Factors affecting the electrochemical and spectroelectrochemical properties of diruthenium(III,II) complexes containing four identical unsymmetrical bridging ligands

Syntheses, crystal structures and MMCT properties of diruthenium-based cyanido-bridged RuV/VI2-NC-RuII complexes

The goal of this study was to investigate how the electron-donating capability around the lower valent metal ion and the electron-accepting capability of the higher valent metal ion influence metal to metal charge transfer (MMCT) properties in mixed-valence complexes. A series of trinuclear ruthenium complexes represented as [Ru2(ap-4-Me)3(CH3COO)NCRuCpMex(dppe)][PF6] (CpMex = polymethylcyclopentadienyl, x = 0, 1, and 5; and dppe = 1, 2-bis(diphenylphosphino)ethane, ap-4-Me = 2-anilino-4-methylpyridine) and their one-electron oxidized products were synthesized and fully characterized. The UV-vis-NIR spectra confirmed that as the electron donor character of the CpMex(dppe)RuCN fragment enhanced or the electron-accepting capability of the higher valent diruthenium cluster increased, the RuII → RuV2 or RuVI2 Ru2 MMCT bands shifted to lower energies, which was supported by TDDFT calculations.

Bisaryl and Bisalkynyl Diruthenium (III,III) Compounds Based on an Electron-Deficient Building Block

Reported herein is a new series of diruthenium(III,III) bisalkynyl and bisaryl diruthenium(III,III) compounds supported with 2-amino-3-(trifluoromethyl)pyridinate (amtfmp). Using Ru₂(amtfmp)₄Cl₂ from a modified preparation, cis 2:2 Ru₂(amtfmp)₄(C≡CPh)₂ (1), cis 2:2 Ru₂(amtfmp)₄(Ph)₂ (2), and 3:1 Ru₂(amtfmp)₄(Ph)₂ (3) were synthesized via a lithium-halogen exchange reaction using LiC₂Ph and LiPh, respectively. Compounds 1-3 are all Ru₂(III,III) species with a ground-state configuration of π⁴δ²(π*)⁴ (S = 0) and were characterized via mass spectrometry, electron absorption and ¹H/¹⁹F NMR spectroscopies, and voltammetry. The molecular structures of 1-3 were established using single-crystal X-ray diffraction analysis, and preliminary density functional theory analysis was performed to elaborate the electronic structures of 1 and 2. Comparisons of the electrochemical properties of 1-3 against the Ru₂(amtfmp)₄Cl₂ starting material reveal cathodic shifts of the Ru₂^7+/6+ oxidation and the Ru₂^6+/5+ and Ru₂^5+/4+ reduction potentials. In comparison to related Ru₂(III,III) bisalkynyl and bisaryl compounds, the electrode potentials for 1-3 are anodically shifted up to ca. 0.95 V, highlighting the strong electron-withdrawing nature of the amtfmp ligand.

Electronic Structure of Ru26+ Complexes with Electron-Rich Anilinopyridinate Ligands

Diruthenium paddlewheel complexes supported by electron-rich anilinopyridinate (Xap) ligands were synthesized in the course of the first in-depth structural and spectroscopic interrogation of monocationic [Ru₂(Xap)₄Cl]⁺ species in the Ru₂⁶⁺ oxidation state. Despite paramagnetism of the compounds, ¹H NMR spectroscopy proved highly informative for determining the isomerism of the Ru₂⁵⁺ and Ru₂⁶⁺ compounds. While most compounds are found to have the polar (4,0) geometry, with all four Xap ligands in the same orientation, some synthetic procedures resulted in a mixture of (4,0) and (3,1) isomers, most notably in the case of the parent compound Ru₂(ap)₄Cl. The isomerism of this compound has been overlooked in previous reports. Electrochemical studies demonstrate that oxidation potentials can be tuned by the installation of electron donating groups to the ligands, increasing accessibility of the Ru₂⁶⁺ oxidation state. The resulting Ru₂⁶⁺ monocations were found to have the expected (π*)² ground state, and an in-depth study of the electronic transitions by Vis/NIR absorption and MCD spectroscopies with the aid of TD-DFT allowed for the assignment of the electronic spectra. The empty δ* orbital is the major acceptor orbital for the most prominent electronic transitions. Both Ru₂⁵⁺ and Ru₂⁶⁺ compounds were studied by Ru K-edge X-ray absorption spectroscopy; however, the rising edge energy is insensitive to redox changes in the compounds due to the broad line shape observed for 4d transition metal K-edges. DFT calculations indicate the presence of ligand orbitals at the frontier level, suggesting that further oxidation beyond Ru₂⁶⁺ will be ligand-centered rather than metal-centered.

