From Mixed Group 13 Cations [M(AlCp*)] (M = Ga/In/Tl) to an Al Cluster

AlCp*-complexes with transition metals have shown to be highly reactive and enable C-H or Si-H bond activation. Yet, complexes of AlCp* with low-valent main-group metals are scarce. Here, we report the syntheses of [M(AlCp*)][Al(OR)] (R = C(CF)) with M = Ga, In, Tl, which include the first covalent Al-In and Al-Tl bonds. For M = Ga, AlCp*-coordination induced the formation of the dication [Ga(AlCp*)] in the solid state, which exhibits a solvent and temperature dependent monomer-dimer equilibrium in solution. By contrast, the In and Tl complexes are monomeric and prone to reduction to the metal by the electron-rich AlCp*-moieties. The QTAIM analysis suggests that the metal centres are already highly reduced in the complexes, while the positive charge is distributed onto the AlCp* units. Addition of MeTACN (1,4,7-trimethyl-1,4,7-triazacyclononane) to the Ga- and Tl-complex salts resulted in an isomerization to the novel low-valent Al cation [(MeTACN)Al(AlCp*)][Al(OR)]. Intermittently formed tetrahedral GaAl clusters could be structurally characterized. From a detailed mechanistic study of this isomerization, the very high yield and clean preparation of [(MeTACN)Al(AlCp*)][Al(OR)] was devised from [M(MeTACN)][Al(OR)] (M = Ga, Tl) and [(AlCp*)].