Coligand modulated oxidative O-demethylation of a methyl ether appended tetradentate N-ligand in Co(ii) complexes.

Two Co(ii) complexes of the formula (CoLX2)-X-OMe (X = Cl- (1a); X = I- (1b)), where L-OMe is 2-methoxy-N,N-bis(pyridin-2-ylmethyl) aniline, were synthesized and their structure, spectra and reactivity were studied. Upon oxidation of 1a and 1b, the ligand L-OMe undergoes demethylation at the metal centre resulting in the formation of Co(iii) complexes with modified phenoxide ligands. This is the very first example of oxidative O-demethylation reported at a Co(ii) centre. The oxidative behaviour exhibits a striking dependence on the nature of coligands coordinated to the metal centre. The Co(ii) complex 1a with stronger chloro coligands requires a strong oxidising agent like t-BuOOH for oxidative demethylation and the subsequent formation of a mononuclear Co(iii) complex with a demethylated ligand, CoLO-Cl2 (2). On the other hand, complex 1b with weaker iodo coligands undergoes oxidation in the presence of the weak oxidant O-2 to form a dihydroxo bridged binuclear Co(iii) complex [Co-2(LO-)(2)(OH)(2)](2+) (3) with modified phenoxide ligands. The oxidation of 1b to 3 is monitored and the intermediate Co(ii) iodo aqua complex [(CoLI)-I-OMe(H2O)](+) and Co(ii) diaqua complex [CoLOMe(H2O)(2)](2+) are isolated and characterised.