The synthesis, spectroscopic, electrochemical and X-ray diffraction characterization of novel bridged ferrocene precursors for use in self-assembled monolayers

The synthesis of 1,6-diferrocenylhexane-1,6-dione (I), 1-ferrocenylcarbonyl-2-ferrocenylcyclopentene (II) and 1,6-diferrocenylhexane (III) is reported. All three compounds were characterized by ¹H NMR, ¹³C NMR, and infra-red spectroscopy, mass spectrometry, cyclic voltammetry and chronoamperometry. Compounds I and III each exhibit a single two electron transfer, while compound (II) exhibits two single electron transfers. Compounds (I) and (II) were further studied by single crystal X-ray diffraction. In compound (I), both carbonyl groups are in plane with the adjacent ferrocenyl Cp ring. For compound (II) one of the ferrocenyl Cp rings is coplanar with the carbonyl group, the other with the double bond of the cyclopentene ring, but the CO moiety and the double bond are basically perpendicular to each other.     

Preparation and reactivity of polyfunctional six- and eight-membered cyclic silicates

Six- and eight-membered cyclic silicates with reactive SiH or Si-vinyl functional groups have been prepared: hexakis(dimethylsiloxy)cyclotrisiloxane (I), hexakis(vinyldimethylsiloxy)cyclotrisiloxane (II), octakis(dimethylsiloxy)cyclotetrasiloxane (III) and octakis(vinyldimethylsiloxy)cyclotetrasiloxane (IV). Reaction of pseudo wollastonite (Ca₃Si₃O₉) with dimethylchlorosilane or vinyldimethylchlorosilane gives I and II, respectively. IV has been prepared similarly by reaction of octakis[chloro calcium oxy]cyclotetrasilicate [Ca₈Si₄O₁₂Cl₈] with vinyldimethylchlorosilane. On the other hand, acid catalyzed siloxane exchange between tetramethyldisiloxane and octakis(trimethylsiloxy)cyclotetrasiloxane (V) gave III. Cyclic silicates (I-VI) are surprisingly resistant to acid catalyzed ring opening polymerization. In addition, II, IV, V and hexakis(trimethylsiloxy)cyclotrisiloxanes (VI) are resistant to phosphazene P₄-t-Bu superbase catalyzed ring opening polymerization.     

Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Three new mononuclear complexes of nitrogen–sulfur donor sets, formulated as [Fe^II(L)Cl₂] (1), [Co^II(L)Cl₂] (2) and [Ni^II(L)Cl₂] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized and isolated in their pure form. All the complexes were characterized by physicochemical and spectroscopic methods. The solid state structures of complexes 1 and 3 have been established by single crystal X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a distorted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit Fe^II/Fe^III, Co^II/Co^III and Ni^II/Ni^III quasi-reversible redox couples in cyclic voltammograms with E_1/2 values (versus Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively.     

Synthesis and electrochemical properties of new cobalt and manganese phthalocyanine complexes tetra-substituted with 3,4-(methylendioxy)-phenoxy

The synthesis and electrochemical properties of new cobalt and manganese phthalocyanine complexes, tetra-substituted with 3,4-(methylendioxy)-phenoxy at the peripheral (complexes 3 and 5) and non-peripheral (complexes 4 and 6) positions, are reported. Complexes 3 and 4 showed Q-band absorption, in DMF, at 668 and 686 nm, respectively while Q-band due to complexes 5 and 6 appeared at 732 and 760 nm, respectively in CHCl₃. All the complexes showed well resolved redox processes attributed to both metal and ring based processes. Complexes 3 and 4 showed four redox processes, labeled I, II, III and IV. For complex 3, process I (Co^IPc⁻²/Co^IPc⁻³) was observed at −1.45 V, II (Co^IIPc⁻²/Co^IPc⁻²) at −0.38 V, III (Co^IIIPc⁻²/Co^IIPc⁻²) at +0.49 V and IV (Co^IIIPc⁻¹/Co^IIIPc⁻²) at +0.97 V versus Ag|AgCl. Similar processes were observed for complex 4 at −1.36 V, −0.27 V, +0.56 V, +1.03 V versus Ag|AgCl, respectively. Complexes 5 and 6 showed two redox processes (I and II). For complex 5, these processes appeared at −0.79 V (Mn^IIPc⁻²/Mn^IIPc⁻³, I) and −0.07 V versus Ag|AgCl (Mn^IIIPc⁻²/Mn^IIPc⁻², II), while for complex 6, they were observed at −0.86 V and −0.04 V versus Ag|AgCl. Spectroelectrochemistry was used to probe and confirm the origin of these processes.     

