Synthesis and Structures of LiBH4 Complexes with N-Heterocycles [1]

Abstract

LiBH4 solutions in diethyl ether or tetrahydrofuran react with N-methylmorpholine, Nmethylimidazole or piperidine not only with the formation of adducts LiBH4(L)n (n = 1 or 3) but also with formation of amine boranes BH3(L). While LiBH4 and N-methylimidazole form the 1 : 3 adduct 1, N-methylmorpholine produces the 1 : 1 adduct 2. In both cases the adducts contain hexacoordinated Li atoms. In 1 the Li atom is coordinated to three N atoms and three H atoms. However, in compound 2 the molecules are connected in the solid state with one another to form a two-dimensional polymer built from dimeric units (LiBH4)2 that are connected to adjacent dimeric units via the O and N atoms of the N-methylmorpholine ligand. Each of the Li atoms in 2 is connected to four H atoms via Li-H-B hydrogen bridges and an O and an N atom. The reaction of LiBH4 with piperidine leads to the compound (LiBH4)6(HNC5H10)16, 3, which consists of two independent LiBH4(HNC5H10)3 molecules and two others of composition (LiBH4)2(HNC5H10)5 containing penta- and hexacoordinated Li atoms.