Inorganic Chemistry, Vol.46, No.18, 7610-7620, 2007
Selective oxidation and reduction of trinuclear titanium(II) hexaazatrinaphthylene complexes - Synthesis, structure, and electrochemical investigations
Titanocene complexes with chelating N- heterocyclic ligand bridges react with ferrocenium salts as selective oxidants to afford air-stable cationic complexes and allow the preparation of exceptional mixed valence hexaazatrinaphthylene complexes [( Cp2Ti) (3)( mu(3)-HATNMe(6))] (n +) ( 1 (n) +) ( n) 1, 2, 3, 4). Cyclic voltammograms ( CV) and differential pulse voltammograms ( DPV) show that nine oxidation states of 1 are generated without decomposition. Comproportionation constants K c have been calculated in order to determine the extent of electronic communication between the titanium centers. The K c values of the mixed valence states are indicative of uncoupled ( 14 +), moderately coupled ( 1(5 +)), and strongly coupled ( 1(-,) 1 (+), and 1(2 +)) systems. Small but significant structural changes occurring upon oxidation of neutral 1 are observed by X- ray structural analysis on 1 (+) - 1(4) +. Anion - pi interactions between the electron- deficient central ring of the HATNMe6 moiety and PF6 -and BF4 - counterions, respectively, are found for 12 +, 13 +, and 14 +. The short cation - anion contacts cause interesting molecular allignments in terms of molecular architecture. For 12 + the assembly of an one- dimensional ( 1D) polymer is observed. Electrochemical investigations on the mononuclear cationic titanocene complexes [( Cp2Ti)( L)] + ( L) 2,2 ' biquinoline ( 2 +), 4,4' dimethyl- 2,2 '-biquinoline ( 3 +), and 5,8 '- dimethyl- 2,3 '- biquinoxaline ( 4 +)) showed similar oxidation and reduction characteristics among each other. Conversion to monoanionic, neutral, and dicationic states is enabled. As found for the trinuclear compounds 1 n +, the molecular structures of 2 + - 4 + reveal significant differences compared to their neutral parents.