A new Ni(ii) complex [NiL] (complex1) of an asymmetrically di-condensed N2O3donor Schiff base ligand,N-salicylidene-N′-3-methoxysalicylidene-1,3-propanediamine (H2L), has been synthesized and utilized for the synthesis of three heterometallic complexes, [(NiL)2Mn(NCS)2(CH3OH)2]·CH3OH (2) [(NiL)2Mn(N(CN)2)2(CH3OH)2]·CH3OH (3) and [(NiL)2Mn2(N3)2(μ1,1-N3)2(CH3OH)2] (4). Single crystal X-ray diffraction analyses show that complexes2and3have linear trinuclear structures where two tridentate O3donor (NiL) units are coordinated to the central octahedral Mn(ii) centre, whereas complex4has a centrosymmetric tetranuclear structure where two binuclear (NiL)Mn units are linkedviatwo phenoxido and two μ1,1-N3bridges. Among the heterometallic complexes (2-4), only4is active towards the catalytic oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone. The turnover number for the aerobic oxidation of 3,5-DTBC is 935 h−1. ESI-mass spectra have been recorded to scrutinize the mechanistic pathway of this catalytic reaction. Variable temperature magnetic susceptibility measurements suggest that complexes2-4are antiferromagnetically coupled with coupling constants (J) of −4.84 and −5.23 cm−1for complexes2and3, respectively andJ1= −2.20 cm−1,J2= 1.13 cm−1andJ3= −1.12 cm−1for complex4. DFT calculations have been used to rationalize the magnetic super-exchange in complexes2-4, by computing the theoretical coupling constants and analyzing the spin density plots. © The Royal Society of Chemistry 2021.