Mixed ligand complexes of AEE hexafluoroacetylacetonates with diglyme: Synthesis,crystal structure and thermal behavior

The novel mixed ligand complexes [Ca(hfa)₂(diglyme)(H₂O)] (I), [Sr(hfa)₂(diglyme)(H₂O)] (II) and [Ba(hfa)₂(diglyme)₂] (III) (Hhfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, diglyme = 2,5,8-trioxanonane) were synthesized by the reactions of the alkaline earth element (AEE) carbonates in n-hexane with a mixture of Hhfa and diglyme, and they were characterized by elemental analysis, ¹H and ¹³C NMR, and FTIR spectroscopy. The crystal structures of I–III, consisting of mononuclear isolated molecules, have been determined. The thermal behavior and composition of the vapor phase have been studied for I–III by thermal analysis at low pressure and mass spectrometry using a Knudsen cell. The stability of the mixed ligand complexes [M(hfa)₂(diglyme)_n] to the removal of diglyme molecules under heating decreases in the row I > II ≈ III, and only I evaporates as the mixed ligand complex after water removal.     

Temperature dependence on recrystallisation of the magnesium phthalocyanine (MgPc) in triethylamine

Three complexes of magnesium phthalocyaninato(2−) derivatives in the crystalline form, MgPc(H₂O)·(C₂H₅)₃N – (I), MgPc(H₂O)₂·2(C₂H₅)₃N – (II) and MgPc(H₂O)₂ – (III), depending on the thermal recrystallisation conditions were obtained and structurally characterised. In complex I, the Mg center exhibits square-pyramidal (4 + 1) coordination environment, whereas in II and III the Mg center of MgPc the biaxial (4 + 2) coordination. Owing to the interaction of the positively charged Mg center with oppositely charged oxygen atom of water molecule in an axial position in I, the Mg atom is significantly displaced (0.451(2) Å) from the plane defined by four isoindole N atoms and leads to distortion of the planar Pc(2−) macrocycle to the saucer-shape form. In II and III due to the biaxial (4 + 2) coordination of the Mg center of MgPc, the Mg atom lies on a N₄-isoindole plane. The triethylamine solvent molecules in I and II interact with mono or bis(aqua)magnesium phthalocyanine via   O–H?$?$N hydrogen bonds. The axial Mg–O bond in I is significantly shorter than that in the II and III complexes. The strength of the Mg–O bond in these complexes is correlated with their thermal stability. From among the complexes only complex I exhibits an intense near-IR absorption band in the solid-state. The spectra of I, II and III in solution are very similar.     

A “sodium trap” based on benzo-15-crown-5 with an exocyclic N-(thiophosphoryl)thiourea moiety

For N-(thio)phosphorylthioureas of the common formula RC(S)NHP(X)(OiPr)₂HL^I (R = N-(4′-aminobenzo-15-crown-5), X = S), HL^II (R = N-(4′-aminobenzo-15-crown-5), X = O), HL^III (R = PhNH, X = S), HL^IV (R = PhNH, X = O), and (N,N′-bis-[C(S)NHP(S)(OiPr)₂]₂-1,10-diaza-18-crown-6) H₂L^V, salts LiL^I,III,IV, NaL^I–IV, KL^I–IVM₂L^V (M = Li⁺, Na⁺, K⁺), Ba(L^I,III,IV)₂, and BaL^V have been synthesized and investigated. Compounds NaL^I,II quantitatively drop out as a deposit in ethanol medium, allowing the separation of Na⁺ and K⁺ cations. This effect is not displayed for the other compounds. The crystal structures of HL^III and the solvate of the composition [K(Me₂CO)L^III] have been investigated by X-ray crystallography.     

