EuFOD

EuFOD
Other names Eu(fod)3
Identifiers
CAS number	17631-68-4
Properties
Molecular formula	C30H30EuF21O6
Molar mass	1037.49 g/mol
Appearance	Yellow powder
Melting point	203-207 °C
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Infobox references

EuFOD is the chemical compound with the formula Eu(OCC(CH₃)₃CHCOC₃F₇)₃, also called Eu(fod)₃. This coordination compound is used primarily as a shift reagent in NMR spectroscopy. It is the premier member of the lanthanide shift reagents and was popular in the 1970s and 1980s.

Structure and reactivity

Eu(fod)₃ consists of three bidentate acetylacetonato ligands bound to a Eu(III) center. This metal atom has an electron configuration of f⁶. The six electrons are unpaired—each in a different singly-occupied f-orbital—which makes the molecule highly paramagnetic. The complex is a Lewis acid, being capable of expanding its coordination number of six to eight. The complex displays a particular affinity for "hard" Lewis bases, such as the oxygen atom in ethers and the nitrogen of amines. It is soluble in nonpolar solvents, even more so than related complexes of acetylacetone and hexafluoroacetylacetone. The fod ligand is a derivative of heptafluorobutyric acid.

Uses

As an NMR shift reagent

The original application of Eu(fod)₃ was for analyzing diastereomeric compounds in NMR spectroscopy. The paramagnetic compound induces additional chemical shift in the protons near any Lewis basic site to which it binds in a molecule. This change helps resolve closely spaced signals by separating the ones from these hydrogens away from others that are not near basic sites but whose normal chemical shift is similar. Only small amounts of shift reagents are used, because otherwise the paramagnetism of the reagent shortens the spin-lattice relaxation times of the nuclei, which causes uncertainty broadening and loss of resolution. The availability of higher magnetic field spectrometers have lowered the demand for NMR shift reagents.

The original shift reagent was Eu(DPM)₃, developed by Hinckley.^[1] Its structure is similar to EuFOD, but with tert-butyl groups in place of heptafluoropropyl substituents. That is, DPM^- is the conjugate base derived from dipivaloylmethane, also known as 2,2,6,6-tetramethylheptane-3,5-dione. The ligand fod^- is more lipophilic and by virtue of the perfluoralkyl substituent, its complexes are more Lewis acidic than those derived from DPM^-.

As a Lewis acid

Eu(fod)₃ serves as a Lewis acid catalyst in organic synthesis including stereoselective Diels-Alder and aldol addition reactions. For example, Eu(fod)₃ catalyzes the cyclocondensations of substituted dienes with aromatic and aliphatic aldehydes to yield dihydropyrans, with high selectivity for the endo product.^[2]

References

1. ^ C. C. Hinckley. "Paramagnetic Shifts in Solutions of Cholesterol and the Dipyridine Adduct of Trisdipivalomethanatoeuropium(III). A Shift Reagent" J. Am. Chem. Soc. 1969, volume 91, pp. 5160–5162.doi:10.1021/ja01046a038. See alsoNature, 1972, 240, 385-390
2. ^ Wenzel, T.J.; Ciak, J.M.; "Europium, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedianato)" in Encyclopedia of Reagents for Organic Synthesis, 2004. John Wiley & Sons, Ltd. doi:10.1002/047084289X.rn00449