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5. Understanding metallophilic interactions

Author

Zheng, Qingshu, Cockroft, Scott, and Love, Jason

Subjects
546, metallophilic interactions, M-M interactions, aurophilic interactions, platinum-platinum interactions, Pt-containing complexes
Abstract

Metallophilic (metal-metal) interactions are weak interactions between closed-shell (d10, s2) or pseudo-closed-shell (d8) metal cations. This type of interaction is generally believed to be responsible for various intriguing structures, luminescence, catalysis and magnetism. To gain a better understanding of metallophilic interactions, both experimental and computational investigations have been carried out in this thesis. Chapter 1 gave an up-to-date literature review on the definition, significance, and methods of estimating metallophilic interactions. The disputed nature and strength of metallophilic interactions encouraged us to further understand them. Chapter 2 focused on aurophilic interactions between AuI cations. Aurophilic interactions were observed in the solid state, but not well expressed in solution. Further experimental and computational results suggested that the strength of aurophilic interactions were weaker than electrostatic interactions. The nature of aurophilic interactions arose from orbital interactions rather than dispersion. Chapter 3 presented the study of metallophilic interactions between group 10 metal centres, including PtII-PtII, PdII-PdII and NiII-NiII. A series of cyclometalated square-planar metal complexes with different metals or substituents were prepared. PtII-PtII interactions were found to be stronger than PdII-PdII and NiII-NiII interactions. The dimerization constants of the Pt-containing complexes increased in line with increasing electron-withdrawing ability. Chapter 4 investigated the solvent-induced and thermally dependent colour changes of the Pt-containing complexes synthesised in chapter 3. Metallophilic interactions were proposed to be important in influencing the luminescence properties.

Published
2018

21. Selective control of secondary alcohols upgrading using Ir-catalyzed cross-coupling strategy

Author

Yang, Siqi, Lu, Zeye, Ji, Jiale, Zheng, Qingshu, and Tu, Tao

Abstract

The selective coupling of alcohols is a fascinating yet challenging approach for upgrading alcohols. Herein, we accomplished the controlled production of β-disubstituted ketones or upgraded secondary alcohols viathe Ir-catalyzed cross-coupling of secondary alcohols in excellent yields with broad substrate scopes. This selective control was achieved by using an in-situgenerated mono-NHC-Ir or a tris-NHC-Ir complex as the catalysts, respectively. Mechanistic studies reavealed that the delicate balance between dehydrogenation and hydrogenation abilities of these bifunctional catalysts is crucial for achieving different selectivity. The tris-NHC-Ir complex effectively facilitated dehydrogenation of alcohols and hydrogenation of intermediates, leading to the desired upgraded secondary alcohols. Conversely, the high dehydrogenation ability of the mono-NHC-Ir complex promoted the conversion of formed secondary alcohols back to ketones.

Published
2023
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26. Selective Catalytic Dehydrogenative Oxidation of Bio-Polyols to Lactic Acid

Author

Wu, Jiajie, Shen, Lingyun, Duan, Sai, Chen, Zhe Ning, Zheng, Qingshu, Liu, Yaoqi, Sun, Zheming, Clark, James H., Xu, Xin, and Tu, Tao

Abstract

The global demand for lactic acid (LA) is increasing due to its successful application as monomer for the manufacture of bioplastics. Although N-heterocyclic carbene (NHC) iridium complexes are promising molecular catalysts for LA synthesis, their instabilities have hindered their utilization especially in commercial applications. Here, we report that a porous self-supported NHC-iridium coordination polymer can efficiently prevent the clusterization of corresponding NHC-Ir molecules and can function as a solid molecular recyclable catalyst for dehydrogenation of bio-polyols to form LA with excellent activity (97 %) and selectivity (>99 %). A turnover number of up to 5700 could be achieved in a single batch, due to the synergistic participation of the Ba2+ and hydroxide ions, as well as the blockage of unwanted pathways by adding methanol. Our findings demonstrate a potential route for the industrial production of LA from cheap and abundant bio-polyols, including sorbitol.

