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首页> 外文期刊>Chemistry: A European journal >Structure and bonding in stannadiphospholes and their dianions SnC _2P_2R_2~m (R=H, tBu m=0, -2): A comparative study with C_5H_5~+ and C _5H_5~- analogues
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Structure and bonding in stannadiphospholes and their dianions SnC _2P_2R_2~m (R=H, tBu m=0, -2): A comparative study with C_5H_5~+ and C _5H_5~- analogues

机译：锡萘二酚及其二价阴离子SnC _2P_2R_2〜m（R = H，tBu m = 0，-2）的结构和键合：与C_5H_5〜+和C _5H_5〜-类似物的比较研究

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The potential energy surfaces of both neutral and dianionic SnC _2P_2R_2 (R=H, tBu) ring systems have been explored at the B3PW91/LANL2DZ (Sn) and 6-311+G* (other atoms) level. In the neutral isomers the global minimum is a nido structure in which a 1,2-diphosphocyclobutadiene ring (1,2-DPCB) is capped by the Sn. Interestingly, the structure established by X-ray diffraction analysis, for R=tBu, is a 1,3-DPCB ring capped by Sn and it is 2.4 kcal mol-1 higher in energy than the 1,2-DPCB ring isomer. This is possibly related to the kinetic stability of the 1,3-DPCB ring, which might originate from the synthetic precursor ZrCp_2tBu_2C_2P_2. In the case of the dianionic isomers we observe only a 6φ-electron aromatic structure as the global minimum, similarly to the cases of our previously reported results with other types of heterodiphospholes.1, 4, 19 The existence of large numbers of cluster-type isomers in neutral and 6φ-planar structures in the dianions SnC_2P_2R_2~(2-) (R=H, tBu) is due to 3D aromaticity in neutral clusters and to 2D φ aromaticity of the dianionic rings. Relative energies of positional isomers mainly depend on: 1) the valency and coordination number of the Sn centre, 2) individual bond strengths, and 3) the steric effect of tBu groups. A comparison of neutral stannadiphospholes with other structurally related C_5H_5~+ analogues indicates that Sn might be a better isolobal analogue to P~+ than to BH or CH~+. The variation in global minima in these C _5H_5~+ analogues is due to characteristic features such as 1) the different valencies of C, B, P and Sn, 2) the electron deficiency of B, 3) weaker pφ-pφ bonding by P and Sn atoms, and 4) the tendency of electropositive elements to donate electrons to nido clusters. Unlike the C_5H_5~+ systems, all C _5H_5~- analogues have 6φ-planar aromatic structures as global minima. The differences in the relative ordering of the positional isomers and ligating properties are significant and depend on 1) the nature of the φ orbitals involved, and 2) effective overlap of orbitals.
机译：已经在B3PW91 / LANL2DZ（Sn）和6-311 + G *（其他原子）能级下探索了中性和双阴离子SnC _2P_2R_2（R = H，tBu）环系统的势能面。在中性异构体中，全局最小值是一个Nido结构，其中1,2-二磷酸环丁二烯环（1,2-DPCB）被Sn覆盖。有趣的是，对于R = tBu，通过X射线衍射分析建立的结构是被Sn覆盖的1,3-DPCB环，其能量比1,2-DPCB环异构体高2.4 kcal mol-1。这可能与1,3-DPCB环的动力学稳定性有关，它可能源自合成前体ZrCp_2tBu_2C_2P_2。在二价阴离子异构体的情况下，我们仅观察到6φ-电子芳族结构为整体最小值，这与我们先前报道的与其他类型的杂二磷化合物的结果类似。1、4、19存在大量簇型阴离子SnC_2P_2R_2〜（2-）（R = H，tBu）中的中性和6φ平面结构的异构体是由于中性簇中的3D芳香性和双阴离子环的2Dφ芳香性所致。位置异构体的相对能量主要取决于：1）Sn中心的化合价和配位数; 2）各个键的强度; 3）tBu基的空间效应。将中性锡烷基二膦与其他与结构相关的C_5H_5〜+类似物进行比较，结果表明，Sn可能是P〜+的等值线比BH或CH〜+的等值线。这些C _5H_5〜+类似物的全局最小值变化是由于以下特征：1）C，B，P和Sn的化合价不同; 2）B的电子缺乏; 3）P弱的pφ-pφ键和Sn原子，以及4）正极性元素将电子提供给Nido团簇的趋势。与C_5H_5〜+系统不同，所有C _5H_5〜-类似物均具有6φ平面的芳香结构作为全局最小值。位置异构体的相对顺序和连接性质的差异是显着的，并且取决于1）所涉及的φ轨道的性质，以及2）轨道的有效重叠。

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