Oxidative Addition of Dihydrogen to (η⁶-Arene)Mo(PMe₃)₃ Complexes: Origin of the Naphthalene and Anthracene Effects

In contrast to the benzene and naphthalene compounds (η6-PhH)Mo(PMe3)3 and (η6-NpH)Mo(PMe3)3, the anthracene complex (η6-AnH)Mo(PMe3)3 reacts with H2 to undergo a haptotropic shift and give the η4-anthracene compound (η4-AnH)Mo(PMe3)3H2. Density functional theory calculations indicate that the increased facility of naphthalene and anthracene to adopt η4-coordination modes compared to that of benzene is a consequence of the fact that the Mo−(η4-ArH) bonding interaction increases in the sequence benzene < naphthalene < anthracene, while the Mo−(η6-ArH) bonding interaction follows the sequence benzene > naphthalene ≈ anthracene.与(η⁶-苯)三(三甲基膦)合钼[(η⁶-PhH)Mo(PMe₃)₃]和(η⁶-萘)三(三甲基膦)合钼[(η⁶-NpH)Mo(PMe₃)₃]两种配合物不同，蒽配合物(η⁶-蒽)三(三甲基膦)合钼[(η⁶-AnH)Mo(PMe₃)₃]可与氢气发生反应，经历η迁移过程，得到η⁴-蒽类配合物(η⁴-AnH)Mo(PMe₃)₃H₂。 密度泛函理论(Density functional theory)计算表明，相较于苯，萘与蒽更易采取η⁴配位模式，其本质原因在于：Mo与η⁴-芳氢的成键相互作用强度遵循苯 < 萘 < 蒽的递增序列，而Mo与η⁶-芳氢的成键相互作用则遵循苯 > 萘 ≈ 蒽的递减序列。