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 LiBH 4 in THF yields [HC(3,5-Me 2 pz) 3 ]Li(η 3 -BH 4 ) (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}(BH 4 ). Reaction of equimolar amounts of LiBH 4 and H 2 C(3,5-Me 2 pz) 2 yields {[H 2 C(3,5-Me 2 pz) 2 ]Li(μ-η 3 -BH 4 )} 2 . This complex is a centrosymmetric dimer in the solid state having two bridging [η 3 -BH 4 ] - ligands. For each [η 3 -BH 4 ] - ligand, there is one μ 3 -H and two μ 2 -H atoms. A similar reaction with H 2 C(pz) 2 yields {[H 2 C(pz) 2 ]Li(BH 4 )} 2 and with 4,4‘-dimethyl-2,2‘-bipyridine (4,4‘-Me 2 bipy) yields {[4,4‘-Me 2 bipy]Li(μ-η 3 -BH 4 )} 2 . The structure of {[4,4‘-Me 2 bipy]Li(μ-η 3 -BH 4 )} 2 in the solid state is similar to that of {[H 2 C(3,5-Me 2 pz) 2 ]Li(μ-η 3 -BH 4 )} 2, except the Li 2 B 2 central core is not planar and both μ 3 -H atoms are on the same side of this core.