| 研究実績の概要 |
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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| 今後の研究の推進方策 |
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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