Coordination‐Driven Selective Formation of D2 Symmetric Octanuclear Organometallic Cages

• Published in: Chemistry : a European journal 2021-07, Vol.27 (37), p.9524-9528
• Main Authors: Zhang, Long, Lin, Yue‐Jian, Li, Zhen‐Hua, Fraser Stoddart, J., Jin, Guo‐Xin
• Format: Article
• Language: English
• Subjects: ambidentate ligands; Assembly; Asymmetry; cage compounds; Cages; Chelation; Chemistry; Computer applications; Coordination compounds; coordination modes; Electronic properties; Iridium; isomers; Ligands; Rhodium; Selectivity; self-assembly
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202101204

The coordination‐driven self‐assembly of organometallic half‐sandwich iridium(III)‐ and rhodium(III)‐based building blocks with asymmetric ambidentate pyridyl‐carboxylate ligands is described. Despite the potential for obtaining a statistical mixture of multiple products, D2 symmetric octanuclear cages were formed selectively by taking advantage of the electronic effects emanating from the two types of chelating sites – (O,O’) and (N,N’) – on the tetranuclear building blocks. The metal sources and the lengths of bridging ligands influence the selectivity of the self‐assembly. Experimental observations, supported by computational studies, suggest that the D2 symmetric cages are the thermodynamically favored products. Overall, the results underline the importance of electronic effects on the selectivity of coordination‐driven self‐assembly, and demonstrate that asymmetric ambidentate ligands can be used to control the design of discrete supramolecular coordination complexes. The electronic effect arising from the different bidentate chelating sites on hydroxamate ligands allows selective coordination modes for the half‐sandwich Ir/Rh metal centers. Despite the potential for obtaining a random statistical mixture of diastereoisomers as a consequence of differences in connectivity, only D2 symmetric octanuclear cages were formed selectively by using asymmetric pyridyl‐carboxylate bridging ligands.