The first example of a formal scandium(I) complex: Synthesis and molecular structure of a 22-electron scandium triple decker incorporating the novel 1,3,5-triphosphabenzene ring
The first example of a formal scandium(I) complex: Synthesis and molecular structure of a 22-electron scandium triple decker incorporating the novel 1,3,5-triphosphabenzene ring
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DOI：
10.1021/ja961253o
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发表时间：
1996-08-14
影响因子：
15
通讯作者：
Nixon, JF
中科院分区：
文献类型：
--
作者：
Arnold, PL;Cloke, FGN;Nixon, JF
多年来，人们对2，2-二甲基丙叉基膦（tBuCP）的三聚反应形成三磷杂苯表现出相当大的兴趣。虽然自由环被计算为化学稳定的，但之前对金属中心上三聚化的少数观察结果导致三聚体以杜瓦-苯形式结合，迄今为止还没有η6-金属结合络合物的结构特征。1最近，宾格等人2报道了由于从[Hf {1，4-（SiMe 3）2COT}（（tBuCP）3）]中消除三个磷杂炔单元而分离出游离环。Zenneck等人已经探索了tBuCP在[Fe（η-PhMe）（C2 H2）2]（通过金属蒸气合成制备）上的环低聚反应，并且通过tBuCP与末端乙炔的共环化形成了连接的1，3二磷杂苯环。3我们一直在探索tBuCP通过与金属原子直接共缩合的环低聚反应，这导致分离出诸如[（V（η5-P3 C2 tBu 2）（η5-P2 C3 tBu 3）]，4 [Mo（η4-P2 C2 tBu 2）3]，5和[Ni（η5-P3 C2 tBu 2）（η3-PC 2 tBu 2）]的配合物。[6]在这篇文章中，我们报道了一种三重德克尔配合物的合成，它代表了第一种钪（I）配合物，并结合了一个类似的独特的、结构上具有特征的1，3，5-三磷杂苯环。电子束蒸发的钪与过量的tBuCP在77 K下共缩合得到森林绿色配合物[{η5-P3 C2 tBu 2）Sc} 2（μ-η6：η6-P3 C3 tBu 3）]，1，后处理后产率为5-10%（基于钪）。[7] 1的分子结构已通过X射线晶体学测定，并在图1中描述。(The化合物与一分子戊烷结晶，为清楚起见省略。8三重德克尔结构中的中心2，4，6-三叔丁基-1，3，5-三磷杂苯环位于晶体学镜像平面上，并且是平面的，环PC键长没有显著变化，表明结合为μ，η6：与游离配体9相比，1中的环显示PC环键延长0.064-0.089 π，PCP角扩大4.3-4.4。由于几乎完全缺乏相关的类似物，进一步的比较是困难的，尽管我们注意到1中的金属-“芳烃”环的质心距离为1.787（5）π，比[Sc（η-C6 tBu 3 MeH 2）2]（1.983 π）短得多。[10]这可能部分反映了形式氧化态的差异{分别为（I）和（0）}，但也可能归因于含磷环系的较大尺寸和较强的结合，如在[V（η6-PC 5 H5）2]与[V（η6-C6 H6）2]中观察到的那样。11外部3，5-二叔丁基-1，2，4-三磷环戊二烯基环显示出与含有该配体的简单金属茂中发现的结构特征基本相似的结构特征，例如。G. [(V（η5-P3C2-tBu2）（η5-P2C3 tBu3）] 4和[Ni（η5-P3C2 tBu2）（η3-PC2 tBu2）]。[6] P3 C2环的质心距离为2.338（6）π in 1，然而，与β烯的质心距离相比，这是不寻常的长（参见。[（V（η5-P3C2 tBu2）（η5-P2C3 tBu3）] 4）。配合物1对空气非常敏感，可溶于戊烷和其他非极性溶剂;它在250 ℃和10-5毫巴下升华，分解最小。该化合物显示出随温度变化的顺磁性，在295 K时溶液磁矩（通过NMR方法测定）为3.98 µB，随温度单调下降，在208 K时为3.69 µB。这些值显然比仅自旋公式（4.47 µB）预测的四个未成对电子的值要低，温度依赖性表明基态或激发态.
