I. Nanocapsules and host-guest chemistry.
Rational design of inorganic artificial receptors for host-guest chemistry is an attractive area in contemporary inorganic chemistry. Self-assembly constitute an elegant method for the preparation of elaborate architectures. The use of appropriate inorganic bricks and rationally chosen ligands allows the preparation of appealing metallo-cages that may display potential applications in various fields such as electronic, ion sensing and catalysis.
Our group is highly active in this area. Previously we described the first examples of irido-cryptand/cryptates, in which the BF4-
anion is encapsulated through hydrogen bonding. Pursuing our research, we recently reported the rational design of a variety of Co(II) and Cu(II) capsules in which the weakly coordinating anion such as BF4- or PF6- play a pivotal role as template, around which, metallic cations and ligands self-assemble. These capsules were obtained in high yields and were fully characterized by X-Ray and solution or solid state NMR.
Figure. Nanocapsules of Co(II) and Cu(II) templated by BF4- anions : ACIE. 2005, 44, 4543. Chem. Eur. J. 2007, 13, 5401. Eur. J. Inorg. Chem, 2009, 29, 4396. Dalton Trans. 2009, 10429.
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 metallo-macrocycles by treating the solvated half-sandwich complexes [(π-arène)M(solvent)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 SMSMSM with a 1 : 1 ratio of both diastereomers. Resolution of these metallo-macrocycles was achieved using chiral anion auxiliary.
Figure. Chiral metallomacrocycles of rhodium RRhRRhRRh / SRhSRhSRh. The S-enantiomer exhibits chiral recognition to Δ-Trisphat. Inorg. Chem. 2004, 43, 6644. Organometallics. 2007, 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 metallomacrocycles with chiral bridging ligands.