Reversible Mechanical Interlocking of D‐Shaped Molecular Karabiners bearing Coordination‐Bond Loaded Gates: Route to Self‐Assembled [2]Catenanes

Complexation of 1,4‐phenylenebis(methylene) diisonicotinate, L1 , with cis ‐protected Pd II components, [Pd( L′ )(NO 3 ) 2 ], in an equimolar ratio yielded binuclear complexes, 1 a – d of [Pd 2 ( L′ ) 2 ( L1 ) 2 ](NO 3 ) 4 formulation where L′ stands for ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), and phenanthroline (phen). The combination of 4,4′‐bipyridine, L2 , with the cis ‐protected Pd II units is known to yield molecular squares, 2 a – d . However, 2 b – d coexist with the corresponding molecular triangles, 3 b – d . Combination of an equivalent each of the ligands L1 and L2 with two equivalents of cis ‐protected Pd II components in DMSO resulted in the D ‐shaped heteroligated complexes [Pd 2 ( L′ ) 2 ( L1 )( L2 )](NO 3 ) 4 , 4 a – d . Two units of the D ‐shaped complexes interlock, in a concentration dependent fashion, to form the corresponding [2]catenanes [Pd 2 ( L′ ) 2 ( L1 )( L2 )] 2 (NO 3 ) 8 , 5 a – d under aqueous conditions. Crystal structures of the macrocycle [Pd 2 (tmeda) 2 ( L1 )( L2 )](PF 6 ) 4 , 4 b′′ , and the catenane [Pd 2 (bpy) 2 ( L1 )( L2 )] 2 (NO 3 ) 8 , 5 c , provide unequivocal support for the proposed molecular architectures.