Double metal cyanides (DMCs) are cyanide bridged transition metal coordination polymers with the general formula M1u[M2(CN)n]v that have been used industrially as solid catalysts for ring opening polymerization reactions since the 1960s. However, one of their drawbacks is that their micropores are usually too small to allow diffusion of reactants and products. In this sense, several strategies have been suggested in order to increase the availability of active sites in the DMCs. Herein, we report the synthesis, structure and catalytic activity of a new DMC phase, consisting of positively charged DMC layers linked by acetate anions, Zn2[Co(CN)6](CH3COO). Such a cationic, layered DMC (LDMC) structure has not yet been reported in literature. Moreover, the advantages of LDMC over the benchmark DMC catalyst and other Lewis acid catalysts are demonstrated for two important catalytic applications of DMCs: intermolecular hydroamination and epoxide polymerization. Single crystals of LDMC were synthesized by slow diffusion in a silica gel and the structure was solved by single crystal X-ray diffraction. Through further synthesis optimization, we were able to obtain a phase pure microcrystalline powder of the LDMC. Synchrotron powder diffraction data were collected and successfully refined by the Rietveld method. The structure crystallizes in the monoclinic space group P21/m. The asymmetric unit consists of two symmetry independent Zn atoms and one Co atom, four cyanide groups, acetate and three water molecules (represented as isolated O atoms). For the ring opening polymerization, a significant increase in the 1,2-epoxyhexane conversion is observed when LDMC is employed as catalyst. For the hydroamination reaction, LDMC also outperforms all the other DMCs and Lewis acid catalysts. The higher catalytic activity of LDMC can be attributed to a combination of the easier accessibility of the catalytic sites and the changed coordination environment of the Zn atoms in the structure (as veryfied by FTIR and solid state NMR studies). As observed in both catalytic activity tests, the differences in activity exhibited by the DMCs highlight the advantages of LDMC as an excellent catalyst.

Layered Zn2[Co(CN)6](CH3COO) double metal cyanide with improved catalytic performance

2019 Fall National Meeting

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