Synthesis, characterization, and structures of divalent europium and ytterbium N, N-dimethylaminodiboranates

Abstract

Treatment of the trichlorides EuCl3 and YbCl3 with Na(H3BNMe2BH3) in tetrahydrofuran (THF) results in a reduction to the corresponding divalent europium and ytterbium N,N-dimethylaminodiboranate (DMADB) complexes Eu(H3BNMe 2BH3)2(THF)2 (1) and Yb(H 3BNMe2BH3)2(THF)2 (2), which can be separated from trivalent Ln(H3BNMe2BH 3)3(THF) byproducts by extraction and crystallization from pentane. No other lanthanide trihalides react with Na(H3BNMe 2BH3) to afford divalent products. Compounds 1 and 2 can also be prepared from the divalent lanthanide iodides EuI2 and YbI2 in higher yield and without the need to separate them from trivalent species. Treatment of 1 and 2 with an excess of 1,2-dimethoxyethane (DME) in pentane affords the new species Eu(H3BNMe2BH 3)2(DME)2 (3) and Yb(H3BNMe 2BH3)2(DME) (4). Compound 1 is dinuclear: each metal center is bound to two chelating DMADB ligands, one of which also bridges to the other metal. Overall, the coordination geometry about each Eu atom can be described as a distorted pentagonal bipyramid, with five B atoms from the DMADB ligands occupying the equatorial sites and two THF molecules occupying the axial sites. Unlike 1, compound 2 is monomeric owing to the smaller radius of YbII versus EuII; the B and O atoms describe a distorted cis octahedron. The Eu(DME) complex 3 is also monomeric; both DMADB ligands and both DME molecules chelate to the metal center. The four B atoms and the four O atoms describe a distorted square antiprism, with the O atoms occupying one square face and the B atoms occupying the other. In addition to X-ray crystallographic studies, IR, NMR, and mass spectrometric data are reported for all four new compounds. © 2010 American Chemical Society.