Synthesis of New Self‐assembled Pd II and Pt II Rectangular Metallomacrocycles: A Comparative Study of their Inclusion Complexes

New palladium and platinum metallocycles have been synthesized by reacting 4,4′‐bipyridinium‐based ligands with Pd II and Pt II complexes. Strict thermodynamic self‐assembly of 1 and [M(en)(NO 3 ) 2 ] (M=Pd, Pt) 6 a , b afforded metallocycles 7 a , b . However, the synthesis of 8 a , b and 9 a , b required a self‐assembly process that used sodium p ‐phenylenediacetate ( 12 ) as a template. Finally, metallocycles 10 a , b were synthesized under high dilution conditions from ligand 4 . The formation of inclusion complexes between metallocycles 7 – 10 and substrates 13 and 14 were studied by low‐temperature 1 H NMR, and the association constants were determined in nitromethane and water by following the characteristic charge‐transfer band that these metallomacrocycles show in their UV‐visible absorption spectra. A clear correlation between the affinity for a substrate and the dimensions of the metallocycle was observed. Metallocycles 8 b and 9 b exhibited the highest binding constants in water and nitromethane. This observation is in agreement with the DFT (B3LYP)‐optimized geometries obtained for the different metallomacrocycles, which indicate that only macrocycles 8 and 9 possess a cavity with a width larger than 3.5 Å. The insertion of hydroquinone or diol 13 into the cavity of metallocycle 11 a was confirmed by single‐crystal X‐ray crystallography.