Photoswitchable Cu(ii)/Cu(i) catalyses assisted by enzyme-like non-covalent interactions in Cu(ii)–melamine coordination polymers for installing CO2/CS2 and CF3 groups in heterocycles

Abstract

Despite concerns over the environmental impact of isoelectronic CO₂ and CS₂, they remain useful C1 building blocks with industrial utility, and trifluoromethylation could enhance the lipophilicity and metabolic stability of agrochemicals and pharmaceuticals. Merging the CO₂/CS₂ moiety together with the CF₃ group in one heterocyclic scaffold is both environmentally and pharmaceutically valuable, but it is still challenging for the homogeneous Cu-catalytic protocols to circumvent the issue of residual heavy metals, and the aggregation and sulfur-poisoning effect of Cu-species. In this report, a highly durable Cu(II)–melamine coordination polymer Cu–TDPAT, assembled from melamine-based ligand H₆TDPAT and Cu(II) salt, was employed in the heterogeneous approach. The photoinduced electron transfer from the melamine-based ligand to the Cu(II) node of Cu–TDPAT and the ground-state back electron transfer enabled the controllable Cu(II)/Cu(I) switch. The enzyme-like non-covalent interactions not only enriched and activated CO₂/CS₂, the allylamine substrate, and Togni's reagent II, the CF₃ radical precursor, but also drew close distances between them to facilitate the reaction. These advantages benefit from synergising the ground-state Cu(II)-triggered CO₂ installation and the photogenerated Cu(I)-catalysed trifluoromethylation steps within the construction of biointeresting heterocycles in a sustainable and recyclable manner. In particular, this heterogeneous approach was applicable to the construction of a central nervous system agent derivative when CS₂ was employed instead of CO₂, showing the superior durability of Cu–TDPAT against sulfur-poisoning compared with its homogeneous counterpart.