Design of nano-capsules: Guest encapsulation, chiral recognition and chemistry in confined environment.

 I. Coordination driven nanocapsules.

Self-assembly constitute an elegant method for the preparation of elaborate architectures. The use of appropriate inorganic metallo-bricks and rationally chosen ligands allows the preparation of appealing metalla-cages that may display potential applications in various fields such as luminescence, ion sensing and catalysis.
Our group is highly active in this area. Previously we described the rational design of a variety of Co(II) and Cu(II) capsules in which the weakly coordinating anion such as BF4or PF6play a pivotal role as template, around which, metallic cations and ligands self-assemble. These capsules were characterized by single crystal X-ray diffraction and solution or solid state NMR.

Figure. Nanocapsules of Co(II) and Cu(II) templated by BF4 anions : ACIE200544, 4543. Chem. Eur. J. 200713, 5401. Dalton Trans2009, 10377 .Chem. Rev. 2012112, 2015.

Moreover we prepared different family of palladium metallacages Pd2L4 containing rigid bidentate ligands. Remarkably we were able to encapsulate a metallic complex Pt(NO2)42- within the cavity of the supramolecular cage.

Figure. Nanocapsule of Pd(II) hosting a metal complex inside the cavity : Inorg. Chem201453, 4287. Materials 2014, 7, 287.

II- Chiral metallamacrocycles

Half-sandwich complexes with three-legged piano stool geometry with different substituents are archetypal examples of optically active chiral-at-metal center. Such species are ubiquitous in organometallic synthesis and catalysis, however more recently it has become clear that they can be very interesting building blocks for supramolecular chemistry. We reported the synthesis of some chiral metallamacrocycles by treating the solvated half-sandwich complexes [π-arène)M(solvant)3]2+ (π-arène = η-C6H6, η-Cp, η-Cp*) with trifunctional ligands (see drawing). These macrocycles are obtained as racemates, through homochiral self-assembly (all metal centers have the same configuration)  RMRMRM and SMSMSMwith a 1: 1 ratio of both diastereomers. Resolution of these metallamacrocycles was achieved using chiral anion auxiliary.       

Figure. Chiral metallomacrocycles of rhodium  RRhRRhRRh / SRhSRhSRh. The S-enantiomer exhibits chiral recognition to Δ-Trisphat. Inorg. Chem200443, 6644. Organometallics2007, 26, 860.

Our current investigations are devoted to the elaboration of new chiral nanocapsules with large cavities capable to house molecules or even inorganic complexes, with the objective to carry out chemical transformations in a confined environment.

Figure. View of metallamacrocycles with chiral bridging ligands.