Published
2020

38. Highly Efficient and Selective N‐Formylation of Amines with CO2 and H2 Catalyzed by Porous Organometallic Polymers.

Author

Shen, Yajing, Zheng, Qingshu, Chen, Zhe‐Ning, Wen, Daheng, Clark, James H., Xu, Xin, and Tu, Tao

Subjects
*FORMYLATION, *ORGANOMETALLIC polymers, *POROUS polymers, *TURNOVER frequency (Catalysis), *DENSITY functional theory, CATALYSTS recycling
Abstract

The valorization of carbon dioxide (CO2) to fine chemicals is one of the most promising approaches for CO2 capture and utilization. Herein we demonstrated a series of porous organometallic polymers could be employed as highly efficient and recyclable catalysts for this purpose. Synergetic effects of specific surface area, iridium content, and CO2 adsorption capability are crucial to achieve excellent selectivity and yields towards N‐formylation of diverse amines with CO2 and H2 under mild reaction conditions even at 20 ppm catalyst loading. Density functional theory calculations revealed not only a redox‐neutral catalytic pathway but also a new plausible mechanism with the incorporation of the key intermediate formic acid via a proton‐relay process. Remarkably, a record turnover number (TON=1.58×106) was achieved in the synthesis of N,N‐dimethylformamide (DMF), and the solid catalysts can be reused up to 12 runs, highlighting their practical potential in industry. [ABSTRACT FROM AUTHOR]

Published
2021
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48. Highly Efficient and Selective N-Formylation of Amines with CO 2 and H 2 Catalyzed by Porous Organometallic Polymers.

Author

Shen Y, Zheng Q, Chen ZN, Wen D, Clark JH, Xu X, and Tu T

Abstract

The valorization of carbon dioxide (CO 2 ) to fine chemicals is one of the most promising approaches for CO 2 capture and utilization. Herein we demonstrated a series of porous organometallic polymers could be employed as highly efficient and recyclable catalysts for this purpose. Synergetic effects of specific surface area, iridium content, and CO 2 adsorption capability are crucial to achieve excellent selectivity and yields towards N-formylation of diverse amines with CO 2 and H 2 under mild reaction conditions even at 20 ppm catalyst loading. Density functional theory calculations revealed not only a redox-neutral catalytic pathway but also a new plausible mechanism with the incorporation of the key intermediate formic acid via a proton-relay process. Remarkably, a record turnover number (TON=1.58×10 6 ) was achieved in the synthesis of N,N-dimethylformamide (DMF), and the solid catalysts can be reused up to 12 runs, highlighting their practical potential in industry., (© 2020 Wiley-VCH GmbH.)

Published
2021
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49. Iridium-Catalyzed Selective Cross-Coupling of Ethylene Glycol and Methanol to Lactic Acid.

Author

Wu J, Shen L, Chen ZN, Zheng Q, Xu X, and Tu T

Abstract

An atom-economic approach that has an unprecedented high selectivity for the synthesis of lactic acid (LA) based on a catalytic dehydrogenative cross-coupling by using inexpensive bulk ethylene glycol and methanol is described. This method relies on the synthesis and utilization of a novel iridium catalyst bearing three N-heterocyclic carbenes derived from 1,3-dimethylbenzimidazolium salts, and exhibits outstanding activity in the production of LA [turnover frequency (TOF) up to 3660 h -1 ] owing to an elegant metal-ligand cooperation., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2020
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50. The Energetic Significance of Metallophilic Interactions.

Author

Zheng Q, Borsley S, Nichol GS, Duarte F, and Cockroft SL

Abstract

Metallophilic interactions are increasingly recognized as playing an important role in molecular assembly, catalysis, and bio-imaging. However, present knowledge of these interactions is largely derived from solid-state structures and gas-phase computational studies rather than quantitative experimental measurements. Here, we have experimentally quantified the role of aurophilic (Au I ⋅⋅⋅Au I ), platinophilic (Pt II ⋅⋅⋅Pt II ), palladophilic (Pd II ⋅⋅⋅Pd II ), and nickelophilic (Ni II ⋅⋅⋅Ni II ) interactions in self-association and ligand-exchange processes. All of these metallophilic interactions were found to be too weak to be well-expressed in several solvents. Computational energy decomposition analyses supported the experimental finding that metallophilic interactions are overall weak, meaning that favorable dispersion and orbital hybridization contributions from M⋅⋅⋅M binding are largely outcompeted by electrostatic or dispersion interactions involving ligand or solvent molecules. This combined experimental and computational study provides a general understanding of metallophilic interactions and indicates that great care must be taken to avoid over-attributing the energetic significance of metallophilic interactions., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2019
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