Ultrasound-assisted synthesis of water-soluble monosubstituted diruthenium compounds

The elusive monosubstituted diruthenium complexes [Ru₂Cl(DAniF)(O₂CMe)₃] (1), [Ru₂Cl(DPhF)(O₂CMe)₃] (2), [Ru₂Cl(D-p-CNPhF)(O₂CMe)₃] (3), [Ru₂Cl(D-o-TolF)(O₂CMe)₃] (4), [Ru₂Cl(D-m-TolF)(O₂CMe)₃] (5), [Ru₂Cl(D-p-TolF)(O₂CMe)₃] (6) and [Ru₂Cl(p-TolA)(O₂CMe)₃] (7) have been synthesized using for the first time ultrasound-assisted synthesis to carry out a substitution reaction in metal-metal bonded dinuclear compounds (DAniF^- = N,N'-bis(4-anisyl)formamidinate; DPhF^- = N,N'-diphenylformamidinate; D-p-CNPhF^- = N,N'-bis(4-cyanophenyl)formamidinate; D-o/m/p-TolF^- = N,N'-bis(2/3/4-tolyl)formamidinate; p-TolA^- = N-4-tolylamidate). This is a simpler and greener method than the tedious procedures described in the literature, and it has permitted to obtain water-soluble complexes with good yields in a short period of time. A synthetic study has been implemented to find the best experimental conditions to prepare compounds 1-7. Two different types of ligands, formamidinate and amidate, have been used to check the generality of the method for the preparation of monosubstituted complexes. Five new compounds (2-6) have been obtained using a formamidinate ligand, the synthesis of the previously described compound 1 has been improved, and an unprecedented monoamidate complex has been achieved (7). The crystal structures of compounds 3 and 7 have been solved by single crystal X-ray diffraction. These compounds show the typical paddlewheel structure with three acetate ligands and one formamidinate (3) or amidate (7) bridging ligand at the equatorial positions. The axial positions are occupied by the chloride ligand giving rise to one-dimensional polymer structures that were previously unknown for monosubstituted compounds.

Synthesis, Structural and Physicochemical Properties of Water-Soluble Mixed-Ligand Diruthenium Complexes Containing Anilinopyridinate Bridging Ligands

A series of water-soluble Ru₂⁵⁺ complexes of the type Ru₂(O₂CCH₃)₃(L)Cl where L = 2,3,4,5,6-F₅ap, 2,4,6-F₃ap, 2-Fap, ap, 2-Meap, 2,6-Me₂ap, or 2,4,6-Me₃ap, where ap is the anilinopyridinate anion, have been characterized as to their structural and physicochemical properties in H₂O and DMSO. Five of the newly synthesized complexes were structurally characterized, and the Ru-Cl bond lengths range from 2.477 to 2.544 Å while the Ru-Ru bond lengths range from 2.2838 to 2.2935 Å. The UV-vis spectra of each compound are characterized by three absorption bands in both H₂O and DMSO, the intensity and position of which vary with both the type of bridging ligand and the solvent. The seven examined Ru₂⁵⁺ complexes exist as 1:1 electrolytes in water, and each undergoes a reversible one-electron reduction assigned to Ru₂⁵⁺/Ru₂⁴⁺ in both investigated solvents. A second irreversible reduction attributed to Ru₂⁴⁺/Ru₂³⁺ is also observed for each compound at more negative potentials in DMSO. A linear free energy relationship exists between the sum of the Hammett substituent constants (Σσ) on the ap-type bridging ligand and the wavenumber of an absorption band for the Ru₂⁵⁺ complexes. A linear relationship is also seen between Σσ and measured E_1/2 values for the Ru₂⁵⁺/Ru₂⁴⁺ process in water containing 0.1 M KCl, but little to no effect is seen between the specific bridging ligand and the structural features of the investigated compounds.

Anilinopyridinate-supported Ru2x+ (x = 5 or 6) paddlewheel complexes with labile axial ligands

Five new metal–metal bonded Ru₂ amidinate compounds with labile axial ligands are presented and discussed.

