Are there analogues of the indenyl effect in larger ring systems: a DFT study of hydride attack on [Mn(CO)3(naphthalene)]+ and [Cr(CO)3(benzotropylium)]+


Two pairs of complexes, [Mn(CO)3(benzene)]+/[Mn(CO)3(naphthalene)]+ and [Cr(CO)3(tropylium)]+/[Cr(CO)3(benzotropylium)]+, have been used as a platform to establish the extent to which the well-known ‘indenyl effect’ translates into other bicyclic ligand systems. Density functional theory (DFT) suggests that the ‘naphthalene effect’ is minimal, the pathway for hydride reduction of [Mn(CO)3(naphthalene)]+ resembling closely that for the benzene analogue. In the benzotropylium system, in contrast, stabilisation of an η5 coordination mode through aromatisation of the six-membered ring plays a similar role to stabilisation of η3 in the indenyl effect. The greater influence of aromatisation in the five- and seven-membered ring systems stems from the presence of formal charge on the ligands in these cases: localisation of this charge on a subset of the available carbon atoms enhances the electrostatic component of the metal-ligand bond. This is particularly dramatic in the benzotropylium case, where the η7–η5 slippage corresponds to a formal 2-electron reduction of the ligand from [C7H7]+ to [C7H7].

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The author is indebted to Professor J. E. McGrady and his group at theoretical chemistry laboratory, Oxford University, for their assistance throughout the work.

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Correspondence to Abdulhakim A. Ahmed.

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Ahmed, A.A. Are there analogues of the indenyl effect in larger ring systems: a DFT study of hydride attack on [Mn(CO)3(naphthalene)]+ and [Cr(CO)3(benzotropylium)]+. Struct Chem 30, 107–114 (2019).

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  • Indenyl effect
  • DFT
  • Naphthalene effect
  • Tropylium and hydride attack