You must include some details on what BPMEN means, and what you think is the structure you have made (a PDF perhaps). I know I can look it up (and I did), but it is best if you can share more info, so your question gets the attention it deserves.

a few questions and suggestions though:

1. How susceptible is the methylene spacer to oxidation? Did you look up structures to see if the CH2 can transform into C=O? (CCDC search, or just a casual google scholar search)

2. Did you look up any info on BPMEN-metal complexes, where MS characterization was performed?

3. If you have proof that the CH2 had indeed transformed into C=O, you could hydrolyze your complex, and acquire an NMR spectrum of your ligand (1H and 13C) to show absence of CH2 resonances, and presence of C=O.

4. I know of instances where "things happen" during ESI-MS (like at the port), so make sure what you are looking at is not a consequence of sample handling issues.

Thanks Sudarsan for your suggestions. I really appreciate it and will definitely add some more information about BPMEN.

According to information I gathered, the structure of BPMEN has  two  susceptible CH2 spacers. One -CH2-CH2- bridge and another is -CH2 attached with nitrogen(attached pdf). Now I need to prove that in both -CH2 spacers, where exactly the transformation is going on? To justify this case I need to perform demetallation so I can get oxidized ligand and can run NMR of that. I think this is exactly what you suggested about to hydrolyze the complex and acquire an NMR of that sample.

I tried to search some metal-BPMEN complexes but didn't get any related articles about demetallation and ligand oxidation.

Thanks for your time.

For early transition metals at least, we add D2O, hydrolyze the metal complex, and get an NMR (without stripping the solvent). I hope you have the NMR resonances for the CH2 group on your ligand. Check if, after demetalation, you observe those resonances. If you do not locate them, then see using 13C if you can find a resonance for a "carbonyl" functionality. That should be proof that you have oxidized the ligand.

If I understand correctly, you added H2O2 to make "mew-oxo" copper complexes, but ended up oxidizing the ligand?

YOu must also be able to prove where the "O" comes from; some labeling experiments must come in handy.  But for now, hydrolysis and acquiring a 1H NMR spectrum should be task # 1.

Yes, I added H2O2 and base to make oxo species of copper complex but ended up with ligand oxidation. I got some references for demetallation experiment in which NaEDTA has been used to demetallate the complex. I couldn't find any reference using D2O but as per your suggestion, I will again look for references that used D2O to hydrolyze the complexes..

After figuring out this ligand oxidation, I will go for labeling studies that will enable me to prove the actual source of oxygen attached.

I really appreciate your help. Thanks so much.

I do not find the use of other complexing reagents (NaEDTA for example) surprising.  That is also a strategy to follow.

I work with early transition metals, and when we wish to study changes on the ligand, we just "quench" with D2O; I have also seen people pass their complex through a pipette filled with silica to analyze for the organic portion that elutes.

I am surprised the ligand reacts in preference to the copper. I wonder if that is because of the chlorates. Anyhow, good luck with your work.