Low oxidation state silicon clusters - synthesis and structure of [NHC^DippCu(η⁴-Si₉)]³

The reaction of NHC^DippCuCl with the silicide phases A₁₂Si₁₇ (A: K, K/Rb, Rb) in NH₃(l) yields [NHC^DippCu(η⁴-Si₉)]^3- (1) as only the third example of a substituted [Si₉] cluster. The corresponding salts A₃[A(2.2.2-crypt)]₃[NHC^DippCu(η⁴-Si₉)]₂·26NH₃ (A: K (1a), K/Rb (1b), Rb (1c)) crystallize isostructurally in the space group P1[combining macron] and have been characterized by single crystal structure determination. ESI-MS and NMR experiments reveal that the anion [NHC^DippCu(η⁴-Si₉)]^3- can also be transferred to pyridine or acetonitrile solutions at low temperature. However, at room temperature dissociation under the release of the NHC ligand occurs. Variation of the NHC ligand in the [Cu-NHC]⁺-substituted silicide clusters is possible, whereas the reactions of K₁₂Si₁₇ with the corresponding NHC^DippMCl (M: Ag, Au) complexes result in a partial oxidation of the silicide clusters, without attachment of [M-NHC]⁺, yielding [Si₉]^3- species.