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

Abstract

Two Co(II) complexes of the formula CoL^OMeX₂ (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, CoL^O−Cl₂ (2). On the other hand, complex 1b with weaker iodo coligands undergoes oxidation in the presence of the weak oxidant O₂ to form a dihydroxo bridged binuclear Co(III) complex [Co₂(L^O−)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 [CoL^OMeI(H₂O)]⁺ and Co(II) diaqua complex [CoL^OMe(H₂O)₂]²⁺ are isolated and characterised.