The reaction of nonacarbonyldiiron with 8-alkynyloxyquinolines: Alkynyl activation, cyclization via C-N bond formation, and C-H bond cleavage

In this work, the reactions of nonacarbonyldiiron with 8-alkynyloxyquinoline ligands (L1-L3) and their resultant iron carbonyl complexes (1a, 1b, 2, and 3) are described. The complexes including the ligands were fully characterized by using a variety of spectroscopic techniques. The four complexes were also crystallographically determined. In the reactions, the quinoline N atom underwent cyclization to form a quinolinium skeleton while the C-H bond of the quinoline at position 2 or the substituted methyl group was cleaved to form Fe-C bond(s). Meanwhile, the alkynyl triple bond was reduced to a single bond (1a) or double bonds (1b, 2, and 3) to further coordinate the iron in sigma-bonds or eta-bonds. Particularly, pathways of hydrogenation (1a and 2) and/or dehydrogenation (1b and 3) were accompanied by the reactions. Moreover, the oxidation states of the iron centers in these complexes were identified through analyses of their bond formation, FTIR and NMR spectroscopic signals (1H NMR and DEPT-135) in combination with their diamagnetic nature, that is, iron (0) for 2 and iron (I) for the rest of the diiron complexes. Affording quinolinium iron carbonyl complexes from the reactions of [Fe2(CO)9] with 8-alkynyloxyquinolines via alkynyl activation, cyclization with C-N bond formation, and cleavage of C-H bond. image