Imidotitanium complexes as hydroamination catalysts: Substantially enhanced reactivity from an unexpected cyclopentadienide/amide ligand exchange
Imidotitanium complexes as hydroamination catalysts: Substantially enhanced reactivity from an unexpected cyclopentadienide/amide ligand exchange
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DOI：
10.1021/ja005685h
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发表时间：
2001-03-28
影响因子：
15
通讯作者：
Bergman, RG
中科院分区：
文献类型：
--
作者：
Johnson, JS;Bergman, RG
在碳碳双键或三键上加成NH键可能是最直接和最有效的胺烷基化方法之一。在寻找过渡金属配合物以促进这种理想的转变方面已经花费了相当大的努力，虽然已经取得了显著的成功，但这个问题的一般解决办法却证明是难以捉摸的。因此，氢胺化反应的发现和发展仍然是重要的目标。相对较少的早期过渡金属配合物已被证明是氢胺化催化剂的前体。其中包括我们小组2和Doye的3,4 （eq 1）先前研究的双（环戊二烯基）锆和钛炔氢胺化催化剂。在这两个体系中，假设关键中间体是16电子亚胺配合物Cp2Md NR。本通讯的目的是报道钛基亚胺配合物5,6作为烯丙烯和炔氢胺化反应的催化剂前体。7-9一项详细的机制研究揭示了一个意想不到的环戊二烯/酰胺配体交换反应，将双环戊二烯基钛前体（Cp2TiLn）转化为单环戊二烯基钛（氨基）配合物（Cp (ArNH) TiLn） 10，表现出比Cp2TiLn前体高得多的反应活性。随着对映纯（ebthi）锆亚胺配合物在化学计量条件下（ebthi）乙烯双（四氢茚）)动力学分解手性外消旋丙烯的发现，我们对催化丙烯氢胺化产生了兴趣。11实验探讨了金属催化丙烯氢胺化的可行性，最终目标是开发这种动力学分辨率的催化变体。一个简短的催化剂筛选显示，钛配合物比它们的锆对应物更具反应性，而cp2time212是一种未定义但有效的催化剂的方便前体
The addition of an NH bond across a carbon-carbon double or triple bond is potentially one of the most direct and efficient methods of alkylating an amine. Considerable effort has been expended in the search for transition metal complexes that will catalyze this desirable transformation, and while notable successes have been realized, general solutions to the problem have proven elusive. 1 As a consequence, the discovery and development of hydroamination reactions remain important goals. Relatively few early transition metal complexes have been shown to be hydroamination catalyst precursors. Among these are the class of bis (cyclopentadienyl) zirconium and titanium alkyne hydroamination catalysts studied earlier by our group2 and by Doye’s3, 4 (eq 1). In both systems it has been assumed that the critical intermediates are the 16-electron imido complexes Cp2Md NR. The purpose of this communication is to report titaniumbased imido complexes5, 6 that function as catalyst precursors for both allene and alkyne hydroamination reactions. 7-9 A detailed mechanistic investigation has revealed an unexpected cyclopentadienide/amide ligand exchange reaction that transforms the biscyclopentadienyltitanium precursors (Cp2TiLn) into a monocyclopentadienyl titanium (amido) complex (Cp (ArNH) TiLn) 10 exhibiting substantially higher reactivity than the Cp2TiLn precursor.We became interested in catalytic allene hydroamination with the discovery that enantiopure (ebthi) zirconium imido complexes kinetically resolve chiral racemic allenes under stoichiometric conditions (ebthi) ethylene bis (tetrahydroindenyl)). 11 Experiments to explore the feasibility of metal-catalyzed allene hydroamination were undertaken with the eventual goal of developing a catalytic variant of this kinetic resolution. A brief screen of catalysts revealed that titanium complexes were more reactive than their zirconium counterparts, and that Cp2TiMe2 12 was a convenient precursor to an undefined, but competent, catalyst