Low oxidation state silicon clusters - synthesis and structure of [NHC Dipp Cu(η 4 -Si 9 )] 3 .

The reaction of NHCDipp CuCl with the silicide phases A12 Si17 (A: K, K/Rb, Rb) in NH3 (l) yields [NHCDipp Cu(η4 -Si9 )]3- (1) as only the third example of a substituted [Si9 ] cluster. The corresponding salts A3 [A(2.2.2-crypt)]3 [NHCDipp Cu(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 [NHCDipp Cu(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 K12 Si17 with the corresponding NHCDipp MCl (M: Ag, Au) complexes result in a partial oxidation of the silicide clusters, without attachment of [M-NHC]+ , yielding [Si9 ]3- species.