Oxomolybdenum(VI) complexes with glycine bisphenol [O,N,O,O′] ligand: synthesis and catalytic studies

The oxomolybdenum(VI) complex [MoOCl(L)] with a tetradentate glycine bisphenol ligand (H₃L) was prepared by reaction of [MoO₂Cl₂(DMSO)₂] with a ligand precursor in hot toluene. The product was isolated in moderate yield as separable cis and trans isomers along with the third minor component, [MoO₂(HL)]. The solid-state structure of trans-[MoOCl(L)] was determined by X-ray diffraction. The ligand has tetradentate coordination through three oxygens and one nitrogen, which is located trans to the terminal oxo whereas the sixth coordination site is occupied by a chloride. Both cis and trans isomers of [MoOCl(L)] are active catalysts for epoxidation of cis-cyclooctene and sulfoxidation of tolyl methyl sulfide. The cis isomer gave higher activity in epoxidation and sulfoxidation reactions at room temperature than the trans isomer but they performed identically at 50?°C.     

Two hydrogen-bond-cross-linked molybdenum (VI) network polymers: synthesis, crystal structures and cyclooctene epoxidation with H2O2

Two molybdenum (VI) hydrogen-bonded network polymers [MoO₂F₄]·(4,4′-H₂bpd)(H₂O)₂ (1) and [MoO₂Cl₃(H₂O)]·(4,4′-H₂bpd)Cl (2) (bpd = bipiperidine) have been synthesized and examined as catalysts for epoxidation of cyclooctene. Complexes of the Mo compounds containing the bpd ligand are prepared and characterized by infrared spectroscopy, thermogravimetric and elemental analyses. They have been structurally characterized by single crystal X-ray diffraction analysis. The structures of both the complexes are shown to be comprised of molybdenum and two protonated N-ligand cations that have resulted in a cross-linked hydrogen-bonded network structure. These complexes are applicable as catalysts for the cis-cyclooctene epoxidation reactions with hydrogen peroxide as a source of oxygen and NaHCO₃ as a cocatalyst. It has been observed that the formation of the oxidant peroxymonocarbonate ion, HCO₄ ⁻ by hydrogen peroxide and bicarbonate enhances the epoxidation reaction. Both the complexes have exhibited a good activity and a very high selectivity for the formation of cyclooctene oxide. An erratum to this article can be found at     

Dioxomolybdenum(VI) complex with N,N′- ethylenebis(salicylideneimine)

The interaction of N,N′-ethylenebis(salicylideneimine), H₂salen, with ammonium molybdate yielded the molybdenum(VI) complex MoO₂(salen) with the cis-dioxostructure as inferred from IR spectral studies. The ¹H NMR chemical shifts of azomethine protons in the free ligand and the complex are 8.14 and 8.39 δ, respectively, suggesting the bonding of the azomethine nitrogen to MoO₂ group. The thermal decomposition behaviour of the complex is discussed.     

cis-Dioxo(N-salicylidene-2-aminophenolato)(imidazole)-molybdenum(VI) complexes

Summary cis-Dioxo(N-salicylidene-2-aminophenolato) (imidazole)-molybdenum(VI) complexes, [MoO₂(Sap)(Im)], (Im = imidazole or its derivatives, sap = salicylidene-2-aminophenolate) are prepared by the ligand substitution of [MoO₂(Sap)(EtOH)] with a unidentate imidazole ligand. All complexes are red or yellow, diamagnetic, non-electrolytes and possess an octahedral stereochemistry. The i.r. spectra shows two bands attributable tocis-MoO₂ stretches in addition to the vibrations of the Schiff base ligand and the imidazole derivatives. Thermal degradation of the complexes result in successive loss of imidazole ligand followed by the Schiff base, with ultimate formation of MoO₃ atca. 500 °C.     

Olefin epoxidation catalyzed by [Ru(TDL)(tmeda)H2O] complexes (TDL = tridentate Schiff-base ligand; tmeda = tetramethylethylenediamine)

