Self-assembly of metallosupramolecular rhombi from chiral concave 9,9’-spirobifluorene-derived bis(pyridine) ligands

Two new 9,9’-spirobifluorene-based bis(4-pyridines) were synthesised in enantiopure and one also in racemic form. These ligands act as concave templates and form metallosupramolecular [(dppp) 2 M 2 L 2 ] rhombi with cis -protected [(dppp)Pd] 2+ and [(dppp)Pt] 2+ ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture of all three possible stereoisomers [(dppp) 2 M 2 {( R )-L} 2 ](OTf) 4 , [(dppp) 2 M 2 {( S )-L} 2 ](OTf) 4 , and [(dppp) 2 M 2 {( R )-L}{( S )-L}](OTf) 4 was obtained in an approximate 1.5:1.5:1 ratio which corresponds to an amplification of the homochiral assemblies by a factor of approximately three as evidenced by NMR spectroscopy and mass spectrometry. The racemic homochiral assemblies could also be characterised by single crystal X-ray diffraction.