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A pentadentate ligand platform, bis[2-(diisopropylphosphino-methylamino)phenyl]ether (1), abbreviated as H2(PNONP), is introduced that enables the isolation of homodinuclear chromium complexes. In a one-step metalation using Cr(III) and Cr(II) chloride reagents, the bimetallic compounds, [Cr(μ-Cl)(PNONP)]2 (2) and [Cr(PNONP)]2 (3), respectively, were synthesized. These complexes have been characterized by X-ray diffraction, NMR spectroscopy, cyclic voltammetry, magnetometry, UV-Vis-NIR spectroscopy, combustion analysis, and computational methods. Complex 3 has a reasonably short Cr-Cr bond length of 2.1342(5) Å. Quantum chemical calculations support a diradical singlet ground-state with a formal triple bond between the chromium centers. By cyclic voltammetry, 3 exhibits two reversible oxidations at E = -470 and -750 mV versus FeCp20/+. The one- and two-electron oxidized analogues, 3+ and 32+, were generated in situ via chemical oxidation using ferrocenium. Based on in situ characterization of 3+ and 32+, we hypothesize the oxidations are metal-based to yield Cr25+ and Cr26+ cores, respectively.
Bibliographical noteFunding Information:
The authors thank Dr. Eckhard Bill and Andreas Göbels (Max Planck Institute) for their expertise in SQUID data collection, as well as Dr. Victor G. Young, Jr. (UMN) for helpful discussions regarding X-ray crystallography. This research was primarily supported as part of the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) , under Award DE-SC0012702 (computational studies), by the National Science Foundation (NSF) under Award CHE 1254621 (experimental work). C.C.L. is grateful to the Alfred P. Sloan Foundation for a research fellowship. R.K.C. thanks the NSF for a graduate fellowship. K.M.B. was funded by UROP . X-ray diffraction experiments were performed using a crystal diffractometer acquired through an NSF-MRI award (CHE-1229400) in the X-ray laboratory.
- Metal-metal multiple bond