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived from condensation of 2-aminophenol or 2-aminobenzoic acid with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde), and tmeda (tetramethylethylenediamine). [Ru^III(hpsd)(tmeda)(H₂O)]⁺ (1), [Ru^III(hppc)(tmeda)(H₂O)]²⁺ (2), [Ru^III(cpsd)(tmeda)(H₂O)]⁺ (3) and [Ru^III(cppc)(tmeda)(H₂O)]²⁺ (4) complexes (where hpsd²⁻ = N-(hydroxyphenyl)salicylaldiminato); hppc⁻ = N-(2-hydroxyphenylpyridine-2-carboxaldiminato); cpsd²⁻ = (N-(2-carboxyphenyl)salicylaldiminato); cppc⁻ = N-2-carboxyphenylpyridine-2-carboxaldiminato) were characterized by microanalysis, spectral (IR and UV–vis), conductance, magnetic moment and electrochemical studies. Complexes 1–4 catalyzed the epoxidation of cyclohexene, styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene, cis- and trans-stilbenes effectively at ambient temperature using tert-butylhydroperoxide (t-BuOOH) as terminal oxidant. On the basis of Hammett correlation (log k_rel vs. σ⁺) and product analysis, a mechanism involving intermediacy of a [Ru–O–OBu^t] radicaloid species is proposed for the catalytic epoxidation process.     

Synthesis, Crystal Structure and Reactivity of Mo4O6(O2)2(μ3-O)2{(μ2-O,μ3-OC8H14}2(OPMePh2)2: A Self-assembled Tetranuclear Cluster Containing Two Peroxide and Two Trans-Cyclooctanediol Ligands*

The reaction of MoO₂Cl₂(OPMePh₂)₂ with t-butylhydroperoxide (TBHP) in the presence of cis-cyclooctene yields the tetrameric complex Mo₄O₆(O₂)₂(μ₃-O)₂{(μ₂-O,μ₃-OC₈H₁₄}₂(OPMePh₂)₂, (1). Additionally in the absence of cis-cyclooctene MoO(O₂)Cl₂(OPMePh₂)₂, MoO(O₂)₂(H₂O)(OPMePh₂), (2), and two novel yellow compounds can be isolated depending on the quantity of TBHP used and the reaction conditions. Both the starting material MoO₂Cl₂(OPMePh₂)₂ and tetramer 1 are capable of accomplishing the epoxidation of cis-cyclooctene as catalysts. The single crystal X-ray determined structures of complexes 1 and 2 are reported.Dedicated to Professor F. A. “Chief” Cotton on the occasion of his 75th birthday     

Reactivity of AlMe3 with titanium(IV) Schiff base complexes: X-ray structure of [Ti{(μ-Br)(AlMe2)}{(μ-Br)(AlMe2X)}(salen)] · C7H8 (X=Me or Br) and reactivity studies of mono-alkylated [Ti(Me)X(L)] complexes

[TiCl₂(salen)] (1) reacts with AlMe₃ (1:2) to give the heterometallic Ti(III) and Ti(IV) complexes [Ti{(μ-Cl)(AlMe₂)}{(μ-Cl)(AlMe₂X)}(salen)] (X=Me or Cl) (2) and [TiMe{(μ-Cl)(AlCl₂Me)}(salen)] (3). Addition of diethyl ether to 3 affords [Ti(Me)Cl(salen)] (4). The analogous reaction of [TiBr₂(salen)] (5) gives the crystallographically characterised [Ti{(μ-Br)(AlMe₂)}{(μ-Br)(AlMe₂X)}(salen)] (X=Me or Br) (6) and [Ti(Me)Br(salen)] (7) in a single step, whilst the comparable reaction of [TiCl₂{(3-MeO)₂salen}] (8) with AlMe₃ yields [Ti(Me)Cl{(3-MeO)₂salen}] (9) with no evidence of titanium(III) species. Reactivity of both halide and methyl groups of 4 has been probed using magnesium reduction, SbCl₅ and AgBF₄ halide abstraction and SO₂ insertion reactions. Hydrolysis of [Ti(Me)X(L)] complexes affords μ-oxo species [TiX(L)]₂(μ-O) [X=Cl, L=salen (13); X=Br, L=salen (14); X=Cl, L=(3-MeO)₂salen (15)].     

Synthesis,crystal structures and catalytic epoxidation properties of dioxomolybdenum(VI) complexes with hydrazone ligands

A series of dioxomolybdenum(VI) complexes with similar hydrazone ligands have been prepared, specifically [MoO₂L¹(MeOH)] (1), [MoO₂L²(MeOH)] (2) and [MoO₂L³(MeOH)] (3), where L¹, L² and L³ are the dianionic forms of 2-chloro-N′-(2-hydroxybenzylidene)benzohydrazide, 2-chloro-N′-(2-hydroxy-5-methylbenzylidene)benzohydrazide and N′-(3-bromo-5-chloro-2-hydroxybenzylidene)-2-chlorobenzohydrazide, respectively. The complexes were characterized by physicochemical and spectroscopic methods and also by single-crystal X-ray determination. The hydrazone ligands coordinate to the Mo atoms through their phenolate O, imine N and enolic O atoms. The Mo atoms are six-coordinated in octahedral geometries. The complexes show high catalytic activities and selectivities in the epoxidation of cyclohexene with tert-butylhydroperoxide as primary oxidant.     

