Creutz Sidney E, Peters Jonas C
California Institute of Technology , Division , of Chemistry and Chemical Engineering , Pasadena , California 91125 , USA . Email:
Chem Sci. 2017 Mar 1;8(3):2321-2328. doi: 10.1039/c6sc04805f. Epub 2016 Dec 8.
Hydrogen bonding and other types of secondary-sphere interactions are ubiquitous in metalloenzyme active sites and are critical to the transformations they mediate. Exploiting secondary sphere interactions in synthetic catalysts to study the role(s) they might play in biological systems, and to develop increasingly efficient catalysts, is an important challenge. Whereas model studies in this broad context are increasingly abundant, as yet there has been relatively little progress in the area of synthetic catalysts for nitrogen fixation that incorporate secondary sphere design elements. Herein we present our first study of Fe-N H complexes supported by new tris(phosphine)silyl ligands, abbreviated as [SiPNMe3] and [SiPiPr2P], that incorporate remote tertiary amine hydrogen-bond acceptors within a tertiary phosphine/amine 6-membered ring. These remote amine sites facilitate hydrogen-bonding interactions a boat conformation of the 6-membered ring when certain nitrogenous substrates (, NH and NH) are coordinated to the apical site of a trigonal bipyramidal iron complex, and adopt a chair conformation when no H-bonding is possible (, N). Countercation binding at the cyclic amine is also observed for anionic {Fe-N} complexes. Reactivity studies in the presence of proton/electron sources show that the incorporated amine functionality leads to rapid generation of catalytically inactive Fe-H species, thereby substantiating a hydride termination pathway that we have previously proposed deactivates catalysts of the type [EPR3]FeN (E = Si, C).
氢键和其他类型的二级球相互作用在金属酶活性位点中普遍存在，并且对于它们所介导的转化至关重要。利用合成催化剂中的二级球相互作用来研究它们在生物系统中可能发挥的作用，并开发效率越来越高的催化剂，是一项重大挑战。尽管在这一广泛背景下的模型研究越来越多，但在结合二级球设计元素的固氮合成催化剂领域，进展相对较少。在此，我们首次报道了由新型三（膦）硅基配体（简称为[SiPNMe3]和[SiPiPr2P]）支持的Fe-N-H配合物的研究，这些配体在叔膦/胺六元环中包含远程叔胺氢键受体。当某些含氮底物（如NH和NH）与三角双锥铁配合物的顶端位点配位时，这些远程胺位点促进六元环的船式构象的氢键相互作用，而当不可能形成氢键时（如N），则采用椅式构象。对于阴离子{Fe-N}配合物，还观察到环胺处的抗衡阳离子结合。在质子/电子源存在下的反应性研究表明，引入的胺官能团导致催化活性的Fe-H物种快速生成，从而证实了我们先前提出的氢化物终止途径使[EPR3]FeN（E = Si，C）型催化剂失活。