Effect of axial ligands on the spectroscopic and electrochemical properties of diruthenium compounds

Three related diruthenium complexes containing four symmetrical anionic bridging ligands were synthesized and characterized as to their electrochemical and spectroscopic properties. The examined compounds are represented as Ru2(dpb)4Cl, Ru2(dpb)4(CO), and Ru2(dpb)4(NO) in the solid state, where dpb = diphenylbenzamidinate anion. Different forms of Ru2(dpb)4Cl are observed in solution depending on the utilized solvent and the counteranion added to solution. Each Ru2(5+) form of the compound undergoes multiple redox processes involving the dimetal unit. The reversibility as well as potentials of these diruthenium-centered electrode reactions depends upon the solvent and the bound axial ligand. The Ru2(5+/4+) and Ru2(5+/6+) processes of Ru2(dpb)4Cl were monitored by UV-vis spectroscopy in both CH2Cl2 and PhCN. A conversion of Ru2(dpb)4Cl to [Ru2(dpb)4(CO)](+) was also carried out by simply bubbling CO gas through a CH2Cl2 solution of Ru2(dpb)4Cl at room temperature. The chemically generated [Ru2(dpb)4(CO)](+) complex undergoes several electron transfer processes in CH2Cl2 containing 0.1 M TBAClO4 under a CO atmosphere, and the same reactions were seen for a chemically synthesized sample of Ru2(dpf)4(CO) in CH2Cl2, 0.1 M TBAClO4 under a N2 atmosphere, where dpf = N,N'-diphenylformamidinate anion. Ru2(dpb)4(NO) undergoes two successive one-electron reductions and a single one-electron oxidation, all of which involve the diruthenium unit. The CO and NO adducts of Ru2(dpb)4 were further characterized by FTIR spectroelectrochemistry, and the IR spectral data of these compounds are discussed in light of results for previously characterized Ru2(dpf)4(CO) and Ru2(dpf)4(NO) derivatives under similar solution conditions.

Synthesis, structure, and electrochemical characterization of a mixed-ligand diruthenium(III,II) complex with an unusual arrangement of the bridging ligands

A mixed-ligand metal-metal bonded diruthenium complex having the formula Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl where ap is the anilinopyridinate anion was synthesized from the reaction of Ru(2)(O(2)CCH(3))(4)Cl and H(2,4,6-(CH(3))(3)ap), after which the isolated product was structurally, spectroscopically and electrochemically characterized. The crystal structure reveals an unusual arrangement of the bridging ligands around the dimetal unit where one ruthenium atom is coordinated to one anilino and two pyridyl nitrogen atoms while the other ruthenium atom is coordinated to one pyridyl and two anilino nitrogen atoms. To our knowledge, Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl is the only example of a mixed-ligand diruthenium complex of the type [Ru(2)L(3)(O(2)CCH(3))](+), where L is an unsymmetrical anionic bridging ligand that has been structurally characterized with a "(2,1)" geometric conformation of the bridging ligands, all others being "(3,0)". The initial Ru(2)(5+) compound in CH(2)Cl(2) or CH(3)CN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) undergoes up to four one-electron redox processes involving the dimetal unit. The Ru(2)(5+/4+) and Ru(2)(5+/6+) processes were characterized under N(2) using thin-layer UV-visible spectroelectrochemistry and this data is compared to UV-visible spectral changes obtained during similar electrode reactions for related diruthenium compounds having the formula Ru(2)L(4)Cl or Ru(2)L(3)(O(2)CCH(3))Cl where L is an anionic bridging ligand. Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl was also examined by UV-visible and FTIR spectroelectrochemistry under a CO atmosphere and two singly reduced Ru(2)(4+) species, [Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO)Cl](-) and Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO) were in situ generated for further characterization. The CO-bound complexes could be further reduced and exhibited additional reductions to their Ru(2)(3+) and Ru(2)(2+) oxidation states.

Chloro and azido diruthenium complexes bearing electron-rich N,N',N''-triphenylguanidinate ligands

The reaction of Ru(2)(OAc)(4)Cl with N,N',N''-triphenylguanidine (HTPG) produces one of two different compounds depending on the reaction conditions. In acetone in the presence of triethyl amine, the reaction produces tri-substituted Ru(2)(TPG)(3)(OAc)Cl, and in refluxing xylene, the tetra-substituted Ru(2)(TPG)(4)Cl is produced. Both of these new complexes can be cleanly converted into their corresponding azido analogues by reaction with sodium azide in methanol. The X-ray crystal structures of Ru(2)(TPG)(3)(OAc)Cl, Ru(2)(TPG)(3)(OAc)N(3), and Ru(2)(TPG)(4)Cl are presented, along with magnetic, electrochemical, and spectral measurements for each compound. Studies in solution show that, in contrast to Ru(2)(TPG)(3)(OAc)Cl, Ru(2)(TPG)(4)Cl is sterically hindered at the axial positions, and readily dissociates a chloride ion at high ionic strength. Equilibrium constants for chloride association and dissociation have been estimated. Mass spectrometric data suggest that the two azido complexes are precursors to new diruthenium nitrido species.

