Synthesis and Characterizations of Bismuth-Bridged Triiridium Carbonyl Complexes Containing Germyl/Germylene and Stannyl/Stannylene Ligands

The reaction of Ir-3(CO)(9)(mu(3)-Bi) with Ph3GeH yielded the compound Ir-3(CO)(6)(GePh3)(3)(mu(3)-Bi)(mu-H)(3) (1). When 1 was heated to reflux in hexane, it was transformed into the compound Ir-3(CO)(6)(mu-GePh2)(3)(mu(3)-Bi) (2), which contains three bridging GePh2 ligands by loss of 3 equiv of benzene. The reaction of Ir-3(CO)(9)(mu(3)-Bi) with Ph3SnH yielded the compounds Ir-3(CO)(6)(SnPh3)(3)(mu(3)-Bi)(mu-H)(3) (3) and Ir-3(CO)(6)(mu-SnPh2)(3)(mu(3)-Bi) (4), respectively. Compounds 1-4 were characterized crystallographically. Compounds 1 and 3 each have three terminally coordinated EPh3 (E = Ge, Sn) ligands in equatorial coordination sites, one on each of the iridium atoms. In solution compounds 1 and 3 exist as two isomers. The major isomer has the structure found in the solid state. The two isomers interconvert rapidly on the NMR time scale by tripodal, trigonal-twist rearrangement mechanisms: for 1, Delta H-double dagger = 66.6 kJ/mol and Delta S-double dagger = 1.58 J/(K mol), and for 3, Delta H-double dagger = 65.6 kJ/mol and Delta S-double dagger = -1.4 J/(K mol). The molecular orbitals and UV-vis spectra of 2 were calculated and analyzed by ADF DFT computational treatments. The visible spectrum is dominated by transitions from the Ir-Bi bonding orbitals HOMO-3 and HOMO-4 to an Ir-Ir antibonding orbital, the LUMO, in the Ir-3 core of the complex.