Diphosphine ligand chelation and bridging and regiospecific ortho metalation in the reaction of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) with Ir-4(CO)(12): X-ray diffraction structures of Ir-4(CO)(7)(mu-CO)(3)( bpcd), Ir-4(CO)(5)(mu-

摘要

Me3NO 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)(11)Br][Et4N] (2) with bpcd in presence of AgBF4 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 HIr4(CO)(4)(mu-CO)(3)(bpcd)[mu-PhP(C6H4)C=C(PPh2)C(O)CH2C(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 Huckel MO calculations and related diphosphine-substituted cluster compounds prepared by our groups. (C) 2007 Elsevier B.V. All rights reserved.