Diastereoselective preparation and characterization of ruthenium bis(bipyridine) sulfoxide complexes

A new concept in the synthesis of optically active octahedral ruthenium complexes was realized for the first time when cis- or trans-Ru(bpy)2Cl, (cis- or trans-1) was reacted with either (R)-(+)- or (S)-(-)-methyl p-tolyl sulfoxide (2 or 3); this novel asymmetric synthesis leads to the diastereoselective formation of the ruthenium bis(bipyridine) complex cis-delta-[Ru(bpy)2(2)Cl]Cl (4) (49.6% de) or cis-lambda-[Ru(bpy)2(3)Cl]Cl (5) (48.4% de), respectively. cis- or trans-Ru(dmbpy)2Cl2 (cis- or trans-6) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine) also reacts with 2 or 3, leading to the diastereoselective formation of cis-delta-[Ru(dmbpy)2(2)Cl]Cl (7) (59.5% de) or cis-lambda-[Ru(dmbpy)2(3)Cl]Cl (8) (57.2% de), respectively. The diastereoselectivity of these reactions is governed solely by the chirality of the sulfoxide nucleophile. This represents the first process by which a sigma-bonded ligand occupying only a single coordination site has had such an important influence on the stereochemical outcome of a ruthenium bis(bipyridine) complex formation. These novel complexes were fully characterized by elemental analysis and IR, UV/vis, and 1H, 13C, and 2D NMR spectroscopy. An investigation into the chiroptical properties of these novel ruthenium bis(bipyridine) sulfoxide complexes has been carried out, and circular dichroism spectra are used to assign absolute stereochemistry.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Radiation synthesis of iron(II) and ruthenium(II) alkylnitroso complexes

The radiolysis of deoxygenated aqueous solutions of Ru(NH₃)₅NO³⁺ and Fe(CN)₅NO²⁻ in the presence of organic compounds (RH) generates alkylnitroso complexes of the form Ru(NH₃)₅N(O)R²⁺ and Fe(CN)₅N(O)R³⁻ where RH = tert-butyl alcohol, tert-butyl amine, N,N-dimethylacetamide, α-aminoisobutyric acid, pivalic acid, and α-hydroxyisobutyric acid. The products form from the rapid combination of the β-carbon radical derived from the reaction of the organic compound with OH radicals (OH + RH → R· + H₂O) and the one-electron reduced metal complex formed by interaction with e_aq⁻: Ru(NH₃)₅NO³⁺ + e_aq⁻ → Ru(NH₃)₅NO²⁺; Fe(CN)₅NO²⁻ + e_aq⁻ → Fe(CN)₅NO³⁻. The alkylnitroso complexes are moderately O₂-insensitive but display varying degrees of thermal stability. Stability permitting, these complexes have been characterized by ion-exchange chromatography and UV-vis-IR spectroscopy. The green ruthenium complexes exhibit λ_max 740 and 342 nm (ϵ 22 and 4.5 × 10³ M⁻¹ cm⁻¹, respectively) and ν_NO in the 1365–1405 cm⁻¹ region. The less stable red iron analogues absorb at 475 and ∼ 250 nm (ϵ 5.0 × 10³ and ∼ 9 × 10³ M⁻¹ cm⁻¹, respectively).     

Electron donor-acceptor dyads based on ruthenium(II) bipyridine and terpyridine complexes bound to naphthalenediimide

Two series of photosensitizer-electron acceptor complexes have been synthesized and fully characterized: ruthenium(II) tris(bipyridine) ([Ru(II)(bpy)(2)(bpy-X-NDI)], where X = -CH(2)-, tolylene, or phenylene, bpy is 2,2'-bipyridine, and NDI is naphthalenediimide) and ruthenium(II) bis(terpyridine) ([Ru(II)(Y-tpy)(tpy-X-NDI)], where Y = H or tolyl and X = tolylene or phenylene, and tpy = 2,2':6',2' '-terpyridine). The complexes have been studied by cyclic and differential pulse voltammetry and by steady state and time-resolved absorption and emission techniques. Rates for forward and backward electron transfer have been investigated, following photoexcitation of the ruthenium(II) polypyridine moiety. The terpyridine complexes were only marginally affected by the linked diimide unit, and no electron transfer was observed. In the bipyridine complexes we achieved efficient charge separation. For the complexes containing a phenyl link between the ruthenium(II) and diimide moieties, our results suggest a biphasic forward electron-transfer reaction, in which 20% of the charge-separated state was formed via population of the naphthalenediimide triplet state.     

