2017 Fiscal Year Annual Research Report
Synthesis, Characterization and Testing of N-Heterocyclic Carbene-modified Magic Number Metallic Clusters for C-H Oxidation Catalysis
| Project/Area Number |
17H03030
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| Research Institution | Nagoya University |
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Principal Investigator |
CRUDDEN Cathleen 名古屋大学, トランスフォーマティブ生命分子研究所, 客員教授 (10721029)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | Nano Materials / Nanocluster / N-Heterocyclic Varbene / Gold / CO2 Reduction / C-H Oxidation |
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| Outline of Annual Research Achievements |
In order to examine the synthesis of NHC-stabilized nanoclusters, we began with preformed phosphine-stabilized undecagold clusters. Treatment of [Au11(PPh3)8Cl2]Cl with di-isopropyl benzimidazolium hydrogen carbonate in THF gave a single cluster species. This cluster results from substitution of one phosphine ligand for the NHC. Conclusive information about the reaction was obtained by mass spectroscopy, which demonstrated that mono-substituted cluster is the predominant product, accompanied by small amounts of disubstituted cluster. This was carried out in collaboration with the Tsukuda group in Tokyo. Increasing the amount of NHCs resulted in a mixture of the monosubstituted cluster and disubstituted cluster. Further increases in NHC stoichiometry did not lead to greater incorporation in the cluster, but improved yields were observed. Interestingly, benzylated NHC gave the highest level of substitution observed, resulting in a mixture of clusters including mono-, di-, tri- and tetra- NHC-containing clusters under all conditions attempted. Observed and calculated optical absorption spectra for various clusters were examined and compared with DFT calculations by the Hakkinen group
All phosphine cluster underwent complete decomposition after heating while NHC-stabilized clusters showed dramatically improved stability. And we found these clusters have catalytic activity for the electrocatalytic reduction of CO2 to CO.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
We have been able to make four examples of gold nanoclusters containing NHC ligands. These nanoclusters are the first example of NHC clusters outside of the area of coordination clusters and promise to be an important starting point for the development of new types of ligands for magic number clusters. We have also demonstrated the use of these nanoclusters in catalysis by showing the electrocatalytic reduction of carbon dioxide. This provides the interesting possible conclusion that it is the clusters that survive thermal treatment that have the highest catalytic activity.
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| Strategy for Future Research Activity |
Future work will entail improving the preparation of nanoparticles such that higher yields are obtained to facilitate catalytic studies. Once we have further tested the stability, improved yields and understood the exchange processes going on, we will then look at catalytic activity. We will begin by benchmarking the nanoclusters we have prepared in reactions that have been reported in the literature for thiol-based nanoclusters. These include the reduction of nitrobenzene, and the oxidation of simple organics such as cyclohexane. Overall catalytic activity will be examined by looking at standard values such as turnover frequency and turnover rate. We will examine the nanoclusters in solution as homogeneous catalysts and also on support such as alumina, silica, titania and ceria.
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