Electrochemical characterisation of tetra- and octa-substituted oxo(phthalocyaninato)titanium(IV) complexes

Abstract

The synthesis and electrochemical characterisation of the following oxotitanium tetra-substituted phthalocyanines are reported: 1,(4)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (5a); 1,(4)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (5b); 2,(3)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (6a) and 2,(3)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (6b). The electrochemical characterisation of complexes octa-substituted with 4-(benzyloxy)phenoxy (9b), phenoxy (9c) and tert-butylphenoxy (9d) groups is also reported. The cyclic voltammograms of the complexes exhibit reversible couples I–III and couple IV is quasi-reversible for complexes 5a, 5b, 6a and 6b. The first two reductions are metal-based processes, confirmed by spectroelectrochemistry to be due to Ti[superscript IV]Pc[superscript 2−]/Ti[superscript III]Pc[superscript 2−] and Ti[superscript III]Pc[superscript 2−]/Ti[superscript II]Pc[superscript 2−] redox processes and the last two reductions are ring-based processes due to Ti[superscript II]Pc[superscript 2−]/Ti[superscript II]Pc[superscript 3−] and Ti[superscript II]Pc[superscript 3−]/Ti[superscript II]Pc[superscript 4−]. Chronocoulometry confirmed a one-electron transfer at each reduction step. The electrochemistry of the above complexes is also compared to the previously reported 5c, 5d, 6c and 6d.