Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part 26. Dicationic η5-aniline and η6-anisole complexes

Abstract

The preparation and properties of a series of dicationic aniline and substituted aniline complexes [M(C₅Me₅)(p-R¹C₆H₄NR²R³)][PF₆]₂(M = Rh or Ir; R¹= R²= R³= H; R¹= R²= H, R³= Me or Ph; R¹= H, R²= R³= Me; R¹= R²= R³= Me; R¹= Me, R²= R³= H) are described. From the ¹H and ¹³C n.m.r. spectra and the i.r. spectra it is concluded that a 6-imino-1–5-η-cyclohexadienyl form is a significant contributor to the bonding in these complexes and accounts, for example, for the barrier to rotation about the C–N bonds observed in the N-methylaniline and diphenylamine complexes. This was confirmed by the single-crystal X-ray structure of [Rh(C₅Me₅)(PhNHMe)][PF₆]₂ even though disorder and rather large estimated standard deviations preclude very accurate bond-length and bond-angle measurements. The related anisole complexes [M(C₅Me₅)(PhOMe)][PF₆]₂ were also prepared. Their n.m.r. spectra are not characteristic of an η⁵-bonded benzene ring, and it is proposed that the anisole is η⁶-bonded. The rhodium–anisole complex is labile and the anisole is easily displaced by acetone; it is concluded that OMe does not significantly stabilise η⁶-arene binding in these complexes in contrast to methyl which does.