Cavitand−Porphyrins

Abstract

The synthesis and characterization of new nanoscale container molecules 7 and 8 are described. They are covalent hybrids of deepened, self-folding cavitands and metalloporphyrins. In receptor 7, the Zn-porphyrin wall is directly built onto the cavitand skeleton. Host 8 features a large unimolecular cavity containing two cavitands attached with the Zn-porphyrin wall. Its dimensions, approximately 10 x 25 A, place it among the largest synthetic hosts prepared to date. A series of adamantyl- and pyridyl-containing guests 14-20 of various lengths were prepared and used to determine the hosts' binding abilities in solution using UV/vis and (1)H NMR spectroscopy. Intramolecular hydrogen bonds at the upper rims of the cavitands resist the unfolding of the inner cavities and thereby increase the energetic barrier to guest exchange. The exchange is slow on the NMR time scale (at < or =300 K), and kinetically stable complexes result. When the cavities and metalloporphyrins participate simultaneously in the binding event, very high affinities for guests are found (-DeltaG295 up to 10 kcal x mol(-1) in toluene), to which the porphyrin fragments contribute significantly (-DeltaG295 up to 6 kcal x mol(-1)). The pairwise selection of two different guests by molecular container 8 is reported, and the termolecular complex formed raises the possibility of metal-catalyzed bimolecular reactions in these containers.

Covalent or supramolecular combinations of resorcinarenes and porphyrinoids

“…Rebek and his team were the first to prepare covalent hybrids of porphyrin and resorcinarene cavitands, first the P1:R1 derivative 18 (Scheme 3, left) [18] then the capsule-like P1:R2 derivative 20 (Scheme 3, right) [19]. The Rebek's deep cavitand scaffold was prepared as usual but letting two amines free (compound 16) that could react with aromatic diketones such as porphyrin 17 [19] and porphyrin 19 [18].…”

“…The Rebek's deep cavitand scaffold was prepared as usual but letting two amines free (compound 16) that could react with aromatic diketones such as porphyrin 17 [19] and porphyrin 19 [18]. Hybrid 20 is actually a hemicarcerand molecule, with a capsule-like structure but open by "large portals" [19].…”

“…The Rebek's deep cavitand scaffold was prepared as usual but letting two amines free (compound 16) that could react with aromatic diketones such as porphyrin 17 [19] and porphyrin 19 [18]. Hybrid 20 is actually a hemicarcerand molecule, with a capsule-like structure but open by "large portals" [19]. Pyridine derivatives bearing one or two adamantane units on spacer of different lengths were used to perform host-guest experiments, with the idea that the pyridine nitrogen atom will interact axial with the Zn atom while the adamantane units will be hosted in the resorcinarene's cavity.…”

Functional cavitands: Chemical reactivity in structured environments

“…The addition of the fourth wall and reduction to the diamine gave the common precursor to the monofunctionalized cavitands. These include the self-complementary structure 11, (25) the introverted acid 12 (26), the dipyrrole 13 (27), the porphyrin 14 (28,29), the biscavitand 15 (30), the phenanthroline 16 (20), salen 17 (31), and the pyridone 18 ( Fig. 5) (32).…”

“…Monofunctionalization of the upper rim of the self-folding cavitand 4 with a porphyrin gave us a host 14 with two binding sites (28,29). The cavitand portion of the molecule retains its affinity for adamantyl groups, and the metalloporphyrin acts as an excellent coordination site for a pyridyl group linked to the adamantane.…”