Reactions of Mesityl Azide with Ferrocene-Based N-Heterocyclic Germylenes, Stannylenes and Plumbylenes, Including PPh₂-Functionalised Congeners

The active PbII/P Lewis pair nature of a PPh₂-functionalised ferrocene-based N-heterocyclic plumbylene is demonstrated by its reaction with mesityl azide to afford a phosphazide, which is in contrast to the inertness of the unfunctionalised congener. The lighter analogues most likely react with MesN₃ at their respective tetrel atom Eᴵᴵ, leading to the formation of N₂ and an Eᶦᵛ=NMes unit, followed by NMes transfer from the Eᶦᵛ to the Pᴵᴵᴵ atom. The reactivity of ferrocene-based N-heterocyclic tetrylenes [{Fe(η⁵−C₅H₄−NSitBuMe₂)₂}E] (E=Ge, Sn, Pb) towards mesityl azide (MesN₃) is compared with that of PPh₂-functionalised congeners exhibiting two possible reaction sites, namely the Eᴵᴵ and Pᴵᴵᴵ atom. For E=Ge and Sn the reaction occurs at the Eᴵᴵ atom, leading to the formation of N₂ and an Eᶦᵛ=NMes unit. The germanimines are sufficiently stable for isolation. The stannanimines furnish follow-up products, either by [2+3] cycloaddition with MesN₃ or, in the PPh₂-substituted case, by NMes transfer from the Snᶦᵛ to the Pᴵᴵᴵ atom. Whereas [{Fe(η⁵−C₅H₄−NSitBuMe2)2}Pb] and other diaminoplumbylenes studied are inert even under forcing conditions, the PPh₂-substituted congener forms an addition product with MesN3, thus showing a behaviour similar to that of frustrated Lewis pairs. The germylenes of this study afford copper(I) complexes with CuCl, including the first structurally characterised linear dicoordinate halogenido complex [CuX(L)] with a heavier tetrylene ligand L.