Research on metal–metal bonds involving f-block actinides, such as thorium, lags far behind the well-studied metal–metal bonds of d-block transition metals. The complexes with Th–TM bonds are extremely rare; all previously identified examples have only a single Th–TM bond with the Th center at an invariably +IV oxidation state. Herein, we report a series of Th₂Pd_n (n = 2, 3, and 6) clusters (complexes 3, 4, and 7) with multiple Th(III)–Pd bonds. Theoretical studies reveal that the Th₂Pd_n unit allows electronic delocalization and σ aromaticity, leading to unexpected closed-shell singlet structures for these Th(III) species. This electronic delocalization is evident in the highest occupied molecular orbital of Th(III) complexes and facilitates a 2e reduction of alkyne by complex 7, resulting in the formation of 8. Complexes 7 and 8 are distinctive in featuring a Th₂Pd₆ core with six and eight Th–Pd bonds, respectively, making them the largest known d–f heterometallic clusters exhibiting metal–metal bonding.

中文翻译：

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具有多重钍-钯键的异金属簇中的电子离域和σ-芳香性

对 f 区锕系元素（例如钍）的金属-金属键的研究远远落后于对 d 区过渡金属的金属-金属键的充分研究。具有Th-TM键的配合物极为罕见；所有先前确定的例子都只有一个Th-TM键，Th中心始终处于+IV氧化态。在此，我们报道了一系列具有多个 Th(III)-Pd 键的 Th ₂ Pd _n ( n = 2、3 和 6) 簇（配合物3、4和7 ）。理论研究表明，Th ₂ Pd _n单元允许电子离域和 σ 芳香性，从而导致这些 Th(III) 物质产生意想不到的闭壳单线态结构。这种电子离域在 Th(III) 配合物的最高占据分子轨道中很明显，并促进配合物7对炔烃进行 2e 还原，从而形成8。配合物7和8 的独特之处在于分别具有 6 个和 8 个 Th-Pd 键的 Th ₂ Pd ₆核，使它们成为已知最大的具有金属-金属键合的 d-f 异金属簇。