Syntheses, electrochemical and spectroelectrochemical properties of novel ball-type and mononuclear Co(II) phthalocyanines substituted at the peripheral and non-peripheral positions with binaphthol groups

Mononuclear cobalt phthalocyanine (CoPc) substituted at the non-peripheral 8 and peripheral positions 9 with 1,1′-binaphthyl-8,8′-diol and ball-type dinuclear Co₂Pc₂ substituted at the non-peripheral 10 and peripheral 11 positions with the same substituent are reported. The complexes with 1,1′-binaphthol-bridges were prepared from the corresponding phthalonitriles 4-7. The effects of the position of substituent on spectral, electrochemical and spectroelectrochemical properties of these complexes were also explored. The mononuclear complexes 8 and 9 exhibited one metal reduction, one ring reduction and one ring oxidation. The redox properties of the ball-type complexes 10 and 11 exhibited two reduction processes assigned to [(Co^IPc⁻²)₂]²⁻/[(Co^IPc⁻³)₂]⁴⁻ (I), (Co^IIPc⁻²)₂/[(Co^IPc⁻²)₂]²⁻ (II) and one oxidation process assigned to [(Co^IIIPc⁻²)₂]²⁺/Co^IIPc⁻²)₂ (III). The ball-type complexes are much easier to oxidize and more difficult to reduce than the corresponding monomers 8 and 9.     

Synthesis, characterization and biocompatibility studies of oligosiloxane modified polythiophenes

This paper describes the preparation and characterization of homopolymers of 3-oligo(dimethylsiloxane)thiophene macromonomers, V-VIII, and copolymers with 3-methylthiophene. The thiophene macromonomers were prepared by hydrosilylation reaction between ω-(Si-H)-oligo(dimethylsiloxane), I-IV, and 3-propenylthiophene using a platinum-divinyltetramethyldisiloxane complex as the catalyst. The products were characterized by ¹H, ¹³C, ²⁹Si NMR and IR spectroscopy; DSC (differential scanning calorimetry) and GPC studies. Two distinct glass transition temperatures are observed for poly[VIII], a T_g at −79 °C corresponds to the soft oligo(dimethylsiloxane) phase and the T_g at 190 °C corresponds to the hard thiophene backbone. Homopolymers of V and VI, and copolymers may be doped with I₂ to generate electronic conductive material, a copolymer of poly[V]-co-poly[3-methylthiophene] (50/50, w/w) has an electronic conductivity value of 5 × 10⁻⁵ S/cm at 25 °C. The polymers are tractable and may be molded into thin films; a number of the polymers are soluble in organic solvents. Polythiophene modified with oligosilioxanes are biocompatibile; the polymers minimally interfere with the growth of HeLa cells.     

Synthesis,crystal structure and some properties of new perrhenate and pertechnetate complexes of Nd and Am with 2,6-bis(tetramethylfurano)-1,2,4-triazin-3-yl)-pyridine,tris(2-pyridylmethyl)amine and N,N′-tetraethylmalonamide

The coordination complexes of trivalent f-element pertechnetates and perrhenates with some N-donor ligands were determined by using X-ray structural analysis: Nd³⁺ perrhenate with 2,6-bis(tetramethylfurano)-1,2,4-triazin-3-yl)-pyridine ([Nd(FBTP)₃ReO₄](ReO₄)₂ · 2H₂O (I)), tris(2-pyridylmethyl)amine ([Nd(TPA)(ReO₄)₃] (II)) and N,N′-tetraethylmalonamide ([Nd(TEMA)₄](ReO₄)₃ (III)). The coordination number of Nd is 10 in I, 9 in II and 8 in III. The complexes of Nd³⁺ pertechnetate and Am³⁺ pertechnetate with TPA have been also synthesized (Nd(TPA)(TcO₄)₃ (IV) and Am(TPA)(TcO₄)₃ (V)). The structure II does not change on replacement of perrhenate by pertechnetate and neodymium by americium.     