Structural and Spectroscopic Characterization of a Diruthenium o-Dioxolene Complex Possessing a Singly Occupied Molecular Orbital Delocalized over the Entire Molecule, [Ru2(3,6-DTBDiox)4]-

Chemical oxidation of [Ru2(6+)(3,6-DTBCat)4]2- affords [n-Bu4N][Ru2(3,6-DTBDiox)4].acetone (2.acetone). The oxidized species was characterized by X-ray crystallographic analysis and EPR, and the delocalization of the unpaired electron over the entire molecule was indicated. This example showed that the utilization of redox-active ligands into a Ru2 complex expanded the degree of freedom in the electronic structure. DFT calculations support this view, and the spin population was estimated to be approximately 18% and 82% for the Ru2 core and the four dioxolene ligands, respectively.

Diosmium(III) Compounds Supported by 2-Anilinopyridinate and Novel Alkynyl Derivatives

The reaction between Os(2)(OAc)(4)Cl(2) and Hap (Hap is 2-anilinopyridine) under prolonged refluxing conditions resulted in an Os(III)(2) compound, Os(2)(ap)(4)Cl(2) (1), that can be crystallized as either the cis-(2,2) isomer from a CH(3)OH-CH(2)Cl(2) solution or the (3,1) isomer from a hexanes-CH(2)Cl(2) solution. Compound 1 undergoes facile reactions with LiC(2)Y to yield a series of Os(2)(ap)(4)(C(2)Y)(2) compounds with Y as Ph (2), ferrocenyl (3), SiMe(3) (4), and C(2)SiMe(3) (5). X-ray diffraction study of compound 2 reveals solvent-dependent isomerism similar to that of the parent compound 1. Compound 1 has Os-Os distances of 2.3937(8) and 2.3913(8) Angstroms for the cis-(2,2) and (3,1) isomers, respectively, and is paramagnetic (S = 1). Both the ethynyl derivatives 2-4 and butadiynyl derivative 5 are diamagnetic and have Os-Os distances of 2.456(1), 2.471(1), and 2.481(1) Angstroms for the cis-(2,2) and (3,1) isomers of 2 and (3,1) isomer of 4, respectively. Compounds 1-5 exhibit multiple one-electron redox couples in their cyclic voltammograms, including a reversible Os(2)(8+/7+) couple for 2. Resonance Raman spectra of both compounds 1 and 2 are reported.

Substituent-Directed Structural and Physicochemical Controls of Diruthenium Catecholate Complexes with Ligand-Unsupported Ru−Ru Bonds

A family of diruthenium complexes with ligand-unsupported Ru-Ru bonds has been systematically synthesized, and their crystal structures and physical properties have been examined. A simple, useful reaction between Ru2(OAc)4Cl (OAc- = acetate) and catechol derivatives in the presence of bases afforded a variety of diruthenium complexes, generally formulated as [Na(n){Ru2(R4Cat)4}] (n = 2 or 3; R4 = -F4, -Cl4, -Br4, -H4, -3,5-di-t-Bu, and -3,6-di-t-Bu; Cat(2-) = catecholate). The most characteristic feature of the complexes is the formation of short ligand-unsupported Ru-Ru bonds (2.140-2.273 A). These comprehensive studies were carried out to evaluate the effects of the oxidation states and the substituents governing the molecular structures and physicochemical properties. The Ru-Ru bond distances, rotational conformations, and bending structures of the complexes were successfully varied. The results presented in this manuscript clearly demonstrate that the complexes with ligand-unsupported Ru-Ru bonds can sensitively respond to redox reactions and ligand substituents on the basis of the greater degree of freedom in their molecular structures.

