N-Heterocyclic Carbene-Stabilized Gold Nanoclusters with Organometallic Motifs for Promoting Catalysis

Abstract

The complexity of heterogeneous metal catalysts makes it challenging to gain insights into their catalytic mechanisms. Thus, there exists a huge gap between heterogeneous catalysis and organometallic catalysis. With the success in the preparation of highly robust atomically precise metal nanocluster catalysts (i.e., [Au16(NHC-1)5(PA)3Br2]3+ and [Au17(NHC-1)4(PA)4Br4]+, where NHC-1 is a bidentate NHC ligand, and PA is phenylacetylide) with surface organometallic motifs anchored on the metallic core, we demonstrate in this work how the metallic core works synergistically with the surface organometallic motifs to enhance the catalysis. More importantly, the discovery allows the development of highly stable and recyclable heterogeneous metal catalysts to achieve efficient hydroamination of alkynes with an extremely low catalyst dosage (0.002 mol %), helping bridge the gap between heterogeneous and homogeneous metal catalysis. The surface modification of metal nanocatalysts with organometallic motifs provides a new design principle of metal catalysts with enhanced catalysis.

Surface and Interface Coordination Chemistry Learned from Model Heterogeneous Metal Nanocatalysts: From Atomically Dispersed Catalysts to Atomically Precise Clusters

“…APMCs can be considered as a unique subclass of metal NPs, whose size is typically smaller than 2 nm, but number of metal atoms and surface ligands is accurately countable for a given one. − As a bridge between metal complexes and NPs, these species have exact molecular formula, including metal, ligand and charge state, and often exhibit molecule-like features. For example, many APMCs display discrete energy levels with nonzero gaps and characteristic absorption profiles in the UV–vis region .…”

“…These clusters exhibited high activity in several thermal reactions with the typical examples of hydrogenation and hydroformylation. − During the past two decades, the rapid progress in the synthesis of ligand-stabilized APMCs has inspired increasing studies on their catalysis. The scope of reactions has been extended beyond hydrogenation and hydroformylation to many other thermal, electrochemical catalytic reactions and even photocatalysis. − ,− Moreover, the combinatory use of advanced techniques, including in situ characterization tools and DFT simulations, has helped to deepen the understanding of the reaction mechanism …”

“…(c) Mechanistic scheme showing the synergistic catalysis between the NHC-Au-PA organometallic motif and the metallic Au core in Au 16 catalysts. Reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

“…On the one hand, the atomic structures of these two classes of model catalysts can be fully characterized by currently available techniques. While X-ray near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques are useful for identifying the local structure of metal centers on ADMCs, − X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy are the most powerful techniques to reveal the molecular structures of APMCs. − These model heterogeneous catalysts share the common feature with the availability of well-defined local coordination structure of catalytic metal centers. On the other hand, unlike homogeneous metal catalysts, the metal centers in supported ADMCs and ligand-protected APMCs are embedded in the extended support matrix or form metal–metal interactions with their neighboring metals, making them ideal systems to illustrate the catalytic mechanism in complex heterogeneous catalytic reactions.…”

Body-Centered-Cubic-Kernelled Ag15Cu6 Nanocluster with Alkynyl Protection: Synthesis, Total Structure, and CO2 Electroreduction

“…Ligand-protected metal nanoclusters with atomic-level structural details, definite composition, and absolutely uniform size have attracted great attention in the field of materials chemistry and nanocatalysis. − The ultrasmall size (typically, <3 nm diameter), unique electronic structure, under-coordinated metal sites, and the tunable size, metal/ligand composition, and molecular structure endow nanoclusters with the potential to control the activity and product selectivity in various catalytic transformations. − Thoroughly characterized core and surface structures and the electronic structures of the metal nanoclusters enable more realistic theoretical calculations to predict and interpret the catalytic results and mechanisms. − More importantly, unlike traditional nanoparticle-based catalysts, the metal clusters exhibit molecule-like properties, enabling the identification of reaction intermediates generated during the catalytic processes through high-resolution mass spectrometry and infrared spectroscopy. − Elucidation of the structure and composition of the intermediates in the catalytic reactions is crucial for revealing the structure–catalysis relationships.…”