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.

将九羰基三(μ₃-铋)合三铱（Ir₃(CO)₉(μ₃-Bi)）与三苯基氢化锗（Ph₃GeH）反应，得到化合物Ir₃(CO)₆(GePh₃)₃(μ₃-Bi)(μ-H)₃（记为1）。将化合物1在己烷中加热回流，其经脱除3当量苯的过程，转化为含有三个桥连GePh₂配体的化合物Ir₃(CO)₆(μ-GePh₂)₃(μ₃-Bi)（记为2）。将九羰基三(μ₃-铋)合三铱与三苯基氢化锡（Ph₃SnH）反应，分别得到化合物Ir₃(CO)₆(SnPh₃)₃(μ₃-Bi)(μ-H)₃（记为3）与Ir₃(CO)₆(μ-SnPh₂)₃(μ₃-Bi)（记为4）。
化合物1~4均经X射线单晶衍射表征。化合物1和3均在三个铱原子各自的赤道配位位点上各连有一个端基配位的EPh₃（E=Ge、Sn）配体，总计三个端基配体。在溶液中，化合物1和3均以两种异构体形式存在，其中主要异构体的结构与固态下的结构一致。两种异构体可通过三脚架形三角扭转重排机理在核磁共振（NMR）时间尺度下快速互变：对于化合物1，活化焓ΔH⧧=66.6 kJ/mol，活化熵ΔS⧧=1.58 J/(K·mol)；对于化合物3，ΔH⧧=65.6 kJ/mol，ΔS⧧=-1.4 J/(K·mol)。
通过ADF密度泛函理论（DFT）计算，对化合物2的分子轨道及紫外-可见（UV–vis）光谱进行了分析与计算。该配合物的可见光谱主要由三铱核中Ir–Bi成键轨道——最高占据分子轨道-3（HOMO-3）与最高占据分子轨道-4（HOMO-4）——向Ir–Ir反键轨道（最低未占据分子轨道（LUMO））的电子跃迁主导。