Effects of Countercations on the Structures and Redox and Spectroscopic Properties of Diruthenium Catecholate Complexes with Ligand-Unsupported Ru−Ru Bonds

The molecular structures and physicochemical properties of diruthenium complexes with ligand-unsupported Ru-Ru bonds, generally formulated as [A2{Ru2(DTBCat)4}] (DTB = 3,5- or 3,6-di-tert-butyl; Cat(2-) = catecholate), were studied in detail by changing the countercations. First, the binding structures of the cations in a family of [{A(DME)n}2{Ru2(3,5-DTBCat)4}] (n = 2 for A+ = Li+ and Na+ and n = 1 for A+ = K+ and Rb+) were systematically examined to reveal the effects of the cations on the molecular structures and electrochemical properties. Second, the complex (n-Bu4N)2[Ru2(3,6-DTBCat)4] with a cation-free structure was synthesized using tetra-n-butylammonium cations. The complex clearly demonstrates first that the ligand-unsupported Ru-Ru bonds are essentially stabilized by the dianionic nature of the catecholate derivatives without any other bridging or supporting species. In contrast, the redox potentials and absorption spectra of the complexes can sensitively respond to the countercations depending upon the polarity of the solvents.

Synthesis and Characterization of Nitrosyl Diruthenium Complexes. Interaction between NO and CO across the Metal−Metal Bond

Two neutral diruthenium complexes and one anionic diruthenium complex, Ru2(dpf)4(NO), Ru2(dpf)4(NO)2, and [Ru2(dpf)4(NO)]-, where dpf is diphenylformamidinate anion, were synthesized and characterized as to their electrochemical and spectroscopic properties. Two of the compounds, Ru2(dpf)4(NO) and Ru2(dpf)4(NO)2, were also structurally characterized. Ru2(dpf)4(NO) undergoes reversible one-electron reductions under N2 at E1/2=0.06 and -1.24 V in CH2Cl2, 0.1 M TBABr. These processes are shifted to E1/2=0.18 and -0.78 V under CO due to the trans-coordination of a CO molecule which stabilizes the singly and doubly reduced forms of the metal-metal bonded complexes, thus leading to easier reductions. CO does not coordinate to Ru2(dpf)4(NO), but it does bind to the singly reduced species to generate [Ru2(dpf)4(NO)(CO)]- under a CO atmosphere in solution; characteristic NO and CO bands are seen for this compound at nuNO=1674 cm(-1) and nuCO=1954 cm(-1). Ru2(dpf)4(NO)2 displays a reversible one-electron reduction at E1/2=-1.24 V versus SCE and an irreversible reduction at Epc=-1.96 V in CH2Cl2, 0.1 M TBAP under N2. There are also two reversible one-electron oxidations at E1/2=0.24 and 1.15 V. Spectroelectrochemical monitoring of the Ru2(dpf)4(NO)2 oxidation processes in a thin-layer cell shows only a single NO vibration for each electrogenerated product and nuNO is located at 1726 (neutral), 1788 (singly oxidized), or 1834 (doubly oxidized) cm(-1). Finally, a labile CO complex, [Ru2(dpf)4(NO)(CO)]-, could be generated by passing CO into a solution of [Ru2(dpf)4(NO)]-. Formation of the mixed CO/NO adduct was confirmed by electrochemistry and infrared spectroscopy. Analysis of the NO and CO stretching vibration frequencies for [Ru2(dpf)4(NO)(CO)]- by in-situ FTIR spectroelectrochemistry and comparisons with data for Ru2(dpf)4(NO) and Ru2(dpf)4(CO) reveal the presence of a strong interaction between NO and CO across the Ru-Ru bond.

Neutral Paddlewheel Diruthenium Complexes with Tetracarboxylates of Large π-Conjugated Substituents: Facile One-Pot Synthesis, Crystal Structures, and Electrochemical Studies

A one-pot reaction of a cationic diruthenium complex, [Ru(2)(II,III)(O(2)CCH(3))(4)(THF)(2)](BF(4)), with arylcarboxylic acids, ArCO(2)H, (PhCO(2)H = benzoic acid, NapCO(2)H = 1-naphthoic acid, AntCO(2)H = 9-anthracenecarboxylic acid) in NDMA (NDMA = N,N-dimethylaniline) has led to isolation of neutral paddlewheel-type diruthenium complexes, [Ru(II)(2)(O(2)CAr)(4)(THF)(2)] (Ar = Ph (1), Nap (2), Ant (3)). Paramagnetic variable temperature (VT) (1)H NMR studies and GC-MS studies show that the reaction consists of two steps: a one-electron reduction of the Ru(2) core by NDMA and a simple carboxylate-exchange reaction. All compounds 1-3 were structurally characterized by X-ray crystallography. While the structural features of the Ru(2) core are very similar in all the compounds, the dihedral angles between the carboxylate plane and the aromatic ring are larger with the expanding of aryl groups from phenyl to anthracene. The effect of pi-pi stacking leads to the formation of a 1-D chain structure in compound 3, whereas compounds 1 and 2 are fully isolated from each other. The electrochemical measurements show that the quasireversible one-electron oxidation step is observed at +0.06, +0.09, and +0.17 V (vs Ag/Ag(+)) for 1-3, respectively, assigned to the Ru(II)(2)/Ru(II,III)(2) redox couple. These potentials are found to demonstrate a linear relationship with the substituent constants for aryl compounds,.

