EuFOD


EuFOD is the chemical compound with the formula Eu3, also called Eu3. 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

Eu3 consists of three bidentate acetylacetonate ligands bound to a Eu 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

NMR shift reagent

The original application of Eu3 was for analyzing diastereomeric compounds in NMR spectroscopy. As is typical in paramagnetic 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 hydrogen atoms 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 Eu3, developed by Hinckley. 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−.

Lewis acid

Eu3 serves as a Lewis acid catalyst in organic synthesis including stereoselective Diels-Alder and aldol addition reactions. For example, Eu3 catalyzes the cyclocondensations of substituted dienes with aromatic and aliphatic aldehydes to yield dihydropyrans, with high selectivity for the endo product.