Diastereoselectively self-sorted low-symmetry binuclear metallomacrocycle and trinuclear metallocage

A pyridine/aniline appended unsymmetrical bis-monodentate ligand N-(3-aminophenyl)nicotinamide, L-un is synthesized via condensation of nicotinic acid with excess m-phenylene diamine. A low-symmetry binuclear complex of the Pd2L ' L-2(2)un type and an extremely rare trinuclear complex of the Pd3L6un type are produced by self-assembly of the ligand L-un with cis-protected palladium(ii) (i.e., PdL ') and palladium(ii), respectively. Two isomers (i.e. [(2,0), (2,0)] and [(1,1), (1,1)]-forms) are theoretically possible for the Pd2L ' L-2(2)un-type complex whereas nine isomers can be envisaged in the case of the Pd3L6un-type arrangement. However, one of the isomers of the Pd2L ' L-2(2)un-type complex as well as the one for the Pd3L6un-type complex are experimentally obtained. The exclusive formation of specific isomers could be predicted from the 1D/2D NMR study in the solution state and the DFT calculations in the gas phase/implicit solvent media. The formation of the predicted all-(1,1)-[Pd-2(en)(2)L-2(un)](NO3)(4) has been confirmed by a single-crystal XRD study. DFT calculations for the isomers of the Pd3L6un-type arrangement show that a [cis(2,2), cis(2,2), cis(2,2)] isomer is energetically favourable than the alternatively predicted [trans(2,2), trans(2,2), trans(2,2)] isomer. Conformational changes within the build of the exclusively formed isomers are proposed on the basis of NMR study.

Automated summary

A low-symmetry binuclear complex and an extremely rare trinuclear complex of palladium were synthesized through self-assembly reactions. The exclusive formation of specific isomers was predicted and confirmed experimentally. NMR study revealed conformational changes within the formed isomers.