The tipping point of the inert pair effect: experimental and computational comparison of In(i) and Sn(ii) bis(imino)pyridine complexes

Abstract

The autoionization reaction of neutral bis(imino)pyridine and SnX₂ led to three compounds [{ArNCPh}₂(NC₅H₃)]SnX⁺SnX₃⁻ (Ar = 2,6-(2,5-^tBu₂C₆H₃), X = Cl, Br; Ar = 2,6-(2,6-Me₂C₆H₃), X = Cl) which display, within the same species, cations and anions possessing Sn(II) centers. Computational analysis compared the ligated Sn(II) cations with bis(imino)pyridine In(I) complexes that showed unprecedented weak metal–ligand covalent interactions, consistent with the In(I) 5s² electrons remaining as an inert nonbonding pair. Analysis of the metal–ligand bonding indicates that the chloride ligand of the Sn(II) complex induces promotion of the metal 5s² electron pair to a stereochemically active hybridized orbital, which, in turn, allows strong coordination of the bis(imino)pyridine to Sn.