Ru(II) with chelating containing N4-type donor quadridentate Pd-oxime metal complexes: Syntheses, spectral characterization, thermal and catalytic properties

Five new metal complexes [Pd(LH)₂] (1), [Pd(L)₂Ru₂(bpy)₄](ClO₄)₂ (2), [Pd(L)₂Ru₂(phen)₄](ClO₄)₂ (3), [Pd(L)₂Ru₂(dafo)₄](ClO₄)₂ (4) and [Pd(L)₂Ru₂(dcbpy)₄](ClO₄)₂ (5), (where, L = ligand, bpy = 2,2′-bipyridine, phen = 1,10-phenantroline, dafo = 4,5-diazafluoren-9-one and dcbpy = 3,3′-dicarboxy-2,2′-bipyridine) have been isolated and characterized by UV-VIS, FT-IR, ¹H NMR, magnetic susceptibility measurements, elemental analysis, molar conductivity, X-ray powder techniques, thermal analyses and their morphology studied by SEM measurements. IR spectra show that the ligand acts in a tetradentate manner and coordinates N₄ donor groups of LH₂ to Pd^II ion. The disappereance of H-bonding (O−H···O) in the trinuclear Ru^II-Pd^II-Ru^II metal complexes, the Ru^II ion centered into the main oxime core by the coordination of the imino groups while the two Ru^II ions coordinate dianionic oxygen donors of the oxime groups and linked to the ligands of bpy, phen, dafo and dbpy. The X-powder results show that 1 metal complex is indicating crystalline nature, not amorphous nature. Whereas, the X-ray powder pattern of the ligand (LH₂) with 2, 3,4 and 5 exhibited only broad humps, indicating its amorphous nature. The catalytic activity of three different complexes were tested in the Suzuki coupling reaction. The 1, 4 and 5 metal complexes catalyse Suzuki coupling reaction between phenylboronic acid and arylbromides affording biphenyls. Also, the thermal results shown that the most stable complex is 1 compound while the less stable is 4 compound.     

Synthesis and molecular structures of lanthanocene amide complexes and their catalytic activity for addition of amines to nitriles

Reaction of (CH₃C₅H₄)₂LnCl(THF) with NaNHAr in a 1:1 molar ratio in THF afforded the amide complexes (CH₃C₅H₄)₂LnNHAr(THF) [(Ar = 2,6-Me₂C₆H_3, Ln = Yb (I), Y (III); Ar = 2,6-ⁱPr₂C₆H₃, Ln = Yb (II)]. X-ray crystal structure determination revealed that complexes I-III are isostructural. The central metal in each complex coordinated to two methylcyclopentadienyl groups, one amide group and one oxygen atom from THF to form a distorted tetrahedron. Complexes I-III and a known complex (CH₃C₅H₄)₂YbNⁱPr₂(THF) IV all can serve as the catalysts for addition of amines to nitriles to monosubstituted N-arylamidines. The activity depended on the central metals and amide groups, and the active sequence follows the trend IV ≈ III < I < II.     

Synthesis, structures and some chemical and electrochemical properties of E-1,2-diferrocenyl-3-methylthioprop-2-enone and its ketals

2,3-Diferrocenyl-1-methylthiocyclopropenylium iodide reacts with water, metal alkoxides, phenolates and with alcohols in the presence of Et₃N to give E-1,2-diferrocenyl-3-methylthioprop-2-enone or its ketals. Their structures were established based on data from ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The mechanistic aspects of these reactions are discussed. Electrochemical properties of 8 and 13b have been studied. The compounds present two oxidation processes (I-II), attributed to the oxidations of the ferrocenes groups, E^0′(I), E^0′(II), ΔE^0′(II-I) and comproportionation constant K_com are reported.     

