Synthesis, Characterization, and Structures of Divalent Europium and Ytterbium N,N-Dimethylaminodiboranates

Abstract

Treatment of the trichlorides EuCl(3) and YbCl(3) with Na(H(3)BNMe(2)BH(3)) in tetrahydrofuran (THF) results in a reduction to the corresponding divalent europium and ytterbium N,N-dimethylaminodiboranate (DMADB) complexes Eu(H(3)BNMe(2)BH(3))(2)(THF)(2) (1) and Yb(H(3)BNMe(2)BH(3))(2)(THF)(2) (2), which can be separated from trivalent Ln(H(3)BNMe(2)BH(3))(3)(THF) byproducts by extraction and crystallization from pentane. No other lanthanide trihalides react with Na(H(3)BNMe(2)BH(3)) to afford divalent products. Compounds 1 and 2 can also be prepared from the divalent lanthanide iodides EuI(2) and YbI(2) 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(H(3)BNMe(2)BH(3))(2)(DME)(2) (3) and Yb(H(3)BNMe(2)BH(3))(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 Yb(II) versus Eu(II); 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.

Developments in the Coordination Chemistry of Europium(II)

“…[25,52–58] An example of a Eu 2+ -containing complex that was prepared from Eu 3+ chlorides with a reducing species is the dinuclear, distorted pentagonal bipyramidal complex [Eu{H 3 BN-(CH 3 ) 2 BH 3 } 2 (THF) 2 ] 2 ( 41 ), which was obtained by using N , N -dimethylaminodiboranate as the reductant (Figure 5). [52] However, the preparation of 41 produced mixtures of divalent and trivalent species. [52] In contrast, only divalent species were obtained when EuI 2 was used as a precursor instead of EuCl 3 .…”

“…[52] However, the preparation of 41 produced mixtures of divalent and trivalent species. [52] In contrast, only divalent species were obtained when EuI 2 was used as a precursor instead of EuCl 3 . [52] Qi and co-workers used Eu 3+ chlorides as starting materials and a Na–K alloy as reductant to prepare [LEu(HMPA) 2 ] 2 (THF) 4 ( 42 ), in which L is 2,2′-methylene bis(6- tert -butyl-4-methylphenoxo) and HMPA is hexamethylphosphoric triamide.…”

“…The reduction of Eu 3+ by either a ligand that is also a reductant or by chemical or electrochemical methods is more common than the oxidation of Eu metal. Eu 3+ halides, triflates, oxides, or nitrates are typically used as the precursors for the preparation of Eu 2+ ‐containing complexes with a variety of ligands including aryloxides, aminodiboranates, crown ethers, and cryptands 25,52–58. An example of a Eu 2+ ‐containing complex that was prepared from Eu 3+ chlorides with a reducing species is the dinuclear, distorted pentagonal bipyramidal complex [Eu{H 3 BN(CH 3 ) 2 BH 3 } 2 (THF) 2 ] 2 ( 41 ), which was obtained by using N , N ‐dimethylaminodiboranate as the reductant (Figure 5).…”

Scandium, yttrium, the lanthanides

“…Dme solvates have also been made, [Eu(H 3 BNMe 2 BH 3 ) 2 (dme) 2 ] and [Yb(H 3 BNMe 2 BH 3 ) 2 (dme)]. 96 In both the compounds mer-[Ln(EC 6 F 5 ) 3 (thf) 3 ] (Ln = Er, E = Se; Ln = Yb, E = S) there is a trans-effect, with Ln-E bonds trans-to thf shorter than Ln-E bonds that are trans-to EC 6 F 5 . DFT calculations indicate that this results from a covalent Ln-E interaction involving ligand p and Ln 5d orbitals.…”

Boron, aluminium, gallium, indium and thallium

“…18 Amine and phosphine adducts of borane have been the focus of considerable attention during 2010, with a large number of publications directed toward the application of these systems in the storage or production of hydrogen, [19][20][21][22][23][24][25] including investigation of metal amino-borane systems. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] New lanthanide CVD precursors of stoichiometry Ln(H 3 BNMe 2 BH 3 ) 3 have been prepared, as potential lanthanum oxide CVD precursors, where LnQLa, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. 42,43 Borane complexes of aziridine phosphorane, cyclopropylamine, cyclopropylphosphine, cyclopropylmethylamine and cyclopropylmethylphosphine have been prepared by reaction with diborane and the free amine or phosphine.…”