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Diphosphine ligand chelation and bridging and regiospecific ortho metalation in the reaction of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) with Ir4(CO)12: X-ray diffraction structures of Ir4(CO)7(μ-CO)3(bpcd), Ir4(CO)5(μ-CO)3(bpcd)(μ-bpcd), and HIr4(CO)4(μ-CO)3(bpcd)[μ-PhP(C6H4)C[dbnd]C(PPh2)C(O)CH2C(O)]

Authors
Journal
Journal of Organometallic Chemistry
0022-328X
Publisher
Elsevier
Publication Date
Volume
693
Identifiers
DOI: 10.1016/j.jorganchem.2007.07.016
Keywords
  • Iridium Clusters
  • Ligand Substitution
  • Diphosphine Ligands
  • C–H Bond Activation
  • Regioselective Ortho Metalation
Disciplines
  • Chemistry

Abstract

Abstract Me 3NO activation of the tetrairidium cluster Ir 4(CO) 12 ( 1) in presence of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the bpcd-substituted clusters Ir 4(CO) 10(bpcd) ( 3) and Ir 4(CO) 8(bpcd) 2 ( 4) as the minor and major products, respectively. Cluster 3 has been isolated as the sole observable product from the reaction of [Ir 4(CO) 11Br][Et 4N] ( 2) with bpcd in presence of AgBF 4 at room temperature. Both 3 and 4 have been isolated and fully characterized in solution by spectroscopic methods. The solid-state structure of 3 reveals that the ancillary bpcd ligand is bound to a single iridium center, with chelating and bridging bpcd ligands found in the X-ray structure of cluster 4. Cluster 4 is unstable at room temperature and slowly loses CO to afford the hydride-bridged cluster HIr 4(CO) 4(μ-CO) 3(bpcd)[μ-PhP(C 6H 4)C C(PPh 2)C(O)CH 2C(O)] ( 5). Cluster 5 has been fully characterized in solution by IR and NMR spectroscopies, and the C–H bond activation attendant in the ortho metalation step is shown to occur regioselectively at one of the aryl groups associated with the bridging bpcd ligand. The redox properties of clusters 3– 5 have been explored and the electrochemical behavior discussed with respect to extended Hückel MO calculations and related diphosphine-substituted cluster compounds prepared by our groups.

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