New organometallic Ru(II) and Fe(II) complexes with tetrathia-[7]-helicene derivative ligands

A series of organometallic complexes possessing new tetrathia-[7]-helicene nitrile derivative ligands [TH-7] as chromophores, of general formula [MCp(P–P)(NC{TH-[7]-Y}Z)][PF₆] (M = Ru, Fe, P–P = DPPE, Y = H, NO₂, Z = H, C≡N; M = Ru, L–L = 2PPh₃, Y = H, Z = H) has been synthesized and fully characterized. ¹H NMR, FT-IR and UV–Vis. spectroscopic data were analyzed with in order to evaluate the existence of electronic delocalization from the metal centre to the coordinated ligand to have some insight on the potentialities of these new compounds as non-linear optical molecular materials. Slow crystallization of compound [RuCp(PPh₃)₂(NC{TH-[7]-H}H)][PF₆] 2Ru revealed an interesting isomerization of the helical ligand with formation of two carbon-carbon bonds between the two terminal thiophenes, leading to the total closure of the helix (2*Ru).     

Inspired by nature: light driven organometallic catalysis by heterooligonuclear Ru(II) complexes

In view of diminishing resources and an ever increasing demand for energy attention has been directed towards the development of new photocatalytic systems modelling natural photosynthesis. Recent investigations have shown that supramolecular devices consisting of photosynthetic reaction centres and catalyst metals--connected via bridging ligands--are capable of performing light driven catalytic reactions such as hydrogen production, reduction of CO(2), and conversion reactions of olefins.     

Triaryl-1,3,5-triazinane-2,4,6-triones functionalized with electron-rich Fe(II) and Ru(II) acetylide complexes: new organometallic octupoles with large hyperpolarizabilities

The synthesis and study of a series of trinuclear organometallic triaryl-1,3,5-triazinane-2,4,6-triones functionalized by d(6)-transition metal acetylides complexes at their periphery are reported. Remarkably large hyperpolarizabilities, far superior to those of related purely organic derivatives, are measured by hyper-Rayleigh scattering (HRS) for these new octupolar chromophores.     

Asymmetric epoxidation of 6-cyano-2,2-dimethylchromene on Mn(salen) catalyst immobilized in mesoporous materials

This article reports our recent work on the heterogeneous asymmetric epoxidation catalyzed by chiral Mn(salen) catalyst axially immobilized via phenoxyl groups and organic sulfonic groups. The asymmetric epoxidation of 6-cyano-2,2-dimethylchromene was especially presented in detail. The factors that affected the asymmetric induction, such as the nanopores and the external surface, the linkage length, and the modification of nanopores with methyl groups were discussed. It was found that the enantioselectivities increased with decreasing the nanopore sizes or increasing the linkage length in nanopore, and the Mn(salen) catalyst immobilized into nanopores generally gave higher ee values than those on the external surface. The heterogeneous Mn(salen) catalysts with modified nanopores gave a TOF of 14.8 h⁻¹ and an ee value of 90.6% for the asymmetric epoxidation of 6-cyano-2,2-dimethylchromene, which were higher than the results (TOF 10.8 h⁻¹, ee 80.1%) obtained for the homogeneous catalyst.     

The electronic structure and spectra of Ru(II) and Ru(III) complexes with imidazole and its derivatives

The calculations of the electronic structure and spectra of [Ru(NH3)5L]2+ (L = imidazole, histidine) and [Ru(NH3)5L]3+ (L = imidazole, N-imidazolate anion, 4-methylimidazole, 4-methyl-1N-imidazolate anion and 1N-bound histidine) complexes are performed in the framework of the CI method in the INDO/CNDO approximation. The MO diagram is obtained. The assignment of all transitions with energies of 4-5 eV is made and the nature of corresponding excited states is discussed. For the Ru(II) complexes, the lower energy observable transition is assigned to d-->pi* type, whereas the higher energy one is assigned to pi-->pi* type. In the spectra of the Ru(III) complexes with charged ligands both transitions are of pi-->d character, while in the case of uncharged ligands, the higher energy transition mostly incorporates pi-->pi* excitations.     

