Treatment of (silox)(3)Ta (1, silox = (Bu3SiO)-Bu-t) with BH3 center dot THF and BCl2Ph afforded (silox)(3)Ta(BH3) (2) and (silox)(3)Ta(eta(2)-B,Cl-BCl2Ph) (3), which are both remarkably stable Ta(III) compounds. NMe3 and ethylene failed to remove BH3 from 2, and no indication of BH3 exchange with BH3 center dot THF-d(8) was noted via variable-temperature H-1 NMR studies. Addition of BH3 center dot THF to (silox)(3)TaH2 provided the borohydride-hydride (silox)(3)HTa(eta(3)-BH4) (5), and its thermolysis released H-2 to generate 2. Exposure of 2 to D-2 enabled the preparation of isotopologues (silox)(3)Ta(BH3-nDn) (n = 0, 2; 1, 2-D; 2, 2-D-2; 3, 2-D-3) for isotopic perturbation of chemical shift studies, but these failed to distinguish between "inverse adduct" (i.e., (silox)(3)Ta -> BH3) or (silox)(3)Ta(eta(2)-B,H-BH3) forms of 2. Computational models (RO)(3)Ta(BH3) (R = H, 2'; SiH3, 2(SiH) SiMe3, 2(SiMe), and (SiBu3)-Bu-t, 2(SiBu)) were investigated to assess the relative importance of steric and electronic effects on structure and bonding. With small R, eta(2)-B,H structures were favored, but for 2(SiMe) and 2(SiBu), the dative structure proved to be similar in energy. The electonic and vibrational features of both structure types were probed. The IR spectrum of 2 was best matched by the eta(2)-B,H conformer of 2(SiBu). In related computations pertaining to 3, small R models favored the oxidative addition of a BCl bond, while with R = (SiBu3)-Bu-t (3(SiBu)), an excellent match with its X-ray crystal structure revealed the critical steric influence of the silox ligands.