Snapshots of sequential polyphosphide rearrangement upon metallatetrylene addition

Insertion and functionalization of gallasilylenes [L(Ph)Si–Ga(Cl)L(BDI)] (L(Ph) = PhC(NtBu)(2); L(BDI) = [{2,6-iPr(2)C(6)H(3)NCMe}(2)CH]) into the cyclo-E(5) rings of [Cp*Fe(η(5)-E(5))] (Cp* = η(5)-C(5)Me(5); E = P, As) are reported. Reactions of [Cp*Fe(η(5)-E(5))] with gallasilylene result in E–E/Si–Ga bond cleavage and the insertion of the silylene in the cyclo-E(5) rings. [(L(Ph)Si-Ga(Cl)L(BDI)){(η(4)-P(5))FeCp*}], in which the Si atom binds to the bent cyclo-P(5) ring, was identified as a reaction intermediate. The ring-expansion products are stable at room temperature, while isomerization occurred at higher temperature, and the silylene moiety further migrates to the Fe atom, forming the corresponding ring-construction isomers. Furthermore, reaction of [Cp*Fe(η(5)-As(5))] with the heavier gallagermylene [L(Ph)Ge–Ga(Cl)L(BDI)] was also investigated. All the isolated complexes represent rare examples of mixed group 13/14 iron polypnictogenides, which could only be synthesized by taking advantage of the cooperativity of the gallatetrylenes featuring low-valent Si(ii) or Ge(ii) and Lewis acidic Ga(iii) units/entities.