Undecaborates M-2[B11H11]: Facile synthesis, crystal structure, and reactions

closo-Undecaborates were synthesized by the deprotonation of B11H13(SMe2) w ith LitBu in thp or K[BHEt3] in thf, [Li(thp)(3)](2)[B11H11] and K-2[B11H11 ] being obtained in 83 and 93% yield, respectively. K-2[B11H11] can be tran sformed into A(2)[B11H11] With the corresponding ammonium chlorides in aque ous solution (A=[NMe3Ph], [NBzlEt(3)], [N(PPh3)(2)]). The crystal structure analysis of [Li(thp)(3)](2)[B11H11] (space group P2(1)/c) reveals a rather distorted octadecahedron for the [B11H11](2-) anion, whereas the correspon ding octadecahedron in [NBzlEt(3)](2)[B11H11] (space group P2(1)2(1)2(1)) e xhibits a structure close to C-2v symmetry, expected for the free anion. Th e protonation of [B11H11](2-) at low temperature gives [B11H12](-), whose s tructure could be elucidated by NMR methods; it is formed, apparently, by t he opening of the B1-B4 edge of [B11H11](2-) in the course of its known deg enerate skeletal rearrangement, followed by the protonation of the B2-B4 ed ge. The reaction of [B11H12](-) with a second molecule of the acid HX (X = CF3COO) gives nido-[B11H13X](-). The addition of BH3 to [B11H11](2-) yields closo-[B12H12] under loss of H-2 Two [B11H11](2-) units are fused by the a id of FeCl3, with the known anion [B22H22](2-) as the product, whose B-11-N MR signals could completely be assigned on the basis of C-s symmetry. The c ompound [NBzlEt(3)][N(PPh3)(2)][B22H22] crystallizes in the space group Pna 2(1).