Counteranion effects on the catalytic activity of copper salts immobilized on the 2,2′-bipyridine-functionalized metal–organic framework MOF-253

The charge-neutral, aluminium-based metal–organic framework containing accessible 2,2′-bipyridine (bpy) sites, MOF-253, is a suitable host material for the immobilization of various copper catalysts. The catalytic performance of CuCl2, Cu(NO3)2, Cu(BF4)2 and Cu(CF3SO3)2 before and after coordination to the bpy ligands in MOF-253 was studied in the Meinwald rearrangement of α-pinene oxide to campholenic aldehyde (CA). The coordination environment of Cu2+ in MOF-253 was further studied via EPR spectroscopy. Although the catalytic activity of the copper salts decreased upon heterogenization through coordination with the bpy linker, the selectivity to campholenic aldehyde markedly increased. Furthermore, the catalytic performance of the MOF loaded with copper salts was shown to vary greatly with the choice of charge compensating anion, allowing for improvement of the heterogeneous catalyst.