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Treatment of 3,4-(ClC(O))2-cC4H2S (1) with [FcCH2OLi] (2-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) in a 1:2 ratio gave 3,4-(FcCH2OC(O))2-cC4H2S (3). Compound 3 decomposes in solution during crystallization to produce FcCH2OH (2) along with 3,4-thiophenedicarboxylic anhydride (4). The cyclic voltammogram of 3 exhibits a reversible ferrocene-related redox couple (E1/2 = 108 mV, vs. Cp2Fe/Cp2Fe+) using [NnBu4] [B(C6F5)4] as the supporting electrolyte. DFT calculations reveal that the energy values of the LUMO orbitals of 3 (3,4-thiophene core) show 1 eV higher energies than that one of 2,5-(FcCH2OC(O))2-cC4H2S (5), both compounds’ HOMO orbitals are close to each other. Compound 4 was characterized by single X-ray structure analysis. It forms a band-type structure based on intermolecular O1···S1 interactions being parallel to (110) and (1–10) in the solid state, while electrostatic C···O interactions between the C=O functionalities of adjacent molecules connect both 3D-networks. Hirshfeld surface analysis was used to gain more insight into the intermolecular interactions in 4, the enrichment ratios (E) suggest that O···H, S···S, and O···C are the most favored intermolecular interactions, as shown by E values above 1.20. The relevance of the weak O···H, O···O, and O···C contacts in stabilizing the molecular structure of 4 was highlighted by the interaction energies between molecular pairs.

Treatment of 3,4-(ClC(O))2-cC4H2S (1) with [FcCH2OLi] (2-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) in a 1:2 ratio gave 3,4-(FcCH2OC(O))2-cC4H2S (3). Compound 3 decomposes in solution during crystallization to produce FcCH2OH (2) along with 3,4-thiophenedicarboxylic anhydride (4). The cyclic voltammogram of 3 exhibits a reversible ferrocene-related redox couple (E1/2 = 108 mV, vs. Cp2Fe/Cp2Fe+) using [NnBu4] [B(C6F5)4] as the supporting electrolyte. DFT calculations reveal that the energy values of the LUMO orbitals of 3 (3,4-thiophene core) show 1 eV higher energies than that one of 2,5-(FcCH2OC(O))2-cC4H2S (5), both compounds' HOMO orbitals are close to each other. Compound 4 was characterized by single X-ray structure analysis. It forms a band-type structure based on intermolecular O1···S1 interactions being parallel to (110) and (1–10) in the solid state, while electrostatic C···O interactions between the C=O functionalities of adjacent molecules connect both 3D-networks. Hirshfeld surface analysis was used to gain more insight into the intermolecular interactions in 4, the enrichment ratios (E) suggest that O···H, S···S, and O···C are the most favored intermolecular interactions, as shown by E values above 1.20. The relevance of the weak O···H, O···O, and O···C contacts in stabilizing the molecular structure of 4 was highlighted by the interaction energies between molecular pairs. [ABSTRACT FROM AUTHOR]

