Restriction of reaction sites on metal-sulfide cores induced by steric repulsion of bis-N-heterocyclic carbene ligands in trinuclear complexes bearing triply bridging sulfide ligands.

Mixed-ligand and mixed-metal trinuclear complexes bearing two {Pt-bisNHC-C1} moieties, [{Pt(bisNHC-C1)}(ML)(μ-S)] (ML = Pt(bisNHC-C2), = 2; ML = Pt(bisNHC-C3), = 2; ML = Rh(cod), = 1; ML = RhCp*, = 2), where bisNHC-C1, bisNHC-C2 and bisNHC-C3 represent methylene-, ethylene- and propylene-bridged bis-NHC ligands, respectively, were synthesised and structurally characterised. Reactions of these complexes with a half eq. of Ag(i) ions were examined using H and Pt NMR spectroscopy. The results exhibit that the trinuclear complexes react with Ag(i) ions accompanied by the formation of Ag-Pt bonds with the {Pt-bisNHC-C1} moieties in the first step affording corresponding heptanuclear complexes except for the RhCp* complex. The RhCp* complex gave a tetranuclear complex bearing the trinuclear unit with an Ag(i) ion. Further addition of Ag(i) ions for the other complexes resulted in disassembling of the heptanuclear clusters affording tetranuclear complexes confirmed by the observation of exchange of the Ag(i) ions in Pt NMR measurements, which exhibited signals with no coupling to Ag nuclei.