Synthesis, Structure, and Reactivity of a Monomeric Iminoalane
Synthesis, Structure, and Reactivity of a Monomeric Iminoalane
复制标题
单体亚氨基丙烷的合成、结构和反应性
DOI：
10.1002/chem.201203298
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发表时间：
2012-11-01
影响因子：
4.3
通讯作者：
Cui, Chunming
中科院分区：
文献类型：
--
作者：
Li, Jianfeng;Li, Xiaofei;Cui, Chunming
重13族亚氨基金属烷（RMNR）n（M= Al，Ga，In）由于其丰富的结构特征和在M-N二元材料中的应用而成为众多研究的对象。[1]由于其高度极化的M-N键，它们很容易形成环状二聚体和三聚体，以及具有三维M-N骨架的簇合物，这取决于金属中心上有机取代基的空间位阻。[2]Power研究小组最近的研究表明，单体镓和铟亚氨基金属烷可以通过使用非常庞大的三联苯和β-二酮亚胺配体来获得。[3]然而，单体亚胺铝烷的制备的平行研究取得了非常有限的成功。在大多数情况下，假定的亚胺铝烷中间体进行C13 H键活化，环加成，和其他分解反应。[4]目前，结构表征的单体亚氨基-ACHTUNGTRENNUNGalanes尚未报道。事实上，相对于镓和铟的那些，式[Al（L）（E）]（L=单阴离子配体，E= NR、PR、O、S、Se）的铝物质很少被报道[5];然而，许多三配位铝化合物是已知的。这一少量的报道可能与更极化的Al = N键和Al= E多重键的小π-键能有关，这是由于铝相对于其他13族元素的正电性更强（鲍林标度）。本文中，我们报告了稳定的单体亚氨基铝烷2的分离、结构表征和初步反应性研究，该亚氨基铝烷2是通过β-二酮亚胺基Al（I）化合物1与N-杂环卡宾（NHC）的缩环反应制备的（方案1）。自从Roesky及其同事分离出第一个β-二酮亚胺基一价铝化合物[Al {HCACHTUNGTRENNUNG [（CMe）2ACHTUNGTRENNUNG（NAr）2]}]（1 '）以来，其反应性已被广泛研究。[6，7]最近，我们报道了AlI单体1的合成（方案1），其在配体骨架的β位上含有较大的基团，即叔丁基，以及其与异氰化物的C3 N键断裂反应。[8]这些结果促使我们研究1与其他刘易斯碱的反应，特别是那些与异氰化物等电子的碱，如NHC，以了解反应机理。在08 ℃下搅拌1和1，3-二-ACHTUNGTRENNUNG异丙基-4，5-二甲基-2-亚基（IiPr 2）在THF中的混合物，导致颜色从红色快速变为蓝色。化合物2分离为蓝色晶体，产率84%。它对空气和水分极其敏感，在室温下在溶液中缓慢分解，产生黄色混合物，无法完全表征。然而，固体样品可以在惰性气氛下储存数周。通过IR、1H NMR、13 C NMR、UV/维斯光谱和元素分析对化合物2进行了表征。2的13 C NMR光谱显示NHC的中心碳原子、C= N部分和直接键合至铝原子的碳原子（Al 2 O3 C = C）分别在166.12、190.75和204.00 ppm处的共振;这些数据与2的缩环衍生结构一致。2的分子结构通过单晶X-射线分析得到证实。在低温下从化合物在THF中的溶液中获得适合于X射线分析的2的单晶。2的结构如图1所示，并具有选定的键合参数。2中的铝原子是四配位的，直接键合的原子形成..
Heavier group 13 iminometallanes (RMNR) n (M= Al, Ga, In) have been the subject of numerous studies because of their rich structural features and applications for M–N binary materials.[1] Owing to their highly polarized MÀN bonds, they have a large tendency to form cyclic dimers and trimers, and clusters with three-dimensional M–N frameworks depending on the steric hindrance of organic substituents on the metal centers.[2] Very recent research by the research group of Power showed that the monomeric gallium and indium iminometallanes can be accessed by employing extremely bulky terphenyl and β-diketiminato ligands.[3] However, parallel studies on the preparation of monomeric iminoalanes had very limited success. In most cases, the putative iminoalane intermediates underwent CÀH bond activation, cycloaddition, and other decomposition reactions.[4] At present, structurally characterized monomeric imino-ACHTUNGTRENNUNGalanes have not been reported. In fact, aluminum species of the formula [Al (L)(E)](L= monoanionic ligand, E= NR, PR, O, S, Se) have been rarely reported [5] relative to those of gallium and indium; however, a number of three-coordinate aluminum compounds are known. This small number of reports may be related to the more polarized AlÀN bond and the small π-bond energy of the Al= E multiple bond owing to more electropositive character of aluminum relative to those of other group13 elements (Pauling scale). Herein, we report on the isolation, structural characterization, and preliminary reactivity studies of the stable monomeric iminoalane 2, which is prepared by the ring-contraction reaction of β-diketiminato Al (I) compound 1 with an N-heterocyclic carbene (NHC)(Scheme1). Compound 2 represents the first structurally characterized monomeric iminoalane.Since the isolation of the first β-diketiminato monovalent aluminum compound [Al {HCACHTUNGTRENNUNG [(CMe) 2ACHTUNGTRENNUNG (NAr) 2]}](1’) by Roesky and co-workers, its reactivity has been extensively investigated.[6, 7] Very recently, we reported the synthesis of AlI monomer 1 (Scheme 1), which contains larger groups, that is, tert-butyl groups, on the β position of the ligand backbone, and its CÀN bond cleavage reaction with an isocyanide.[8] The results prompted us to examine reactions of 1 with other Lewis bases, especially those that are isoelectronic with isocyanides, such as NHCs, for the understanding of the reaction mechanism. Stirring a mixture of 1 and 1, 3-di-ACHTUNGTRENNUNGisopropyl-4, 5-dimethyl-2-ylidene (IiPr2) in THF at 08C led to a rapid change of color from red to blue. Compound 2 was isolated as blue crystals in 84% yield. It is extremely air and moisture sensitive and slowly decomposed in solution at room temperature to give a yellow mixture, which could not be completely characterized. However, the solid sample can be stored under an inert atmosphere for weeks. 2 has been characterized by IR, 1H NMR, 13C NMR, and UV/Vis spectroscopy and elemental analysis. The 13C NMR spectrum of 2 displays resonances at 166.12, 190.75, and 204.00 ppm for the central carbon atom of the NHC, the C= N moiety, and the carbon atom directly bonded to the aluminum atom (AlÀC= C), respectively; these data are consistent with the ring-contraction derived structure of 2. The molecular structure of 2 was confirmed by single-crystal X-ray analysis. Single crystals of 2 suitable for X-ray analysis were obtained from a solution of the compound in THF at low temperature. The structure of 2 is shown in Figure 1 with selected bond parameters. The aluminum atom in 2 is four coordinate and the directly bonded atoms form a …