Core-modified isophlorin–metal complexes were successfully prepared by redox-coupled complexation of P,S,N2-hybrid porphyrin with zerovalent palladium, nickel, and platinum. In this transformation, the core-phosphorus atom plays crucial roles in enhancing the electron-accepting ability of the 18π porphyrin ring and stabilizing the 20π isophlorin ring owing to high P–M affinity. The isolated Pd and Pt complexes are chemically stable under ambient conditions. The Pd–P,S,N2 isophlorin complex was structurally characterized by X-ray crystallography, which revealed a distorted 20π plane with a square planar palladium(II) center. Experimental (1H, UV–vis, and X-ray) and theoretical (density functional theory calculations) results suggest that the P,S,N2–isophlorin–metal complexes possess nonaromaticity in terms of both magnetic and geometrical criteria.