Synthesis, Molecular Structure, Properties, and Electronic Structures of [Cp*(dppe)FeC≡C-TTFMe3][PF6]n (n = 0, 1): Electronic Coupling between the Inorganic and Organic Electrophores

Hybrid molecular systems containing tetrathiafulvalene and iron-alkynyl electrophores: five-component functional molecules obtained from C-H bond activation

Treatment of [Cp*(dppe)Fe-C≡C-TTFMe3] (1) with Ag[PF6] (3 equiv) in DMF provides the binuclear complex [Cp*(dppe)Fe=C=C=TTFMe2 =CH-CH=TTFMe2 =C=C=Fe(dppe)Cp*][PF6]2 (2[PF6 ]2) isolated as a deep-blue powder in 69 % yield. EPR monitoring of the reaction and comparison of the experimental and calculated EPR spectra allowed the identification of the radical salt [Cp*(dppe)Fe=C=C=TTFMe2 =CH][PF6]2 ([1-CH][PF6]) an intermediate of the reaction, which results from the activation of the methyl group attached in vicinal position with respect to the alkynyl-iron on the TTF ligand by the triple oxidation of 1 leading to its deprotonation by the solvent. The dimerization of [1-CH][PF6] through carbon-carbon bond formation provides 2[PF6]2. The cyclic voltammetry (CV) experiments show that 2[PF6]2 is subject to two sequential well-reversible one-electron reductions yielding the complexes 2[PF6] and 2. The CV also shows that further oxidation of 2[PF6]2 generates 2[PF6]n (n=3-6) at the electrode. Treatment of 2[PF6]2 with KOtBu provides 2[PF6] and 2 as stable powders. The salts 2[PF6] and 2[PF6]2 were characterized by XRD. The electronic structures of 2(n+) (n=0-2) were computed. The new complexes were also characterized by NMR, IR, Mössbauer, EPR, UV/Vis and NIR spectroscopies. The data show that the three complexes 2[PF6]n are iron(II) derivatives in the ground state. In the solid state, the dication 2(2+) is diamagnetic and has a bis(allenylidene-iron) structure with one positive charge on each iron building block. In solution, as a result of the thermal motion of the metal-carbon backbone, the triplet excited state becomes thermally accessible and equilibrium takes place between singlet and triplet states. In 2[PF6], the charge and the spin are both symmetrically distributed on the carbon bridge and only moderately on the iron and TTFMe2 electroactive centers.

Reactions of 7,7,8,8-Tetracyanoquinodimethane (TCNQ) with Alkynyl-Iron- and -Ruthenium Complexes: Synthesis of Ru{C=CC(CN)=C6H4=C(CN)2}(PPh3)2Cp, a New Donor - Acceptor Molecular Array

Reactions of 7,7,8,8-tetracyanoquinodimethane (TCNQ) with the alkynyl-iron and ruthenium complexes [M](C≡CR) {[M] = Fe(dppe)Cp*, Ru(PPh3)2Cp; R = H, Ph} are described. The iron complex Fe(C≡CPh)(dppe)Cp* (2a) is oxidized by TCNQ to give the kinetically stable salt [2a•+][TCNQ]•– . Displacement of [TCNQ]•– is achieved by ionic metathesis upon addition of KPF6 to produce [2a•+]PF6. In contrast, Fe(C≡CH)(dppe)Cp* (2b) reacted with TCNQ to give a mixture of compounds containing Fe(=C=CH2)(dppe)Cp* (3a), {Fe(dppe)Cp*}2(μ-C=CHCH=C) (3b), and the zwitterionic complex Fe+{=C=CHC(CN)2C6H4C–(CN)2}(dppe)Cp* (3c). In contrast, the reaction of TCNQ with Ru(C≡CR)(PPh3)2Cp (4a, R = Ph; 4b, R = H) gave selectively the zwitterionic vinylidenes Ru+{=C=CRC(CN)2C6H4C–(CN)2}(PPh3)2Cp (5a, R = Ph; 5b, R = H), in which the Ru centres are positively charged and the counter-anion is located on the further C(CN)2 group. On heating 5b, elimination of HCN affords Ru{C≡CC(CN)=C6H4=C(CN)2}(PPh3)2Cp (1), while similar treatment of 5a gives Ru{η3-C(CN)2CPh=C6H4=C(CN)2}(PPh3)Cp (6) with loss of PPh3. X-ray structures of 1, 5a, and 6, cyclic voltammetry, and UV-vis spectroscopy of 1 provided evidence for the electronic structures of the new complexes.