Ligand substitution processes in tetranuclear carbonyl clusters. 4. Molecular structure and reactivity of octacarbonyltetrakis(trimethylphosphine)tetrairidium
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The structure of Ir4(CO)8[PMe3]4 has been determined by a single-crystal X-ray investigation. The structure consists of a slightly distorted tetrahedron of iridium atoms containing three symmetrical edge-bridging CO ligands along one triangular face and each metal atom bearing a trimethylphosphine ligand. The geometry of phosphines about the tetranuclear metal centers is one apical, two axial, and one equatorial. The complex crystallizes in the monoclinic space group P21/n with a = 12.114 (4) Å, b = 12.469 (5) Å, c = 22.056 (5) Å, β = 98.91 (2)°, V= 3291 (2) Å3, Z = 4, and p(calcd) = 2.62 g cm-3. Diffraction data (2θ out to 55°) were collected with a four-circle autodiffractometer using Mo Kα radiation. The structure was refined by using the full-matrix least-squares procedure, and the resulting discrepancy indices were R1 = 0.058 and R2 = 0.074 for 5043 independent reflections. Important bond distance parameters are as follows: Ir-Ir (apical-basal) = 2.737 (1, 2, 2, 3) Å, Ir-Ir (basal-basal) = 2.720 (1, 5, 5, 2) Å and 2.794 (1) Å (where the longer bond involves the iridium atoms with axial PMe3 ligands), and Ir-P = 2.312 (6, 14, 23, 4) Å.1 The reaction of Ir4(CO)8[PMe3]4 with CO to afford Ir4(CO)9[PMe3]3 was found to occur via a dissociative process and at a rate 3300 times slower than that for the analogous process involving the sterically more demanding PEt3 ligand. © 1981, American Chemical Society. All rights reserved.
author list (cited authors)
Darensbourg, D. J., & Baldwin-Zuschke, B. J.