Driving forces in substitution reactions of octahedral complexes: The influence of the competitive effect

The reaction of cis-[RuCl₂(P–P)(N–N)] type complexes (P–P = 1,4-bis(diphenylphosphino)butane or (1,1′-diphenylphosphino)ferrocene; N–N = 2,2′-bipyridine or 1,10-phenantroline) with monodentate ligands (L), such as 4-methylpyridine, 4-phenylpyridine and benzonitrile forms [RuCl(L)(P–P)(N–N)]⁺ species. Upon characterization of the isolated compounds by elemental analysis, ³¹P{¹H} NMR and X-ray crystallography it was found out that the type of the L ligand determines its position in relation to the phosphorus atom. While pyridine derivatives like 4-methylpyridine and 4-phenylpyridine coordinate trans to the phosphorus atom, the benzonitrile ligand (bzCN), a good π acceptor, coordinates trans to the nitrogen atom. A ³¹P{¹H} NMR experiment following the reaction of the precursor cis-[RuCl₂(dppb)(phen)] with the benzonitrile ligand shows that the final position of the entering ligand in the complex is better defined as a consequence of the competitive effect between the phosphorus atom and the cyano-group from the benzonitrile moiety and not by the trans effect. In this case, the benzonitrile group is stabilized trans to one of the nitrogen atoms of the N–N ligand. A differential pulse voltammetry experiment confirms this statement. In both experiments the [RuCl(bzCN)(dppb)(phen)]PF₆ species with the bzCN ligand positioned trans to a phosphorus atom of the dppb ligand was detected as an intermediate complex.     

Luminescent mononuclear and dinuclear cycloplatinated (II) complexes comprising azide and phosphine ancillary ligands

A new series of cycloplatinated (II) complexes with general formulas of [Pt (bhq)(N₃)(P)] [bhq = deprotonated 7,8‐benzo[h]quinoline, P = triphenyl phosphine (PPh₃) and methyldiphenyl phosphine], [Pt (bhq)(P^P)]N₃ [P^P = 1,1‐bis (diphenylphosphino)methane (dppm) and 1,2‐bis (diphenylphosphino)ethane] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂] [P^P = dppm and 1,2‐bis (diphenylphosphino)acetylene] is reported in this investigation. A combination of azide (N₃^?) and phosphine (monodentate and bidentate) was used as ancillary ligands to study their influences on the chromophoric cyclometalated ligand. All complexes were characterized by nuclear magnetic resonance spectroscopy. To confirm the presence of the N₃^? ligand directly connected to the platinum center, complex [Pt (bhq)(N₃)(PPh₃)] was further characterized by single‐crystal X‐ray crystallography. The photophysical properties of the new products were studied by UV–Vis spectroscopy in CH₂Cl₂ and photoluminescence spectroscopy in solid state (298 or 77 K) and in solution (77 K). Using density functional theory calculations, it was proved that, in addition to intraligand charge‐transfer (ILCT) and metal‐to‐ligand charge‐transfer (MLCT) transitions, the L′LCT (L′ = N₃, L = C^N) electronic transition has a remarkable contribution in low energy bands of the absorption spectra (for complexes [Pt (bhq)(N₃)(P)] and [Pt₂(bhq)₂(μ‐P^P)(N₃)₂]). It is indicative of the determining role of the N₃^? ligand in electronic transitions of these complexes, specifically in the low energy region. In this regard, the photoluminescence studies indicated that the emissions in such complexes originate from a mixed ³ILCT/³MLCT (intramolecular) and also from aggregations (intermolecular).     

Structural variations in nickel, palladium, and platinum complexes containing pyrimidyl N-heterocyclic carbene ligand

Nickel(II), palladium(II), and platinum(II) complexes of 2-(3-mesitylimidazolylidenyl)pyrimidine (L), [Ni₂(μ-Cl)₂(L)₄][Ag₂Cl₄] (3), [Ni₂(μ-I)₂(L)₄][NiI(L)₂(CH₃CN)]₂[Ag₄I₈] (4), [PdCl₂(L)] (5), [PdI₂(L)] (6), and [PtCl(L)₂][AgCl₂] (7) have been obtained from the carbene transfer reactions of [Ag(L)Cl] (2). These complexes have been fully characterized by spectroscopic methods and single-crystal X-ray structure analyses. The mono(carbene)palladium and bis(carbene)platinum complexes display normal square–planar structures. Nickel complexes 3 and 4 are rare examples of paramagnetic nickel(II) complexes of N-heterocyclic carbenes having octahedral geometry.     

