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

Abstract

In contrast to the benzene and naphthalene compounds (eta(6)-PhH)Mo(PMe(3))(3) and (eta(6)-NpH)Mo(PMe(3))(3), the anthracene complex (eta(6)-AnH)Mo(PMe(3))(3) reacts with H(2) to undergo a haptotropic shift and give the eta(4)-anthracene compound (eta(4)-AnH)Mo(PMe(3))(3)H(2). Density functional theory calculations indicate that the increased facility of naphthalene and anthracene to adopt eta(4)-coordination modes compared to that of benzene is a consequence of the fact that the Mo-(eta(4)-ArH) bonding interaction increases in the sequence benzene < naphthalene < anthracene, while the Mo-(eta(6)-ArH) bonding interaction follows the sequence benzene > naphthalene approximately anthracene.

{Rh(PiBu3)2}+ Fragments Ligated to Arenes: From Benzene to Polyaromatic Hydrocarbons, Part II – Computational Analysis of Pathways for Haptotropic Migration

“…0.4 Å longer. The qualitative nature of this "ring slippage" is identical to that noted in early work on the Cr(CO) 3 complex of naphthalene, [2,4,8] although the hinging is less pronounced in that case (5.5°) as is the distinction between bonded-and nonbonded M-C distances (ΔCr-C 0.12 Å). The hapticity in the chromium case has been assigned as "slipped η 6 " rather than η 4 .…”

“…The presence of a node at the central C-C unit in the HOMO reduces the overlap with the xz component, resulting in a slip towards the outer C=C bond. In d 8 ML 2 fragment such as {Rh(PR 3 ) 2 } + there is only a single vacant Rh-P antibonding orbital (d yz ) and so interactions with the HOMO-1 are repulsive ("filled-filled"). The result is more pronounced slippage, the limit of which is the square-planar η 4 -coordination mode and 16-electron configuration apparent in Nap1.…”

“…[2] Since that initial work numerous studies have used density functional theory to compute minimum energy pathways for haptotropic shifts for PAHs [3][4][5][6] and also carbon nanotubes. [7] Analogous processed in isolobal M(PR 3 ) 3 [8] and M(Cp) [9] (M = Cr, Mo, W) have also been discussed. Albright has also identified the key differences between ML 3 fragments and their ML 2 analogues (such as the {Rh(PR 3 ) 2 } + of direct interest here).…”

“…Albright has also identified the key differences between ML 3 fragments and their ML 2 analogues (such as the {Rh(PR 3 ) 2 } + of direct interest here). [10] Most pertinently, the d 6 ML 3 fragment has a degenerate pair of vacant M-L antibonding orbitals that interact strongly with the π system of the PAH while the d 8 ML 2 fragment has only one, and this proves to have a significant impact on both structure and dynamics.…”

Secondary Interactions or Ligand Scrambling? Subtle Steric Effects Govern the Iridium(I) Coordination Chemistry of Phosphoramidite Ligands

“…[21] This is because the HOMO has a lower symmetry in naphthalene (and anthracene) than benzene and features a nodal plane at the ring junction, which optimizes the d p interaction with the nonjunction carbon atoms in the ring-slipped structure. [22] We believe that this argument qualitatively holds in the case of 3 a and 3 b, despite the fact that this comparison involves the h 2 and h 4 binding modes instead of h 6 and h…”