Reactions of the organodiborane (mu-H)(2)(BC5H10)(2), 1, With the Lewis bases, N(CH3)(3), P(CH3)(3), NH3, and H-, produced the cyclic adducts LHBC5H10 (L = N(CH3)(3), P(CH3)(3), NH3, H-) through symmetrical cleavage of the hydrogen bridge system. The salt [(NH3)(2)BC5H10][H2BC5H10] was produced through unsymmetrical cleavage of the hydrogen bridge system. An improved, synthesis of the anion [H2BC5H10](-), 3, is described. It can function as a hydride transfer reducing agent in its reactions with BH3THF and 4-tert-butylcyclohexanone. In its reactions with (eta(5)-C5H5)(2)MCl2 it serves as a chelating agent to produce (eta(5)-C5H5)(2)MCl(mu-H)(2)BC5H10 (M = Zr, 4; Hf, 5). The molecular structures of 1 and 4 are reported here. Crystal data for 1 : space group P (1) over bar, a = 6.415(3) <(A)Angstrom>, b = 9.260(4) <(A)Angstrom>, c = 10.291(5) <(A)Angstrom, alpha = 114.53(4)degrees, beta = 104.25(4)degrees, gamma = 90.01(4)degrees, Z = 2. Crystal data for 3 : space group P2(1)/c, a = 12.584(2) <(A)Angstrom>, b = 9.511(1) (A) over circle, c = 12.813(2) <(A)Angstrom>, beta = 100.26(1)degrees, Z = 4.