Dioxomolybdenum(VI) complexes of hydrazone phenolate ligands - syntheses and activities in catalytic oxidation reactions

The new cis-dioxomolybdenum (VI) complexes [MoO₂(L²)(H₂O)] (2) and [MoO₂(L³)(H₂O)] (3) containing the tridentate hydrazone-based ligands (H₂L² = N'-(3,5-di-tert-butyl-2-hydroxybenzylidene)-4-methylbenzohydrazide and H₂L³ = N'-(2-hydroxybenzylidene)-2-(hydroxyimino)propanehydrazide) have been synthesized and characterized via IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction analysis. The catalytic activities of complexes 2 and 3, and the analogous known complex [MoO₂(L¹)(H₂O)] (1) (H₂L¹ = N'-(2-hydroxybenzylidene)-4-methylbenzohydrazide) have been evaluated for various oxidation reactions, viz. oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, sulfoxidation of methyl-p-tolylsulfide or epoxidation of different alkenes using tert-butyl hydroperoxide as terminal oxidant. The catalytic activities were found to be comparable for all three complexes, but complexes 1 and 3 showed better catalytic performances than complex 2, which contains a more sterically demanding ligand than the other two complexes.     

Luminescence of Salen Lanthanide Bimetallic Complexes: Dual Emission and Energy Transfer

The luminescence properties of the tetranuclear bimetallic lanthanide complexes Sm₂Eu₂ ( 1 ) and Eu₂Tb₂ ( 2 ), were compared with those of the analogous homometallic complexes [Sm₄(μ₃‐OH)₂(salen)₂(acac)₆(CH₃OH)₂] · CH₃OH ( 3 ) and [Eu₄(μ₃‐OH)₂(salen)₂(acac)₆(CH₃OH)₂] ( 4 ) [H₂salen = N, N′‐ethylenebis(salicylideneimine), Hacac = acetylacetonate]. X‐ray crystallographic analysis reveals that complexes 3 and 4 have planar tetranuclear structures. For the Eu₂Tb₂ configurational isomer, the Tb^III ion in complex 2 mainly serves as a sensitizer. The quantum yields and lifetime measurements for 2 support the premise that Ln/Ln energy transfer occurs in such lanthanide bimetallic complexes, along with the usual ligand‐to‐metal triplet energy pathways. Complexes 3 and 4 exhibit the characteristic metal‐centered emission.     

Co(III) complexes of Me-salpn and Me-salbn and the ring size effect on the coordination modes and electrochemical properties: The crystal structures of trans-[Co(Me-salpn)(py)2]PF6 and cis-α-[Co(Me-salbn)(4-Mepy)2]BPh4 · 4-Mepy

The synthesis and characterization of a series of cobalt(III) complexes of the general type [Co(N₂O₂)(L₂)]⁺ are described. The N₂O₂ Schiff base ligands used are Me-salpn (H₂Me-salpn = N,N′-bis(methylsalicylidene)-1,3-propylenediamine) (1–3) and Me-salbn (H₂Me-salbn = N,N′-bis(methylsalicylidene)-1,4-butylenediamine) (4–5). The two ancillary ligands L include: pyridine (py) 1, 3-metheylpyridine (3-Mepy) 2, 1-methylimidazole (1-MeIm) 3, 4-methylpyridine (4-Mepy) 4 and pyridine (py) 5. These complexes have been characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structures of trans-[Co^III(Me-salpn)(py)₂]PF₆, 1, and cis-α-[Co^III(Me-salbn)(4-Mepy)₂]BPh₄ · 4-Mepy, 4, have been determined by X-ray diffraction. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the complexes exerts a noticeable influence on the inner coordination sphere of the Co(III) ion. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co^III–Co^II is electrochemically irreversible, which is accompanied by the dissociation of the axial (R-py)–cobalt bonds. It has also been observed that the Co(III) state is stabilized with increasing the flexibility of the ligand environment.     

