Formation of Carboalkoxyiridium Complexes by Carbonylation of Alkoxylridium Complexes and the Crystal Structure of trans-PhOIr(CO)(PPh₃)₂

The preparation of iridium alkoxide complexes trans-ROIr(CO)(PPh₃)₂and their carbonylation to carboalkoxy complexes ROC(O)Ir(CO)₂(PPh₃)₂are described for R = Me, n-Pr, t-Bu, and Ph. The preparations involve metathetical reactions between trans-Ir(CO)(PPh₃)₂Cl and NaOR. In the carbonylation an intermediate can be identified by infrared and conductivity studies as [Ir(CO)₃(PPh₃)₂⁺][OR^-]. Thus a mechanism involving alkoxide displacement by CO and subsequent nucleophilic attack of alkoxide on a CO of the cation is indicated. The complex trans-PhOIr(CO)(PPh₃)₂crystallizes in the centrosymmetric monoclinic space group P2₁/c (no. 14) with a = 15.790 (3) Å, b = 11.461 (3), c = 19.986 (5) Å, β= 100.326 (18)°, V = 3558 (2) ų, and Z = 4. Diffraction data (Mo Kα, 2θ= 5-55°) were collected with a Syntex P2₁automated four-circle diffractometer, and the structure was solved and refined to R_F = 6.2% and R_wF= 4.6% for all 8220 reflections (R_F= 3.8% and R_wF= 4.1% for those 5981 reflections with |F₀| > 6σ(|F₀|)). The iridium atom has the expected square-planar geometry with Ir-P(1) = 2.328 (1) Å, Ir-P(2) = 2.344 (1) Å, Ir-CO = 1.795 (5) Å, and Ir-OPh = 2.049 (4) Å. The phenoxide ligand is “bent” with (Ir-O-C(ipso) = 126.5 (3)°.