Mono- and dinuclear cyanodithioformate complexes of bis(bipyridine)ruthenium(II)

Summary A series of mono- and dinuclear cyanodithioformate complexes containing (bipy)₂Ru^II and CpRu^II moieties were prepared. The complexes were characterized using various physico-chemical techniques; spectral and electro-chemical studies of selected complexes were also made.     

Asymmetric transfer hydrogenation of ketones catalyzed by ruthenium(II) complexes bearing a chiral phosphinoferrocenyloxazoline ligand

The catalytic activity in asymmetric transfer hydrogenation of ketones using octahedral and half-sandwich (η⁵-indenyl and η⁶-arene) ruthenium(II) complexes containing the chiral ligand (4S)-2-[(S_p)-2-(diphenylphosphino)ferrocenyl]-4-(isopropyl)oxazoline (FcPN) has been explored. Catalytic studies with complex fac-[RuCl₂{η²(P,N)-FcPN}(PMe₃)₂] (1) show excellent TOF values (9600 h⁻¹). Experiments in the presence of free FcPN, which lead to an increase in conversion rates and ee values when the catalyst is complex [Ru(η⁵-C₉H₇){κ²(P,N)-FcPN}(PPh₃)][PF₆] (4) have been carried out. The characterization of the new complexes mer-trans-[RuCl₂{P(OMe)₃}₂{κ²(P,N)-FcPN}] and of the water-soluble complexes fac- and mer-trans-[RuCl₂(PTA)₂{κ²(P,N)-FcPN}] is also reported.     

Bis(bipyridine)ruthenium(II) complexes with an aliphatic sulfinato donor: synthesis, characterization, and properties

Treatment of a thiolato-bridged Ru(II)Ag(I)Ru(II) trinuclear complex, [Ag{Ru(aet)(bpy)(2)}(2)](3+) (aet = 2-aminoethanthiolate; bpy = 2,2'-bipyridine), with NaI in aqueous ethanol under an aerobic condition afforded a mononuclear ruthenium(II) complex having an S-bonded sulfinato group, [1](+) ([Ru(aesi-N, S)(bpy)(2)](+) (aesi = 2-aminoethanesulfinate)). Similar treatment of optically active isomers of an analogous Ru(II)Ag(I)Ru(II) trinuclear complex, Δ(D)Δ(D)- and Λ(D)Λ(D)-[Ag{Ru(d-Hpen-O,S)(bpy)(2)}(2)](3+) (d-pen = d-penicillaminate), with NaI also produced mononuclear ruthenium(II) isomers with an S-bonded sulfinato group, Δ(D)- and Λ(D)-[2](+) ([Ru(d-Hpsi-O,S)(bpy)(2)](+) (d-psi = d-penicillaminesulfinate)), respectively, retaining the bidentate-O,S coordination mode of a d-Hpen ligand and the absolute configuration (Δ or Λ) about a Ru(II) center. On refluxing in water, the Δ(D) isomer of [2](+) underwent a linkage isomerization to form Δ(D)-[3] (+) ([Ru(d-Hpsi-N,S)(bpy)(2)](+)), in which a d-Hpsi ligand coordinates to a Ru(II) center in a bidentate-N,S mode. Complexes [1](+), Δ(D)- and Λ(D)-[2](+), and Δ(D)-[3](+) were fully characterized by electronic absorption, CD, NMR, and IR spectroscopies, together with single-crystal X-ray crystallography. The electrochemical properties of these complexes, which are highly dependent on the coordination mode of sulfinate ligands, are also described.     

