On-demand switching from mono-silylene to bis-silylene to access mono-, di- and mixed coinage metal complexes

Recently, we discovered that silaiminyl-silylene, [LSi-Si(NDipp)L] (L = PhC(NtBu)2, Dipp = 2,6-diisopropylphenyl), can be converted from a mono-silylene to bis-silylene by using Lewis acids. This revelation led us to further use silaiminyl-silylene as a silylene-based ligand, which can coordinate to one metal center and later, on demand, release one more silylene center to coordinate to a second metal. Furthermore, an insight into the mechanism of this unusual rearrangement reaction is presented. Initially, mono-silylene complexes [LSi{M(Mes)}-Si(NDipp)L] (M = Ag, Au) were isolated. These complexes were then used as templates to access bis-silylene coordinated homo-dinuclear, [LSi{M(Mes)}-(NDipp)-{M(Mes)}SiL] (M = Ag, Au) and hetero-dinuclear, [LSi{Ag(Mes)}-(NDipp)-{Au(Mes)}SiL] complexes via a Lewis acid triggered ligand rearrangement. Notably, using this silylene, a selective coordination of the two different coinage metals Ag and Au was achieved stepwise. This differs from the reactivity when a conventional bis-silylene is employed. The isolation of [LSi{Ag(Mes)}-(NDipp)-{Au(Mes)}SiL] showcases the utility of strong σ-donor silylene-based switchable ligands. This represents the first example of a heterobimetallic complex ligated by a spacer-separated bis-silylene ligand.