The adsorption of the carbene precursor diphenyldiazomethane (DPDMA) on clean and CO-precovered Ru(0001) has been investigated using infrared reflection absorption spectroscopy (IRAS). Deposition of DPDMA in a control experiment onto the clean metal surface leads to a cleavage of the diazo group, yielding an upright standing diphenylmethylene species. To inhibit this instant dissociation and to control the state of the carbene precursor, adsorption was studied on a CO-spacer layer on the Ru-surface. The reaction of the photochemically or thermally formed diphenylcarbene with the underlying CO molecules yields a new carbonyl-containing species, which is proposed to be a surface bound diphenylketene.