麻豆视频

A joint research team led by Prof. Sun Zhongming from Nankai University and Prof. Zhao Lili from Nanjing Tech University has achieved a breakthrough in transition metal chemistry. Their research outcome, titled “Synthesis of Triple-Decker Sandwich Compounds Featuring a M–M Bond Through Cyclo-Bi? and Cyclo-Sb?&苍产蝉辫;搁颈苍驳蝉”, was recently published in Nature Chemistry. Using Zintl-phase compounds as Sb/Bi sources, the researchers successfully synthesized Cyclo-Bi? and Cyclo-Sb? rings and achieved the first-ever isolation of Bi?? anions in a one-step reaction at room temperature. They conducted detailed experimental characterization and theoretical calculations, achieving a significant breakthrough in the field of main-group and transition metal coordination chemistry.

Ligands comprising π-aromatic pentagonal rings have been widely employed in transition metal chemistry. Since the discovery of ferrocene, the cyclopentadienyl anion (C?H??), particularly, has been one of the most frequently used ligands. Pn??, a purely inorganic ligand, can be derived by substituting CR groups in the general formula (C?R?)? (where R = H or organic substituents) with isoelectronic Group 15 elements (Pn). Bismuth (Bi), the heaviest pnictogen homolog, has remained elusive and represents a significant synthetic challenge in inorganic synthetic chemistry that persists to date. Lighter pnictogen homologs have been successfully synthesized as such ligands: N?? can be synthesized via C-N bond cleavage of aryl pentazides with m-CPBA and transition metal complexes serving as stabilizing agents (Nature 2017, 549, 78-81); P?? and As?? are typically synthesized through reduction of white phosphorus or yellow arsenic, or alternatively from organic cyclic phosphorus/arsenic compounds. These reactions require elevated temperatures and prolonged reaction times, ultimately yielding stable triple-decker sandwich compounds (Angew. Chem. Int. Ed. 1986, 25, 363-364; J. Am. Chem. Soc. 1982, 104, 4727-4729). The synthesis of Sb?? and Bi?? proves more challenging, as these heavy pnictogen atoms preferentially form clusters rather than multiply-bonded rings. To date, only one Sb?? species has been reported, synthesized from ^tBu?Sb? as the starting material (Angew. Chem. Int. Ed. 2000, 39, 4148-4150) (Figure 1).

Figure 1. Reported triple-decker sandwich compounds and the synthetic route developed in this work

The research team led by Prof. Sun and Prof. Zhao used Zintl-phase compounds as Sb/Bi sources to synthesize cyclo-Sb? and cyclo-Bi? and achieve the first-ever isolated Bi₅^- via a one-step reaction at room temperature. The anionic complexes [CpV(cyclo-Sb?)V-Cp]?? and [CpNb(cyclo-Bi?)Nb-Cp]?? feature pentagonal bipyramidal core structures, where the planar Pn? rings are sandwiched between two transition metals (V or Nb). The unique V–V and Nb–Nb bonds penetrating the Sb?/Bi? centers exert a significant impact on the electronic structure of these clusters and distinguish them from previously reported neutral sandwich compounds (Figure 2).

Figure 2. The structure and mass spectrum of the cluster [CpNb(cyclo-Bi?)NbCp]?? (Isostructural to [CpV(cyclo-Sb?)VCp]??)

Adaptive Natural Density Partitioning (AdNDP) analysis of [V?Cp?Sb?]?? reveals only two 3c-2e bonds in the Sb? ring, in addition to ten 2c-2e V-Sb bonds, five 1c-2e lone pairs, as well as a V-V bond with high occupancy up to 1.93. AdNDP analysis of [Nb?Cp?Bi?]?? reveals bonding patterns analogous to its [V?Cp?Sb?]?? counterpart (Figure 3). 

Figure 3. QTAIM and AdNDP analyses of [V?Cp?Sb?]?? and [Nb?Cp?Bi?]??

To verify the existence of a 2c-2e M–M bond penetrating the E? ring center in the M(cyclo-E?)M core unit, the research team conducted EDA-NOCV calculations on [V?Cp?Sb?]?? and [Nb?Cp?Bi?]??. They used cyclo-Sb?/Bi? and (VCp)?/(NbCp)? as interacting fragments and conducted analyses under varying charge and electronic states. Analysis of the deformation densities and bonding orbitals reveals that ten orbital interactions originate from M-E? cage bond formation, while one distinct orbital interaction is unequivocally associated with M-M bonding, with negligible contribution (ΔE??_b(4) from the E?? ring (?E??_b(4) in [V?Cp?Sb?]?? and ?E??_b(1) in [Nb?Cp?Bi?]??), which nevertheless represents the strongest orbital contribution in these molecules. The Nb–Nb bond formed through the orbital interaction ΔE_orb(1) primarily involves the HOMO-3 and LUMO of the [(NbCp)?]? fragment. The corresponding charge flow eigenvalue (0.074) confirms negligible contribution from the [cyclo-Bi₅]^- unit. This phenomenon is mirrored in the ?E_orb(4) interaction of [V₂Cp₂Sb₅]^2- (Figure 4), conclusively demonstrating that both V–V and Nb–Nb bonds physically penetrate the central cavity of the E₅ rings.

Figure 4. The deformation density (Δρ) and corresponding interfragment orbital interaction associated with the dominant ?Eorb(1) term in [Nb₂Cp₂Bi₅]^2-

Dr. Xu Yuhe from 麻豆视频 and Yang Xing from NTU equally as co-first authors. Corresponding authors include Prof. Sun Zhongming from 麻豆视频, Prof. Zhao Lili from NTU, and Prof. Gernot Frenking from Philipps-Universit?t Marburg, Germany (Adjunct Professor at NTU).

Read the paper at

（Edited and translated by Nankai News Team.)