Synthesis of Binucleating Macrocycles and Their Nickel(II) Hydroxo- and Cyano-Bridged Complexes with Divalent Ions: Anatomical Variation of Ligand Features
datasetposted on 2016-02-20, 09:04 authored by Xiaofeng Zhang, Deguang Huang, Yu-Sheng Chen, R. H. Holm
The planar NNN-pincer complexes [MII(pyN2Me2)(OH)]1– (MII = Ni, Cu) fix CO2 in η1-OCO2H complexes; results for the copper system are described. MnII, FeII, CoII, and ZnII behave differently, forming [MII(pyN2Me2)2]2– with N4O2 coordination. Incorporation of the NiII pincer into binucleating macrocycle 2 containing a triamino MII locus connected by two 1,3-biphenylene groups affords proximal NiII and MII sites for investigation of the synthesis, structure, and reactivity of Ni–X–M bridge units. This ligand structure is taken as a reference for variations in MII atoms and binding sites and bridges X = OH– and CN– to produce additional members of the macrocyclic family with improved properties. Macrocycle 2 with a 22-membered ring is shown to bind MII = Mn, Fe, and Cu with hydroxo bridges. Introduction of the 4-BuiO group (macrocycle 3) improves the solubility of neutral complexes such as those with NiII–OH–CuII and NiII–CN–FeII bridges. Syntheses of macrocycle 5 with a 7-Me-aneSN3 and macrocycle 6 with a 1,8-Me2-aneN4 MII binding site are described together with hydoxo-bridged Ni/Cu and cyano-bridged Ni/Fe complexes. This work was motivated by the presence of a Ni···(HO)–Fe bridge grouping in a reactive state of carbon monoxide dehydrogenase. Attempted decrease in Ni–(OH)–M distances (3.70–3.87 Å) to smaller values observed in the enzyme by use of macrocycle 4 having 1,2-biphenylene connectors led to a mononuclear octahedral NiII complex. Bridge structural units are summarized, and the structures of 14 macrocyclic complexes including 8 with bridges are described.
Anatomical Variationmacrocycle 4macrocycle 5reactive stateN 4O coordinationBinucleating Macrocyclestriamino MII locus2HOHOCO14 macrocyclic complexesbinding sitesMII atomsligand structureLigand FeaturesThemacrocycle 6CO 2bind MIIMacrocycle 2binucleating macrocycle 2CNhydroxo bridgesAttempted decreasemacrocyclic familyDivalent Ionscopper systemoctahedral NiIIbridges XMII sitesNiII pincercarbon monoxide dehydrogenase