The nido-metalloborane complexes Ta-2(mu(2),eta(4)-B2H6)(DTolF)(4) . 2Et(2)O, 1, DTolF(-) = [(p-tolyl)NCHN(p-tolyl)](-), and Ta-2(mu(4)-B2H6)(DPhF)(4) . Et(2)O, 2, DPhF(-) = [phenylNCHNphenyl](-), are formed as the products of tantalum pentachloride with lithium borohydride followed by the addition of LiDTolF or LiDPhF. Complexes 1 and 2 are the first structurally characterized compounds in which two metal atoms that are bonded to each other are also bridged by an hexahydroborate ligand through four B-H-M three-center bonds in a symmetric bonding mode. The Ta-Ta distances are 2.725(1) Angstrom in 1 and 2.728(1), 2.736(1) Angstrom in 2. Crystallographic data are as follows : compound 1, P (1) over bar, a = 15.197(3) Angstrom, b = 15.675(2) Angstrom, c = 16.449(6) Angstrom, alpha = 102.50(1)degrees, beta = 99.04(1)degrees, gamma = 117.10(2)degrees, and Z = 2; compound 2, P (1) over bar with a = 11.547(5) Angstrom, b = 20.03(1) Angstrom, c = 29.934(8) Angstrom, alpha = 107.60(1)degrees, beta = 100.86(2)degrees, gamma = 95.65(2)degrees, and Z = 4. In these two molecules there are two ArNC(H)NAr- ligand coordinated in a chelating manner to each of two tantalum atoms. These two Ta(DTolF)(2) or Ta(DPhF)(2) fragments are united by a Ta=Ta bond (ca. 2.73 Angstrom), and a B2H6 unit lies across the bond forming two B-H-Ta bridge bonds to each tantalum atom. The B2H6Ta2 moiety constitutes a B2Ta2 nido-metalloborane, formally similar to B4H10.