Synthesis and characterization of organometallic chalcones functionalized with a crown ether fragment. Spectroscopic and electrochemical behavior

Abstract

Organometallic chalcone complexes functionalized with a macrocyclic fragment [( 5 -C 5 H 4 C(O)CH=CH-4-benzo-15-crown-5)MLn] (ferrocenyl, cyrhetrenyl, and cymantrenyl) have been synthesized. The complexes are characterized by IR spectroscopy, 1 H and 13 C NMR spectroscopies, elemental analyses, and HR-MS. The stereochemistry for the chalcone compounds was determined using the 1 H and 13 C NMR spectroscopy data, which indicated that they are isolated as a single isomer (E). In addition, the syntheses of the chalcone-imine derivatives are described, and they adopt an anti-(E,E) conformation in solution, confirmed by the X-ray crystal structures in the solid state. The UV-Visible and electrochemical behavior of the organometallic complexes are reported. Keywords: Organometallic chalcone and imine complexes, crown ether, crystal structures. examples of their application as chemosensors. Delavaux-Nicot et al. have investigated a series of ferrocenyl chalcones, mono and 1,1'-disubstituted, functionalized with an amine moiety or an aza-macrocycle. 13 These metallo-ligands have shown selectivity toward Ca 2+ and Ba 2+ in acetonitrile. Another important class of functionalized rhenium(I) complexes with aza-crown ether pendants, synthetized by Yam et al., exhibit a high specificity towardPb(II). 14 Previously, our research group reported the synthesis of new cyrhetrenyl tricarbonyl complexes functionalized with 4'-benzo-crown or 2-methyl-crown ether fragments, bridged by an imine linker. The cyclic voltammograms showed positive anodic waves arising from the Re(II)/Re(I) redox process (I). It was concluded that the size of the crown ether did not change the anodic potential significantly. Nevertheless, the metal centered redox processes of complexes that possess a methylene moiety were shifted to positive potentials compared to a benzo group. 15 In this work, we report the synthesis, X-ray structures and electrochemical and spectroscopic behaviour of new ferrocenyl, cyrhetrenyl and cymantrenyl complexes functionalized with 4'-benzo-15-crown-5 fragment. In addition we have included the synthesis of related species with a chalcone-imine as linker.2. Results and discussion. Synthesis of the organometallic chalcones 2-3.The compounds were synthesized following a procedure similar to that described for ferrocenyl and cymantrenyl chalcone derivatives. 11,16 It is based on the Claisen-Schmidt reaction involving the condensation of the organometallic ketones 1a-c and the corresponding crown ether or organic aldehydes Id-e (Scheme 1). Derivatives 2a-c and 3awere obtained by reaction of the corresponding precursors in the presence of NaOH and were dissolved in water/ethanol mixed solvent for greater solubility of the components. A modification of the experimental procedure was used for the preparation of the cyrhetrenyl derivative 3b. The carbanion containing solution was added dropwise to an ethanolic solution of terephthalaldehyde (Ie) over a period of 2 h. in order to control the proportion of nucleophile generated. The genera...

Kinetic and Mechanistic Observations on the Photoinduced Isomerization Reaction of Organometallic Chalcones: A Steady State and Flash Photolysis Study

“…We have recently reported the synthesis and structural properties of new organometallic chalcones bearing cyrhetrenyl, ferrocenyl and cymantrenyl fragments functionalized with a benzo‐15‐crown‐5 ether (Figure ) . These complexes were designed as optical ion chemosensors but we are also interested in their unknown photochemical behavior.…”

“…The presence of the photoredox pathway in the ferrocenyl but not in the cyrhetrenyl chalcones can be rationalized on the basis of their redox potentials. Indeed, because the redox potential of the couple (η 5 ‐C 5 H 4 C(O)CH=CH‐benzo‐15‐crown‐5)Fe(η 5 ‐C 5 H 5 ) +/0 ( 2 b ) is more negative than the potential of the couple (η 5 ‐C 5 H 4 C(O)CH=CH‐benzo‐15‐crown‐5)Re(CO) 3 +/0 ( 1 b ), the ferrocenyl MLCT Fe→L excited states will be then populated as a result of the λ =300 or 350 nm light used in the photolyses. In contrast, similar MLCT excited states of the cyrhetrenyl chalcones will be placed at higher energies and will be available.…”

Novel organometallic chalcones functionalized with a crown ether fragment as optical ion chemosensors

“…These observations are in good agreement with the electronic properties of the organometallic moiety, i.e. a more electron‐withdrawing character for cyrhetrenyl chalcone with respect to ferrocenyl chalcone . On the other hand, higher association constants have been determined using 1 H NMR spectroscopy for complexation reaction of ferrocenyl chalcones 1,1′‐disubstituted with aza‐macrocycles towards calcium ions …”

“…Free metalloligands 1 and 2 (Figure ) have been previously synthetized and fully characterized by Agurto et al . and the structural and electrochemical properties have been studied.…”

“…The synthesis and characterization of cyrhetrenyl, ferrocenyl and cymantrenyl chalcones were reported in a previous work . The compounds were used without further purifications.…”