The redox properties of ferrocenyl-substituted aryl azines

Sauro, Vittorio A; Workentin, Mark S
March 2002
Canadian Journal of Chemistry;Mar2002, Vol. 80 Issue 3, p250
Academic Journal
A series of ferrocenyl substituted azines (1-Fc/Ar, where Ar = 4-NO[sub 2] C[sub 6] H[sub 4] , 4-CNC[sub 6] H[sub 4] , 4-OCH[sub 3] C[sub 6] H[sub 4] , C[sub 5] H[sub 4] N, ferrocene, anthracene, and pyrene) were investigated by electrochemical and photochemical techniques. All the 1-Fc/Ar exhibited oxidation waves within 60 mV of each other, consistent with the expected oxidation of the ferrocene moiety. The reduction properties of 1-Fc/Ar is governed by the nature of the Ar substituent. The standard reduction potentials suggest that ferrocene has comparable electron donating abilities as a 4-methoxyphenyl and 4-dimethyl aminophenyl group. The anthracenyl azines exhibit one-electron reversible reduction followed by dimerization of the radical anion resulting in dimerization rate constants (k[sub d] ) between 5.1 � 10[sup 4] and 1.5 � 10[sup 5] M[sup �1] s[sup �1] . 1-Fc/Anth and related azines undergo photochemical E/Z isomerization of the C=N bonds to produce E/Z and Z/Z isomers from the thermodynamically most stable E/E form. Fluorescence at 77 K, was observed for these compounds only after long- wavelength irradiation to produce a mixture of E/E, E/Z, and Z/Z isomers. Fluorescence quantum yields of 0.042, 0.090, and 0.176 were determined for 2-Anth/H, 2-Anth/Anth, and 1-Fc/Anth, respectively. The electrochemical, photochemical, and X-ray data suggest that the azine unit is a conjugation "limiter" and may be a general characteristic of azine molecules.Key words: azines, electrochemistry, cyclic voltammetry, reduction, electron transfer.Faisant appel � des techniques �lectrochimiques ainsi que photochimiques, on a �tudi� une s�rie d'azines de ferroc�nyles substitu�s (1-Fc/Ar dans lesquels Ar = 4-NO[sub 2] C[sub 6] H[sub 4] , 4-CNC[sub 6] H[sub 4] , 4-OCH[sub 3] C[sub 6] H[sub 4] , C[sub 5] H[sub 4] N, ferroc�ne, anthrac�ne et pyr�ne). Tous les 1-Fc/Ar pr�sentent des vagues d'oxydation � moins de 60 mV les uns des autres, ce � quoi on peut s'attendre pour l'oxydation de la partie ferroc�ne. Les propri�t�s de r�duction des 1-Fc/Ar sont d�finies par la nature du substituant Ar. Les potentiels de r�duction standards sugg�rent que les propri�t�s du ferroc�ne en ce qui a trait � ses possibilit�s de donner des �lectrons sont semblables � celles des groupes 4-m�thoxyph�nyle et 4-dim�thylaminoph�nyle. Les azines d�riv�s de l'anthrac�ne donnent lieu � une r�duction r�versible � un �lectron suivie d'une dim�risation de l'anion radical avec des constantes de vitesse de dim�risation (k[sub d] ) qui vont de 5,1 � 10[sup 4] � 1,5 � 10[sup 5] M[sup �1] s[sup �1] . La 1-Fc/Anth et les azines apparent�es subissent des isom�risations photochimiques E/Z des liaisons C=N qui conduisent � des m�langes d'isom�res E/Z et Z/Z � partir de la forme E/E, thermodynamiquement la plus stable. Ces compos�s ne donnent lieu � de la fluorescence � 77 K qu'apr�s avoir �t� soumis � une irradiation � grande longueur d'onde qui permet de produire un m�lange des isom�res E/E, E/Z et Z/Z. On a d�termin� des rendements quantiques de fluorescence de 0,042, 0,090 et 0,176 respectivement pour les 2-Anth/H, 2-Anth/Anth et 1-Fc/Anth. Les donn�es �lectrochimiques, photochimiques ainsi que celles relatives � la diffraction des rayons X sugg�rent que l'unit� azine � limite � la conjugaison et que cette propri�t� est peut-�tre une caract�ristique g�n�rale pour les mol�cules d'azine.Mots cl�s : azines, �lectrochimie, voltamp�rom�trie cyclique, r�duction, transfert d'�lectron.[Traduit par la R�daction]


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