Syntheses, Characterization, Redox Properties, and Mixed-Valence Chemistry of Tetra- and Hexanuclear Diyndiyl Complexes

Bis-alkynyl Diruthenium Compounds with Built-in Electronic Asymmetry: Toward an Organometallic Aviram–Ratner Diode

Conditions to prepare trans-[Ru2(dmba)4(C[triple chemical bond]CAr)2] from [Ru2(dmba)4(NO(3))2] (DMBA=N,N'-dimethylbenzamidinate) and HC[triple chemical bond]CAr were optimized; Et2NH was found to be the most effective among a number of weak bases in facilitating the product formation. Furthermore, a series of unsymmetric trans-[(ArC[triple chemical bond]C)Ru(2)(dmba)4(C[triple chemical bond]CAr')] compounds were prepared under optimized conditions, in which one or both of Ar and Ar' are donor (NMe2)-/acceptor (NO(2))-substituted phenyls. While the X-ray crystallographic studies revealed a minimal structural effect upon donor/acceptor substitution, voltammetric measurements indicated a significant influence of substituents on the energy level of frontier orbitals. In particular, placing a donor and an acceptor on the opposite ends of trans-[(ArC[triple chemical bond]C)Ru2(dmba)4(C[triple chemical bond]CAr')] moiety results in an energetic alignment of frontier orbitals that favors a directional electron flow, a necessary condition for unimolecular rectification.

Synthesis, Electrochemical, and Optical Properties of Linear Homo- and Heterometallocene Triads

The synthesis, electrochemical, and optical properties of homo- (5, 8, 9, and 12) and heterometallic (6, 7, 10, and 11) ferrocene-ruthenocene triads, are presented. Triferrocenyl derivatives 5 and 9 form the mixed-valence species 5*+ and 92+ by partial oxidation, which show intramolecular electro-transfer phenomena. Interestingly, spectroelectrochemical studies of compound 11, bearing two peripheral ferrocene units and one central ruthenocene moiety, revealed the presence of low-energy bands in the near-infrared (NIR) region, which indicate a rather unusual intramolecular charge-transfer between the ferrocene and ruthenocene units. The value of the electronic coupling parameter V(ab) = 150 cm(-1) calculated by deconvolution of the observed Fe(II)-Fe(III) IVCT transition in the mixed-valence compound 11*+, (d(Fe(II)-Fe(III)) = 18.617 A), indicates the ability of the ruthenocene system to promote a long distance intervalence electron-transfer. Moreover, the reported triads show selective cation sensing properties. Triads 5, 9, and 11 behave as dual redox and optical chemosensors for Zn(2+), Hg(2+), and Pb(2+). Their oxidation redox peaks are anodically shifted (up to 130 mV), and their low-energy (LE) bands of the absorption spectra are red-shifted (up to 115 nm) upon complexation with these metal cations. These changes in the absorption spectra are accompanied by dramatic color changes which allow the potential for "naked eye" detection.

Wirelike Dinuclear Ruthenium Complexes Connected by Bis(ethynyl)oligothiophene

Preparation and characterization of a series of rodlike binuclear ruthenium polyynediyl complexes capped with redox-active organometallic fragments [(bph)(PPh3)2Ru]+ (bph=N-(benzoyl)-N'-(picolinylidene)-hydrazine) or [(Phtpy)(PPh3)2Ru]2+ (Phtpy=4'-phenyl-2,2':6',2' '-terpyridine) have been carried out. The length of the molecular rods is extended by successive insertion of 2,5-thiophene or 1,4-phenylene spacers in the bridging ligands. Oxidation of thiophene-containing Ru2II,II complexes induces isolation of stable Ru2II,III or Ru2III,III species. Electrochemical and UV-vis-NIR spectral studies demonstrate that the polyynediyl bridges with 2,5-thiophene units are more favorable for metal-metal charge transfer compared with those containing the same number of 1,4-phenylene units. Successive increase of thiophene spacers in mixed-valence complexes {RuII}-CC(C4H2S)mCC-{RuIII} (m=1, 2, 3) induced a smooth transition from almost electronic delocalization (m=1) to localization (m=3). For binuclear ruthenium complexes with intramolecular electron transfer transmitted across nine Ru-C and C-C bonds, electronic conveying capability follows {Ru}-CC(CC)2CC-{Ru}>{Ru}-CC(C4H2S)CC-{Ru}>{Ru}-CC(C6H4)CC-{Ru}>{Ru}-CC(CH=CH)2CC-{Ru}. It is revealed that molecular wires capped with electron-rich (bph)(PPh3)2Ru endgroups are much more favorable for electronic communication than the corresponding electron-deficient (Phtpy)(PPh3)2Ru-containing counterparts. The intermetallic electronic communication is fine-tuned by modification of both the bridging spacers and the ancillary ligands.

Multifunctional Ferrocene−Ruthenocene Dyads Linked by Single or Double Aza-Containing Bridges Displaying Metal−Metal Interactions and Cation Recognition Properties

The synthesis, electrochemical, electronic, and cation sensing properties of the ruthenocene-terminated 2-aza-1,3-butadiene 2, linear ferrocene-ruthenocene dyads 3 and 5, and the new structural motifs diaza[4.4]ruthenocenophane 7 and mixed ferrocene and ruthenocene metallocenophanes 8 and 10 are presented. The properties of these compounds have been systematically varied by introducing the ferrocene and ruthenocene moieties at the 1- or 4-position of the unsymmetrical 2-aza-1,3-butadiene bridge. Spectroelectrochemical studies of compounds 3 and 8, in which the ruthenocene unit appended at the 1-position of the bridge exhibits a rather unusual electrochemical behavior, revealed the presence of low-energy bands in the near-infrared (NIR) region in the partially oxidized forms, at 1070 and 1163 nm, respectively, which indicate the existence of intramolecular charge transfer between the iron and the ruthenium centers. The electrochemical and intermetallic charge-transfer (MMCT) studies (HAB, lambda and alpha parameters) indicate that the 3*+ and 8*+ systems belong to the Class II classification for a mixed-valence compound. In addition, the low-energy (LE) band of the absorption spectra of all compounds prepared, except compound 10, are red-shifted by complexation with divalent Mg2+, Zn2+, Cd2+, Hg2+, and Ni2+ metal ions. For open dyads, biruthenocene compound 2 exhibited the higher red-shift by 92 nm, whereas for closed compounds the [4.4]ruthenocenoferrocenophane 8 displayed a remarkable red-shift by about 180 nm for Zn2+, Cd2+, Hg2+, and Ni2+ metal ions and by about 146 nm for Mg2+ cation. The changes in the absorption spectra are accompanied by dramatic color changes which allow the potential for "naked eye" detection. The experimental data and conclusions are supported by DFT computations.

Strong Electronic Couplings between Ferrocenyl Centers Mediated by Bis-Ethynyl/Butadiynyl Diruthenium Bridges

A series of trans-(FcC(2n))Ru(2)(Y-DMBA)(4)(C(2m)Fc) with n, m = 1 and 2 and Y-DMBA as N,N'-dimethylbenzamidinate or N,N'-dimethyl-(3-methoxy)benzamidinate have been synthesized and characterized. The intramolecular Fc...Fc distances, established through single-crystal X-ray diffraction studies, range from 11.6 to 16.6 A. Results from both voltammetric and spectroelectrochemical studies indicate that the (-C(2n))Ru(2)(Y-DMBA)(4)(C(2m-) fragments are among the most efficient mediators of intramolecular hole transfer. Density-functional calculations offer both the insight on the ground-state electronic properties and unambiguous assignment for the observed electronic absorptions.