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.