Triaryl- and trialkylantimony(V) Bis(catecholates) based on 1,1'-spirobis[3,3-dimethylindanequinone-5,6]: Spectroscopic and electrochemical studies

A series of new binuclear bis(catecholate) antimony(V) complexes based on 1,1'-spirobis[3,3-dimethylindanequinone-5,6] with various substituents at the central antimony atoms, R3Sb(Cat-Spiro-Cat)SbR3 (I-IV) and R3Sb(Cat(Br)-Spiro-(Br)Cat)SbR3 (V-VIII) (R = p-fluorophenyl, phenyl, p-tolyl, and ethyl), were synthesized. Spirobis(catecholates) I-III exhibit two one-electron oxidation waves on the cyclic voltammograms, whereas bromo-substituted spirobis(catecholates) V-VII undergo two-electron oxidation immediately at the first stage. The two-electron oxidation of the complexes results in the loss of one of the organoantimony fragments and the formation of mononuclear catecholate-quinone complexes (Q-Spiro-Cat)SbR3 or (Q(Br)-Spiro-(Br)Cat)SbR3, respectively. An insignificant delocalization of the charge and spin between two redox centers is observed in the complexes. The nature of substituents at the antimony atom exerts an effect on the values of redox potentials of the complexes: more donating groups decrease the oxidation potentials of the catecholate fragments and more withdrawing groups increases these values.