Cyclic organohydroborate complexes of zirconium monocyclopentadienyl CpZr{(mu-H)(2)BC5H10}(3), 1, and CpZr{(mu-H)(2)BC8H14}(3), 2, were prepared from the reaction of CpZrCl3 with 3 mol of K[H2BC5H10] and K[H2BC8H10], respectively, in diethyl ether. Compounds 1 and 2 react with the hydride ion abstracting agent B(C6F5)(3) to form the same salt [CpZr(OEt)(OEt2)(mu-OEt)](2)[HB(C6F5)(3)](2), 5. The complexes CpZr(Cl){(mu-H)(2)BC8H14}(2), 3, and Cp*Zr(Cl){(mu-H)(2)BC8H14}(2) [where Cp* = C-5(CH3)(5)], 4, were prepared from the reaction of CpZrCl3 and Cp*ZrCl3 with K[H2BC9H10] in 1:2 molar ratios, respectively. An alpha-hydrogen of a BC8H14 unit forms an agostic interaction with Zr in compound 3 but not in 4. All of the compounds were characterized by single-crystal X-ray diffraction analysis.