Novel polyphenylene–metal complexes with discotic, linear, and dendritic geometries are synthesized by using a facile approach consisting of reactions between Co2(CO)8 and ethynyl functionalities in dichloromethane. Various carbon nanoparticles (CNPs), including graphitic carbon nanotubes (CNTs), graphitic carbon rods, and carbon–metal hybrid particles are obtained from the solid-state pyrolysis of these complexes. The ultimate structures of the CNPs are found to be dependant on the structure and composition of the starting compounds. Precursors containing graphenes always result in graphitic CNTs in high yield, whereas dendritic precursors give rodlike carbon materials. Alternatively, linear oligo(arylethylene) precursors afford mostly carbon–metal hybrids with large amounts of amorphous carbon. Furthermore, the CNP structures could be controlled by adjusting the carbon/metal ratio, the type and position of the metal incorporated into the precursor, and the mode of pyrolysis. These results provide further chances toward understanding the mechanism of CNP formation.