Synthesis, Characterization, and Encapsulation Properties of Rigid and Flexible Porphyrin Cages Assembled from N-Heterocyclic Carbene–Metal Bonds

Abstract

Four porphyrins equipped with imidazolium rings on the para positions of their meso aryl groups were prepared and used as tetrakis(N-heterocyclic carbene) (NHC) precursors for the synthesis of porphyrin cages assembled from eight NHC-M bonds (M = Ag + or Au + ). The conformation of the obtained porphyrin cages in solution and their encapsulation properties strongly depend on the structure of the spacer -(CH2)n-(n = 0 or 1) between meso aryl groups and peripheral NHC ligands. In absence of methylene groups (n = 0), porphyrin cages are rather rigid and the short porphyrin-porphyrin distance prevents encapsulation of guest molecules like 1,4diazabicyclo[2.2.2]octane (DABCO). By contrast, the presence of methylene functions (n = 1) between meso aryl groups and peripheral NHCs offers additional flexibility to the system allowing the inner space between the two porphyrins to expand enough to encapsulate guest molecules like water molecules or DABCO. The peripheral NHC-wingtip groups also play a significant role on the encapsulation properties of the porphyrin cages.

A Highly Sterically Congested Bis‐Zinc‐Porphyrin Containing a Single Buta‐1,3‐diyne Linkage: From a Serendipitous Finding to Supramolecular Encapsulation

“…Although the encapsulation of small molecules such as DABCO within supramolecular cages made from zinc-porphyrins is known, the vast majority of examples concern cyclic systems bearing at least two linkers to connect both zinc-porphyrin units or rather flexible single junctions. [7,8,21,23,28] In the present case, we show that such a strong pre-organization or flexibility is not required for DABCO encapsulation since a simple acyclic and highly rigid bis-zinc-porphyrin system such as 2 is adaptable enough to drive the self-assembly process to a selective 1 : 1 encapsulation. In addition, this supramolecular system provides a significant space available around the encapsulated guest to further explore new physicochemical processes that are less available for the typical cases in which the highly sophisticated (supra)molecular cages impose little access to additional events.…”

“…À 1 ppm values, which we tentatively attributed to water bound to zinc. [21] As such, dimer 2 likely exists as a mixture of two interconverting species, namely a closed form (CF), in which both zinc-porphyrin backbone stuck each other, and an open form (OF), in which the zinc-porphyrins reach the maximal distance between both zinc atoms by pointing to opposite directions (Scheme 3). This interconversion Table 2.…”

“…These values, which are currently obtained in a system comprising a single linkage between the two zinc-porphyrins, compare well with previous systems exhibiting a 1 : 1 binding stoichiometry in which the host concerned was a cyclic system bearing at least two linkers to connect both zinc-porphyrin units. [21,23] Additional experimentation and analysis did not provide evidences of an eventual second binding of DABCO to 2 in solution or it is too small to be measured so far (see Supporting Information) as it was seen by Ballester and co-workers in a more flexible zincporphyrin tweezer. [7b] However, a solution of 2 containing an excess of DABCO afforded single crystals suitable for X-ray diffraction studies which revealed the presence of two DABCO molecules binding each zinc-porphyrin unit within 2 (Figure 6).…”

Metal Atoms (Li, Na, and K) Tuning the Configuration of Pyrrole for the Selective Recognition of C60

“…The metal-mediated self-assembly supramolecular hosts with a nano-sized cavity have been extensively explored in the last few decades. ,− In particular, the palladium-mediated assembly is dedicated to the reasonable construction of less symmetric architectures. Clever and co-workers have constructed a family of heteroleptic [Pd 2 L 2 L′ 2 ] cages .…”

Coordination-Driven Tetragonal Prismatic Cage and the Investigation on Host–Guest Complexation

“…The porphyrin unit is a good contender due to its large planar structure and appealing physical characteristics, such as molecular recognition, oxygen transport, electron transfer, and energy migration and conversion. Metal–organic assemblies − including tweezers, , clips, prisms, − boxes, − and macrocycles have been built for catalysis, light harvesting, and, in particular, host–guest chemistry using porphyrin-based building blocks. , Porphyrins are typically used as the primary functional group to identify the guest in research on the host–guest nature of these porphyrin-based assemblies; however, the bridging groups that connect the porphyrin groups are infrequently taken into account in the host–guest identification system.…”