Stabilization of lithium borohydride with nitrogen donor, chelating ligands.: Syntheses and solid state structures of [HC(3,5-Me2pz)3]Li(η3-BH4), {[H2C(3,5-Me2pz)2]Li(μ-η3-BH4)}2, and {[4,4′-Me2bipy]Li(μ-η3-BH4)}2 (pz = pyrazolyl, bipy = bipyridyl)

The reaction of HC(3,5-Me(2)pz)(3) and LiBH4 in THF yields [HC(3,5-Me(2)pz)(3)]Li(eta(3)-BH4) (pz = pyrazolyl). In the solid state, the borohydride ligand is tridentate with an octahedral arrangement about the lithium. A similar reaction using HC(pz)(3) yields the insoluble ionic compound {[HC(pz)(3)](2)Li}(BH4). Reaction of equimolar amounts of LiBH4 and H2C(3,5-Me(2)pz)(2) yields {[H2C(3,5-Me(2)pz)(2)]Li(mu-eta(3)-BP4)}(2). This complex is a centrosymmetric dimer in the solid state having two bridging [eta(3)-BH4](-) ligands. For each [eta(3)-BH4](-) ligand, there is one mu(3)-H and two mu(2)-H atoms. A similar reaction with H2C(pz)(2) yields {[H2C(pz)(2)]Li(BH4)}(2) and with 4,4'-dimethyl-2,2'-bipyridine (4,4'-Me(2)bipy) yields {[4,4'-Me(2)bipy]Li(mu-eta(3)-BH4)}(2). The structure of {[4,4'-Me(2)bipy]Li(mu-eta(3)-BH4)}(2) in the solid state is similar to that of {[H2C(3,5-Me(2)pz)(2)]Li(mu-eta(3)-BH4)}(2), except the Li2B2 central core is not planar and both mu(3)-H atoms are on the same side of this core.