Ferrocenyl-Pyrenes, Ferrocenyl-9,10-Phenanthrenediones, and Ferrocenyl-9,10-Dimethoxyphenanthrenes: Charge-Transfer Studies and SWCNT Functionalization.

The synthesis of 1-Fc- (3), 1-Br-6-Fc- (5 a), 2-Br-7-Fc- (7 a), 1,6-Fc2 - (5 b), 2,7-Fc2 -pyrene (7 b), 3,6-Fc2 -9,10-phenanthrenedione (10), and 3,6-Fc2 -9,10-dimethoxyphenanthrene (12; Fc=Fe(η5 -C5 H4 )(η5 -C5 H5 )) is discussed. Of these compounds, 10 and 12 form 1D or 2D coordination polymers in the solid state. (Spectro)Electrochemical studies confirmed reversible Fc/Fc+ redox events between -130 and 160 mV. 1,6- and 2,7-Substitution in 5 a (E°'=-130 mV) and 7 a (E°'=50 mV) influences the redox potentials, whereas the ones of 5 b and 7 b (E°'=20 mV) are independent. Compounds 5 b, 7 b, 10, and 12 show single Fc oxidation processes with redox splittings between 70 and 100 mV. UV/Vis/NIR spectroelectrochemistry confirmed a weak electron transfer between FeII /FeIII in mixed-valent [5 b]+ and [12]+ . DFT calculations showed that 5 b non-covalently interacts with the single-walled carbon nanotube (SWCNT) sidewalls as proven by, for example, disentangling experiments. In addition, CV studies of the as-obtained dispersions confirmed exohedral attachment of 5 b at the SWCNTs.

Influence of P-Bonded Bulky Substituents on Electronic Interactions in Ferrocenyl-Substituted Phospholes.

2,5-Diferrocenyl-1-Ar-1H-phospholes 3 a-e (Ar=phenyl (a), ferrocenyl (b), mesityl (c), 2,4,6-triphenylphenyl (d), and 2,4,6-tri-tert-butylphenyl (e)) have been prepared by reactions of ArPH2 (1 a-e) with 1,4-diferrocenyl butadiyne. Compounds 3 b-e have been structurally characterized by single-crystal XRD analysis. Application of the sterically demanding 2,4,6-tri-tert-butylphenyl group led to an increased flattening of the pyramidal phosphorus environment. The ferrocenyl units could be oxidized separately, with redox separations of 265 (3 b), 295 (3 c), 340 (3 d), and 315 mV (3 e) in [NnBu4 ][B(C6 F5 )4]; these values indicate substantial thermodynamic stability of the mixed-valence radical cations. Monocationic [3 b](+)-[3 e](+) show intervalence charge-transfer absorptions between 4650 and 5050 cm(-1) of moderate intensity and half-height bandwidth. Compounds 3 c-e with bulky, electron-rich substituents reveal a significant increase in electronic interactions compared with less demanding groups in 3 a and 3 b.

Anion and solvent dependency of the electronic coupling strength in mixed valent class II systems.

The influence of the coordination and ion pairing properties of electrolyte anions on electronic coupling in cationic class II mixed valent species was studied. In order to cover a range of electronic coupling strengths within the class II regime, weakly coupled 2,5-diferrocenyl-3,4-thiadiazol, moderately coupled 2,5-diferrocenyl thiophene and strongly coupled N-(4-dimethylaminophenyl)-2,5-diferrocenyl-1H-pyrrole were chosen as analytes. The electrochemical properties of these compounds were determined by cyclic and square wave voltammetry using electrolytes with varying ion pairing capabilities, such as [NBu4][Cl], [NBu4][PF6] and [NBu4][BArF] ([NBu4][B(C6F5)4]), as well as solvents with increasing dielectric constants (dichloromethane (εr = 8.93), acetone (εr = 20.56), acetonitrile (εr = 35.94) and propylene carbonate (εr = 64.92)). It is shown that the choice of electrolyte has a considerable impact on the electrostatic and the electron transfer features of the mixed valent compounds when solvents of low polarity and low relative permittivity such as dichloromethane are used. For the use of more polar solvents such as propylene carbonate the electrochemical and spectroscopic properties are almost electrolyte independent. The solvatochromic and ion-related changes in the spectroscopic properties are most pronounced for weakly coupled systems and decrease with an increase in the electron transfer coupling strength.

