Half‐Sandwich, Bent‐Sandwich and Triple‐Decker Molybdenum Complexes of S2N2 – Fluxionality and Metal‐Metal Bond

Abstract

AbstractThe instability of the π‐complexes of electron‐rich inorganic aromatics with transition metal fragments, contrary to their conventional aromatic analogues, was investigated by taking the four‐membered 6π‐electron S2N2. Our theoretical investigation based on fragment molecular orbitals and Energy Decomposition Analysis with Natural Orbitals for Chemical Valence (EDA‐NOCV) on the bonding nature of different types of π‐complexes of S2N2 viz. half‐sandwich, bent‐sandwich and triple‐decker type complexes with molybdenum fragment reveals that S2N2 can potentially act as a six π‐electron donor. However, due to the lower energy π* MOs the π‐back donation from metal fragment is stronger than the π‐donation, which might lead to weaking of the overall ring structure and low dissociation energy. The dissociation energy for dissociation of one S2N2 ring increases with the increasing number of S2N2 in the complex. The smaller size of the ring leads to fluxional behaviour in order to attain orbital compatibility between the π‐MOs and the metal orbitals. Also, the triple decker complex depicts an unsymmetric middle deck, where the middle S2N2 ring has been fragmented into two SN units along with a Mo−Mo bond. The higher dissociation energy of triple‐decker complexes can be corroborated well with the report of an isoelectronic triple‐decker complex [Mo2Te12]6+.