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 ( L 1 ‐ L 3 ) 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 σ ‐bonds or η ‐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 ( 1 H 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.