Ligand substitution reactions in new square-planar iridium, rhodium and platinum complexes containing a potentially terdentate C,N,N′ ligand system; crystal structure of [Ir{C6H4CH2N(Me)CH2CH2NMe2-2-C,N,N′}(cod)](cod = cycloocta-1,5-diene)

Abstract

Transmetallation reactions with the new dimeric compound [LiL]₂[L = C₆H₄CH₂N(Me)CH₂CH₂NMe₂-2] have incorporated the potentially terdentate monoanionic C,N,N′ ligand system L into the new complexes [M^IL(cod)](M = Rh or Ir, cod = cycloocta-1,5-diene) and [Pt^IICl(L)] which have been characterized by ¹H and ¹³C NMR spectroscopy. In solution these complexes are square-planar with L co-ordinated as a C,N bidentate in [ML(cod)] and as a C,N,N′ terdentate in [PtCl(L)]. However, the solid-state molecular structure of [IrL(cod)] shows a C,N,N′ terdentate co-ordination mode of L; the square-pyramidal geometry reflects a situation in the direction of the reaction transition state of a nucleophile (NMe₂) attacking a d⁸ metal centre. Crystals of [IrL(cod)](C₂₀H₃₁IrN₂) are orthorhombic, space group P2₁2₁2₁, with a= 7.956(3), b= 14.090(1), c= 16.484(2)Å, Z= 4, final R= 0.0284 for 2078 reflections with I 2.5σ(I) and 221 parameters. The neutral monodentate ligands CO and PPh₃ replace the bidentate cod ligand in [ML(cod)](M = Rh or Ir) to afford complexes which in solution on the NMR time-scale are fluxional and in which L is either bi- or ter-dentate.