American Chemical Society, Journal of the American Chemical Society, 7(137), p. 2680-2687, 2015
DOI: 10.1021/ja512637k
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Regio and enantioselective hydroformylation of styrenes is described upon embedding a chiral Rh complex in a non-chiral supramolecular cage formed from coordination-driven self-assembly of macrocyclic dipalladium complexes and tetracarboxylate zinc porphyrins. The supramolecular catalyst that results converts styrene derivatives into aldehyde products with much higher chiral induction in comparison to the non-encapsulated Rh catalyst. Spectroscopic analysis shows that encapsulation does not change the electronic properties of the catalyst, nor changes its first coordination environment. Instead, enhanced enantioselectivity is rationalized by the modification of the second coordination sphere occurring upon catalyst inclusion inside the cage, being one of the few examples in achieving enantioselective outcome via indirect through-space control of the chirality around the catalyst center. This effect resembles those taking place in enzymatic sites, where structural constrains imposed by the enzyme cavity can impart stereoselectivities that cannot be attained in bulk. These results are a showcase for the future development of asymmetric catalysis by using size-tunable supramolecular capsules.