Cobalt(II) schiff base functionalized mesoporous silica as an efficient and recyclable chemoselective acetalization catalyst

Cobalt(II) Schiff base functionalized mesoporous silica was synthesized from covalent attachment via the introduction of Co(OAc)₂ to salicylaldimine functionalized mesoporous silica. The catalyst proved to be chemoselective one for the acetalization of aldehydes to the corresponding acetals in alcohol. The immobilized catalyst can be easily recovered and reused for at least ten reaction cycles without significant loss of its catalytic activity.     

Phototriggered sulfoxide isomerization in [Ru(pic)2(dmso)2

We report the characterization and photochemistry of a simple ruthenium coordination complex containing only picolinate (pic) and dmso, which exhibits a large isomerization quantum yield (Phi(SS-->OO) = 0.50) in various solvents. The picolinate ligands of [Ru(pic)(2)(dmso)(2)] are in a cis arrangement so that the carboxylate oxygen of one pic ligand (O1) is trans to the pyridine of the second picolinate (N2). One dmso ligand (S1) is trans to a pyridine nitrogen (N1), while the second dmso (S2) is trans to a carboxylate oxygen (O3). The cyclic voltammetry, (1)H NMR, IR, and UV-vis spectroscopy data suggest that while both dmso ligands isomerize photochemically, only one dmso ligand isomerizes electrochemically. Isomerization quantum yields for each dmso ligand differ by an order of magnitude (Phi(SS-->SO) = 0.46 and Phi(SO-->OO) = 0.036). In agreement with previous results, the isomerization quantum yield for each dmso is dependent on the ligand that is trans to the dmso.     

trans-Cyclopropyl beta-amino acid derivatives via asymmetric cyclopropanation using a (Salen)Ru(II) catalyst

trans-Cyclopropyl beta-amino acid derivatives can be synthesized in five steps with excellent enantioselectivities using a chiral (Salen)Ru(II) cyclopropanation catalyst in the key asymmetry-induction step. This facile synthesis proceeds with high overall yield and can be used to prepare a number of carbamate-protected (Cbz and Boc are demonstrated) beta-amino acid derivatives.     

Chiral Mn(III) salen complex immobilized on imidazole-modified mesoporous material via co-condensation method as an effective catalyst for olefin epoxidation

An imidazole modified mesoporous material has been prepared through a co-condensation procedure and adopted to covalently anchor chiral Mn(III) salen complex. The active centers in the as-synthesized catalyst were presented in the form of ionic species. The results of XRD, FTIR, DRUV-Vis, and N₂ sorption confirmed the successful immobilization of chiral Mn(III) salen complex inside the channels of the modified support and the maintenance of the mesoporous structure of parent support in the immobilized catalyst. This heterogeneous catalyst exhibited comparable catalytic activity and enantioselectivity to those of the homogeneous counterpart in the asymmetric epoxidation of unfunctionalized olefins. Furthermore, notably high turnover frequencies have been obtained over this heterogeneous catalyst for the relatively short reaction time and low catalyst amount, due in part to the ionic property as well as the uniform distribution of the active centers.     

Periodic mesoporous silica-immobilized palladium(II) complex as an effective and reusable catalyst for water-medium carbon-carbon coupling reactions

Ethyl-bridged periodic mesoporous organosilicas (PMOs) functionalized with diphenylphosphino (PPh₂) ligands were synthesized by one-step evaporation-induced self-assembly (EISA), which were used as a support to immobilize Pd(II) organometallic catalyst by coordination reaction. The as-prepared Pd(II)-PPh₂-PMO(Et) exhibited high activity in water-medium C-C coupling reactions and could be used repetitively. The high activity could be attributed to the high dispersion of Pd(II) active sites and ordered mesopore channels which effectively diminished the steric hindrance and thus, diffusion limit. Meanwhile, the ethyl-fragments and the PPh₂-ligands in the support wall could synergic enhance surface hydrophobicity, which promoted the adsorption for organic reactant molecules.     

