Synthesis, Structure, Electrochemical, and Spectroscopic Properties of Hetero-Bimetallic Ru(II)/Fe(II)-Alkynyl Organometallic Complexes

Abstract

A series of heterobimetallic wire-like organometallic complexes [(tpy-C6H4-R)­(PPh3)2Ru–CC–Fc]+ (tpy-C6H4-R = 4′-(aryl)-2,2′:6′,2′′-terpyridyl, Fc = [(η5-Cp)2Fe], R = -H, -Me, -F, -NMe2 in complexes 5–8, respectively) featuring ferrocenyl and 4′-(aryl)-2,2′:6′,2′′-terpyridyl ruthenium­(II) complexes as redox active metal termini, have been synthesized. Various spectroscopic tools, such as multinuclear NMR, IR spectra, HRMS, CHN analyses, and single crystal X-ray crystallography have been utilized to characterize the heterobimetallic complexes. The electrochemical and UV–vis–NIR spectroscopic studies have been investigated to evaluate the electronic delocalization across the molecular backbones of the Ru­(II)–Fe­(II) heterobinuclear organometallic dyads. Electrochemical studies reveal two well-separated reversible redox waves as a result of successive oxidation of the ferrocenyl and Ru­(II) redox centers. The spin density distribution analyses reveal that the initial oxidation process is associated with the Fe­(II)/Fe­(III) couple followed by one electron oxidation of the ruthenium­(II) center. The high K c value (0.11–1.73 × 1012) and intense NIR absorption, with molar absorption coefficient (in the order of 103 M–1 cm–1) for the RuIIFeIII mixed-valence species, signify strong electronic communication between the two metal termini. The electronic coupling constant (H ab) has been estimated to be 492 and 444 cm–1 for the structurally characterized complexes 6 and 7, respectively. The redox and NIR absorption features indicate that the mixed-valence system of the heterobinuclear dyads belongs to a Robin and Day “class II” system.

The Electron Transfer Process in Mixed Valence Compounds with a Low‐lying Energy Bridge in Different Oxidation States

“…The Δ G 0 of 1 4+ is the largest, the ET rate is the slowest and the electron coupling is the smallest (1543 cm −1 ) due to the weaker donor character of CpFe II (dppe) compared to CpMe x Fe II (dppe) ( x =1, 3, 4, and 5). The similar phenomenon that the weak donor is unbeneficial to ET was previously reported [9, 29] . The PES of 1 4+ (Figure 10 a) has three minimums, and the PES contour (Figure 10 c) shows that the ET process between the lowest minima present a high barrier (1320 cm −1 , yellow arrow).…”

“…that the weak donor is unbeneficial to ET was previously reported. [9,29] TheP ES of 1 4+ (Figure 10 a) has three minimums,a nd the PES contour (Figure 10 c) shows that the ET process between the lowest minima present ah igh barrier (1320 cm À1 ,y ellow arrow). This corresponds to the superexchange mechanism.…”

The Electron Transfer Process in Mixed Valence Compounds with a Low‐lying Energy Bridge in Different Oxidation States

“…Forschungsartikel that the weak donor is unbeneficial to ET was previously reported. [9,29] TheP ES of 1 4+ (Figure 10 a) has three minimums,a nd the PES contour (Figure 10 c) shows that the ET process between the lowest minima present ah igh barrier (1320 cm À1 ,y ellow arrow). This corresponds to the superexchange mechanism.…”

Benchmarking DFT Calculations of 1H and 13C Chemical Shifts in Monosubstituted Ferrocenes

“…The experimental chemical shifts were obtained from the literature: ferrocene ( a ), [ 98–99 ] methylferrocene ( b ), [ 100 ] ethylferrocene ( c ), [ 101 ] phenylferrocene ( d ), [ 102–103 ] 4‐iodophenylferrocene ( e ), [ 104 ] ethynylferrocene ( f ), [ 105 ] ferrocenylmethanol ( g ), [ 106 ] 1‐ferrocenylethanol ( h ), [ 107 ] N , N ‐dimethylaminomethylferrocene ( i ), [ 108 ] formylferrocene ( j ), [ 108 ] ferrocenecarboxylic acid ( k ), [ 109 ] acetylferrocene ( l ), [ 108 ] N , N ‐dimethylferroceneamide ( m ), [ 106 ] fluoroferrocene ( n ), [ 110–111 ] chloroferrocene ( o ), [ 112 ] bromoferrocene ( p ), [ 112 ] trimethylferrocenylphosphonium hexafluorophosphate ( q ), [ 113 ] iodoferrocene ( r ), [ 112 ] cyanoferrocene ( s ), [ 114 ] ferroceneboronic acid ( t ), [ 115 ] 1,1′‐dimethylferrocene, [ 116–117 ] 1,1′‐diphenylferrocene, [ 118 ] 1,1′‐ferrocenediboronic acid, [ 118 ] 1,1′‐ferrocenedicarboxylic acid, [ 119–120 ] 1,1′‐diacetylferrocene, [ 120–121 ] 1′‐trimethylsilylethynyl‐1‐ethynylferrocene, [ 122 ] 1′‐bromo‐1‐ferrocenylcarboxylic acid, [ 123 ] and decamethylferrocene. [ 124 ] The extracted data are given in Tables S10 and S14.…”