With the help of DFT calculations the possibility of stabilizing non-standard flat conformations of cyclooctatetraene and cyclodecapentaene by equatorially located metalcarbonyl substituents has been predicted. Structures and stabilities of a new family of metalcarbonyl Cr(CO)5, Fe(CO)4, Ni(CO)3, Ti(CO)4, and Ni(CO)2 cyclooctatetraene and cyclodecapentaene derivatives have been studied. All cyclooctatetraene derivatives, except the Ti(CO)4 derivative, have planar structures and are characterized by the pronounced anti-aromaticity of the core cycle. In the case of cyclodecapentaene complexes, the planar structures are formed by only Fe(CO)4 and Ni(CO)3 derivatives. Stabilization of non-standard planar forms is caused by both sterically enforced flattening of the core cycles and their π-interactions with metalcarbonyl moieties.