Encapsulation of Metalloporphyrins in a Self‐Assembled Cubic M₈L₆ Cage: A New Molecular Flask for Cobalt–Porphyrin‐Catalysed Radical‐Type Reactions

Abstract

The synthesis of a new, cubic M8L6 cage is described. This new assembly was characterised by using NMR spectroscopy, DOSY, TGA, MS, and molecular modelling techniques. Interestingly, the enlarged cavity size of this new supramolecular assembly allows the selective encapsulation of tetra(4-pyridyl)metalloporphyrins (M(II)(TPyP), M = Zn, Co). The obtained encapsulated cobalt-porphyrin embedded in the cubic zinc-porphyrin assembly is the first example of a catalytically active encapsulated transition-metal complex in a cubic M8L6 cage. The substrate accessibility of this system was demonstrated through radical-trapping experiments, and its catalytic activity was demonstrated in two different radical-type transformations. The reactivity of the encapsulated Co(II)(TPyP) complex is significantly increased compared to free Co(II)(TPyP) and other cobalt-porphyrin complexes. The reactions catalysed by this system are the first examples of cobalt-porphyrin-catalysed radical-type transformations involving diazo compounds which occur inside a supramolecular cage.

Encapsulated Cobalt–Porphyrin as a Catalyst for Size‐Selective Radical‐type Cyclopropanation Reactions

“…Earlier reports, using different diazo substrates, showed that catalytic substrate activation took place inside the cavity of these type of molecular flasks, thus leading to different selectivities compared to similar but non-encapsulated catalysts. [3] In good agreement, the results described in this paper show that allows size-selective substrate transformations. This is most easily explained by a slower migration of larger substrates through the pores of the cage compared to smaller substrates (Figure 2).…”

“…Recently, we have reported the synthesis of the Nitschke-type M 8 L 6 cubic cage 1 through self-assembly (Scheme 1). [2,3] Furthermore, we showed that 1 is suitable to encapsulate tetra(4-pyridyl)metalloporphyrins (M(TPyP) (2) with M = Zn, Co) to give the M 8 L 6 P 1 cubic cages and (P= porphyrin guest). In particular, the encapsulation of a cobalt-porphyrin is interesting, because these complexes are known for their catalytic activity in radical-type reactions.…”

A Switchable Gold Catalyst by Encapsulation in a Self‐Assembled Cage

“…Interestingly, many catalytic reactions operate through ad inuclear mechanism [7] or deactivate via ad inuclearp athway; [8,9] by encapsulation of at ransition metal complex, such decomposition pathways can be suppressed, leading to higher catalytic turnover numbers. [10] In principle, an encapsulatione ventc ould also change the catalyticp athway of ar eaction, and as such can be used as as witch for ac atalytict ransformation. Switchable catalysis is an interesting upcoming field of research as it provides new tools to control the reaction process with externals timuli such as light, pH, or metalc oordination, ac onceptt hat is important to control reactions in nature.…”

Stereochemical plasticity modulates cooperative binding in a CoII12L6 cuboctahedron

“…26 As a result, large architectures capable of binding small substrates are rare. Closing off the interior void with bulky organic units, 27,28 using rigid ligands with cavity-directed substituents, 29 or exploiting unsaturated metal coordination sites, 30 are useful means of enforcing the binding of guests into discrete spaces. 31 However, these methods rely on pre-programmed features within the assembly.…”