Metal oxygen-containing complex and its use as a pre-oxidant

A metal oxygen-containing complex, which comprises a transition metal element as central atom and an oxygen-containing heterocyclic organic compound containing a substituent as ligand;

• wherein the ligand is a compound having a structure shown in formula (I),
• in formula (I), n is an integer of 0-5, A is —CH(R5)—;
• R1 and R2 at each occurrence are each independently selected from C1-C8 alkyl, and R3, R4 and R5 at each occurrence are each independently selected from H, C1-C8 alkyl, phenyl C1-C8 alkyl and C1-C8 alkylphenyl.