The Stereoselective Self‐Assembly of Chiral Metallo‐Organic Cryptophanes

Abstract

International audienceCryptophanes are macropolycyclic cyclophanes constructed from two triply bridged concave cyclotriveratrylene analogues that encapsulate a large range of molecular and monoatomic substrates. Self-assembled metallo-organic cryptophanes based on M2+–carbonitrile (M = Pd or Pt) interactions have been obtained through the reactions of chiral nitrile-substituted cyclotribenzylenes (CTBs) 1 and 2 with [M(dppp)][OTf]2 (dppp = 1,3-bisdiphenylphosphinopropane, OTf = triflate) in 2:3 ratios in chlorinated solvents. The cryptophanes [Pd3(dppp)3(1)2]6+ and [Pd3(dppp)3(2)2]6+ were obtained exclusively in the chiral anti form in solution at room temperature whatever solvent was used; however the meso,syn form was identified as the major isomer of [Pd3(dppp)3(1)2]6+ at low temperature in CD2Cl2, and – in the case of [Pt3(dppp)3(1)2]6+ – it formed in a minor amount at room temperature. [Pd3(dppp)3(1)2][OTf]6 and [Pt3(dppp)3(1)2][OTf]6 crystallized in the anti forms with an encapsulated chloroform molecule, and gas-phase DFT calculations with the dispersion-corrected B97-D3 functional show that it is stabilized by 34.6 kJ mol–1. Interestingly, the heteroleptic cryptophane [Pd3(dppp)3(1)(2)]6+ was not detected in mixtures of [Pd(dppp)]2+ and CTBs 1 and 2 in a 3:1:1 ratio or through the equilibration of a 1:1 mixture of the preformed homoleptic cryptophanes; this points to favored self-sorting processes

Homochiral Self‐Sorted and Emissive IrIII Metallo‐Cryptophanes

“…Homochiral metallo‐cages with tris‐chelate metal coordination are known both from achiral, and resolved chiral ligands –. Metallo‐cages that show homochiral self‐sorting from a racemic mixture of ligand enantiomers observed in solution are rare, although these include Pd II metallo‐cryptophanes . The simultaneous chiral self‐sorting of both ligand and pre‐formed inert metallo‐tecton as reported here have not been previously reported.…”

Self-assembled Cages and Capsules Using Cyclotriveratrylene-type Scaffolds

“…26 At room temperature, the cages [(Pd 3 (dppe) 3 6+ did not undergo ligand exchange, and self-assembly of [Pd(dppe)(OTf) 2 ] with both L2a and L2b resulted in only the homoleptic cages being formed.…”

Influencing the Self‐Sorting Behavior of [2.2]Paracyclophane‐Based Ligands by Introducing Isostructural Binding Motifs

“…Although the formation of helical polymeric structures from discrete cyclic structures, as observed in case of [(dppp)Pd{( S p )‐ L iso }] n (OTf) 2 n and [(dppp)Pd{( R p )‐ L nit }] n (OTf) 2 n , is in accordance with earlier observations and other self‐assembled polymers, the formation of bowl‐shaped, concave, yet polymeric, structures as observed in [(dppp) 2 Pd 2 {( S p )‐ L nit }{( R p )‐ L nit }] n (OTf) 4 n , is more scarce, both on the level of discrete supramolecular structures as well as on the level of self‐assembled polymers.…”