Iron phthalocyanine (FePc) is adsorbed to graphene on Ir(111) at cryogenic temperature. In addition to mobile FePc with four lobes, imaging and spectroscopy with a scanning tunneling microscope reveal immobile molecules that exhibit fewer lobes. A reversible transformation between four- and three-lobed molecules has been induced by current injection. The data are consistent with chemical bonding of lobes to graphene on Ir, pinning down the graphene area toward Ir. Similar observations are made from NiPc, CoPc, CuPc, and H2Pc. The experimental findings can be explained by ab initio calculations, which suggest that a Diels-Alder-type reaction may be involved with an allyl unit of graphene in the top-fcc moiré registry.