Effect of ligand structure, solvent, and temperature on the electrochemical behavior of polyarene–iron complexes

Abstract

Abstract:The electrochemical investigation of a number of polyarene-iron complexes ([3]"-[915+) containing etheric, sulphide, and sulphone bridges indicated that there were various degrees of interaction based on the nature of the bridging heteroatoms. While the electrochemical investigation of all etheric complexes showed that the metallic moieties behaved as isolated redox centers, it was found that there was electronic communication (ca. 70-80 mV) for the isomeric sulphide complexes [412+ and [612+. The rate constant of the following chemical reaction (k,) was calculated for some of these complexes and it was found that these rates were affected by the nature of the solvent, the bridging ligand, and the temperature. At various temperatures, kfindicated a higher degree of stability for complexes containing sulphide bridges than for those containing etheric bridges, especially at room temperature. The effect of a strong coordinating solvent, such as acetonitrile, on the k, of complex [3]'+ indicated that the substitution of the arene ligand with acetonitrile molecules proceeded as a dissociative mechanism. Controlled potential coulometry was also used to verify the transfer of two electrons in the first reduction process of the di-iron complexes.Key words: cyclopentadienyliron, cyclic voltammetry, arene complexes, isolated and interacting redox centers.

Synthesis of norbornenes containing cationic mono‐ and di(cyclopentadienyliron)arene complexes and their ring‐opening metathesis polymerization

“…It is well known that the exceptional electron‐withdrawing ability of the CpFe + moiety facilitates the nucleophilic aromatic substitution (S N Ar) reaction of complexed chloroarenes under mild conditions 21, 24–26, 29–33, 36–38. Scheme illustrates the synthesis of various monometallic complexes containing terminal hydroxyl groups ( 3a – 3c ) via the reaction of 1a or 1b with phenolic dinucleophiles 2a – 2c .…”

“…The electrochemical properties of the organoiron polynorbornenes were examined with CV. It is well known that cationic η 6 ‐arene‐η 5 ‐cyclopentadienyliron complexes undergo reversible reduction processes to produce neutral 19‐electron iron complexes 30, 44. Similar redox behavior has been observed for the organoiron polynorbornene; for example, Figure 3 shows the cyclic voltammogram of polymer 22b at −40 °C with a sweep rate of 0.2 V/s.…”

“…Macromolecules containing organometallic moieties in either their side chains or backbones have been the focus of many researchers over the past few decades. The remarkable properties that the resulting polymers exhibit include hardness, magnetism, catalytic behavior, and redox activity 21–33. Schrock et al11 previously reported the synthesis of electrochemically active polynorbornenes containing neutral iron centers via ROMP.…”

“…The resulting polymers displayed redox active properties and were used in the preparation of a modified electrode surface. Our research has focused on the synthesis of monomeric and polymeric materials containing arenes coordinated to cationic cyclopentadienyliron moieties in their backbones or side chains 21, 24–26, 30–35. Recently, we synthesized thermally stable polynorbornene with pendant ether linkages 36–38.…”

Star-Shaped Polyaromatic Ethers Coordinated to Redox-Active Cyclopentadienyliron Moieties

“…All of these complexes were found to undergo chemically reversible reduction processes, which is characteristic of arene cyclopentadienyliron complexes. [14,17] The cyclic voltammetric studies were carried out in DMF from -40 to +20 8C at sweep rates of 0.1 to 5 V/s using an Ag/AgCl reference electrode, a glassy carbon working electrode and a Pt auxiliary electrode. The E 1/2 value corresponding to reduction of complex 3 a, containing terminal chloro groups was found to be -0.99 V (Figure 1), while the E 1/2 value corresponding to reduction of complex 3 b was -1.41 V at -40 8C, m = 0.1 V/s.…”