Redox‐Active Tetraruthenium Macrocycles Built from 1,4‐Divinylphenylene‐Bridged Diruthenium Complexes

Abstract

Metallamacrocylic tetraruthenium complexes were generated by treatment of 1,4-divinylphenylene-bridged diruthenium complexes with functionalized 1,3-benzene dicarboxylic acids and characterized by HR ESI-MS and multinuclear NMR spectroscopy. Every divinylphenylene diruthenium subunit is oxidized in two consecutive one-electron steps with half-wave potential splittings in the range of 250 to 330 mV. Additional, smaller redox-splittings between the + /2 + and 0/ + and the 3 + /4 + and 2 + /3 + redox processes, corresponding to the first and the second oxidations of every divinylphenylene diruthenium entity, are due to electrostatic effects. The lack of electronic coupling through bond or through space is explained by the nodal properties of the relevant molecular orbitals and the lateral side-by-side arrangement of the divinylphenylene linkers. The polyelectrochromic behavior of the divinylphenylene diruthenium precursors is retained and even amplified in these metallamacrocyclic structures. EPR studies down to T = 4 K indicate that the dications 1-H 2 + and 1-OBu 2 + are paramagnetic. The dications and the tetracation of macrocycle 3-H display intense (dications) or weak (3-H 4 + ) EPR signals. Quantum chemical calculations indicate that the four most stable conformers of the macrocycles are largely devoid of strain. Bond parameters, energies as well as charge and spin density distributions of model macrocycle 5-H Me were calculated for the different charge and spin states.

A “Pretender” Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities

“…3:2 ( Scheme 1 and Figures S1 and S2 of the Supplementary Materials ). This pattern is suggestive of two kinds of macrocyclic complexes that differ in their nuclearities, similar to what we have observed on previous occasions [ 27 , 30 , 31 ]. High-resolution mass spectro-metry indeed provides a molar peak at 2336.78 g mol −1 (calcd.…”

“…This pattern indicates the nearly coincident charging of the opposite {Ru}-CH=CH-Aryl-CH=CH-{Ru} electrophores by first one and then a second electron. The only small or vanishing potential splitting between the 0/+ and +/2+ or the 2+/3+ and 3+/4+ waves reflects electrostatic interactions between them, as the insulating dicarboxylate linkers prevent through-bond electronic coupling [ 27 , 28 , 29 , 30 , 31 ]. In this particular case, however, an alternative scenario, where one of these composite waves originates from the first oxidations of opposite croconate linkers, is also conceivable, such that the loci of the individual oxidations remain to be verified.…”

“…The occupied frontier orbitals of such repeat units spread over the entire Ru-CH=CH-Aryl entity [ 22 , 23 , 24 ], while the carboxylate linker represents a local node, thereby attenuating electronic coupling in the mixed-valent states [ 25 , 26 ]. In contrast, structurally similar macrocyclic ruthenium complexes built from {Ru}-CH=CH-Aryl-CH=CH-{Ru} entities, capable of forming fully delocalized mixed-valent radical cations, and isophthalate, terephthalate, isonicotinate or pyrrole-, furan- or thiophene-2,5-dicarboxylate linkers do not exhibit any signs of electronic coupling between the π-conjugated diruthenium entities, as the dicarboxylate linkers do not contribute to the relevant redox orbitals [ 25 , 27 , 28 , 29 , 30 , 31 , 32 ].…”

Ferrocene‐ and Biferrocene‐Containing Macrocycles towards Single‐Molecule Electronics

“…Multiple redox‐active groups within molecular wires show interesting results in conductance modulation 12, 13, 14. Currently, little research has been pointed towards redox‐active groups in parallel or in rings within electronic systems 2, 15, 16, 17. Ferrocene is often incorporated into molecular wires due to its stability, high conductance levels, and ability to act as a redox switch 18, 19, 20, 21.…”

Ferrocene‐ and Biferrocene‐Containing Macrocycles towards Single‐Molecule Electronics

“…Multiple redox‐active groups within molecular wires show interesting results in conductance modulation . Currently, little research has been pointed towards redox‐active groups in parallel or in rings within electronic systems . Ferrocene is often incorporated into molecular wires due to its stability, high conductance levels, and ability to act as a redox switch .…”