Iridium thioether chemistry: the synthesis and structures of [IrL2][PF6]3 and [IrHL2][PF6]2(L = 1,4,7-trithiacyclononane)

Abstract

Reaction of [{IrCl(C₈H₁₄)₂}₂] with 4 molar equivalents of 1,4,7-trithiacyclononane (L) in water–methanol (2 : 1, v/v) in the presence of HBF₄ affords the iridium(III) hydrido complex [IrHL₂]²⁺. The complex [IrHL₂][PF₆]₂·2MeNO₂ crystallises in the monoclinic space group Cc, a= 19.456 0(17), b= 8.152 5(9), c= 21.935(3)Å, β= 117.008(7)°, and Z= 4. The single-crystal X-ray structure of the complex shows one L ligand bound facially to Ir^III, Ir–S(1)(trans to H) 2.476(5), Ir–S(4) 2.298(5), Ir–S(7) 2.321(5)Å, with the second L bound as a bidentate ligand through only two S donors, Ir–S(11) 2.344(5), Ir–S(41) 2.319(5)Å; the dangling donor S(71) lies 4.329(6)Å from the iridium centre. The sixth co-ordination site is taken up by a hydride, Ir–H 1.58(6)Å. Treatment of [IrHL₂][PF₆]₂ with aqueous HNO₃ affords the homoleptic thioether complex [IrL₂]³⁺. The complex [IrL₂][PF₆]₃·5MeNO₂ crystallises in the monoclinic space group C2/c, a= 8.581 7(13), b= 21.338(4), c= 23.482(7)Å, β= 90.94(2)°, and Z= 4. The single-crystal X-ray structure of the complex confirms homoleptic hexathia co-ordination at a centrosymmetric, octahedral iridium(III) centre, Ir–S(1) 2.342(3), Ir–S(4) 2.341(3), Ir–S(7) 2.338(3)Å. The redox properties of [IrL₂]³⁺ are discussed and compared to those of the rhodium(III) analogue [RhL₂]³⁺. Spectroelectrochemical measurements using a u. v. –visible optically transparent electrode system confirm the isosbestic and reversible interconversion of [RhL₂]³⁺, [RhL₂]²⁺, and [RhL₂]⁺.