Deegan Meaghan M, Peters Jonas C
Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , CA 91125 , USA . Email:
Chem Sci. 2018 Jun 29;9(29):6264-6270. doi: 10.1039/c8sc02380h. eCollection 2018 Aug 7.
One of the emerging challenges associated with developing robust synthetic nitrogen fixation catalysts is the competitive formation of hydride species that can play a role in catalyst deactivation or lead to undesired hydrogen evolution reactivity (HER). It is hence desirable to devise synthetic systems where metal hydrides can migrate directly to coordinated N in reductive N-H bond-forming steps, thereby enabling productive incorporation into desired reduced N-products. Relevant examples of this type of reactivity in synthetic model systems are limited. In this manuscript we describe the migration of an iron hydride (Fe-H) to N of a disilylhydrazido(2-) ligand (Fe[double bond, length as m-dash]NNR) derived from N double-silylation in a preceding step. This is an uncommon reactivity pattern in general; well-characterized examples of hydride/alkyl migrations to metal heteroatom bonds (, (R)M[double bond, length as m-dash]NR' → M-N(R)R') are very rare. Mechanistic data establish the Fe-to-N hydride migration to be intramolecular. The resulting disilylhydrazido(1-) intermediate can be isolated by trapping with CN Bu, and the disilylhydrazine product can then be liberated upon treatment with an additional acid equivalent, demonstrating the net incorporation of an Fe-H equivalent into an N-fixed product.
开发强大的合成固氮催化剂所面临的一个新挑战是氢化物物种的竞争性形成，这些氢化物物种可能在催化剂失活中起作用，或导致不期望的析氢反应（HER）。因此，设计合成体系是很有必要的，在该体系中，金属氢化物可以在还原性N-H键形成步骤中直接迁移到配位的N上，从而能够有效地掺入所需的还原态N产物中。在合成模型体系中，这种反应类型的相关例子有限。在本论文中，我们描述了在前一步骤中通过N的双硅基化衍生得到的二硅基肼基（2-）配体（Fe[双键，长度为m破折号]NNR）的N上氢化铁（Fe-H）的迁移。一般来说，这是一种不常见的反应模式；氢化物/烷基迁移到金属杂原子键（，（R）M[双键，长度为m破折号]NR' → M-N（R）R'）的特征明确的例子非常罕见。机理数据表明Fe到N的氢化物迁移是分子内的。通过用CN Bu捕获可以分离得到生成的二硅基肼基（1-）中间体，然后用额外的一当量酸处理可以释放出二硅基肼产物，这表明一个Fe-H当量净掺入到了一个N固定产物中。
