[AuGe₁₈{Si(SiMe₃)₃}₆]⁻: A Soluble Au–Ge Cluster on the Way to a Molecular Cable?

Abstract

Metalloid clusters of Group 14 have been established as a discrete group of cluster compounds [1,2] during the last years. [3,4] The metalloid clusters of the general formula [M n R m ] (n > m; M = Si, Ge, Sn, Pb) contain ligand-bound metal atoms as well as "naked" metal atoms. Since the "naked" metal atoms inside these clusters exhibit an oxidation state of 0, the average oxidation state of the metal atoms within metalloid Group 14 cluster compounds is between 0 and 1. Therefore, these cluster compounds can be seen as intermediates on the way to the elemental state, and structural approaches toward the solid-state phase have been reported recently. [2,5] Another interesting class of Group 14 cluster compounds that has been known for a long time is the Zintl anions.[6] In the case of the Zintl anions, characterization of the anionic species could be accomplished and subsequent reactions could be established during the last few years. Most results were obtained with the Zintl anion [Ge 9 ] 4À , which was linked to a dimer, [7] an oligomer, [8] or a polymer.[ , in which two {Ge 9 } units are connected through a {Ni 3 } bridge.[10] Furthermore, Au-bound Zintl anions such as [Au 3 Ge 18 ] 5À (1) [11] and [Au 3 Ge 45 ] 9À (2) [12] could be synthesized. In the case of metalloid Group 14 cluster compounds no subsequent reaction has been reported, and thus we wondered if such reactions might also be possible. A promising candidate for such reactions seemed to be the metalloid cluster compound [Ge 9 R 3 ] À (3, R = Si(SiMe 3 ) 3 ), [13] in which six naked germanium atoms are readily available for subsequent reactions. First results prove the case for our assumption, and we present herein the first subsequent reaction of a metalloid cluster compound, leading to the cluster compound [AuGe 18 R 6 ] À (4, R = Si(SiMe 3 ) 3 ). For the synthesis of 4, we treated a solution of 3 in THF with [AuCl(PPh 3 )]. The reaction solution changed color from orange to red, and a white precipitate of LiCl was formed. After workup of the reaction mixture, the anionic cluster 4, which crystallizes together with [Li(thf) 6 ] + as counterion, could be isolated in the form of red crystals.As shown in Figure 1, the molecular structure of 4 consists of two {Ge 9 R 3 } units which are connected by a central gold atom. The [Li(thf) 6 ] + salt of 4 crystallizes in the trigonal crystal system in the space group R3 , whereby the gold atom is located at the center of inversion. The central {Ge 18 Au} unit has D 3d symmetry, and since the Si(SiMe 3 ) 3 ligands are twisted by 37.78 against the mirror plane, the symmetry of the whole cluster is reduced to C 3i . The steric demand of the six Si(SiMe 3 ) 3 ligands is so large that the ligands are interlocked, [14] totally shielding the central gold atom against the exterior (Figure 2).The gold atom is bound trigonal-antiprismatic to six germanium atoms and owing to the high coordination

Coordination of Tri-Substituted Nona–Germanium Clusters to Cu(I) and Pd(0)

“…The formation of 1 can be viewed in light of the previously suggested formation of the gold analogue of 3, that is, [(Ge 9 R 3 )Au I (Ge 9 R 3 )] − (4). 46 While 3 is made by reacting Ge 9 R 3 − with the salt-like Cu(I) compound with weakly coordinating anions, Cu(Al(OR) 4 ), 47 4 is made by a reaction with a salt with ligated Au(I), (PPh 3 )AuCl, just like the reaction with (PPh 3 ) 3 CuBr for the formation of 1. It has been speculated that the formation of 4 begins with a salt-metathesis reaction to form the neutral [(Ge 9 R 3 )Au−PPh 3 ], which then exchanges the neutral PPh 3 ligand with another anionic Ge 9 R 3 − to form [(Ge 9 R 3 )Au I (Ge 9 R 3 )] − , that is: 46…”

N-Heterocyclic Carbene Coinage Metal Complexes of the Germanium-Rich Metalloid Clusters [Ge9R3]− and [Ge9RI2]2− with R = Si(iPr)3 and RI = Si(TMS)3

“…The resulting bis- and tris-silylated cluster species [Ge 9 R 2 ] 2− (R = Si(TMS) 3 ) [14] and [Ge 9 R 3 ] − (R: various silyl groups) [15,16,17,18,19,20] are, due to their lower charge, soluble in common solvents (acetonitrile, thf, toluene). Subsequent reactions of the tris-silylated cluster [Ge 9 R 3 ] − (R: Si(TMS) 3 ) with coinage metal complexes, in most cases coinage metal phosphine complexes, commonly yield coinage metal-bridged cluster dimers, under the loss of the original ligand sphere of the transition metal [19,21,22]. However, there are also a few reports in which the Cu-phosphine bond is retained [18,23].…”

The Largest Metalloid Group 14 Cluster, Ge18[Si(SiMe3)3]6: An Intermediate on the Way to Elemental Germanium

“…[6] Aside from structural similarities to known solid-state structures,c ompletely novel structures have also been observed within metalloid clusters,f or example,the empty polyhedral arrangement of 14 germanium atoms in {Li(thf) 2 } 3 {Ge 14 [E(SiMe 3 ) 3 ] 5 }( E= Si, Ge), [7,8] or the arrangement of 17 tin atoms in Sn 17 [GaCl(ddp)] 4 (ddp = HC(CMeNDipp) 2 ). [9] This structural variety shows that there is high complexity in the nanoscale regime,a nd the study of metalloid cluster compounds provides first insights into the seemingly simple process of the formation of ametal or semi-metal.…”