Four- and five-co-ordinate nitrosyl complexes of iridium(I)

Abstract

[IrCl{(NO)(PPh₃)₂]⁺, the nitrosyl analogue of IrCl(CO)(PPh₃)₂ has been prepared by chlorination of [Ir(NO)₂-(PPh₃)₂]⁺ or by reaction of IrHCl(NO)(PPh₃)₂ with non-co-ordinating acids. Five-co-ordinate addition products are formed with the neutral ligands CO, PPh₃, Ph₂PCH₂CH₂PPh₂, Ph₂PCHCHPPh₂, and P(OPh)₃ while the co-ordinating anions (X^–), NO₂^–, Cl^– and HS^–, form IrX₂(NO)(PPh₃)₂. Hydrolysis of [IrCl(NO)(PPh₃)₂]⁺ produces [Ir(OH)(NO)(PPh₃)₂]⁺ and this same hydroxo-cation, together with triphenylphosphine oxide, results from the reaction of [IrH(NQ)(PPh₃)₂]⁺ with dioxygen. [Ir(OH)(NO)(PPh₃)₂]⁺ forms [Ir(OR)(NO)(PPh₃)₂]⁺ in alcohols, (R = Et or Prⁿ) and these cations are returned to [IrH(NO)(PPh₃)₃]⁺ by the action of hydrogen in the presence of triphenylphosphine. Another member of this four-co-ordinate, d⁸, nitrosyl cation series, [Ir(CH₉)(NO)(PPh₃)₂]⁺, was prepared from Ir(CH₄)I(NO)(PPh₃)₂ by reaction with silver ions. The tendency towards five-co-ordination within the series is compared.