Robust and Porous β‑Diketiminate-Functionalized Metal–Organic Frameworks for Earth-Abundant-Metal-Catalyzed C–H Amination and Hydrogenation

We
have designed a strategy for postsynthesis installation of the
β-diketiminate (NacNac) functionality in a metal–organic
framework (MOF) of UiO-topology. Metalation of the NacNac-MOF (I) with earth-abundant metal salts afforded the desired MOF-supported
NacNac-M complexes (M = Fe, Cu, and Co) with coordination environments
established by detailed EXAFS studies. The NacNac-Fe-MOF catalyst, I•Fe­(Me), efficiently catalyzed the challenging intramolecular
sp3 C–H amination of a series of alkyl azides to
afford α-substituted pyrrolidines. The NacNac-Cu-MOF catalyst, I•Cu­(THF), was effective in promoting the intermolecular
sp3 C–H amination of cyclohexene using unprotected
anilines to provide access to secondary amines in excellent selectivity.
Finally, the NacNac-Co-MOF catalyst, I•Co­(H),
was used to catalyze alkene hydrogenation with turnover numbers (TONs)
as high as 700 000. All of the NacNac-M-MOF catalysts were
more effective than their analogous homogeneous catalysts and could
be recycled and reused without a noticeable decrease in yield. The
NacNac-MOFs thus provide a novel platform for engineering recyclable
earth-abundant-element-based single-site solid catalysts for many
important organic transformations.

本研究设计了一种后合成修饰策略，可在UiO拓扑结构的金属有机框架（metal–organic framework, MOF）中引入β-二亚胺基（β-diketiminate，简称NacNac）功能基团。将该NacNac功能化MOF（记为I）与地壳丰产金属盐进行金属化反应，可得到目标MOF负载型NacNac-M配合物（M为Fe、Cu、Co），其配位环境通过扩展X射线吸收精细结构（extended X-ray absorption fine structure, EXAFS）测试得以精准表征。其中，NacNac-Fe-MOF催化剂（记为I•Fe(Me)）可高效催化具有挑战性的分子内sp³ C-H胺化反应，以一系列烷基叠氮为底物，生成α-取代吡咯烷产物。NacNac-Cu-MOF催化剂（记为I•Cu(THF)，其中THF为四氢呋喃（tetrahydrofuran））可有效介导分子间sp³ C-H胺化反应：以未保护的苯胺为胺源，环己烯为底物，可高选择性地生成二级胺类产物。最后，NacNac-Co-MOF催化剂（记为I•Co(H)）可用于催化烯烃氢化反应，其转化数（turnover number, TON）最高可达700000。所有NacNac-M-MOF催化剂的催化性能均优于其对应的均相催化剂，且可循环复用多次，催化活性无明显下降。综上，NacNac功能化MOF为构建可循环复用、基于地壳丰产金属的单一位点固相催化剂提供了全新平台，可应用于多种重要有机转化反应。