Copper(II)-Assisted Ligand Fragmentation Leading to Three Families of Metallamacrocycle

Fei Yu; Bao-Qian Ji; Marko Jagodič; Yan-Min Su; Shan-Shan Zhang; Lei Feng; Mohamedally Kurmoo; Zvonko Jagličić; Di Sun

doi:10.1021/acs.inorgchem.0c01915

Copper(II)-Assisted Ligand Fragmentation Leading to Three Families of Metallamacrocycle

Inorg Chem. 2020 Sep 21;59(18):13524-13532. doi: 10.1021/acs.inorgchem.0c01915. Epub 2020 Aug 31.

Authors

Fei Yu¹, Bao-Qian Ji², Marko Jagodič³, Yan-Min Su², Shan-Shan Zhang², Lei Feng², Mohamedally Kurmoo⁴, Zvonko Jagličić⁵, Di Sun^{2

6}

Affiliations

¹ Institute of Advanced Materials and Flexible Electronics (IAMFE), School of Chemistry and Materials Science, Nanjing University of Information Science & Technology, Nanjing 210044, PR China.
² Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100, PR China.
³ Institute of Mathematics, Physics and Mechanics, Jadranska 19, SI-1000 Ljubljana, Slovenia.
⁴ Institut de Chimie de Strasbourg, Université de Strasbourg, CNRS-UMR 7177, 4 rue Blaise Pascal, Strasbourg CEDEX 67008, France.
⁵ Faculty of Civil and Geodetic Engineering & Institute of Mathematics, Physics and Mechanics, University of Ljubljana, Jamova 2, 1000 Ljubljana, Slovenia.
⁶ Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, and School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252000, PR China.

PMID: 32865402
DOI: 10.1021/acs.inorgchem.0c01915

Abstract

We present an unprecedented copper(II)-assisted organic ligand fragmentation process under basic conditions leading to several ligands within three families of metallamacrocycle, Cu₆, Cu₈, and Cu₁₆. The sequential multistep reaction include (i) the deprotonation of the starting alcohol, 1,2-bis(3,5-dimethyl-pyrazol-1-yl)ethane-1,2-diol (H₂bdped) to its diolate bdped followed by complexation through six bonds (μ₆) to three copper atoms in a ring, (ii) the breaking of the ethane-pyrazole C-N bonds by the different solvent alcohols to form 1-(3,5-dimethyl-pyrazol-1-yl)-2-methoxyethane-1,2-diolate (dpmed) or 2-(3,5-dimethyl-pyrazol-1-yl)-2-hydroxyacetate (dpet), while retaining coordination to the copper centers and (iii) the final step to ethane-1,1,2,2-tetraolate, C₂H₂O₄^4- (et). Importantly, the latter product, only observed on two previous occasions, occupies the core of Cu₆ and Cu₁₆ through exceptionally eight coordination bonds (μ₈). Its alkyl esters, 2-alkoxyethane-1,1,2-triolate (met, eet, and pet), also occupy the central parts of Cu₈ but forming six bonds (μ₆) instead. The other product, 3,5-dimethylpyrazolate (dp), acts as peripheral bridges (μ₂) but it is not involved in coordination if the starting salt is copper acetate, this may be a consequence of acetate being a better μ₂-chelating ligand. In the presence of an oxidizing agent, K₂Cr₂O₇, C₂H₂O₄^4- (et) is oxidized to oxalate, C₂O₄^2- (ox). Thus, an additional μ₃-hydroxide and μ₄-oxalate in Cu₁₆ widen the complexity of the structures, not to mention the range of coordination geometries of the copper centers, though in the present cases they can be classed in only two types: distorted square-planar and square-pyramid. In addition to single-crystal crystallography, the results from different techniques such as IR, ESI-MS, optical UV-vis, and SQUID magnetometry help in the characterization of these rare metallamacrocycles made from unexpected and in situ generated ligands. We believe the results of the organic transformations are highly relevant to von Liebig's benzil-benzilic acid rearrangement.