“Tail–Tail Dimerization” of Ferrocene Amino Acid Derivatives

Siebler, Daniel; Förster, Christoph; Heinze, Katja

doi:10.1002/ejic.201000384

Cited by 13 publications

(23 citation statements)

References 42 publications

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“…data reports the connecting O3 atom of the anhydride unit that results in a torsion angle of approximately 57.36 for O1-C1Á Á ÁC2-O2. Similar torsional geometry is observed in the ruthenium analogue IVOYOY (62.31 ;Micallef et al, 2011), the 1 0 ,2 0 -bissubstituted ferrocene system KAJBUU (57.04 ;Siebler et al, 2010) and the vanadium compound NEWFIE (66.68 ;Elschenbroich et al, 1997). In the bis-ferrocenophanone structure HOVYEY (Liu et al, 2015) where two ferrocene groups are constrained by two anhydride linkages, the two carbonyl groups are still inclined at an O-CÁ Á ÁC-O torsion angle of 27.47 despite the fact that the bridged Cp rings are almost coplanar, suggesting the O-CÁ Á ÁC-O torsion is a mechanism to relieve steric strain in the molecule.…”

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confidence: 60%

Ferrocenecarboxylic anhydride: a redetermination

McAdam

2016

IUCr Data

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The title molecule, [Fe2(C5H5)2(C12H8O3)], briefly reported previously [Zhang (2015). Private Communication (CCDC reference 1056736). CCDC, Cambridge, England], comprises two ferrocenyl units connected by an acid anhydride bridge. Both ferrocene units have near coplanar [dihedral angles between the ring planes = 2.84 (4) and 1.74 (13)°] and eclipsed [pseudo torsion angles = 6.3 (2) and 5.1 (2)°] cyclopentadienyl (Cp) rings. A twist through the anhydride linkage results in a dihedral angle of 73.81 (8)° between the two substituted Cp rings planes. An intramolecular C—H...O hydrogen bond is also found. In the crystal, C—H...O hydrogen bonds link the molecules into a three-dimensional network.

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confidence: 60%

Ferrocenecarboxylic anhydride: a redetermination

McAdam

2016

IUCr Data

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“…The solution IR and NMR data are also consistent with the presence of such a hydrogen bond in solution. DFT calculations of (MeO-CO-Fca) 2 O confirm the stability of the hydrogen-bonded 12-membered ring as compared to a non-hydrogen-bonded conformation (31 kJ mol À1 ) [21].…”

Section: Simple Ferrocene Amino Acid (Bio)conjugatesmentioning

confidence: 73%

“…A multitude of simple conjugates of H-Fca-OH has been prepared and analyzed with respect to conformational preferences, namely conjugates featuring a single hydrogen bond between the strands (Scheme 21.2, A-D) [4,[13][14][15], two hydrogen bonds between the arms (Scheme 21.2, E-I) [14,15,[17][18][19][20], and a single hydrogen bond between the termini of symmetrical anhydrides of H-Fca-OH (Scheme 21.2, J) [21].…”

Section: Simple Ferrocene Amino Acid (Bio)conjugatesmentioning

confidence: 99%

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Elucidation of the Conformational Freedom of Ferrocene Amino Acid (Bio)Conjugates: A Complementary Theoretical and Experimental Approach

Heinze

Hüttinger

Siebler

2011

Modeling of Molecular Properties

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Introduction1-Amino-1 0 -carboxyferrocene H-Fca-OH [1-4] (Scheme 21.1) is a versatile starting material for the preparation of 1,n 0 disubstituted ferrocenes with distinguished and unique properties. By placing the hydrogen atom donor and hydrogen atom acceptor sites in the different strands of 1,n 0 disubstituted ferrocene derivatives, interstrand hydrogen bonds are feasible giving ansa-ferrocenes. For example, an interstrand hydrogen bond has been observed in Me-CO-Fca-OBt (Bt ¼ 1-benzotriazole) with the triazole heterocycle acting as hydrogen atom acceptor and the NH group acting as hydrogen atom donor, giving an eight-membered ring, excluding the iron center ( Figure 21.1a) [4]. In contrast, the N-acyl urea derivative Me-CO-Fca-NCy-CO-NHCy (Cy ¼ cyclohexyl) features a more strained six-membered ring with the Fca carbonyl unit CO Fca being the acceptor, although larger ring motifs are also possible -for example, an eight-membered ring with the ureylene carbonyl CO ureylene as acceptor and a 10-membered ring with the acetyl carbonyl CO Ac as acceptor and the NH ureylene as donor (Figure 21.1b) [4].In cases where there are several acceptor and donor sites in the two arms, many ring motifs become possible. This holds especially true for peptidic Fca conjugates with organic amino acids or with further Fca units as arms, with each additional amide group providing both a potential hydrogen acceptor and donor site. In natural peptides built from a-amino acids, both intramolecular and intermolecular hydrogen bonds allow the formation of a-helices, b-sheets, or turns. In conjugates incorporating 1,n 0 ferrocene units, a very flexible hinge is introduced into the backbone which allows for small and large hydrogen-bonded ring systems. The two strands can be oriented approximately in the same direction (v ¼ 0 AE 36 ; 1,1 0 rotational isomer), rotated clockwise by 360 /5 ¼ 72 (v ¼ 72 AE 36 ; 1,2 0 rotational isomer), rotated clockwise by 2 Â 360 /5 ¼ 144 (v ¼ 144 AE 36 ; 1,3 0 rotational isomer), rotated anticlockwise by À2 Â 360 /5 ¼À 144 (v ¼À 144 AE 36 ; 1,4 0 rotational isomer), or rotated anticlockwise by À360 /5 ¼À 72 (v ¼À 72 AE 36 ; 1,5 0 rotational isomer).

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“…Electronic interaction across the amide bridge is feasible, as shown by analysis of well-defined mixed-valent systems similar to urea-bridged ferrocenes [59] and in contrast to anhydride-bridged systems. [60] According to modelling studies full charging should unfold the zigzag conformations of the oligoferrocene amides to give extended systems (mechanoelectrical motion, "electrochemically powered artificial muscle"). On the other hand mechanical changes are expected to change conductivity in these foldamers.…”

Section: Resultsmentioning

confidence: 99%

Oligonuclear Ferrocene Amides: Mixed‐Valent Peptides and Potential Redox‐Switchable Foldamers

Siebler

Linseis

Gasi

et al. 2011

Chemistry A European J

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Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic ¹H NMR and Mössbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin-Day class II mixed-valent systems. Mössbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form).

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“Tail–Tail Dimerization” of Ferrocene Amino Acid Derivatives

Cited by 13 publications

References 42 publications

Ferrocenecarboxylic anhydride: a redetermination

Ferrocenecarboxylic anhydride: a redetermination

Elucidation of the Conformational Freedom of Ferrocene Amino Acid (Bio)Conjugates: A Complementary Theoretical and Experimental Approach

Oligonuclear Ferrocene Amides: Mixed‐Valent Peptides and Potential Redox‐Switchable Foldamers

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