Correspondence of Ru(III) Ru(II) and Ru(IV) Ru(III) mixed valent states in a small dinuclear complex

The diruthenium(III) compound [(μ-oxa){Ru(acac)(2)}(2)] [1, oxa(2-) =oxamidato(2-), acac(-) =2,4-pentanedionato] exhibits an S=1 ground state with antiferromagnetic spin-spin coupling (J=-40 cm(-1)). The molecular structure in the crystal of 1?2 C(7)H(8) revealed an intramolecular metal-metal distance of 5.433 ? and a notable asymmetry within the bridging ligand. Cyclic voltammetry and spectroelectrochemistry (EPR, UV/Vis/NIR) of the two-step reduction and of the two-step oxidation (irreversible second step) produced monocation and monoanion intermediates (K(c) =10(5.9)) with broad NIR absorption bands (ε ca. 2000 M(-1)cm(-1)) and maxima at 1800 (1(-)) and 1500 nm (1(+)). TD-DFT calculations support a Ru(III)Ru(II) formulation for 1(-) with a doublet ground state. The 1(+) ion (Ru(IV)Ru(III)) was calculated with an S=3/2 ground state and the doublet state higher in energy (ΔE=694.6 cm(-1)). The Mulliken spin density calculations showed little participation of the ligand bridge in the spin accommodation for all paramagnetic species [(μ-oxa){Ru(acac)(2)}(2)](n), n=+1, 0, -1, and, accordingly, the NIR absorptions were identified as metal-to-metal (intervalence) charge transfers. Whereas only one such NIR band was observed for the Ru(III)Ru(II) (4d(5)/4d(6)) system 1(-), the Ru(IV)Ru(III) (4d(4)/4d(5)) form 1(+) exhibited extended absorbance over the UV/Vis/NIR range.     

Further observations on water oxidation catalyzed by mononuclear Ru(II) complexes

A family of 28 mononuclear Ru(II) complexes have been prepared and characterized by (1)H NMR, electronic absorption, and cyclic voltammetry. These complexes are studied as catalysts for water oxidation. All the catalysts possess one tridentate ligand, closely related to 2,2';6,2'-terpyridine (tpy) and may be divided into two basic types. In the type-1 catalyst, the three remaining coordination sites are occupied by a bidentate closely related to 2,2'-bipyridine (bpy) and a monodentate halogen (Br, Cl, or I) or water molecule. In the type-2 catalyst, the three remaining coordination sites are occupied by two axial 4-picoline molecules and an equatorial halogen or water. In general the type-2 catalysts are more reactive than the type-1. The type-2 iodo-catalyst shows first-order behavior and, unlike the bromo- and chloro-catalysts, does not require water-halogen exchange to show good activity. The importance of steric strain and hindrance around the metal center is examined. The introduction of three t-butyl groups at the 4, 4', and 4' positions of tpy sometimes improves catalyst activity, but the effect does not appear to be additive.     

Oxidation of carbon monoxide over a copper(II) oxide catalyst

Transient FTIR observations in conjuction with gas phase CO conversion measurements indicate an adsorbed CO species which seems not to participate directly in the oxidation reaction over a silica supported copper(II) oxide catalyst. This observation together with order of reaction determinations suggest that oxidation occurs via an Eley-Rideal mechanism.

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CO CO, (II), . , , , -.

     

Synthesis, characterization and molecular structure of Ru(II) complex with 8-hydroxyquinoline derivative

The new (E)-8-hydroxyquinoline-2-carbaldehyde O-benzyl oxime ligand and its hydride-carbonyl complex of ruthenium was synthesized and characterized by infrared, proton and phosphorus nuclear magnetic resonance, electronic absorption and emission spectroscopy and X-ray crystallography. The experimental studies were complemented by theoretical calculations. From the electronic spectrum of the complex the Racah’s and nepheloauxetic parameters are calculated. The electronic structure of the complexes, presented in particular by the density of states diagram, have been correlated with its ability to fluoresce and used to analyze the UV-Vis spectra.     