Studies of β-turn opening with model peptides containing non-coded α-amino isobutyric acid

Single crystal X-ray diffraction studies show that among the three terminally protected model tripeptides I-III, Boc-Ile-Aib-Xx-OMe (Xx in peptide I: Val; II: Leu; III: Phe) with a centrally placed non-coded amino acid Aib (Aib: α-amino isobutyric acid), peptide I displays a conformational preference for β-turn, peptide II forms a hydrated β-turn representing the solvent mediated intermediate for the interconversion between β-turn and β-strand and peptide III adopts a completely unfolded β-strand like structure. By varying the steric bulk of the third residue, Xx(3), various conformations related to the structural interconversion between the β-turn and β-strand have been isolated. The peptide conformations in the solution phase have been probed by solvent dependent NMR titration and CD spectroscopy. Morphological studies with scanning electron microscopy (SEM) reveal that among the three peptides only peptide III can form filamentous fibrils in the solid state.     

Ruthenium monoterpyridine complexes with 2,6-bis(benzoxazol-2-yl)pyridine as an ancillary ligand: Synthesis,structure and spectral studies

Ruthenium monoterpyridine complexes, [1]⁺ and [2]²⁺, with 2,6-bis(benzoxazol-2-yl)pyridine as an ancillary ligand, L, have been synthesized and characterized by UV–Vis, FT-IR and ¹H NMR spectroscopic techniques. The formulations of the complexes were confirmed by the single crystal structure of their perchlorate salts. In both complexes, the Ru^II center is hexa-coordinated in a distorted geometry. In complex [1]⁺, the ancillary ligand L behaves as a bidentate ligand; in [2]²⁺, however, it binds the metal center as a tridentate ligand. The central pyridine nitrogen of terpyridine (N_p,trpy) is in a cis position with respect to the central pyridine nitrogen of the ancillary ligand (N_p,benz) in complex [1]⁺ and in a trans-position in complex [2]²⁺. The cis orientation of N_p,trpy and N_p,benz in complex [1]⁺ forces L to behave as bidentate. The quasi-reversible Ru^II/Ru^III couple appears at 0.90 and 1.44 V versus SCE in the case of complex [1]⁺ and [2]²⁺, respectively. [1]⁺, in the presence of aqueous AgNO₃, affords [2]²⁺ through an intramolecular dissociative interchange pathway.     

Modelling the use of lanthanides(III) as probes at calcium(II) binding sites in biological systems: Preparation and characterization of neodymium(III) and calcium(II) malonamato(-1) complexes

A bioinorganic approach into the problem of the isomorphous substitution of calcium(II) by lanthanide(III) ions in biological systems is discussed. Reactions of malonamic acid (H₂malm) with Ca^II and Nd^III sources under similar conditions yielded the compounds [Ca(Hmalm)₂]_n (1), [Nd(Hmalm)₂(H₂O)₂]_n(NO₃)_n (2) and [Nd(Hmalm)₂(H₂O)₂]_nCl_n·2nH₂O (3·2nH₂O). Their X-ray crystal structure data show that the malonamate(-1) ligand presents two different ligation modes and coordinates through the two carboxylate and the amide-O atoms, thus bridging three Ca^II ions in 1 and two Nd^III ions in 2 and 3·2nH₂O. Complex 1 is a 3D coordination polymer based on neutral repeating units, whereas 2 and 3·2nH₂O are 1D coordination polymers based on the same cationic repeating unit. Hydrogen bonding interactions further stabilize the 3D framework structure of 1 and assemble the 1D chains of 2 and 3·2nH₂O into 3D networks. The three complexes were characterized spectroscopically (IR, far-IR, and Raman) and the thermal decomposition of 2 and 3·2nH₂O was monitored by TG/DTA and TG/DTG measurements. Variable-temperature magnetic susceptibility data for 2 are also reported. The bioinorganic chemistry relevance of our results is discussed.     

Multi-metal complexation and partially templated synthesis of metal clusters by using triangular trisaloph ligands

On the basis of the concept of partial template, triangular trisaloph ligands 2a and 2b reacted with excess Zn^II to give heptanuclear Zn clusters with a similar geometry. The Zn complex of 2c, which was difficult to be prepared according to a previous procedure, was synthesized in high yield in a one-pot fashion. Various multi-nuclear complexes of 2a with Mn, Co, Ni, and Cu were also produced, although the trinuclear Mn^II and Co^II complexes were smoothly oxidized to the Mn^III and Co^III complexes.     

