Man Chen

Metal Exchange Method Using Au25 Nanoclusters as Templates for Alloy Nanoclusters with Atomic Precision

A metal exchange method based upon atomically precise gold nanoclusters (NCs) as templates is devised to obtain alloy NCs including CuxAu25-x(SR)18, AgxAu25-x(SR)18, Cd1Au24(SR)18, and Hg1Au24(SR)18 via reaction of the template with metal thiolate complexes of Cu(II), Ag(I), Cd(II), and Hg(II) (as opposed to common salt precursors such as CuCl2, AgNO3, etc.). Experimental results imply that the exchange between gold atoms in NCs and those of the second metal in the thiolated complex does not necessarily follow the order of metal activity (i.e., galvanic sequence). In addition, the crystal structure of the exchange product (Cd1Au24(SR)18) is successfully determined, indicating that the Cd is in the center of the 13-atom icosahedral core. This metal exchange method is expected to become a versatile new approach for synthesizing alloy NCs that contain both high- and low-activity metal atoms.

Crystal Structure and Optical Properties of the [Ag62S12(SBut)32]2+ Nanocluster with a Complete Face-Centered Cubic Kernel

The crystal structure of the [Ag62S12(SBu(t))32](2+) nanocluster (denoted as NC-I) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag14 core structure with a Ag48(SBu(t))32 shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag62S13(SBu(t))32](4+) structure (denoted as NC-II for short) reported by Wang. Interestingly, NC-I exhibits prominent differences in the optical properties in comparison with the case of the NC-II nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in NC-I in comparison to that of NC-II is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of NC-I and NC-II. These findings offer a new insight into the structure and property evolution of silver cluster materials.

Ag50(Dppm)6(SR)30 and Its Homologue AuxAg50–x(Dppm)6(SR)30 Alloy Nanocluster: Seeded Growth, Structure Determination, and Differences in Properties

A large thiolate/phosphine coprotected Ag50(Dppm)6(SR)30 nanocluster was synthesized through the further growth of Ag44(SR)30 nanocluster and characterized by X-ray photoelectron spectroscopy (XPS), electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray analysis. This new nanocluster comprised a 32-metal-atom dodecahedral kernel and two symmetrical Ag9(SR)15P6 ring motifs. The 20 valence electrons correspond to shell closure in the Jellium model. Moreover, this nanocluster could be alloyed by templated/galvanic metal exchange to the homologue AuxAg50-x(Dppm)6(SR)30 nanocluster; the latter showed much higher thermal stability than the Ag50(Dppm)6(SR)30 nanocluster. Further experiments were conducted to study the optical, electrical, and photoluminescence properties of both nanoclusters. Our work not only reports two new larger size nanoclusters but also reveals a new way to synthesize larger size silver and alloy nanoclusters, that is, controlled growth/alloying.

Heterobimetallic dinuclear lanthanide alkoxide complexes as acid-base difunctional catalysts for transesterification.

A practical lanthanide(III)-catalyzed transesterification of carboxylic esters, weakly reactive carbonates, and much less-reactive ethyl silicate with primary and secondary alcohols was developed. Heterobimetallic dinuclear lanthanide alkoxide complexes [Ln2Na8{(OCH2CH2NMe2)}12(OH)2] (Ln = Nd (I), Sm (II), and Yb (III)) were used as highly active catalysts for this reaction. The mild reaction conditions enabled the transesterification of various substrates to proceed in good to high yield. Efficient activation of transesterification may be endowed by the above complexes as cooperative acid-base difunctional catalysts, which is proposed to be responsible for the higher reactivity in comparison with simple acid/base catalysts.

Thiol-Induced Synthesis of Phosphine-Protected Gold Nanoclusters with Atomic Precision and Controlling the Structure by Ligand/Metal Engineering

Efficient synthesis of atomically precise phosphine-capped gold nanocluster (with >10 metal atoms) is important to deeply understand the relationship between structure and properties. Herein, we successfully utilize the thiol-induced synthesis method and obtain three atomically precise phosphine-protected gold nanoclusters. Single-crystal X-ray structural analysis reveals that the nanoclusters are formulated as [Au13(Dppm)6](BPh4)3, [Au18(Dppm)6Br4](BPh4)2, and [Au20(Dppm)6(CN)6] (where Dppm stands for bis(diphenylphosphino)methane), which are further confirmed by electrospray ionization mass spectrometry, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Meanwhile, [Au18(Dppm)6Br4](BPh4)2 could be converted into [Au13(Dppm)6](BPh4)3 and [Au20(Dppm)6(CN)6] by engineering the surface ligands under excess PPh3 or moderate NaBH3CN, respectively. Furthermore, according to the different binding ability of silver with halogen, we successfully achieved target metal exchange on [Au18(Dppm)6Br4](BPh4)2 with Ag-SAdm (where HS-Adm stands for 1-adamantane mercaptan) complex and obtained [AgxAu18-x(Dppm)6Br4](BPh4)2 (x = 1, 2) alloy nanoclusters. Our work will contribute to more intensive understanding on synthesizing phosphine-protected nanoclusters as well as shedding light on the structure-property correlations in the nanocluster range.

Heterobimetallic dinuclear lanthanide alkoxide complexes as acid–base bifunctional catalysts for synthesis of carbamates under solvent-free conditions

Heterobimetallic dinuclear lanthanide alkoxide complexes Ln2Na8(OCH2CH2NMe2)12(OH)2 [Ln: I (Nd), II (Sm), III (Yb) and IV (Y)] were used as efficient acid–base bifunctional catalysts for the synthesis of carbamates from dialkyl carbonates and amines as well as the N-Boc protection of amines. The cooperative catalysts showed high catalytic activity and a wide scope of substrates with good to excellent yields under solvent-free conditions. The systems have shown higher catalytic activities due to the noteworthy synergistic interactions of Lewis acid center–Bronsted basic center. The comparison of catalytic efficiency between mono- and dinuclear heterobimetallic lanthanide alkoxide analogues was also investigated.

An Efficient and Green Approach to Synthesizing Enamines by Intermolecular Hydroamination of Activated Alkynes

An efficient, atom-economic and green approach to synthesizing enamines was developed by intermolecular hydroamination of activated alkynes with high yields under catalyst- and solvent-free conditions. β-Dimethylamino-acrylate derivatives were also obtained with high yields. In the synthetic process of the derivatives, N,N-dimethylformamide(DMF) pretreated with metal Na, was used as reactant instead of dimethylamine gas. The proposed synthetic method can be used for the synthesis of (E)-ethyl-3-(dimethylamino)acrylate(3cl), and provide a new possible way to the synthesis of Quinolones.