Synthesis and Structural Diversity of Barium (N,N-Dimethylamino)diboranates

The School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
Inorganic Chemistry (Impact Factor: 4.76). 06/2012; 51(12):6449-59. DOI: 10.1021/ic2016879
Source: PubMed


The reaction of a slurry of BaBr(2) in a minimal amount of tetrahydrofuran (THF) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in diethyl ether followed by crystallization from diethyl ether at -20 °C yields crystals of Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(2) (1). Drying 1 at room temperature under vacuum gives the partially desolvated analogue Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(x) (1') as a free-flowing white solid, where the value of x varies from <0.1 to about 0.4 depending on whether desolvation is carried out with or without heating. The reaction of 1 or 1' with Lewis bases that bind more strongly to barium than diethyl ether results in the formation of new complexes Ba(H(3)BNMe(2)BH(3))(2)(L), where L = 1,2-dimethoxyethane (2), N,N,N',N'-tetramethylethylenediamine (3), 12-crown-4 (4), 18-crown-6 (5), N,N,N',N'-tetraethylethylenediamine (6), and N,N,N',N",N"-pentamethylethylenetriamine (7). Recrystallization of 4 and 5 from THF affords the related compounds Ba(H(3)BNMe(2)BH(3))(2)(12-crown-4)(THF)·THF (4') and Ba(H(3)BNMe(2)BH(3))(2)(18-crown-6)·2THF (5'). In addition, the reaction of BaBr(2) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in the presence of diglyme yields Ba(H(3)BNMe(2)BH(3))(2)(diglyme)(2) (8), and the reaction of 1 with 15-crown-5 affords the diadduct [Ba(15-crown-5)(2)][H(3)BNMe(2)BH(3)](2) (9). Finally, the reaction of BaBr(2) with Na(H(3)BNMe(2)BH(3)) in THF, followed by the addition of 12-crown-4, affords the unusual salt [Na(12-crown-4)(2)][Ba(H(3)BNMe(2)BH(3))(3)(THF)(2)] (10). All of these complexes have been characterized by IR and (1)H and (11)B NMR spectroscopy, and the structures of compounds 1-3, 4', 5', and 6-10 have been determined by single-crystal X-ray diffraction. As the steric demand of the Lewis bases increases, the structure changes from polymers to dimers to monomers and then to charge-separated species. Despite the fact that several of the barium complexes are monomeric in the solid state, none is appreciably volatile up to 200 °C at 10(-2) Torr.

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    ABSTRACT: The reaction of CaBr2 with 2 equiv of sodium N,N-dimethylaminodiboranate, Na(H3BNMe2BH3) in Et2O at 0 °C followed by crystallization and drying in vacuum yields the unsolvated calcium compound Ca(H3BNMe2BH3)2, 1. Before the vacuum drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Ca(H3BNMe2BH3)2(Et2O)2, 2. If the reaction of CaBr2 with 2 equiv of Na(H3BNMe2BH3) is carried out in the more strongly coordinating solvent tetrahydrofuran (thf), the solvate Ca(H3BNMe2BH3)2(thf)2, 3, is obtained. This compound does not desolvate as easily in vacuum as the diethyl ether compound 2. Treating the thf adduct 3 with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or N,N,N',N'-tetramethylethylenediamine (tmeda) in thf affords the new compounds Ca(H3BNMe2BH3)2(dme), 4, Ca(H3BNMe2BH3)2(diglyme), 5, and Ca(H3BNMe2BH3)2(tmeda), 6, respectively, in greater than 60% yields. Treatment of 3 with 2 equiv of the crown ether 12-crown-4 in thf affords the charge-separated salt [Ca(12-crown-4)2][H3BNMe2BH3]2, 7. Crystal structures of all the Lewis base adducts are described. Compounds 2-6 all possess chelating κ(2)-BH3NMe2BH3-κ(2) groups, in which two hydrogen atoms on each boron center are bound to calcium. Compound 7 is the only ionic compound in the series; the Ca atom is completely encapsulated by two 12-crown-4 rings, and the anions are charge-separated counterions within the unit cell. When heated, the dme, diglyme, and tmeda compounds 4, 5, and 6 melt without decomposition, and can be sublimed readily under reduced pressure (1 Torr) at 90 °C (4) and 120 °C (5, 6). The dme adduct is one of the most volatile calcium compounds known, and is a promising CVD precursor for the growth of calcium-containing thin films.
    Inorganic Chemistry 12/2013; 53(2). DOI:10.1021/ic402237b · 4.76 Impact Factor


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