Molybdenum Schiff base-polyoxometalate hybrid compound: A heterogeneous catalyst for alkene epoxidation with tert-BuOOH

The hybrid compound consisting of molybdenum(salen) [salen = N,N′-bis(salicylidene)ethylnediamine] complex covalently linked to a lacunary Keggin-type polyoxometalate, K₈[SiW₁₁O₃₉] (POM), was synthesized and characterized by elemental analysis, FT-IR, ¹H NMR and diffuse reflectance UV–Vis spectroscopic methods and BET analysis. The complex, [Mo(O)₂(salen)–POM], was studied, for the first time, in the epoxidation of various alkenes with tert-BuOOH and in 1,2-dichloroethane as solvent. This catalyst can catalyze epoxidation of various olefins including non-activated terminal olefins. The effect of the other parameters such as solvent, oxidant and temperature on the epoxidation of cyclooctene was also investigated. The interesting characteristic of this catalyst is that, in addition to being a heterogeneous catalyst, it gives higher yields towards epoxidation of olefins in comparison to the corresponding homogeneous [Mo(O)₂(salen)] complex.     

Monooxorhenium(V) complexes with the tridentate Schiff baseN-(2-hydroxyphenyl)salicylideneimine

Summary The reactions of the tridentate Schiff base ligandN-(2-hydroxyphenyl) salicylideneimine (HOPhsalH) with oxotetrachlororhenate (IV) have been investigated. The complexes (Bu₄N)[ReOCl₃(HOPhsal)], (Bu₄N)[ReOCl₂(OPhsal)],cis- [ReOCl(MeOH)(OPhsal)],trans-[ReOCl(MeOH)(OPhsal)] (1), trans-[ReOCl(OH₂)(OPhsal)] · Et₂O (2), trans-[ReOCl(OH₂)(OPhsal)] · Me₂CO,cis-[ReOCl(PPh₃)(OPhsal)],cis-[ReOCl(PMe₂Ph)(OPhsal)](3) have been synthesized and characterized. The crystal structures of(1), (2) and(3) have been solved from three-dimensional x-ray data by Patterson and Fourier methods and refined by least-squares methods to R 0.10 for(1), 0.042 for(2) and 0.059 for(3). In all the three complexes, the ligands surrounding the rhenium atom are at the apices of a distorted octahedron, with the equatorial ONO donor atoms of the tridentate Schiff base bent away from the O_oxo and toward the loosely bound MeOH in(1), H₂O in(2) and Cl in(t3). The fourth equatorial substituent is Cl (1 and2) and PMe₂Ph(3) and the rhenium atoms lie 0.30–0.37 Å above the best plane through the four equatorial atoms, in the direction of the O_oxo. All interatomic distances and angles are normal.     

The mer-[RuCl3(dppb)(H2O)] complex: A versatile tool for synthesis of Ru compounds

The complex mer-[RuCl₃(dppb)(H₂O)] [dppb = 1,4-bis(diphenylphosphino)butane] was used as a precursor in the synthesis of the complexes tc-[RuCl₂(CO)₂(dppb)], ct-[RuCl₂(CO)₂(dppb)], cis-[RuCl₂(dppb)(Cl-bipy)], [RuCl(2Ac4mT)(dppb)] (2Ac4mT = N(4)-meta-tolyl-2-acetylpyridine thiosemicarbazone ion) and trans-[RuCl₂(dppb)(mang)] (mang = mangiferin or 1,3,6,7-tetrahydroxyxanthone-C2-β-D-glucoside) complexes. For the synthesis of Ru^II complexes, the Ru^III atom in mer-[RuCl₃(dppb)(H₂O)] may be reduced by H₂(g), forming the intermediate [Ru₂Cl₄(dppb)₂], or by a ligand (such as H2Ac4mT or mangiferin). The X-ray structures of the cis-[RuCl₂(dppb)(Cl-bipy)], tc-[RuCl₂(CO)₂(dppb)] and [RuCl(2Ac4mT)(dppb)] complexes were determined.     

