Competitive Transmetalation of First-Row Transition-Metal Ions between Trinuclear Triple-Stranded Side-by-Side Helicates

• Published in: Inorganic chemistry 2017-10, Vol.56 (20), p.12505-12513
• Main Authors: Jana, Barun, Cera, Luca, Akhuli, Bidyut, Naskar, Sourenjit, Schalley, Christoph A, Ghosh, Pradyut
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b01980

A hybrid tris-bidentate neutral ligand (L) composed of a central 2,2′-bipyridine and two terminal triazolyl-pyridine chelating units connected by methylene spacers is employed to synthesize trinuclear triple-stranded side-by-side helicates of first-row transition-metal­(II) ions. Three such new homometallic helicates L3M3(OTf)6 [ M = Cu2+ (4); Ni2+ (5); Co2+ (6)], along with our recently reported helicates L3Fe3(OTf)6 (1), L3Zn3(OTf)6 (2), and L3Fe2Zn­(OTf)6 (3) are taken into consideration for competitive formation and transmetalation studies. Single-crystal X-ray structures of L3Cu3(OTf)6 (4) and L3Ni3(OTf)6 (5) show the formation of trinuclear triple-stranded side-by-side helicates with alternating Λ and Δ chiralities at the metal ions as earlier observed in cases of L3Fe3(OTf)6 (1), L3Zn3(OTf)6 (2), and L3Fe2Zn­(OTf)6 (3). ESI-FTICR mass spectrometry and UV–vis spectroscopy studies show that helicates L3Fe3(OTf)6 (1), L3Zn3(OTf)6 (2), L3Fe2Zn­(OTf)6 (3), and L3Co3(OTf)6 (6) can easily be transmetalated to helicate L3Cu3(OTf)6 (4) in the presence of Cu­(OTf)2. On the other hand, only a trace amount of heterometallic helicate L3Ni2Cu­(OTf)6 forms even after several days, when Cu­(OTf)2 is added to a the solution of homometallic helicate L3Ni3(OTf)6 (5). Further, we have demonstrated the formation of a heterometallic helicate L3Ni2Co­(OTf)6 (7) from a 1:1:1 reaction mixture of L, Ni­(OTf)2, and Co­(OTf)2, which can also be prepared from homometallic helicate L3Co3(OTf)6 (6) by transmetalation with Ni­(OTf)2.