Studies of thallium-iridium bonding

Article abstract of DOI:10.1021/ja00008a030

New examples of complexes with TI-Ir bonds have been prepared and structurally characterized. Treatment of Ph₂PCH₂N{(CH₂)₂O(CH ₂)₂O(CH₂)₂}₂NCH ₂PPh₂, crown-P₂, with Ir(CO)₂Cl(p-toluidine) yields yellow (crown-P₂)Ir(CO)Cl which reacts with thallium(1) nitrate to give yellow-orange crystals of [Tl(crown-P₂)Ir(CO)Cl](NO₃)-CH₂Cl₂. These form in the triclinic space group P1? (No. 2) with a = 11.350 (4) ?, b = 13.519 (4) ?, c = 15.022 (4) ?, α = 97.64 (2)^○, β = 101.20 (3)^○, γ = 93.63 (3)^○ at 130 K with Z = 2. Refinement of 6298 reflections and 243 parameters yielded R = 0.070, R_w = 0.078. The complex consists of a nearly planar Ir(CO)ClP₂ unit and a thallium ion within the aza-crown portion. The Tl-Ir distance is 2.875 (I)?. The presence of the thallium ion perturbs the electronic spectrum of the IrP₂(CO)Cl chromophore. The Tl-Ir complex has absorbance at 400 nm (ε = 17700) and 500 nm (ε = 452) at 23 °C in dichloromethane and strong emission at 580 nm in frozen dichloromethane at 77 K which is not observed when the sample is warmed to 23 °C. This Tl-Ir complex undergoes oxidative addition of iodine or chlorine (from iodobenzene dichloride) to form [ITl(crown-P₂)Ir(CO)ClI]NO₃ or [ClTl(crown-P₂) Ir(CO)Cl₂] (NO₃). These show significant increases in ν(CO) and (Tl,P) that are consistent with oxidation. As a model for the formation of these oxidation products which should have TI-Ir single bonds, the structure of (CH₃CO₂)₂Tl(μ-O₂CCH ₃)Ir(CO)(PPh₃)₂(O₂CCH ₃)-CHCl₃ has been determined. Colorless crystals form in the monoclinic space group P2_1/c (No. 14) with a = 10.815 (3) ?, b = 22.909 (8) ?, c = 21.582 (7) ?, β = 118.63 (2)^○ at 130K with Z = 4. Refinement of 3961 reflections with 296 parameters yielded R = 0.063, R_w = 0.059. The structure has a short Tl-Ir bond (2.611 (1) ?) with an acetate ion bridging the Tl-Ir unit. Two chelating acetate ligands are bound to the thallium while a terminal monodentate acetate is bound to iridium, whose coordination sphere is completed by a terminal carbonyl group and the pair of trans triphenylphosphine ligands. Thus all three common modes of acetate coordination are present in one compound. These structures are compared to that of Ir₂(TlNO₃)(CO)₂Cl₂Gi-Ph ₂PCH₂As(Ph)CH₂PPh₂)₂. The thallium atoms in these complexes show considerable variation in coordination number and angular ligand distribution, while the iridium atoms have rectilinear coordination. The bonding within the Tl-Ir units is discussed.