The remarkable chemistry of mononuclear complexes featuring tridentate, meridionally chelating “pincer” ligands has stimulated the development of ligand frameworks containing multiple pincer sites. Here, the coordination chemistry of a novel pentadentate ligand (L^N3O2) that provides two closely spaced NNO pincer-type compartments fused together at a central diarylamido unit is described. The trianionic L^N3O2 chelate supports homobimetallic structures in which each M(II) ion (M = Co, Cu, Zn) is bound in a meridional fashion by the bridging diarylamido N atom and O,N-donors of the salicyaldimine arms. The metal centers are also coordinated by a mono- or bidentate auxiliary ligand (L^aux), resulting in complexes with the general form [M₂(L^N3O2)(L^aux)₂]⁺ (where L^aux = 1-methyl-benzimidazole (1MeBI), 2,2′-bipyridine (bpy), 4,4′-dibromo-2,2′-bipyridine (bpy^Br2), or (S)-2-(4-isopropyl-4,5-dihydrooxazolyl)pyridine (S-^iPrOxPy)). The fused nature of the NNO pincer sites results in short metal–metal distances ranging from 2.70 Å for [Co₂(L^N3O2) (bpy)₂]⁺ to 3.28 Å for [Zn₂(L^N3O2) (bpy)₂]⁺, as revealed by X-ray crystallography. The complexes possess C₂ symmetry due to the twisting of the aryl rings of the μ-NAr₂ core; spectroscopic studies indicate that chiral L^aux ligands, such as S-^iPrOxPy, are capable of controlling the helical sense of the L^N3O2 scaffold. Since the four- or five-coordinate M(II) centers are linked solely by the amido moiety, each features an open coordination site in the intermetallic region, allowing for the possibility of metal–metal cooperativity in small-molecule activation. Indeed, the dicobalt(II) complex [Co₂(L^N3O2) (bpy^Br2)₂]⁺ reacts with O₂ to yield a dicobalt(III) species with a μ-1,2-peroxo ligand. The bpy-containing complexes exhibit rich electrochemical properties due to multiple metal- and ligand-based redox events across a wide (3.0 V) potential window. Using electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT), it was determined that one-electron oxidation of [Co₂(L^N3O2) (bpy)₂]⁺ results in formation of a S = 1/2 species with a L^N3O2-based radical coupled to low-spin Co(II) centers.

Comments

Accepted version. Inorganic Chemistry, Vol. 54, No. 47 (2015): 8744-8754. DOI. © 2015 American Chemical Society. Used with permission.

Recommended Citation

Wang, Denan; Lindeman, Sergey; and Fiedler, Adam T., "Bimetallic Complexes Supported by a Redox-Active Ligand with Fused Pincer-Type Coordination Sites" (2015). Chemistry Faculty Research and Publications. 466.
https://epublications.marquette.edu/chem_fac/466