Heteroleptic Four-Coordinate Tris(oxazolinyl)borato Iron(II) Compounds

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2019-04-17
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Reinig, Regina
Ellern, Arkady
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Sadow, Aaron
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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Chemistry

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The Department of Chemistry was founded in 1880.

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Abstract

The reaction of FeBr2 and 1 equiv of thallium tris(4,4-dimethyl-2-oxazolinyl)phenylborate (TlToM) in THF provides ToMFeBr (1), whereas FeBr2 and 2 equiv of TlToM react to give (ToM)2Fe (2). Two νCN bands at 1604 and 1548 cm–1 indicated bidentate coordination of ToM to iron in 2. Homoleptic 2 and FeBr2 react in THF overnight through an unusual ligand exchange process to give compound 1, which is apparently the thermodynamic product. The salt metathesis reaction of 1 and KCH2Ph affords ToMFeCH2Ph (3). The effective magnetic moments of compounds 1–3 range from 4.9 to 5.4 μB, and these values are consistent with high-spin iron(II) (S = 2). A single 1H NMR signal assigned to the methyl groups of the ToM ligand suggested tridentate coordination of the ToM ligand to iron in 1 and 3. X-ray crystallography studies of 1–3 establish their structure as four-coordinated tetrahedral iron complexes. ToMFeBn and CO (1 atm) react to afford isolable ToMFe{C(═O)Bn}(CO)2 (4) as a yellow solid. Complex 4 is diamagnetic (S = 0), and the three distinct methyl signals in the 1H NMR spectrum are consistent with a six-coordinate, Cs-symmetric species. This assignment is supported by its IR spectrum, which revealed intense bands at 2004 and 1935 cm–1 (symmetric and asymmetric νCO), at 1680 and 1662 cm–1 (acyl rotamers, νCO), and at 1593 and 1553 cm–1 (νCN) and is confirmed by a single-crystal X-ray diffraction study.

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