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Low oxidation state silicon clusters – synthesis and structure of [NHCᴰⁱᵖᵖCu(η⁴-Si₉)]³⁻

Geitner, Felix S., Fässler, Thomas F.
Chemical communications 2017 v.53 no.96 pp. 12974-12977
acetonitrile, ambient temperature, ammonia, copper, crystal structure, crystallization, dissociation, electrospray ionization mass spectrometry, gold, ligands, nuclear magnetic resonance spectroscopy, oxidation, potassium, pyridines, rubidium, salts, silicon, silver
The reaction of NHCᴰⁱᵖᵖCuCl with the silicide phases A₁₂Si₁₇ (A: K, K/Rb, Rb) in NH₃(l) yields [NHCᴰⁱᵖᵖCu(η⁴-Si₉)]³⁻ (1) as only the third example of a substituted [Si₉] cluster. The corresponding salts A₃[A(2.2.2-crypt)]₃[NHCᴰⁱᵖᵖCu(η⁴-Si₉)]₂·26NH₃ (A: K (1a), K/Rb (1b), Rb (1c)) crystallize isostructurally in the space group P1̄ and have been characterized by single crystal structure determination. ESI-MS and NMR experiments reveal that the anion [NHCᴰⁱᵖᵖCu(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 NHCᴰⁱᵖᵖMCl (M: Ag, Au) complexes result in a partial oxidation of the silicide clusters, without attachment of [M–NHC]⁺, yielding [Si₉]³⁻ species.