The synthesis of Fe(η 5-C 5 H 4 CH 2 OC(O)R) 2 , 1,2-/1,3-/1,4-(FcCH 2 O) 2 -C 6 H 4 and 1,3,5-(FcCH 2 O) 3 -C 6 H 3 is discussed. The solid state structures of five compounds are reported. Electrochemical investigations show reversible Fc/Fc+ redox events. DFT calculations reveal different HOMO-LUMO gaps depending on the aryl substituent pattern. • Synthesis of ferrocenylmethyl aryl esters; electrochemistry shows reversible Fc/Fc+ events. • Molecular solid state structures confirm anti-periplanar orientations of the 1,1′-positioned substituents. • DFT calculations revealed different degrees of HOMO-LUMO gaps depending on the positions of the carboxylic ester substituents on the aryl rings. The reaction of [Fe(η 5-C 5 H 4 CH 2 OH) 2 (1) with 2 equiv of ClC(O)R (2) (a , R = C 6 H 5 ; b , R = 2-CH 3 -C 6 H 4 ; c , R = 3-CH 3 -C 6 H 4 , d , R = 4-CH 3 -C 6 H 4) produced the corresponding ferrocenyl carboxylates [Fe(η 5-C 5 H 4 CH 2 OC(O)R) 2 (3a–d). Treatment of [FcCH 2 OLi] (4 -Li) (Fc = Fe(η 5-C 5 H 5)(η 5-C 5 H 4)) with (ClC(O)) 2 C 6 H 4 (5) (a , 1,2-((ClC(O)) 2 -C 6 H 4 ; b , 1,3-((ClC(O)) 2 -C 6 H 4 ; c , 1,4-((ClC(O)) 2 -C 6 H 4) in a 2:1 M ratio gave (FcCH 2 OC(O)) 2 -C 6 H 4 (6a – c), while with 1,3,5-(ClC(O)) 3 -C 6 H 3 (7) in a 3:1 M ratio produced 1,3,5-(FcCH 2 OC(O)) 3 -C 6 H 3 (8). All compounds were characterized by NMR (1H, 13C{1H}) and IR spectroscopy, ESI-TOF mass spectrometry and elemental analysis. The molecular structures of 3a – d and 6b in the solid state were determined by single crystal X-ray structure analysis, showing anti-periplanar orientations of the 1,1′-positioned substituents at ferrocene (3a – d). In the cyclic voltammograms of 3a – d , 6a – d and 8 reversible electrochemical redox processes (Fc/Fc+) were observed, ranging between 146 and 164 mV for 3a – d , ca. 100 mV for 6a – d and at 113 mV for 8 using [N n Bu 4 [B(C 6 F 5) 4 as the supporting electrolyte. The molecular electronic structure of 3 , 6 and 8 was calculated by DFT methods in order to obtain the HOMO and LUMO absolute and relative energies in addition to electron density and distribution within the molecular arrangements. It was found that different degrees of HOMO-LUMO energy gaps within the series, due to a lowering in the LUMO energy depending on the positions of the carboxylic ester substituents on the aryl rings, are in agreement with the electrochemical results obtained. [ABSTRACT FROM AUTHOR]

Treatment of Fe( η 5 -C 5 H 4 CH 2 OH) 2 ( 1 ) with two equivalents of ClC(O)R ( 2 ) ( a , R = 2- c C 4 H 3 O; b , R = 2- c C 4 H 3 S; c , R = 2- c C 4 H 3 Se; d , R = 3- c C 4 H 3 S) produced the corresponding ferrocenylmethyl carboxylates Fe( η 5 -C 5 H 4 CH 2 OC(O)R) 2 ( 3a – d ), while the reaction of FcCH 2 OLi (Fc = Fe( η 5 -C 5 H 5 )( η 5 -C 5 H 4 )) with 2,5-(ClC(O)) 2 - c C 4 H 2 X ( 5 ) ( a , X = O; b , X = S; c , X = Se) in a 2:1 molar ratio gave 2,5-(FcCH 2 OC(O)) 2 - c C 4 H 2 X ( 6a – c ). Compounds 3a – d and 6a – c were characterized by elemental analysis, NMR ( 1 H and 13 C{ 1 H}) and IR spectroscopy. The molecular structures of 3a , b , d in the solid state were determined by single crystal X-ray structure analysis. Compound 3a crystallizes in the monoclinic space group P 2 1 / c , while 3b , d crystallize in the triclinic space group P - 1 ¯ . The ester groups and the heteroatoms are in an anti arrangement with respect to each other. Cyclic voltammetry measurements for 3a – d and 6a – c show reversible electrochemical processes (Fc/Fc + ) between 165 and 176 mV for 3a – d , and 94 and 116 mV for 6a – cb , using [N n Bu 4 ][B(C 6 F 5 ) 4 ] as the supporting electrolyte. It was found that for 3a , a somewhat higher Fc/Fc + redox potential ( E 0′ ) is observed when compared with the more electron-rich systems 3b , c , d . The molecular electronic structures of the title compounds were additionally investigated by DFT calculations, revealing different degrees of HOMO–LUMO energy gaps within the series, due to a lowering of the LUMO energy, depending on the nature of the heterocyclic ring. [ABSTRACT FROM AUTHOR]