A series of amine solvates of LiBH4 and NaBH4 have been prepared and characterized by IR and NMR spectroscopy as well as by X-ray single-crystal structure determinations. LiBH4 crystallizes from pyridine as LiBH4·3(py), 1, in which the BH4 anion acts as a bidentate ligand. However, in the structure of LiBH4·3py*, 2 (py* = p-benzylpyridine), a tridentate BH4 group is observed. In contrast, LiBH4·2(coll), 3 (coll = 2,4,6-trimethylpyridine, collidine), possesses only a bidentate tetrahydridoborate group, while a tridentate BH4 group is present in monomeric LiBH4·PMDTA, 4 (PMDTA = pentamethyldiethylenetriamine). In contrast, NaBH4·PMDTA, 6, is dimeric in the solid state:  three of the four H atoms of each BH4 group coordinate to the Na atoms; two form a double bridge to two Na atoms while the third one is bonded only to one Na center. LiBH4·TMTA, 5 (TMTA = trimethylhexahydrotriazine), is also dimeric; however, only two of the nitrogen atoms of the TMTA ligand coordinate to Li. The BH4 groups bridge the two Li centers each with one H atom coordinating to two Li atoms, and two bind to a single Li atom. A totally different situation exists for NaBH4·TMTCN, 7 (TMTCN = trimethyltriazacyclononane), which is tetrameric in the crystal. Only one hydrogen atom of the BH4 group functions as a hydride bridge and binds to three Na centers. The molecule contains a Na4B4 heterocubane core. Thus, the different modes of the interaction of the BH4 groups with the alkali metal atoms are determined by the number of donor atoms from the neutral amine ligand and the size of the cation. No definitive conclusion as to the structure of the amine solvates can be derived from IR and/or 11B NMR spectra for the solution state. The crystallographic data are as follows. 1:  a = 10.9939(5) Å, b = 9.9171(4) Å, c = 14.8260(8) Å, β = 94.721(3)°, V = 1611.0(1) Å3, monoclinic, space group P2(1)/n, Z = 4, R 1 = 0.0823. 2:  a = 10.121(1) Å, b = 12.417(2) Å, c = 13.462(3) Å, α = 83.189(2)°, β = 86.068(3)°, γ = 69.166(4)°, V = 1369.3(5) Å3, triclinic, space group P1̄, Z = 2, R 1 = 0.0689. 3:  a = 28.527(3) Å, b = 10.858(1) Å, c = 11.319(1) Å, V = 3505.7(6) Å3, orthorhombic, space group Fdd2, Z = 8, R 1 = 0.0502. 4:  a = 7.591(3) Å, b = 15.325(6) Å, c = 8.719(4) Å, β = 99.80(2)°, V = 999.5(7) Å3, monoclinic, space group P2(1)/c, Z = 4, R 1 = 0.0416. 5:  a = 14.68(1) Å, b = 11.830(7) Å, c = 16.960(8) Å, V = 2946(3) Å, orthorhombic, space group P2(1)2(1)2(1), Z = 8, R 1 = 0.0855. 6:  a = 9.993(2) Å, b = 10.008(3) Å, c = 14.472(4) Å, β = 93.55(2)°, V = 1444.6(7) Å3, monoclinic, space group P2(1)/n, Z = 4, R 1 = 0.0455. 7:  cubic, a = b = c = 13.859(5) Å, V = 2662(2) Å3, cubic, space group I4̄3m, Z = 8, R 1 = 0.0871.

