Low‐Valent M_xAl₃Cluster Salts with Tetrahedral [SiAl₃]⁺and Trigonal‐Bipyramidal [M₂Al₃]²⁺Cores (M=Si/Ge)

Abstract

Schnöckel's [(AlCp*) 4 ] and Jutzi's [SiCp*][B-(C 6 F 5 ) 4 ] (Cp* = C 5 Me 5 ) are landmarks in modern maingroup chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*] + fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si-(AlCp*) 3 ][WCA] ([WCA] À = [Al(OR F ) 4 ] À and [F{Al-(OR F ) 3 } 2 ] À ; R F = C(CF 3 ) 3 ). The tetrahedral [SiAl 3 ] + core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also-due to its facile accessibility and high stability-provides a convenient preparative entry towards low-valent SiÀ Al clusters in general. For example, an elusive binuclear [Si 2 -(AlCp*) 5 ] 2 + with extremely short AlÀ Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge 2 -(AlCp*) 5 ] 2 + dication were also obtained and represent the first mixed AlÀ Ge cluster.

Synthesis and Reactivity of Aluminum Disilacyclopropenes. Cyclic AlSi2 Delocalized 2π Systems

“…The Si–Al bond lengths of 2.3521 and 2.3506(12) Å in 2 and 2.3595 and 2.3512(11) Å in 4b are markedly shorter than a typical Si–Al single bond length of avg. 2.45 Å . Interestingly, the Si–Al bond lengths of 2.3153 and 2.3186(9) Å in 3 and 2.3194 and 2.3262(6) Å in 5 are shorter than those found in 2 and 4b but nearly identical with the terminal Si–Al bond length of 2.327(1) Å observed in the dicationic cluster [Si 2 (AlCp*) 5 ] 2+ .…”

Metal–Metal Bonding in Late Transition-Metal [M2L5] Complexes: Exploring the Limits of the Isolobal Analogy between the CO and AlCp* Ligands

“…It should be noted that a series of isostructural main-group clusters of the type [E 2 (AlCp*) 5 ] (E = As, Bi, Cp*AlSi +69 and Cp*AlGe +69 have been characterized, which have also been described as closo species bearing six skeletal electron pairs, despite the fact that some of them , exhibit long non-bonding Al...Al contacts. The relationship between the electronic structure of these species and that of [Au 2 (AlCp*) 5 ] will be the subject of further investigations.…”

Three-Membered Aluminacycles

“…Figure shows the representative examples of relatively small and structurally characterized Al clusters involving three-membered Al n E m rings. Since the seminal report of (AlCp*) 4 by Schnöckel et al in 1991, clusters featuring Al 3 , Al 4 , , Al 7 , Al 8 , and Al 12 scaffolds have emerged. Remarkably, some clusters exhibit a topological similarity to the structure of solid aluminum, indicating that they represent the transition between single atoms and the bulk solid.…”