Synthesis, Structural, Spectroscopic, and Electrochemical Characterization of High Oxidation State Diruthenium Complexes Containing Four Identical Unsymmetrical Bridging Ligands

Six Ru2(6+) derivatives of the form Ru2(L)4(C[triple bond]CC6H5)(2), where L = 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, or 2,4,6-F(3)ap, are synthesized and characterized as to their electrochemical, spectroscopic, and/or structural properties. These compounds are synthesized from a reaction between LiC[triple bond]CC6H5 and Ru2(L)4Cl. Two of the investigated complexes exist in a (4,0) isomeric form while four adopt a (3,1) geometric conformation. These two series of geometric isomers are compared with previously characterized (4,0) Ru2(ap)4(C[triple bond]CC6H5)(2), (4,0) Ru2(F5ap)4(C[triple bond]CC6H5)(2), and (3,1) Ru2(F5ap)4(C[triple bond]CC6H5)(2). The overall data on the nine compounds thus provide an opportunity to systematically examine how the electrochemical and structural properties of these Ru2(6+) complexes vary with respect to isomer type and electronic properties of the bridging ligands.

Electrochemical and Spectroelectrochemical Characterization of Ru24+ and Ru23+ Complexes under a CO Atmosphere

Eleven different Ru(2)(4+) and Ru(2)(3+) derivatives are characterized by thin-layer FTIR and UV-visible spectroelectrochemistry under a CO atmosphere. These compounds, which were in-situ electrogenerated from substituted anilinopyridine complexes with a Ru(2)(5+) core, are represented as Ru(2)(L)(4)Cl where L = 2-CH(3)ap, ap, 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, 3,5-F(2)ap, 2,4,6-F(3)ap, or F(5)ap. The Ru(2)(5+) complexes do not axially bind CO while mono- and bis-CO axial adducts are formed for the Ru(2)(4+) and Ru(2)(3+) derivatives, respectively. Six of the eleven investigated compounds exist in a (4,0) isomeric form while five adopt a (3,1) geometric conformation. These two series of compounds thus provide a large enough number of derivatives to examine trends and differences in the spectroscopic data of the two types of isomers in their lower Ru(2)(4+) and Ru(2)(3+) oxidation states. UV-visible spectra of the Ru(2)(4+) derivatives and IR spectra of the Ru(2)(3+) complexes under CO are both isomer dependent, thus suggesting that these data can be used to reliably predict the isomeric form, i.e., (3,1) or (4,0), of diruthenium complexes containing four unsymmetrical substituted anilinopyridinate bridging ligands; this was confirmed by X-ray crystallographic data for seven compounds whose structures were available.

Substituent and Isomer Effects on Structural, Spectroscopic, and Electrochemical Properties of Dirhodium(III,II) Complexes Containing Four Identical Unsymmetrical Bridging Ligands

Substituent and isomer effects on the structural, spectroscopic, (UV-visible and ESR) and electrochemical properties of dirhodium(III,II) complexes containing four identical unsymmetrical bridging ligands are reported for seven related compounds of the type Rh(2)(L)(4)Cl where L = 2-(2-fluoroanilino)pyridinate (2-Fap), 2-(2,6-difluoroanilino)pyridinate (2,6-F(2)ap), 2-(2,4,6-trifluoroanilino)pyridinate (2,4,6-F(3)ap), or 2-(2,3,4,5,6-pentafluoroanilino)pyridinate (F(5)ap) anion. Rh(2)(2-Fap)(4)Cl exists only in a (4,0) isomeric conformation while Rh(2)(2,6-F(2)ap)(4)Cl, Rh(2)(2,4,6-F(3)ap)(4)Cl, and Rh(2)(F(5)ap)(4)Cl exist as both (4,0) and (3,1) isomers. It had earlier been demonstrated that Rh(2)(L)(4)Cl complexes can adopt different geometric conformations of the bridging ligands, but the current study provides the first example where two geometric isomers of Rh(2)(5+) complexes are obtained for one compound using the same synthetic procedure. The synthesis, structural, spectroscopic, and/or electrochemical properties of (3,1) Rh(2)(2,6-F(2)ap)(4)CN and (4,0) Rh(2)(2,4,6-F(3)ap)(4)(C triple bond C)(2)Si(CH(3))(3) are also reported and the data on these compounds is discussed in light of their parent complexes, (3,1) Rh(2)(2,6-F(2)ap)(4)Cl and (4,0) Rh(2)(2,4,6-F(3)ap)(4)Cl.

