Dipartimento di Chimica e Chimica Industriale dell'Università di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy.
Inorg Chem. 2013 Apr 15;52(8):4635-47. doi: 10.1021/ic400251y. Epub 2013 Mar 28.
This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBu(t)2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e(-). The new species were obtained by an apparent bielectronic oxidation of the 44e(-) monohalides Pt3(μ-PBu(t)2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e(-) analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBu(t)2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e(-) intermediate Pt3(μ-PBu(t)2)3(CO)2I was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(μ-PBu(t)2)3I3, the transient 44e(-) species Pt3(μ-PBu(t)2)3(CO)3 is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e(-) intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e(-) associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e(-) phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.
本文介绍了前所未有的三膦桥联化合物 Pt3(μ-PBu(t)2)3X3(X = Cl, Br, I)的合成和结构特征，这些化合物具有仅 42 个价电子，而迄今为止类似的配合物通常具有 44e(-)。这些新物种是通过对 44e(-)单卤化物 Pt3(μ-PBu(t)2)3(CO)2X 与相应的二卤化物 X2 的明显双电子氧化获得的。它们的 X 射线结构接近 D3h 对称，与具有三个末端羰基配体的 44e(-)类似物相似。在存在相应卤化物的情况下，通过电化学氧化相同的单卤化物也可获得这些产物。在对 Pt3(μ-PBu(t)2)3I3 形成的详细研究中，氧化还原电位表明 I2 只能进行第一次单电子氧化，但不适合第二次氧化。因此，确定 43e(-)中间体Pt3(μ-PBu(t)2)3(CO)2I发挥了关键作用。另一个信息是，与完全氧化产物 Pt3(μ-PBu(t)2)3I3 一起，在反应的早期步骤中形成瞬态 44e(-)物种Pt3(μ-PBu(t)2)3(CO)3。为了提取涉及末端配体取代和电子转移过程的形成途径的详细信息，进行了 DFT 研究，并定义了所有可能的中间体及其相关的能量成本。该概况突出了许多重要方面，例如形成具有不同末端配位体的适当的 43e(-)中间体对，以及转移一个电子的合适氧化还原电位。在配体取代反应中优化 45e(-)缔合中间体表明它们可能参与氧化还原过程，降低了整体能量成本。最后，根据 MO 论证，膦桥联 Pt3 簇的独特稳定性可以归因于同时存在三个末端卤化物。