Cyclometalated ruthenium(II) complexes with a bis-carbene CCC-pincer ligand

The first series of cyclometalated ruthenium complexes with a CCC-pincer bis-carbene ligand have been obtained as bench-stable compounds. Single-crystal X-ray analysis of one of these complexes with 4'-di-p-anisylamino-2,2':6',2'-terpyridine is presented. The Ru(II/III) redox potentials and MLCT absorptions of these complexes can be varied by attaching an electron-donating or -withdrawing group on the noncyclometalating ligand.     

Ligand-ligand inter-valence charge-transfer absorption in reduced ruthenium(II) bipyridine complexes

An electronic absorption band at 4000 cm^?1 in incompletely reduced Ru(II)-bipyridine and Ru(II)-bipyride-pyridine complexes is characteristic of co-existing bpy^o and bpy^?1 ligands and assigned to bpy^?/bpy⁰ inter-valence charger transfer.     

Synthesis and cytotoxicity of dinuclear complexes containing ruthenium(II) bipyridyl units linked by a bis(pyridylimine) ligand

Enantiopure dinuclear ruthenium polypyridyl complexes of the form [Ru(2)(LL)(4)L(1)](PF(6))(4) (LL = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen); L(1)= C(25)H(20)N(4) a bis(pyridylimine) ligand containing a diphenylmethane spacer) have been synthesized using the chiral building blocks cis-[Ru(bpy)(2)(py)(2)](2+) and cis-[Ru(phen)(2)(py)(2)](2+). These dinuclear ruthenium complexes have been characterised using NMR, mass spectrometry, UV-visible absorbance, circular dichroism and linear dichroism. The compounds exhibit good photo and thermal stability. The extinction coefficient for the bpy complex at 478 nm is epsilon(478) = 15,700 mol(-1) cm(-1) dm(3) and for the phen complex is epsilon(478) = 24,900 mol(-1) cm(-1) dm(3). Both complexes have their longest wavelength (metal to ligand charge transfer) transition predominantly x/y (short axis)-polarised while the transitions at shorter wavelength are a mixture of x/y and z-polarisations, similar to both the copper helicate and iron triple helicate studied previously. Cytotoxicity studies reveal that the compounds are dramatically less active against cancer cell lines than the recently reported supramolecular cylinders prepared from the same bis(pyridylimine) ligand.     

Electron-transfer kinetics of copper(II/I) tripodal ligand complexes

The electron-transfer kinetics for each of three copper(II/I) tripodal ligand complexes reacting with multiple reducing and oxidizing counter reagents have been examined in aqueous solution at 25 degrees C, mu = 0.10 M. For all of the ligands studied, an amine nitrogen serves as the bridgehead atom. Two of the ligands (PMMEA and PEMEA) contain two thioether sulfurs and one pyridyl nitrogen as donor atoms on the appended legs while the third ligand (BPEMEA) has two pyridyl nitrogens and one thioether sulfur. Very limited kinetic studies were also conducted on two additional closely related tripodal ligand complexes. The results are compared to our previous kinetic study on a Cu(II/I) system involving a tripodal ligand (TMMEA) with thioether sulfur donor atoms on all three legs. In all systems, the Cu(II/I) electron self-exchange rate constants (k(11)) are surprisingly small, ranging approximately 0.03-50 M(-)(1) s(-)(1). The results are consistent with earlier studies reported by Yandell involving the reduction of Cu(II) complexes with four similar tripodal ligand systems, and it is concluded that the dominant reaction pathway involves a metastable Cu(II)L intermediate species (designated as pathway B). Since crystal structures suggest that the ligand reorganization accompanying electron transfer is relatively small compared to our earlier studies on macrocyclic ligand complexes of Cu(II/I), it is unclear why the k(11) values for the tripodal ligand systems are of such small magnitude.     

Trigonal bi- and monopyramidal cobalt(II) complexes of a novel guanidine-based tripodal ligand

The novel ligand DIG(3)tren has three N',N'-diisopropylguanidinyl (DIG) moieties. We report on the structures of two cobalt complexes that show how an isopropylamino group from each DIG acts as a flap that can either close over the metal or rotate away from the metal to open up a site for auxiliary ligand binding. Two of the -NH(iPr) flaps are open in pink [Co(DIG(3)tren)(OAc)]OAc (1), and each of these flaps provides a hydrogen bond to stabilize acetate binding to trigonal bipyrimidal cobalt. The flaps are closed in blue [Co(DIG(3)tren)][BPh(4)](2) (2), yielding a rare example of a trigonal (mono)pyramidal [ML](2+) ion.     

