Synthesis and characterization of a novel polystyrene-tethered niobium methoxo species. Its application in the CO2-based carboxylation of methanol to afford dimethyl carbonate

In this paper we describe the synthesis and characterization of a polystyrene-tethered Nb-complex, namely P-C6H4-p-CH2CH2–NbCl4, 1 which reacts with CH3OH to afford P-C6H4-p-CH2CH2–NbCl(OCH3)32. The latter inserts CO2 to afford P-C6H4-p-CH2CH2–NbCl[O–C(O)OCH3](OCH3)2, 3, active in the catalytic carboxylation of methanol. The insertion of only one mol CO2 per Nb has been determined both by measuring the CO2 released upon treatment with HCl and by solid state 13C NMR. 3 is easily recovered from the reaction medium and re-used; it can also be used in a flow reactor without decomposition after days. It shows good recycling properties and is much easier to use than the relevant homogeneous catalyst Nb(OCH3)4[O–C(O)OCH3].

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (32 K)Download as PowerPoint slideResearch highlights▶ Synthesis and characterization of a polystyrene-tethered Nb-complex. ▶ The direct carboxylation of methanol represents an interesting alternative synthetic route from the point of view of both atom economy and risk reduction. ▶ The use of heterogenized catalysts bearing the catalytic centre tethered to a solid matrix would be interesting because they would potentially combine the high selectivity typical of the homogeneous catalysts with the easy recoverability of the heterogeneous system.