Eur J Inorg Chem 2025 Prediction of Metallo‐Annulenes

Inspired by the newly discovered in-plane [55555] metallo-annulene frameworks in 3D [Os]C15H10 ([Os] = OsL1L2 and L represents PPh3, CO, or PEt3 σ-ligands) and based on extensive first-principles theory calculations, herein a series of perfect 2D in-plane [55555] metallo-annulene complexes D5h MC15H10 (1) (M = Pt, Pd, Ni), D5h MC15H10− (2) (M = Ir, Rh), D5h MC15H102− (3) (M = Os, Ru), and D5h MC15H10+ (4) (M = Au, Ag) is predicted in which the penta-coordinate transition metal center η5-M and [15]annulene ligand C15H10 match both electronically and geometrically, without the two extra σ-ligands needed on the top and bottom. Detailed bonding pattern analyses indicate that metal dxz and dyz orbitals in these [55555] metallo-annulenes participate in π-conjugation with the five-membered rings to form nine delocalized π-bonds in total over the molecular plane following Hückel's [4 n + 2] rule (n = 4), rendering overall π-aromaticity and extra stability to the systems. Such a structural and bonding pattern can be adapted to form the highly stable perfect on-surface [55555] metallo-fullerenes D5d M2C50 (5) (M = Pt, Pd) and nonmetal bis([55555] metallo-annulene) sandwich complexes D5h C2(MC15H10)2 (6) (M = Ir, Rh) and D5h N2(MC15H10)2 (7) (M = Os, Ru).