Syntheses and molecular structures of 18/16-electron half-sandwich iridium(III) complexes with chelating anilido-imine ligands

A 18-electron complex Cp^∗IrClo-C₆H₄N(C₆H₃-Me-p) (CHNC₆H₃-Me-p)] (Cp^∗ = η⁵-pentamethylcyclopentadienyl) (1a) was obtained by the reaction of the lithium salt of o-C₆H₄N (C₆H₃-Me-p)(CHNHC₆H₃-Me-p) (L₁) with Cp^∗IrCl(μ-Cl)]₂ in toluene. However, when bulkier ligands (L₂ = o-C₆H₄N(C₆H₃-Me-p)(CHNHC₆H₃-i-Me₂-2,6), L₃ = o-C₆H₄N(C₆H₃-Me-p) (CHNHC₆H₃-i-Pr₂-2,6)) were employed in the same reaction, two 16-electron complexes {Cp^∗Iro-C₆H₄N(C₆H₃-Me-p)(CHNC₆H₃-i-Me₂-2,6)]}⁺Cl⁻ (2b) and {Cp^∗Iro-C₆H₄N(C₆H₃-Me-p)(CHNC₆H₃-i-Pr₂-2,6)]}⁺Cl⁻ (3b) were formed. A 16-electron complex {Cp^∗Ir o-C₆H₄N(C₆H₃-Me-p) (CHNC₆H₃-Me-p)]}⁺SO₃ CF⁻₃ (1b) bearing L₁ could be achieved by the reaction of 1a with AgSO₃CF₃ in CH₃CN solution. The molecular structures of 1a and 2b were determined by X-ray crystallography. Theoretical calculations of all the 18/16-electron species were performed to study their bonding characters and electronic properties. Electron donating effect of Cp^∗ and steric effect of anilido-imine ligand were considered as major factors in the formation of coordinative unsaturated complexes 1b, 2b, 3b.