The Stereoselective Self‐Assembly of Chiral Metallo‐Organic Cryptophanes

Cryptophanes 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 M 2+ –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 [Pd 3 (dppp) 3 ( 1 ) 2 ] 6+ and [Pd 3 (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 [Pd 3 (dppp) 3 ( 1 ) 2 ] 6+ at low temperature in CD 2 Cl 2 , and – in the case of [Pt 3 (dppp) 3 ( 1 ) 2 ] 6+ – it formed in a minor amount at room temperature. [Pd 3 (dppp) 3 ( 1 ) 2 ][OTf] 6 and [Pt 3 (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 [Pd 3 (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.