The reduction of TaCl5 with LiBH4 in the presence of the bidentate ligand bis(dimethylphosphino)methane, dmpm, produces the novel BH3-bridged ditantalum complex Ta-2(mu-BH3)(mu-dmDm)(3)(eta(2)-BH4)(2) (1) and the acid-base adduct dmpm(BH3)(2) (2). Two crystalline forms of 1 were obtained, and their structures have been determined by X-ray crystallography. The unique feature of 1 is that the bridging borane is bound only to the ditantalum metal center, forming a simple metallaborane cluster, Ta2B, with averaged Ta-Ta and Ta-B bond distances of 2.7792[5] and 2.307[9] Angstrom, respectively; the averaged Ta-B separation for the axially coordinated BH4-groups, which are bound to the Ta atoms through hydrogen atoms, is similar to 0.2 Angstrom longer than that of the bound BH3 group. The mu-BH3 group has one exo-hydrogen atom with a B-H-exo distance of 1.10-[8] Angstrom. The distance between the endo-hydrogen atom and the boron atom is 1.23[8] Angstrom. Each of the two endo-hydrogen atoms is also bound to a Ta atom with the Ta-H distance of 1.97[8] Angstrom. Compound 1 represents the first example of a structurally characterized metallaborane complex containing a mu-BH3 group bridging two metal centers. The structure of the air-stable compound 2 has also been determined; it shows a strong P to B dative bond with the P-B distance of 1.903(4) Angstrom.