Synthesis of a Series of Diiron Complexes Based on a Tetraethynylethene Skeleton and Related C₆-Enediyne Spacers, (dppe)Cp*Fe−C⋮CC(R)C(R)C⋮C−FeCp*(dppe):  Tunable Molecular Wires

Abstract

A series of 3,4-disubstituted (hex-3-ene-1,5-diyne-1,6-diyl)diron complexes with FeCp*(dppe) ( Fe ) end caps, Fe −C⋮CC(R)C(R)C⋮C− Fe (R = H, C⋮C−SiMe3, C⋮C−H, C6H5, p-C6H4CF3), and the related (octa-3,5-diene-1,7-diyne-1,8-diyl)diron complex, Fe −C⋮C−C(H)C(H)C(H)C(H)C⋮C− Fe , has been prepared, and their performance as molecular wires has been evaluated. The enyne complexes have been synthesized via vinylidene intermediates, [ Fe CC(H)C(R)C(R)C(H)C Fe ]2+, derived from the corresponding terminal alkynes or the Me3Si-protected precursors (XC⋮CCC(R)C(R)C⋮C−X; X = H, SiMe3), and the products have been characterized spectroscopically and crystallographically. The performance of the obtained dinuclear enyne complexes as molecular wires has been evaluated on the basis of the comproportionation constants (K C) obtained by electrochemical measurements and the V ab values obtained from the spectral parameters of the intervalence charge transfer bands of the isolated monocationic radical species appearing in the near-IR region. As a result, the C6-enediyne complexes turn out to be excellent molecular wires, with K C values larger than 108 as well as V ab values larger than 0.35, belonging to class III compounds according to the Robin and Day classification and being comparable to the related polyynediyl complexes as well. It is notable that, in the enyne system, the performance can be readily tuned by introduction of appropriate substituents onto the olefinic part. Thus, diiron complexes containing an enyne spacer can be regarded as tunable molecular wires.

p-Diethynylbenzene-based molecular wires, Fe–C C-p-C6H2X2–C C–Fe [Fe= Fe(η5-C5Me5)(dppe)]: Synthesis, substituent effects and unexpected formation of benzodifuran complex

“…As a result, the DE values become larger compared to the other derivatives (Scheme 4). Similar effects were reported for the endiyne system [7] described in Introduction and other systems [20].…”

“…THF, toluene, pentane (Na-K alloy), CH 2 Cl 2 , MeCN (P 2 O 5 ), and MeOH (Mg(OMe) 2 ) were treated with appropriate drying agents, distilled, and stored under argon. For the analytical instruments used in the present study, see our previous papers [7]. Fe-Cl [21], benzodithiophene [22], and the precursors 1b-e,g [23] were prepared according to the reported methods, and the synthetic procedures for 1a,f are included in the Supporting Information.…”

“…The polyynediyl ligands, however, cannot be modified, because no substituent can be introduced onto the sp-hybridized carbon atoms. In a previous paper, we reported synthesis of a series of endiyne-diiron complexes, Fe-C"C-C(R)@C(R)-C"C-Fe [Fe = FeCp * (dppe)], and the substituent effects [7,8]. It is notable that some of the aryl-substituted derivatives show wire-like performance even superior to the polyynediyl complexes and thus the family of the complexes is regarded as ''tunable molecular wires".…”

Synthesis, characterization, and substituent effects of mononuclear ruthenium complexes [RuCl(CO)(PMe3)3(CHCH-C6H4-R-p)] (R=H, CH3, OCH3, NO2, NH2, NMe2)

“…1, the complex contains a p-anisyl moiety linked via a trans-CH@CH group to the ruthenium center. The structure displays an extended conformation, in which the C(11)-C(12) double bond, O(2), and the benzene ring are nearly coplanar, with maximum deviations from the leastsquares plane of 0.0042 Å for C (12) …”

“…Highly unsaturated, rigid -(C"C) n -and -(C@C) n -bridges offer an extended p-system and have been recognized as being particularly efficient in mediating electronic transfer [5][6][7][8][9][10]. In this context, a vast number of mono-and bimetallic complexes with polyynediyl or polyacetylene bridges have been extensively studied [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. For example, as model complexes to aid understanding of the influence of substituents on the bonding properties within the metal-acetylide backbone, mononuclear metal r-arylacetylides [(g 2 -dppe)(g 5 -C 5 Me 5 )M(C"C)-1,4-(C 6 H 4 )X] (M = Fe or Ru) have recently been reported by Paul and Bruce et al [4].…”