Exocyclic coordination of the η3-fluorenyl, η3-cyclopenta[def]phenanthrenyl and η3-8,9-dihydrocyclopenta[def]phenanthrenyl anions: X-ray crystal structures, NMR fluxionality and theoretical studies

Abstract

The novel complexes IndMo(η³-Flu)(CO)₂ (Flu = fluorenyl), (η⁵-Ind)Mo(η³-cpp)(CO)₂ (cpp = cyclopenta[def]phenanthrenyl) and (η⁵-Ind)Mo(η³-H₂cpp)(CO)₂ (H₂cpp = 8,9-dihydrocyclopenta[def]phenanthrenyl) have been prepared and their molecular structures determined. X-Ray crystallographic studies show an exocyclic η³-coordination for the Flu, cpp and H₂cpp ligands, which is also predicted from DFT calculations. ¹H NMR spectra, recorded at temperatures between 303 and 318 K, indicated that exchange broadening was taking place for the protons near the η³-coordination site. It was found that ring slippage occurred at lower temperatures for Mo-Flu and Mo-H₂cpp than for Mo-cpp. This result is in agreement with the order of the Mo–X bond strengths determined using DFT calculations and the calculated activation energies.