A family of diruthenium compounds with dianionic tridentate ligands of N-(2-pyridyl)-2-oxy-5-R-benzylaminate (R = H, Me, Cl, Br, NO(2)): isolation, structure determination, and electrochemistry

The ligand substitution reaction of Ru(2)(O(2)CCH(3))(4)Cl with 5-substituted N-(2-pyridyl)-2-oxy-5-R-benzylaminate (R = H, Me, Cl, Br, NO(2)) resulted in a family of anionic diruthenium species of [Ru(2)(O(2)CCH(3))(2)(R-salpy)(2)](-) that were isolated by using Na(+)- or K(+)-18-crown-6-ether as the countercation: [A(18-crown-6)(S)(x)()][Ru(2)(O(2)CCH(3))(2)(R-salpy)(2)] (A = Na(+), K(+); S = solvent; R = H, 1; Me, 2; Cl, 3; Br, 4; NO(2), 5). All compounds were structurally characterized by X-ray crystallography. The structural features of the anionic parts are very similar among the compounds: two acetate and two R-salpy(2)(-) ligands are, respectively, located around the Ru(2) unit in a trans fashion, where the R-salpy(2)(-) ligand acts as a tridentate ligand having both bridging and chelating characters to form the M-M bridging/axial-chelating mode. Compounds 1 and 5 with K(+)-18-crown-6-ether have one-dimensional chain structures, the K(+)-18-crown-6-ether interacting with phenolate oxygens of the [Ru(2)(O(2)CCH(3))(2)(R-salpy)(2)](-) unit to form a repeating unit, [.K.O-Ru-Ru-O.], whereas 2-4 are discrete. Cyclic voltammetry and differential pulse voltammetry revealed systematic redox activities based on the dimetal center and the substituted ligand, obeying the Hammett law with the reaction constants per substituent, rho, for the redox processes being 127 mV for Ru(2)(5+)/Ru(2)(4+), 185 mV for Ru(2)(6+)/Ru(2)(5+), 92 mV for Ru(2)(7+)/Ru(2)(6+), and 179 mV for R-salpy(-)/R-salpy(2)(-). For 3, the singly oxidized and reduced species, Ru(2)(6+) and Ru(2)(4+), respectively, generated by bulk controlled-potential electrolyses were finally monitored by spectroscopy. The singly oxidized species can also be slowly generated by air oxidation.

Solvent Effects on the Electrochemistry and Spectroelectrochemistry of Diruthenium Complexes. Studies of Ru2(L)4Cl Where L = 2-CH3ap, 2-Fap, and 2,4,6-F3ap, and ap Is the 2-Anilinopyridinate Anion

Three Ru2(5+) diruthenium complexes, (4,0) Ru2(2-CH3ap)4Cl, (3,1) Ru2(2-Fap)4Cl, and (3,1) Ru2(2,4,6-F3ap)4Cl where ap is the 2-anilinopyridinate anion, were examined as to their electrochemical and spectroelectrochemical properties in five different nonaqueous solvents (CH2Cl2, THF, PhCN, DMF, and DMSO). Each compound undergoes a single one-electron metal-centered oxidation in THF, DMF, and DMSO and two one-electron metal-centered oxidations in CH2Cl2 and PhCN. The three diruthenium complexes also undergo two reductions in each solvent except for CH2Cl2, and these electrode processes are assigned as Ru2(5+/4+) and Ru2(4+/3+). Each neutral, singly reduced, and singly oxidized species was characterized by UV-vis thin-layer spectroelectrochemistry, and the data are discussed in terms of the most probable electronic configuration of the compound in solution. The three neutral complexes contain three unpaired electrons as indicated by magnetic susceptibility measurements using the Evans method (3.91-3.95 muB), and the electronic configuration is assigned as sigma2pi4delta2pi(*2)delta, independent of the solvent. The three singly oxidized compounds have two unpaired electrons in CD2Cl2, DMSO-d6, or CD3CN (2.65-3.03 muB), and the electronic configuration is here assigned as sigma2pi4delta2pi(*2). The singly reduced compound also has two unpaired electrons (2.70-2.80 muB) in all three solvents, consistent with the electronic configuration sigma2pi4delta2pi(*2)delta(*2) or sigma2pi4delta2pi(*3)delta*. Finally, the overall effect of solvent on the number of observed redox processes is discussed in terms of solvent binding, and several formation constants were calculated.