Synthesis of an Alternated Heterobimetallic Supramolecular Polymer Based on Ru(II) and Fe(II)

A heterobimetallic supramolecular polymer (polyRuFe) with alternately complexed Ru(II) and Fe(II) is prepared following a stepwise synthetic route through harnessing first the strongly binding metal ion Ru(II) and then the weakly binding metal ion Fe(II). A high yield of product is achieved in each step. The heterometal ions are incorporated into the polymer chain in identical coordination environments formed by two 2,2′:6′,2″-terpyridine moieties. Characterization is accomplished by NMR spectroscopy, MALDI–TOF mass spectrometry, UV–Vis spectroscopy, and cyclic voltammetry. PolyRuFe shows a wide optical window (λ = 311–577 nm) and a broad distinct reversible redox nature of two types, originated from the coupling of the two heterometallic segments into the polymer chain. Such characteristics of polyRuFe suggest its potential for various electrochemical and electro-optical applications.     

Synthesis of 3,4-dihydropyrimidin-2-ones (DHPMs) using mesoporous aluminosilicate (AlKIT-5) catalyst with cage type pore structure

Here we demonstrate on the synthesis of 3,4-dihydropyrimidin-2-ones (DHPMs) and their derivatives through a three-component condensation reactions of aldehyde, β-ketoester and urea or thiourea using mesoporous aluminosilicate (AlKIT-5) nanocage as catalyst and acetonitrile as solvent under reflux conditions. The catalyst was found to be highly active and selective, affording a high yield of DHPMs. Compared to the classical Biginelli reaction conditions, this new approach consistently has the advantage of excellent yields (80-96%) and short reaction times, 3.0-4.0 h. The effect of the acidity and the concentration of the catalyst on the above process was investigated. We also demonstrate the synthesis of various multifunctional Biginelli compounds using the highly active AlKIT-5 catalysts.     

Photoredox vs. energy transfer in a Ru(II)-Fe(II) supramolecular complex built with an heteroditopic bipyridine-terpyridine ligand

A trinuclear [[Ru(II)(bpy)(2)(bpy-terpy)](2)Fe(II)](6+) complex (I) in which a Fe(II)-bis-terpyridine-like centre is covalently linked to two Ru(II)-tris-bipyridine-like moieties by a bridging bipyridine-terpyridine ligand has been synthesised and characterised. Its electrochemical, photophysical and photochemical properties have been investigated in CH(3)CN and compared with those of mononuclear model complexes. The cyclic voltammetry of (I) exhibits, in the positive region, two successive reversible oxidation processes, corresponding to the Fe(III)/Fe(II) and Ru(III)/Ru(II) redox couples. These systems are clearly separated (DeltaE(1/2) = 160 mV), demonstrating the lack of an electronic connection between the two subunits. The two oxidized forms of the complex, [[Ru(II)(bpy)(2)(bpy-terpy)](2)Fe(III)](7+) and [[Ru(III)(bpy)(2)(terpy-bpy)](2)Fe(III)](9+), obtained after two successive exhaustive electrolyses, are stable. (I) is poorly luminescent, indicating that the covalent linkage of the Ru(II)-tris-bipyridine to the Fe(II)-bis-terpyridine subunit leads to a strong quenching of the Ru(II)* excited state by energy transfer to the Fe(II) centre. Luminescence lifetime experiments show that the process occurs within 6 ns. The nature of the energy transfer process is discussed and an intramolecular energy exchange is proposed as a preferable deactivation pathway. Nevertheless this energy transfer can be efficiently quenched by an electron transfer process in the presence of a large excess of the 4-bromophenyl diazonium cation, playing the role of a sacrificial oxidant. Finally complete photoinduced oxidation of (I) has been performed by continuous photolysis experiments in the presence of a large excess of this sacrificial oxidant. The comparison with a mixture of the corresponding mononuclear model complexes has been made.