2,3-Bis(1-methylimidazol-2-yl)quinoxaline (bmiq), a new ligand with decoupled electron transfer and metal coordination sites: The very different redox behaviour of isoelectronic complexes with PtCl2 and AuCl2+
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Dalton Transactions 40 (12): 2757--2763 (2011)

The potentially ambidentate heterocyclic ligand 2,3-bis(1-methylimidazol-2-yl)quinoxaline (bmiq) was obtained from 2,3-bis(1-methylimidazol-2-yl)glyoxal and 1,2-diaminobenzene. Its coordination to PtCl2 and to the isoelectronic AuCl2+ in AuCl2(bmiq)(AuCl4) occurs via the imine N donors of the imidazolyl groups, giving seven-membered chelate rings with boat conformation. According to the spectroelectrochem. (UV-visible-NIR, ESR), the reversible electron addn. to the PtCl2(bmiq) and the free ligand takes place in the (non-coordinated) quinoxaline part of the mol., similarly as for related complexes of dipyrido3,2-a:2',3'-cphenazines (dppz), 2,3-bis(2-pyridyl)quinoxalines (bpq) and 2,3-bis(dialkylphosphino)quinoxalines (QuinoxP). DFT calcns. confirm the exptl. results (structures, spectroscopy) and also point to the coordination potential of the quinoxaline N atoms. The electron addn. to AuCl2(bmiq)+ takes place not at the ligand but at the metal site, according to exptl. and DFT results. on SciFinder(R)
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