Formation and crystal structure of MeIr(CO)(PPh₃)₂(MeCO₂CHCHCO₂Me). Comparison of the structures of analogous alkene and alkyne complexes

The complex MeIr(CO)(PPh₃)₂(MeCO₂CHCHCO₂Me), synthesized from trans-MeIr(CO)(PPh₃)₂ and dimethyl maleate, crystallizes in the centrosymmetric monoclinic space group P2/n with a 13.997(5), b 17.878(5), c 15.709(4) Å, β 91.00(2)°, V 3930(2) ų and Z = 4. X-ray data (Mo-K_α, 2θ 4.5-45.0°) were collected with a Syntex P2₁ automated four-circle diffractometer; the structure was solved and converged with R 5.5% for all 5069 unique reflections and R 4.3% for those 4343 data with |F_o| > 3σ(|F_o|). The iridium(I) center has a distorted trigonal bipyramidal geometry with the Me and CO ligands occupying axial sites (Ir-Me(1) 2.159(8), IrCO 1.907(8) Å. The MeCO₂CHCHCO₂Me ligand is bonded in η² fashion to the iridium, with its coordinated double bond parallel to the equatorial plane. Bonds to the equatorial ligands are IrP(1) 2.344(2), Ir-P(2) 2.376(2) and Ir-(center of olefin) 2.017 Å. The observed ligand configuration is different from that for MeIr(CO)(PPh₃)₂(MeCO₂CCCO₂Me) which has axial Me and PPh₃ ligands in its thermodynamically stable isomer.