The Heaviest Bottleable Metallylone: Synthesis of a Monatomic, Zero-Valent Lead Complex (“Plumbylone”)

The elusive plumbylone {[Si^II(Xant)Si^II]Pb⁰} 3 stabilized by the bis(silylene)xanthene chelating ligand 1, [Si^II(Xant)Si^II=PhC(NtBu)₂Si(Xant)Si(NtBu)₂CPh], and its isolable carbonyl iron complex {[Si^II(Xant)Si^II]Pb⁰Fe(CO)₄} 4 are reported. The compounds 3 and 4 were obtained stepwise via reduction of the lead(II) dibromide complex {[Si^II(Xant)Si^II]PbBr₂} 2, prepared from the bis(silylene)xanthene 1 and PbBr₂, employing potassium naphthalenide and K₂Fe(CO)₄, respectively. While the genuine plumbylone 3 is rather labile even at −60 °C, its Pb⁰→Fe(CO)₄ complex 4 turned out to be relatively stable and bottleable. However, solutions of 4 decompose readily to elemental Pb and {[Si^II(Xant)Si^II]Fe(CO)₃} 5 at 80 °C. Reaction of 4 with [Rh(CO)₂Cl]₂ leads to the formation of the unusual dimeric [(OC)₂RhPb(Cl)Fe(CO)₄] complex 6 with trimetallic Rh−Pb−Fe bonds. The molecular and electronic structures of 3 and 4 were established by Density Functional Theory (DFT) calculations.