The π‐conjugated molecule N,N′‐bis(4′‐dimethylaminophenyl)‐1,4‐benzoquinone diimine (L2) was incorporated into the palladium(II) complex 1 bearing the N,N′‐bis(2‐phenylethyl)‐2,6‐pyridinedicarboxamide ligand, to afford the redox‐active conjugated palladium(II) homobimetallic complex 2. An X‐ray crystal structure determination of 2 reveals that two palladium complex units are bridged by the quinone diimine moiety to form the C2‐symmetrical 2:1 complex with an anti configuration, and that the bridging π‐conjugated spacer moieties are aligned along a straight line almost parallel to the a axis, to form the columns of the π‐conjugated molecules in the molecular packing. Variable temperature 1H NMR studies of the conjugated complex 2 indicate that the syn configuration is enthalpically more favorable than the anti configuration in CD2Cl2 by 1.0 kcal/mol, but entropically less favorable by 4.5 cal/mol from the van’t Hoff plot. The redox function of the quinone diimine moiety is modulated by complexation with the palladium complex 1. The conjugated complex 2 shows three separate redox waves assignable to the successive one‐electron reduction of the quinone diimine moiety and one‐electron oxidation process of the two terminal dimethylamino groups. Chemical reduction of 2 in THF with CoCp2 resulted in the appearance of ESR signals with weak 105Pd coupling centered around g = 2.0041. The added electrons are considered to be delocalized over the PdII‐quinone diimine d‐π* system in the complex.

The palladium homobimetallic complexes 2a and 2b with a bridging π-conjugated molecule, N,N′-bis(4′-pyridylmethylidene)-1,4-phenylenediamine (L2a) and 2′-pyridyl derivative L2b, were respectively synthesized and characterized by X-ray crystal structure analysis and cyclic voltammetry. 1H-NMR of 2b indicates the five-coordinate geometry on the palladium center.

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The conjugated homobimetallic palladium(II) complex [(L1)Pd(qd)Pd(L1)] (qd = quinonediimine) was obtained in a one-pot reaction by the in-situ oxidative complexation of 1,4-phenylenediamine with the palladium(II) complex [(L1)Pd(MeCN)] (H2L1 = N,N'-bis(2-phenylethyl)-2,6-pyridinedicarboxamide) while in the absence of an additional ligand [(L1)Pd(MeCN)] was converted to the amide-bridged macrocyclic tetramer [Pd(L1)]4.

A π-conjugated quinonediimine ligand possessing two terminal redox-active ferrocenyl groups, N,N′-bis{(4′-ferrocenylcarboxamide)phenyl}-1,4-benzoquinonediimine (Lox), was synthesized. The quinonediimine ligand Lox was reduced to Lred composed of the phenylenediamine moiety on treatment with hydrazine hydrate. The reaction of Lox with the palladium(II) complex 1 bearing the N,N′-bis(2-phenylethyl)-2,6-pyridinedicarboxamide ligand afforded the multimetallic complex 2. Variable temperature 1H NMR studies of 2 indicated the existence of syn and anti isomers, in which the anti isomer is enthalpically more favorable than the syn isomer in CD2Cl2 by 0.9 kcal mol−1, but entropically less favorable by 2.6 cal mol−1 K−1 from the van’t Hoff plot. The redox function of the quinonediimine moiety is modulated by complexation with 1. The complex 2 showed three separate redox waves, which are assignable to the successive one-electron reduction of the quinonediimine moiety and oxidation of the two terminal ferrocenyl groups. Chemical reduction of 2 in CH2Cl2 with [Co(Cp)2] resulted in the appearance of ESR signals with weak 105Pd coupling centered around g = 2.004. The unpaired electron appears to locate mostly on the quinonediimine moiety with some delocalization onto the palladium center.