Iron Carbonyl Complexes Containing N,C,S-Tridentate Ligands with Quinoline, Vinyl, and Benzenethiolate Units

Abstract

Iron­(III) carbonyl complexes of N,C,S-tridentate ligands containing quinoline-N, vinyl-C, and benzenethiolate-S donors were synthesized by three steps from quinolyl-substituted benzothiophenes via C–S bond cleavage, and their photoreactivity was investigated. The starting complexes [Fe2(μ-L)­(CO)5] (L = qvbt and qvbt-OMe) were synthesized by the photoreactions of the ligand precursors with [Fe­(CO)5], where qvbt and qvbt-OMe are a doubly deprotonated form of 2-[2-(quinolin-8-yl)­vinyl]­benzenethiol and its methoxy derivative, respectively. The methoxy group is bound to the vinyl moiety of the ligand, which is the β-position to Fe in the C,S-chelate. The N,C,S-pincer iron­(II) carbonyl complexes trans-[Fe­(L)­(CO)­(PMe3)2] were obtained by treatment of [Fe2(μ-L)­(CO)5] with PMe3. One-electron oxidation of the iron­(II) complexes afforded the N,C,S-pincer iron­(III) carbonyl complexes trans-[Fe­(L)­(CO)­(PMe3)2]­PF6. The iron­(III) carbonyl complex of qvbt was adequately stable in both the solid and solution state, whereas the qvbt-OMe complex underwent thermal decomposition in solution. The instability is related to the steric demand of the methoxy group in the coordinated ligand. Both iron­(III) complexes showed the CO-releasing properties induced by visible light in dichloromethane, which is enhanced by the methoxy group on the vinyl moiety.

Desulfurization and N2 Binding at an Iron Complex Derived from the C–S Activation of Benzothiophene

“…As noted in the Introduction section, there are few examples of using C–S activation to generate new ligand scaffolds, but this area has been pioneered by Hirotsu. − The new PCS ligand platform described here is distinguished by its ability to perform successive reductive bond cleavages and to bind N 2 . This increased reactivity may be attributed to the strongly donating phosphine side arm compared to the less-donating quinoline and thioether derivatives in the compounds from Hirotsu (Scheme ) and to the lack of strongly bound CO ligands.…”

“…12,13 Due to the presence of CO in the iron source, they have used some of the resulting iron complexes to examine ligand effects on CO binding and its light-induced release. 12,14 To our knowledge, such strategies have not been pursued with other iron precursors that are more amenable to reactivity with small molecules other than CO.…”

“…Their studies have revealed that C–S activation of a variety of functionalized thiophene derivatives is possible using low-valent Fe­(CO) 5 under irradiation (Scheme ). , Due to the presence of CO in the iron source, they have used some of the resulting iron complexes to examine ligand effects on CO binding and its light-induced release. , To our knowledge, such strategies have not been pursued with other iron precursors that are more amenable to reactivity with small molecules other than CO.…”

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

“…The bond distance of C12-C13 in 2 is 1.421( 5) Å (Table 2 and Figure 4), falling in the range between a single bond and a double bond, which is consistent with bond elongation caused by η-bonding between a metal center and a C=C bond. [44][45][46][47] For example, in iron(0) tricarbonyl η 4 -1-azadiene complexes ([Fe 0 (CO) 3 (η 4 -N(R 1 ) = C-C=C(R 2 )]), the distance of C=C bond is ca. 1.41 Å.…”