Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2'-bipyridine

Group 13 M(I) compounds often disproportionate into M(0) and M(III). Here, however, we show that the reaction of the M(I) salt of the weakly coordinating alkoxyaluminate [Ga(I)(C(6)H(5)F)(2)](+)[Al(OR(F))(4)](−) (R(F)=C(CF(3))(3)) with 2,2'-bipyridine (bipy) yields the paramagnetic and distorted octahedral [Ga(bipy)(3)](2+)(•){[Al(OR(F))(4)](−)}(2) complex salt. While the latter appears to be a Ga(II) compound, both, EPR and DFT investigations assign a ligand-centred [Ga(III){(bipy)(3)}(•)](2+) radical dication. Surprisingly, the application of the heavier homologue [(I)n(I)(C(6)H(5)F)(2)](+)[Al(OR(F))(4)](−) leads to aggregation and formation of the homonuclear cationic triangular and rhombic [In(3)(bipy)(6)](3+), [In(3)(bipy)(5)](3+) and [In(4)(bipy)(6)](4+) metal atom clusters. Typically, such clusters are formed under strongly reductive conditions. Analysing the unexpected redox-neutral cationic cluster formation, DFT studies suggest a stepwise formation of the clusters, possibly via their triplet state and further investigations attribute the overall driving force of the reactions to the strong In−In bonds and the high lattice enthalpies of the resultant ligand stabilized [M(3)](3+){[Al(OR(F))(4)](−)}(3) and [M(4)](4+){[Al(OR(F))(4)](−)}(4) salts.