Using O=Cc1cc2ccc(Cl)cc2nc1Cl, O=[Cr](=O)([O-])O[Cr](=O)(=O)[O-] to produce O=C(O)c1cc2ccc(Cl)cc2nc1Cl, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.