Electrochemical synthesis and study of coordination compounds part 1: tin(II) catechol complexes

The electrochemical synthesis of tin(II) complexes of catechols, Sn(O₂Ar) (1a–9a), have carried out using tin metal as a sacrificial anode in acetonitrile, in the presence of catechol derivatives. The cyclic voltammetric characteristics of the synthesized complexes Sn(O₂Ar) (1a–9a) have been studied at glassy carbon electrode in dichloromethane. Anodic oxidation of Sn(O₂Ar) produces a single wave which shows irreversibility. Also, the electronic effects of ligands on the redox potential of complexes 1a–9a have been investigated. The synthesis of Sn(O₂Ar) species in high yields and purity has been successfully performed in an undivided cell using constant current conditions.     

Synthesis of platinum(II) chiral tetraamine coordination complexes

The individual and combinatorial syntheses of individual as well as a mixture-based diversity of 195 112 platinum(II) coordination complexes of chiral tetraamines are described. The use of both solid-phase synthesis and solution phase follow-on approaches were found to best afford the title compounds.     

Mechanistic aspects of ligand substitution incis-diaquabis(bipyridine)ruthenium(II) ion by acetyl acetone

The effects of pH, temperature, acetyl acetone (acacH) concentration and substrate complex concentration on the rate of aqua ligand substitution in the title complex in aqueous medium have been studied. The following rate expression is proposed for the 5.0–6.5 pH range.

Synthesis and characterization of seven-coordinate tripodal imidazole complexes of iron(II) and manganese(II)

The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 1-methyl-2-imidazolecarbaldehyde and the manganese(II) complex of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 4-imidazolecarbaldehyde are high-spin mono capped octahedral seven-coordinate complexes with a short, approximately 2.44 è, metal to apical nitrogen bond.     

Six-coordinate titanium complexes of a tripodal aminetris(phenoxide) ligand: synthesis, structure, and dynamics

The five-coordinate titanium(IV) alkoxide LTi(O(t)Bu) (LH(3) = tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine) is protonolyzed readily by the conjugate acids of monoanionic bidentate ligands, both symmetrical (tropolone, acetylacetone, di-p-toluoylmethane) and unsymmetrical (8-hydroxyquinoline, salicylaldehyde, 2,6-diformyl-p-cresol, anthrarufin). The geometry of these complexes, which is pseudo-octahedral with the tripodal ligand adopting a chiral, propeller-like conformation, has been confirmed in four cases by X-ray crystallography. Variable-temperature NMR spectroscopy indicates that the six-coordinate complexes undergo two dynamic processes. First, the ligands undergo a twisting motion that results in racemization, a process which is over 10(4) times faster than in five-coordinate complexes. The rate acceleration upon binding of an equatorial ligand is ascribed to steric repulsions with one of the cis phenoxides; the dynamics of a binuclear dibenzyl phosphate-bridged compound, which has a unique conformation of the tripodal ligand, indicates that flexing the cis phenoxide is the rate-limiting step in racemization. Second, the complexes undergo a process that interchanges the inequivalent arms of the tripodal ligand. This process involves a trigonal twist that shifts the bidentate ligand between clefts in the tripod. The intermediate geometry in the reaction appears to be a transition state and not a long-lived intermediate, as judged from the relative rates of interconversion of tripod arms and chelate ends in the ditoluoylmethane complex. Tripod arm interchange takes place without partial dissociation of the bidentate chelate, a reaction that has been observed on a slower time scale in one case.     

Tuning metal coordination number by ancillary ligand steric effects: synthesis of a three-coordinate iron(II) complex

The coordination number of the metal in iron(II) beta-diketiminate complexes can be tuned through the size of the alkyl substituents on the ligand backbone.