Prediction of Perfect Aromatic In‐Plane [55555] Metallo‐Annulenes

Inspired by the newly discovered in‐plane [55555] metallo‐annulene frameworks in 3D [Os]C 15 H 10 ([Os] = OsL 1 L 2 and L represents PPh 3 , CO, or PEt 3 σ‐ligands) and based on extensive first‐principles theory calculations, herein a series of perfect 2D in‐plane [55555] metallo‐annulene complexes D 5 h MC 15 H 10 ( 1 ) (M = Pt, Pd, Ni) , D 5 h MC 15 H 10 − ( 2 ) (M = Ir, Rh), D 5 h MC 15 H 10 2− ( 3 ) (M = Os, Ru), and D 5 h MC 15 H 10 + ( 4 ) (M = Au, Ag) is predicted in which the penta‐coordinate transition metal center η 5 ‐M and [15]annulene ligand C 15 H 10 match both electronically and geometrically, without the two extra σ‐ligands needed on the top and bottom. Detailed bonding pattern analyses indicate that metal d xz and d yz 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 D 5 d M 2 C 50 ( 5 ) (M = Pt, Pd) and nonmetal bis([55555] metallo‐annulene) sandwich complexes D 5 h C 2 (MC 15 H 10 ) 2 ( 6 ) (M = Ir, Rh) and D 5 h N 2 (MC 15 H 10 ) 2 ( 7 ) (M = Os, Ru).