Key Words: Borate lithium (dimethy1amino)trihydrido-/ TMEDA complex / Dioxane complex / 12-Crown-4 complex Li(Me2NBH3) (1) was prepared by deprotonation of Me2NH . BH3 with LiBu and its solubility determined in various solvents. Compound 1 is unstable in most ethereal solvents and decomposes in a reversible reaction into LiH and Li-(Me2N-BH,-NMe2-BH,). Five solvates of 1 were characterised by X-ray structure analysis. Li(Me,NH,) . TMEDA is a dimer in the solid state, and two units are connected to one another by B-H...Li bonds. The crystal structure of Li(Me2NBH,) . 0.5 dioxane is represented by layers consisting of tetrameric Li(Me,NBH,) units connected via dioxane molecules. Each Li atom is coordinated to one oxygen atom, one nitrogen atom, and two hydrogen atoms. Also Li-(Me2NBH3) . 0.5 02C3H6 forms an extended layer, however with pentacoordinated Li atoms which bear one oxygen, one nitrogen, and three hydrogen atoms. A similar layer structure was also found for Li(Me2NBH3) . 03C3H6 where each Li atom is bound to two oxygen atoms of different trioxane molecules, one nitrogen atom, and two hydrogen atoms. Finally, Li(Me2NBH3) . 12-crown-4 retains its molecular integrity in the solid state. Its Li atom is pentacoordinated by four oxygen atoms and one nitrogen atom.Although alkali metal (dia1kyJaniino)trihydroborates are known since 1961[2,31 they have received little attention until re~entlyr~,~'. This renewed interest is associated with their use as powerful but also selective reducing reagents in organic synthe~is[~,~! Nevertheless, our knowledge of their structure as well as our knowledge of their solution state is only marginal although they are well-defined by their "B-NMR data"]. In contrast to the structures of metal tetrahydroborates which contain p1-BH4. p2-BH4, and p3-BH4 groups['], the structure of metal aminotrihydroborates may be even more variable because one can expect the formation of B-N-M (M = metal atom) units besides B(H),M interactions. Li(Me2NBH1) seemed to be a suitable model compound to study this aspect. Synthesis and Physical Properties of Li(MeZNBH3)Li(Me2NBH3) (1) was readily synthesised by the known deprotonation of MezNH . BH3l61 with LiBu in h e~a n e [~] as depicted by eq. (1). However, small amounts of Bu2BNMe,, B(NMe&, and LiBBu4 are also formed as shown by "B-NMR spectroscopy. The formation of these species is formally described by eqs. (2j to (4). The solvates Li-(Me2NBH3) . 0.5 dioxane, Li(Me2NBH3) . 0.5 dioxolane, Li(Me2NBH3) . trioxane, and Li(Me2NBH3) . 12-crown-4 were obtained by adding the ether ligand to a solution of Me2NH . BH3 in toluene followed by deprotonation of the amine-borane with butyllithium. Lo] Part 20: Me,NH BH3 + LiBu --f Li(Me2NBH3) + BuH (1) (2) (3) (4) 1 1 + 2 LiBu --+ 3 LiH + Bu2BNMe2 3 Bu2BNMe2 -+ 2 BBu? + B(NMc2), BBu3 + LiBu + LiBBu4 Figure 1. Schematic rcpresentatioii of the solubility of LI-(Me2NBH,) (1) in various solvents and a1 different temperatures Solubility of Li[MezNMH31 in g/1 350.0 T m.0 t 250,O UI 0°C 0 Z O T e 40°C 200.0 150.0 100.0 ...

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The reaction of sodium metal with dimethylamine–borane in THF yields Na[(H3B)2NMe2] (1) which can be isolated as {Na[(H3B)2NMe2]}5·THF or as Na[(H3B)2NMe2]·15‐crown‐5 (2) and Na[(H3B)2NMe2]·benzo‐15‐crown‐5 (3) after addition of the appropriate crown ether to the THF solution of 1. Reaction of 1 with ZrCl4 yields Me2HN–BH2–NMe2–BH3 (4), the structure of which has been determined. In THF solution, 1 reduces aldehydes, ketones, acyl chlorides, and esters to the corresponding alcohols. It also reacts slowly with nitriles and allylbenzene. Compound (1)5·THF crystallizes in an extended three‐dimensional lattice, in which the Na atoms are coordinated by 6–9 hydridic H atoms, while 3 is a molecular compound in the solid state. Only one hydrogen atom of each BH3 group coordinates to the sodium center. On the other hand, 4 forms dimeric associates in the solid state through N–H···H–B interactions.

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