Cyanide Adducts on the Diruthenium Core of [Ru2(L)4]+ (L = ap, CH3ap, Fap, or F3ap). Electronic Properties and Binding Modes of the Bridging Ligand

The products of the reaction between CN(-) and four different diruthenium complexes of the type Ru(2)(L)(4)Cl where L = 2-CH(3)ap (2-(2-methylanilino)pyridinate anion), ap (2-anilinopyridinate anion), 2-Fap (2-(2-fluoroanilino)pyridinate anion), or 2,4,6-F(3)ap (2-(2,4,6-trifluoroanilino)pyridinate anion) are reported. Mono- and/or dicyano adducts of the type Ru(2)(L)(4)(CN) and Ru(2)(L)(4)(CN)(2) are found exclusively as reaction products when either the 2-CH(3)ap or the ap derivative is reacted with CN(-), but diruthenium complexes with formulations of the type Ru(2)(F(x)ap)(3)[mu-(o-NC)F(x-1)ap](mu-CN) or Ru(2)(F(x)ap)(4)(mu-CN)(2) (x = 1 or 3) are also generated when Ru(2)(Fap)(4)Cl or Ru(2)(F(3)ap)(4)Cl is reacted with CN(-). More specifically, four products formulated as Ru(2)(Fap)(4)(CN), Ru(2)(Fap)(4)(CN)(2), Ru(2)(Fap)(3)[mu-(o-NC)ap](mu-CN), and Ru(2)(Fap)(4)(mu-CN)(2) can be isolated from a reaction of CN(-) with the Fap derivative, but the exact type and yield of these compounds depend on the temperature at which the experiment is carried out. In the case of the F(3)ap derivative, the only diruthenium complex isolated from the reaction mixture has the formulation Ru(2)(F(3)ap)(3)[mu-(o-NC)F(2)ap](mu-CN) and this compound has structural, electrochemical, and spectroscopic properties quite similar to that of previously characterized Ru(2)(F(5)ap)[mu-(o-NC)F(4)ap](mu-CN). Both the mono- and dicyano derivatives synthesized in this study possess the isomer type of their parent chloro complexes. The Ru-Ru bond lengths of Ru(2)(ap)(4)(CN) and Ru(2)(2-CH(3)ap)(4)(CN) are longer than those of Ru(2)(ap)(4)Cl and Ru(2)(CH(3)ap)(4)Cl, respectively, and this is accounted for by the strong sigma-donor properties of the CN(-) ligand as compared to Cl(-). The Ru-C bonds in Ru(2)(ap)(4)(CN)(2) are significantly shorter than those in Ru(2)(ap)(4)(CN), thus revealing a greatly enhanced Ru-CN interaction in the dicyano adduct, a result which is also indicated by the fact that nu(CN) in Ru(2)(ap)(4)(CN)(2) is 50 cm(-1) higher than nu(CN) in Ru(2)(ap)(4)(CN). Although both (4,0) Ru(2)(ap)(4)(CN)(2) and (3,1) Ru(2)(Fap)(4)(CN)(2) possess the same formulation, there are clear structural differences between the two complexes and this can be explained by the fact that the two cyano derivatives possess a different binding symmetry of the bridging ligands. Each mono- and dicyano adduct was electrochemically investigated in CH(2)Cl(2) containing TBAP as supporting electrolyte. Ru(2)(ap)(4)(CN), Ru(2)(CH(3)ap)(4)(CN), and Ru(2)(Fap)(4)(CN) undergo one reduction and two oxidations. The two dicyano adducts of the ap and Fap derivatives are characterized by two reductions and one oxidation. The potentials of these processes are all negatively shifted in potential by 400-720 mV with respect to half-wave potentials for the same redox couples of the monocyano derivatives, with the exact value depending upon the specific redox reaction.