Nitric oxide and singlet oxygen photo-generation by light irradiation in the phototherapeutic window of a nitrosyl ruthenium conjugated with a phthalocyanine rare earth complex

The photochemical, photophysical and photobiological studies of a mixture containing cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] (H₂-dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and Na₄[Tb(TsPc)(acac)] (TsPc = tetrasulfonated phthalocyanines; acac = acetylacetone), a system capable of improving photodynamic therapy (PDT), were accomplished. cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] was obtained from cis-[Ru(H₂-dcbpy)₂Cl₂]·2H₂O, whereas Na₄[Tb(TsPc)(acac)] was obtained by reacting phthalocyanine with terbium acetylacetonate. The UV–Vis spectrum of cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] displays a band in the region of 305 nm (λ_max in 0.1 mol L⁻¹ HCl)(π–π*) and a shoulder at 323 nm (MLCT), while the UV–Vis spectrum of Na₄[Tb(TsPc)(acac)] presents the typical phthalocyanine bands at 342 nm (Soret λ_max in H₂O) and 642, 682 (Q bands). The cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] FTIR spectrum displays a band at 1932 cm⁻¹ (Ru–NO⁺). The cyclic voltammogram of the cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)] complex in aqueous solution presented peaks at E = 0.10 V (NO^+/0) and E = −0.50 V (NO^0/−) versus Ag/AgCl. The NO concentration and ¹O₂ quantum yield for light irradiation in the λ > 550 nm region were measured as [NO] = 1.21 ± 0.14 μmol L⁻¹ and ø_OS = 0.41, respectively. The amount of released NO seems to be dependent on oxygen concentration, once the NO concentration measured in aerated condition was 1.51 ± 0.11 μmol L⁻¹ The photochemical pathway of the cis-[Ru(H-dcbpy⁻)₂(Cl)(NO)]/Na₄[Tb(TsPc)(acac)] mixture could be attributed to a photoinduced electron transfer process. The cytotoxic assays of cis-[Ru(H-dcbpy^-)₂(Cl)(NO)] and of the mixture carried out with B16F10 cells show a decrease in cell viability to 80% in the dark and to 20% under light irradiation. Our results document that the simultaneous production of NO and ¹O₂ could improve PDT and be useful in cancer treatment.     

Synthesis, DNA-binding and photocleavage studies of [Ru(phen)2(pbtp)] and [Ru(bpy)2(pbtp)] (phen = 1,10-phenanthroline; bpy = 2,2′-bipyridine; pbtp = 4,5,9,11,14-pentaaza-benzo[b]triphenylene)

Based on the ligand dppz (dppz = dipyrido-[3,2-a:2′,3′-c]phenazine), a new ligand pbtp (pbtp = 4,5,9,11,14-pentaaza-benzo[b]triphenylene) and its polypyridyl ruthenium(II) complexes [Ru(phen)₂(pbtp)]²⁺ (1) (phen = 1,10-phenanthroline and [Ru(bpy)₂(pbtp)]²⁺ (2) (bpy = 2,2′-bipyridine) have been synthesized and characterized by elemental analysis, ES-MS and ¹H NMR spectroscopy. The DNA-binding of these complexes were investigated by spectroscopic methods and viscosity measurements. The experimental results indicate that both complexes 1 and 2 bind to CT-DNA in classical intercalation mode, and can enantioselectively interact with CT-DNA. It is interesting to note that the pbtp ruthenium(II) complexes, in contrast to the analogous dppz complexes, do not show fluorescent behavior when intercalated into DNA. When irradiated at 365 nm, both complexes promote the photocleavage of pBR 322 DNA.     

How 5 f Electron Polarisability Drives Covalency and Selectivity in Actinide N-Donor Complexes

We report a series of isostructural tetravalent actinide (Th, U−Pu) complexes with the N-donor ligand N,N’-ethylene-bis((pyrrole-2-yl)methanimine) (H₂ L , H₂pyren). Structural data from SC-XRD analysis reveal [An(pyren)₂] complexes with different An−N_imine versus An−N_pyrrolide bond lengths. Quantum chemical calculations elucidated the bonding situation, including differences in the covalent character of the coordinative bonds. A comparison to the intensely studied analogous N,N′-ethylene-bis(salicylideneimine) (H₂salen)-based complexes [An(salen)₂] displays, on average, almost equal electron sharing of pyren or salen with the An^IV, pointing to a potential ligand-cage-driven complex stabilisation. This is shown in the fixed ligand arrangement of pyren and salen in the respective An^IV complexes. The overall bond strength of the pure N-donor ligand pyren to An^IV (An=Th, U, Np, Pu) is slightly weaker than to salen, with the exception of the Pa^IV complex, which exhibits extraordinarily high electron sharing of pyren with Pa^IV. Such an altered ligand preference within the early An^IV series points to a specificity of the 5f¹ configuration, which can be explained by polarisation effects of the 5 f electrons, allowing the strongest f electron backbonding from Pa^IV (5f¹) to the N donors of pyren.