Enhancing the Variability of [Ge₉] Cluster Chemistry through Phosphine Functionalization

The synthetic approach towards molecules that contain Ge atoms with oxidation state 0, and which are exclusively connected to other Ge atoms, is explored by using anionic clusters extracted from binary solids. Besides providing a novel variable method for the introduction of alkenyl moieties to [Ge₉] cluster compounds, this work expands the spectrum of mixed-functionalized [Ge₉] cluster anions, which are suitable for the straightforward synthesis of zwitterionic compounds upon coordination to metal cations. In detail, the synthesis of a series of mixed-functionalized [Ge₉] clusters is reported, including [Ge₉{Si(TMS)₃}₃PRR^I] (R=tBu, R^I=(CH₂)₃CH=CH₂; 2) and [Ge₉{Si(TMS)₃}₂PRR^I]⁻ (R and R^I: alkyl, alkenyl, aryl, aminoalkyl; 3 a to 11 a, TMS: (trimethyl)silyl). In 2 and 3 a, pentenyl functionalization of the [Ge₉] clusters was achieved by reaction of the novel chlorophosphine tBu{(CH₂)₃CH=CH₂}PCl (1) with silylated [Ge₉] clusters. Furthermore, the reactivity of the cluster anions 3 a to 11 a towards NHC^DippMCl (NHC^Dipp=1,3-di(2,6-diisopropylphenyl)imidazolylidine; M=Cu, Ag) showed a dependency on the steric demand of the phosphine either zwitterions (3-MNHC^Dipp to 7-MNHC^Dipp) featuring P–M interactions are formed, or Ge–M coordination (8-MNHC^Dipp to 11-MNHC^Dipp) occurs. For M=Ag, the formation of zwitterionic complexes was unequivocally proven by NMR investigations showing ¹J(³¹P-¹⁰⁷Ag/¹⁰⁹Ag) spin-spin coupling.