Synthesis, characterisation and catalytic activities of manganese(III) complexes of pyridoxal-based ONNO donor tetradenatate ligands

Reaction of Mn^II(CH₃COO)₂ with dibasic tetradentate ligands, N,N′-ethylenebis(pyridoxylideneiminato) (H₂pydx-en, I), N,N′-propylenebis(pyridoxylideneiminato) (H₂pydx-1,3-pn, II) and 1-methyl-N,N′-ethylenebis(pyridoxylideneiminato) (H₂pydx-1,2-pn, III) followed by aerial oxidation in the presence of LiCl gives complexes [Mn^III(pydx-en)Cl(H₂O)] (1) [Mn^III(pydx-1,3-pn)Cl(CH₃OH)] (2) and [Mn^III(pydx-1,2-pn)Cl(H₂O)] (3), respectively. Crystal and molecular structures of [Mn(pydx-en)Cl(H₂O)] (1) and [Mn(pydx-1,3-pn)Cl(CH₃OH)] (2) confirm their octahedral geometry and the coordination of ligands through ONNO(2-) form. Reaction of manganese(II)-exchanged zeolite-Y with these ligands in refluxing methanol followed by aerial oxidation in the presence of NaCl leads to the formation of the corresponding zeolite-Y encapsulated complexes, abbreviated herein as [Mn^III(pydx-en)]-Y (4), [Mn^III(pydx-1,3-pn)]-Y (5) and [Mn^III(pydx-1,2-pn)]-Y (6). These encapsulated complexes are used as catalysts for the oxidation, by H₂O₂, of methyl phenyl sulfide, styrene and benzoin efficiently. Oxidation of methyl phenyl sulfide under the optimized reaction conditions gave ca. 86% conversion with two major products methyl phenyl sulfoxide and methyl phenyl sulfone in the ca. 70% and 30% selectivity, respectively. Oxidation of styrene catalyzed by these complexes gave at least five products namely styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde with a maximum of 76.9% conversion of styrene by 4, 76.3% by 5 and 76.0% by 6 under optimized conditions. The selectivity of the obtained products followed the order: benzaldehyde > benzoic acid > styrene oxide > phenylacetaldehyde > 1-phenylethane-1,2-diol. Similarly, ca. 93% conversion of benzoin was obtained by these catalysts, where the selectivity of the products followed the order benzil > benzoic acid > benzaldehyde-dimethylacetal. Tests for the recyclability and heterogeneity of the reactions have also been carried. Neat complexes are equally active. However, the recycle ability of encapsulated complexes makes them better over neat ones.     

Magnetic coupling in EE and EO azido-bridged binuclear copper complexes: Synthesis,structure and magnetic studies

Four azide bridged dinuclear copper(II) complexes, [Cu₂(L^X)₂(N₃)₂](ClO₄)₂, with L^X = substituted N,N-bis[(3,5-dimethylpyrazole-1-yl)-methyl]benzylamine, [X = H (1), OMe (2), Me (3) and Cl (4)] have been synthesized, out of which complexes 1 and 2 have been characterized structurally. In Complex 1 the two bridging azide ligands have connected the two metal centers in an end-on (EO) fashion with aSP (asymmetric Square Pyramidal) geometry and showed an weak antiferromagnetic interaction (J = −3.34 cm⁻¹). On the contrary, in complex 2, the two metal centers have been connected in end-to-end (EE) fashion exhibiting moderately strong ferromagnetic interaction (J = +19.7 cm⁻¹). Cyclic voltammetric studies performed on all the four complexes show a reasonably good correlations when E_1/2 for Cu^IICu^II → Cu^IICu^III and Cu^IICu^III → Cu^IIICu^III oxidations are plotted against σ (substituent constants) with ρ = −0.182 (R² = 0.92) and −0.684 (R² = 0.99) respectively.