One-step Synthesizable Lindqvist-isopolyoxometalates as Promising New Catalysts for Selective Conversion of Glucose as a Model Substrate for Lignocellulosic Biomass to Formic Acid

A series of Lindqvist-isopolyoxometalates [M6O19](n-) (M=W, V) were synthesized under one-pot conditions and were applied in the homogeneous oxidation of glucose as a model substrate for lignocellulosic biomass to formic acid (FA), which offers a new field for application of isopolyoxometalates (IPA) in catalysis. Their low molecular weight and facile accessibility in aqueous solution together with their tuneable redox properties offers a new and straightforward path for optimized precious metal free oxidation catalysts. We have systematically synthe-sized and characterized a series of vanadium-and tungsten-based Lindqvist structures and verified their applicability in the selective oxidation of glucose to FA. Maximum FA-yields of 39 % in aqueous solution under non-optimized conditions were observed for Cs-4[V2W4O19] and it is shown that reactivity and selectivity can be tuned by metal substitution of the cluster: FA formation is favoured with increasing V-substitution of the [W6O19](2-) -framework. Moreover, the influence of different inorganic counter cations was investigated.