Treatment of the barium hydride complex [(Tp^Ad,iPr)Ba(μ-H)]₂ (Tp^Ad,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (1) with an excess amount of 1,1-diphenylethylene (DPE) afforded the corresponding mono-DPE adduct [(Tp^Ad,iPr)Ba(η⁶-Ph)C(Ph)Me] (2) and di-DPE adduct [(Tp^Ad,iPr)Ba(η⁶-Ph)C(Ph)-CH₂-C(Ph)₂Me] (3), which could convert to each other through a reversible equilibrium reaction. Complex 1 catalysed DPE hydrogenation under mild conditions (30 °C, 6 atm, 5 mol% cat.).