Synthesis of Heavy N-Heterocyclic Tetrylenes: Influence of Ligand Sterics on Structure

The synthesis and structural characterisation of [(NON^R)M] (NON=O(SiMe₂NR)₂]²⁻; R=tBu, Ph, 2,6-Me₂C₆H₃ (Dmp), 2,6-iPr₂C₆H₃ (Dipp); M=Ge, Sn, Pb) is described. Germanium complexes [(NON^Ph)Ge], [(NON^Dmp)Ge] and [(NON^Dipp)Ge] are monomeric. Tin complexes [(NON^Ph)Sn]₂, [(NON^Dmp)Sn]₂ and [(NON^tBu)Sn]₂ are dimeric in the solid-state, with [(NON^Ph)Sn]₂ forming a link through bridging N-atoms, [(NON^Dmp)Sn]₂ linked through Sn⋅⋅⋅Ar contacts and [(NON^tBu)Sn]₂ forming the first distannene bearing two amido ligands. In contrast, [(NON^Dipp)Sn] is monomeric in the solid-state. The lead complexes [(NON^Ph)Pb]₂ and [(NON^Dmp)Pb]₂ are isostructual with their tin analogues while [(NON^tBu)Pb] is monomeric in the solid-state. Solution phase NMR spectroscopic data suggest that all [(NON^R)M] compounds are monomeric in solution. Structural parameters, including buried volume (%V_bur) are discussed.