Stepwise Construction of an Iron-Substituted Rigid-Rod Molecular Wire: Targeting a Tetraferra–Tetracosa–Decayne

Abstract

trans-Fe(depe)2I2 (depe =1,2-bis(diethylphosphino)ethane) was employed to stepwise incorporate Fe(II) centers into a rigid-rod butadiyne based 5,10,15,20-tetraferratetracosa-1,3,6,8,11,13,16,18,21,23-decayne. The iterative synthesis first connects two Fe(II) centers via a central butadiynediyl ligand to provide I-Fe(depe)2-C4-Fe(depe)2-I (2), then extends the system by substituting the terminal halides of 2 to yield Me3SiC4-Fe(depe)2-C4-Fe(depe)2-C4SiMe3 (3). Further modification of the termini gives the deprotected and stannylated compounds RC4-Fe(depe)2-C4-Fe(depe)2-C4R (4 and 5; R = H, Sn(CH3)3, respectively). Transmetalation with two more mononuclear units furnishes the homometallic tetranuclear compound I-Fe(depe)2-C4-Fe(depe)2-C4-Fe(depe)2-C4-Fe(depe)2-I (6), to which two more butadiynyl units were attached to give Me3SiC4-Fe(depe)2-C4-Fe(depe)2-C4-Fe(depe)2-C4-Fe(depe)2-C4SiMe3 (7). All compounds were characterized by NMR, IR, and Raman spectroscopies and by elemental analyses. X-ray diffraction studies were carried out on the dinuclear complexes revealing highly symmetrical rigid-rod structures. Cyclic voltammetric studies showed that compounds 2-7 undergo reversible and well-defined oxidations with high Kc values indicating thermodynamically stable mixed valence species. While the number of the oxidation waves of compounds 2, 6, and 7 are equivalent to the number of metal centers, the dinuclear complexes 3, 4, and 5 exhibit three reversible oxidation waves, one at significantly more positive potential. Two redox waves were attributed to the oxidation of the metal centers, while the remaining one is due to the oxidation of the butadiynediyl ligand. The electronic properties of complexes 2, 3, and 7 were investigated by spectroelectrochemical measurements.

High-Conductive Organometallic Molecular Wires with Delocalized Electron Systems Strongly Coupled to Metal Electrodes

“…All [FeC 4 Fe] compounds exhibit a high charge-delocalization between the two metal centers and can be oxidized or reduced reversibly in solution with up to three oxidation states at relatively low potentials (< 1.0 V). 19,20 (see SI).To perform transport measurements, we use electron-beamstructured break-junctions ( Fig. 1 B) that are mechanically actuated in a three-point bending mechanism ( Fig.…”

Structural and Electronic Variations of sp/sp2 Carbon-Based Bridges in Di- and Trinuclear Redox-Active Iron Complexes Bearing Fe(diphosphine)2X (X = I, NCS) Moieties

“…20,57 The signals of the C α nuclei appear between 122.7 ppm for 1 and 137.6 ppm for 4, marking an explicit downfield shift compared to the different previously described (depe) 2 Fe−C 4 −Fe(depe) 2 species, C α signals of which were found between 85 and 99 ppm. 20,36 While this shift could be indicative of a double-bond character, it has to be noted that other spectroscopic and structural data are consistent with alkynyl sp C α atoms. The observed shift is therefore likely to have a different origin than rehybridization.…”

“…65 On the basis of earlier experiments, we aimed to use transmetalation reactions to obtain dinuclear complexes of the X(PP) 2 Fe−R−Fe(PP) 2 X type. 20 To maintain a reasonable solubility of the targeted complexes, depe was chosen for the "equatorial" ligands of the tetragonally distorted iron octahedra. Axial iodo substituents were selected as the anionic groups of the starting materials.…”

“…20 The terminal iodo ligands are reactive and allow subsequent substitution with a number of different functional groups, while maintaining the intrinsic redox functionality of the highly delocalized (depe) 2 Fe−C 4 −Fe(depe) 2 core. 20,36 On the basis of these results, we targeted access to dinuclear entities of the type I(depe) 2 Fe−R−Fe(depe) 2 I by transmetalation of trans-Fe-(depe) 2 I 2 with different stannylated sp/sp 2 bridging ligands.…”

Syntheses and Structures of Buta-1,3-Diynyl Complexes from “on Complex” Cross-Coupling Reactions

“…Metal oligo/polyynyl M{(C≡C) n H}L x species have attracted significant interest over several decades, serving as scaffolds for the assembly of bi- [1][2][3][4][5][6][7][8][9][10][11][12][13] and poly-metallic [14][15][16][17][18][19][20][21][22][23][24][25][26] complexes, and as models and building blocks for metallomacrocycles, 15,[27][28][29] and metallo-polymers. [30][31][32][33][34][35] Detailed studies of the underlying electronic structure of this family of complexes have been undertaken, using a variety of computational and spectroscopic methods, often with a view to modelling the behavior of these prototypical molecular wires.…”