There is a clear trend in homogeneous catalysis towards the development of substitutes of rare late transition metals, notably through the use of more abundant main group elements. In that respect, we have shown that cationic gallium and indium complexes of type [L.MX2][EFn], where L is a carbon-based ligand such as the IPr N-heterocyclic carbene and EFn- a weakly coordinating perfluoroanion, can catalyze reactions that are usually the territory of noble metals. In this presentation, we will summarize our quest for stable and catalytically active cationic gallium and indium complexes. In short, we have prepared these species from a variety of LMX3 complexes and AgEFn. The electronic ligand properties influence the structure of the former, i.e. a molecular adduct of type L.MX3 or an ion pair of type [L2MX2][MX4]. The electropositivity of L also influences the metal pyramidalization in L.MX3. These structural effects have been rationalized by computations. The choice of the silver salt used as anion metathesis agent is also crucial. In fact, treatment of L.MX3 with AgEFn leads to fluorine-bridged complexes of type L.MX2(µ-F)EFn-1 that is catalytically active but fragile. Depending on E (Sb, B, P), anion cleavage can take place, leading to inactive species. Besides, L.MX2+ ions readily react with water to give super Brønsted acids such as HSbF6 which we could characterize for the first time in the solid state. Ways to tame the strong Lewis acidity of these cationic gallium and indium complexes so as to make them useful in molecular catalysis will be presented.

Cationic gallium and indium complexes as Lewis acids for molecular catalysis: Structure-stability-activity relationships

251st National Meeting (2016)

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