Ferrocenyl naphthalenes: substituent- and substitution pattern-depending charge transfer studies.

The synthesis of a series of ferrocenyl-functionalized naphthalenes of type 2-Fc-C10H7 (3a), 1-Fc-2-R-C10H6 (3b, R = OMe; 3c, R = Me; 3d, R = H; 3e, R = CH(O)), 1,1'-(C10H7)2Fc' (4), 1-Br-4-Fc-C10H6 (6a), 1-Br-5-Fc-C10H6 (6b), 1-Br-8-Fc-C10H6 (6c), 2-Br-6-Fc-C10H6 (6d), 1,4-Fc2-C10H6 (7a), 1,5-Fc2-C10H6 (7b), 1,8-Fc2-C10H6 (7c) and 2,6-Fc2-C10H6 (7d) (Fc = Fe(η5-C5H4)(η5-C5H5), Fc' = Fe(η5-C5H4)2) is reported. They are accessible either by the Suzuki-Miyaura or Negishi C,C cross-coupling reaction of FcB(OH)2 (1a) or FcZnCl (1b) with the appropriate bromo-naphthalenes 2a-e and 5a-d, respectively. The molecular structures of 3a-c, 3e, 4, 6b-d and 7a-d in the solid state were determined by single-crystal X-ray diffraction analysis. They show inter- (3b,c,e, 6b,d, 7a) and intramolecular (7c) π-interactions in the form of T-shaped or parallel displaced π arrangements (3c,e, 6b), whereby 3e displays a columnar stacking of the condensed aromatic unit with plane distances of 3.485(5) to 3.525(5) Å. The (spectro)electrochemical behaviour of 3-4 and 6-7 in dichloromethane in the presence of the weakly coordinating anion [B(C6F5)4]- is discussed, showing reversible redox events in the range of -140-150 mV vs. FcH/FcH+. The electrochemical response of 3a-e and 4 depends on the electron-withdrawing and -donating groups present. The redox processes of mono Fc-substituted 6a-d are affected by the naphthalene substitution pattern, which also influences the redox separations ΔE of Fc2-naphthalenes 7a-d, confirming a significant effect of the different electron transfer pathways through the aromatic core. The UV/vis/NIR spectra of mixed-valent [7a,b,d]+ show broad and weak absorptions in the NIR region, allowing a classification as weakly coupled class II systems according to Robin and Day.

Synthesis and (spectro)electrochemistry of mixed-valent diferrocenyl-dihydrothiopyran derivatives.

Three novel diferrocenyl complexes were prepared and characterised. 2,2-Diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran (1, sulphide) was accessible by the hetero-Diels-Alder reaction of diferrocenyl thioketone with 2,3-dimethyl-1,3-butadiene. Stepwise oxidation of 1 gave the respective oxides 2,2-diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1-oxide (2, sulfoxide) and 2,2-diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1,1-dioxide (3, sulfone), respectively. The molecular structures of 1 and 3 in the solid state were determined by single crystal X-ray crystallography. The oxidation of sulphide 1 to sulfone 3, plays only a minor role on the overall structure of the two compounds. Electrochemical (cyclic voltammetry (= CV), square wave voltammetry (= SWV)) and spectroelectrochemical (in situ UV-Vis/NIR spectroscopy) studies were carried out. The CV and SWV measurements showed that an increase of the sulphur atom oxidation from -2 in 1 to +2 in 3 causes an anodic shift of the ferrocenyl-based oxidation potentials of about 100 mV. The electrochemical oxidation of 1-3 generates mixed-valent cations 1(+)-3(+). These monooxidised species display low-energy electronic absorption bands between 1000 and 3000 nm assigned to IVCT (= Inter-Valence Charge Transfer) electronic transitions. Accordingly, the mixed-valent cations 1(+)-3(+) are classified as weakly coupled class II systems according to Robin and Day.