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

The reaction of Ir3(CO)9(μ3-Bi) with Ph3GeH yielded the compound Ir3(CO)6(GePh3)3(μ3-Bi)­(μ-H)3 (1). When 1 was heated to reflux in hexane, it was transformed into the compound Ir3(CO)6(μ-GePh2)3(μ3-Bi) (2), which contains three bridging GePh2 ligands by loss of 3 equiv of benzene. The reaction of Ir3(CO)9(μ3-Bi) with Ph3SnH yielded the compounds Ir3(CO)6(SnPh3)3(μ3-Bi)­(μ-H)3 (3) and Ir3(CO)6(μ-SnPh2)3(μ3-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, ΔH⧧ = 66.6 kJ/mol and ΔS⧧ = 1.58 J/(K mol), and for 3, ΔH⧧ = 65.6 kJ/mol and ΔS⧧ = −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 Ir3 core of the complex.