For a number of years considerable interest has been shown in the trimerization of 2, 2-dimethylpropylidynephosphine (tBuCP) to form a triphosphabenzene. Although the free ring is calculated to be thermodynamically stable, the few previous observations of trimerization on a metal center have resulted in the trimer binding as a Dewar-benzene form, and no η6-metal bound complex has been structurally characterized to date. 1 Very recently, Binger et al. 2 have reported isolation of the free ring as a result of elimination of three phosphaalkyne units from [Hf {1, 4-(SiMe3) 2COT}((tBuCP) 3)]. Cyclooligomerization reactions of tBuCP on [Fe (η-PhMe)(C2H2) 2](prepared by metal vapor synthesis) have been explored by Zenneck et al. and have led to the ligated 1, 3 diphosphabenzene ring formed by cocyclization of tBuCP with terminal acetylenes. 3 We have been exploring the cyclooligomerization reactions of tBuCP Via direct cocondensation with metal atoms, which result in the isolation of complexes such as [(V (η5-P3C2 tBu2)(η5-P2C3 tBu3)], 4 [Mo (η4-P2C2 tBu2) 3], 5 and [Ni (η5-P3C2 tBu2)(η3-PC2 tBu2)]. 6 In this communication we report the synthesis of a triple decker complex which represents the first scandium (I) complex and incorporates a similarly unique, structurally characterized example of a ligated 1, 3, 5-triphosphabenzene ring. Cocondensation of electron beam vaporized scandium with an excess of tBuCP at 77 K affords the forest-green complex [{η5-P3C2 tBu2) Sc} 2 (µ-η6: η6-P3C3 tBu3)], 1, in 5-10% yield (based on scandium) after workup. 7 The molecular structure of 1 has been determined by X-ray crystallography and is depicted in Figure 1.(The compound crystallizes with one molecule of pentane, omitted for clarity.) 8 The central 2, 4, 6-tri-tert-butyl-1, 3, 5-triphosphabenzene ring in the triple decker structure lies on a crystallographic mirror plane and is planar with no significant variation in ring PC bond lengths, indicative of binding as a µ, η6: η6 aromatic ligand.In comparison to the free ligand, 9 the ring in 1 shows lengthening of the PC ring bonds by 0.064-0.089 Å and an expansion of the PCP angles by 4.3-4.4. Further comparisons are difficult due to the almost complete lack of related analogues, although we note that the metal-“arene” ring centroid distance of 1.787 (5) Å in 1 is considerably shorter than that in [Sc (η-C6 tBu3MeH2) 2](1.983 Å). 10 This is presumably partially a reflection of the formal oxidation state difference {(I) and (0), respectively}, but may also be attributed to the larger size and stronger binding of the phosphorus-containing ring system, as has been observed in [V (η6-PC5H5) 2] Vs [V (η6-C6H6) 2]. 11 The outer 3, 5-di-tert-butyl-1, 2, 4-triphosphacyclopentadienyl rings display structural features essentially analogous to those found in simple metallocenes containing this ligand, e. g.[(V (η5-P3C2-tBu2)(η5-P2C3 tBu3)] 4 and [Ni (η5-P3C2 tBu2)(η3-PC2 tBu2)]. 6 The P3C2-ring centroid distance of 2.338 (6) Å in 1, however, is unusually long compared with those in the metallocenes (cf. 1.972 Å in [(V (η5-P3C2 tBu2)(η5-P2C3 tBu3)] 4). Complex 1 is very air sensitive and soluble in pentane and other nonpolar solvents; it sublimes at 250 C at 10-5 mbar with minimal decomposition. The compound displays temperature dependent paramagnetism with a solution magnetic moment (determined by the NMR method) of 3.98 µB at 295 K, which decreases monotonically with temperature to a value of 3.69 µB at 208 K. These values are clearly somewhat lower than the value predicted for four unpaired electrons by the spin only formula (4.47 µB), and the temperature dependence suggests either ground or excited state …