Crystal structures of the (η2:η2-cyclo­octa-1,5-diene)(η6-toluene)­iridium(I) cation and μ-chlorido-iridium(III) complexes of 2-(phosphinito)- and 2-(phosphinometh­yl)anthra­quinone ligands

Abstract

Phosphinito and phosphinomethyl ligands incorporating an anthra­quinone moiety were reacted with bis­(cyclo­octa-1,5-diene)diiridium(I) dichloride to afford novel diiridium species. Intended as pincer-type tridentate ligands, bidentate binding modes were determined by X-ray crystallography. The anionic μ-tri­chlorido phosphinito complex formed is charged-balanced by one [Ir(toluene)(cyclo­octa-1,5-diene)]⁺ per asymmetric unit, the structure of which has not previously been reported despite a long history of use as an Ir^I source in organometallic chemistry.

When reacted in dry, degassed toluene, [Ir(COD)Cl]₂ (COD = cyclo­octa-1,5-diene) and 2 equivalents of 2-(di-tert-butyl­phosphinito)anthra­quinone (^tBuPOAQH) were found to form a unique tri-iridium compound consisting of one monoanionic dinuclear tri-μ-chlorido complex bearing one bidentate ^tBuPOAQ ligand per iridium, which was charge-balanced by an outer sphere [Ir(toluene)(COD)]⁺ ion, the structure of which has not previously been reported. This product, which is a toluene solvate, namely, (η²:η²-cyclo­octa-1,5-diene)(η⁶-toluene)­iridium(I) tri-μ-chlorido-bis­({3-[(di-tert-butyl­phosphan­yl)­oxy]-9,10-dioxoanthracen-2-yl}hydridoiridium(III)) toluene monosolvate, [Ir(C₇H₈)(C₈H₁₂)][Ir₂H₂(C₂₂H₂₄O₃P)₂Cl₃]·C₇H₈ or [Ir(toluene)(COD)][Ir(κ-P,C-^tBuPOAQ)(H)]₂(μ-Cl)₃]·toluene, formed as small orange platelets at room temperature, crystallizing in the triclinic space group P

. The cation and anion are linked via weak C—H⋯O inter­actions. The stronger inter­molecular attractions are likely the offset parallel π–π inter­actions, which occur between the toluene ligands of pairs of inverted cations and between pairs of inverted anthra­quinone moieties, the latter of which are capped by toluene solvate mol­ecules, making for π-stacks of four mol­ecules each. The related ligand, 2-(di-tert-butyl­phosphinometh­yl)-anthra­quinone (^tBuPCAQH), did not form crystals suitable for X-ray diffraction under analogous reaction conditions. However, when the reaction was conducted in chloro­form, yellow needles readily formed following addition of 1 atm of carbon monoxide. Diffraction studies revealed a neutral, dinuclear, di-μ-chlorido complex, di-μ-chlorido-bis­(carbon­yl{3-[(di-tert-butyl­phosphan­yl)­oxy]-9,10-dioxoanthracen-2-yl}hydridoiridium(I)), [Ir₂H₂(C₂₃H₂₆O₂P)₂Cl₂(CO)₂] or [Ir(κ-P,C-^tBuPCAQ)(H)(CO)(μ-Cl)]₂, Ir₂C₄₈H₅₄Cl₂O₆P₂, again crystallizing in space group P

. Offset parallel π–π inter­actions between anthra­quinone groups of adjacent mol­ecules link the mol­ecules in one dimension.