Unsymmetrical cyrhetrenyl and ferrocenyl azines derived from 5-nitrofurane: Synthesis,structural characterization and electrochemistry

A new series of unsymmetrical cyrhetrenyl and ferrocenyl azines that were monosubstituted [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)]M {with MRe(CO)₃ and RH (1a) or RMe (1b); MFe(η⁵-C₅H₅) and RH (2a) or RMe (2b)} and disubstituted [Fe{(η⁵-C₅H₄)–C(Me)N–NCH(5-NO₂–2-C₄H₂O)}₂] (3a) were prepared by condensation reactions of the corresponding organometallic hydrazone [(η⁵-C₅H₄)–C(R)N–NH₂)]M with 5-nitro-2-furaldehyde. The ¹H and ¹³C{¹H} NMR spectra indicated that these compounds adopted an (E,E)-configuration about the ˃CN − bond and an s-trans conformation about the N1–N2 bond, and this result was confirmed by X-ray crystallographic analyses of 1a and 2b. The opposite electronic effects of the organometallic fragments correlate with the co-planarity of the [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)] system, the reduction potential of the nitro group (E_1/2) and the chemical shifts of the iminic carbons.     

Preparation and characterization of carboximidate iron(II) complexes

The reactions of C₅H₄NCHNNHC(O)Ph (1) with Fe(II) chloride gave [Fe₂(C₅H₄NC(OEt)NNHC(O)Ph)₂(μ-OEt)₂Cl₂]) (2) in ethanol and [Fe₂(C₅H₄NC(OMe)NNHC(O)Ph)₂(μ-OMe)₂Cl₂] (3) in methanol as well as [Fe(C₅H₄NCHNNHC(O)Ph)Cl₂] (4) in tetrahydrofuran, respectively. The X-ray diffraction analysis reveals their structures and complex 4 is proposed as an intermediate of formation of complexes 2 and 3.     

Nonlinear optical properties in tetrametallic Fe3Mn complexes with pseudo-C3 symmetry

New type of 3D chromophores [{CpFeC₅H₄CRCH4-py}₃Mn(CO)₃]BF₄ (1) with weakly interaction subchromophore were synthesized and found to display improved nonlinearity compared with their 1D reference systems [(CpFeC₅H₄CRCH4-py)Mn(CO)₅]BF₄ (2).     

Study of the cytotoxic activity of alkenyl-substituted ansa-titanocene complexes

The cytotoxic activity on tumour cell lines, human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x and normal immunocompetent cells, was tested for four different ansa-titanocene dichloride derivatives with potentially reactive substituents [Ti{Me(CH₂CH)Si(η⁵-₅Me₄) (η⁵-C₅H₄)}Cl₂] (1), [Ti{Me(H)Si(η⁵-C₅Me₄)₂}Cl₂] (2), [Ti{Me{(CH₂CH)Me₂SiCH₂CH₂}Si(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (3) and [Ti{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃(CMe₂(CH₂CH₂CHCH₂)))}Cl₂] (4), showing a very promising activity and opening up the possibility of extensive investigation in this field.     

Palladium (II) and platinum (II) complexes containing organometallic thiosemicarbazone ligands: Synthesis,characterization, X-ray structures and antitubercular evaluation

A new series of palladium (II) and platinum (II) complexes containing ferrocenyl and cyrhetrenyl thiosemicarbazone ligands were synthesized and characterized. The two-step reaction of the organometallic thiosemicarbazones with i) K₂MCl₄ and ii) PPh₃ and their subsequent recrystallization from CH₂Cl₂/hexane yielded the binuclear complexes [Mˋ{ML_n(η⁵-C₅H₄)C(H)NNC(S)NHR}–(Cl)(PPh₃)] (M′Pd, Pt; ML_nRe(CO)₃, FeCp; RH, CH₃). The structures of the products were inferred from elemental analyses and IR, ¹H and ³¹P NMR spectroscopies. The molecular structures of 2b and 3d were confirmed by single crystal X-ray analysis. All complexes were screened in vitro against Mycobacterium tuberculosis and exhibited only moderate activity in the low micromolar range.     

Synthesis and reactivity of an 2-azabutadiene-based π-conjugated dithioether: Formation of a N,S-ligated molybdenum chelate complex and C,N,S-pincer complexes of palladium and platinum

Nucleophilic attack of sodium isopropylthiolate on 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl₂CC(H)–NCPh₂}] (1) affords the 2-azabutadiene derivative [(i-PrS)₂CC(H)–NCPh₂] (2). Upon irradiation of Mo(CO)₆ in THF in the presence of 2, the chelate complex cis-[(OC)₄Mo{(i-PrS)₂CC(H)–NCPh₂}] (3) is obtained. Coordination on Mo occurs through the imine nitrogen and a thioether group. Polydentate dithioether 2 acts as N,C,S-pincer ligand after orthometallation reaction with Pd(II) or Pt(II). The molecular structures of 2 and (C,N,S)-[(i-PrS)₂CC(H)–NC(Ph)C₆H₄)PtCl] (4b) have been determined by X-ray diffraction studies.     

A new imine ligand avoiding imine–enamine rearrangement and cyclometallation: Synthesis and coordination of Me3C6H2CH2NCHtBu

The new imine ligand (E)-2,4,6-Me₃C₆H₂CH₂NCH^tBu (1) has been prepared from 2,4,6-trimethylbenzylamine and trimethylacetaldehyde. In this imine, the ortho-positions of the benzyl group are blocked by methyl groups, and there are no β-hydrogen atoms susceptible for imine–enamine rearrangement. Thus, reaction with [PdCl₂(C₆H₅CN)₂] leads to the complex trans-[PdCl₂(2,4,6-Me₃C₆H₂CH₂NCH^tBu)₂] (2) that cannot undergo cyclopalladation. The single-crystal X-ray structure analysis of trans-[PdCl₂(2,4,6-Me₃C₆H₂CH₂NCH^tBu)₂] (2) confirms the trans-coordination of the imine ligands in this square-planar complex.     

Synthesis and structural characterizations of organolanthanide complexes with amino-tethered guanidinate ligand (C5H5)2Ln[H2N(CH2)3NC(NHiPr) NiPr)] (Ln = Yb,Y, Er,Dy)

Reaction of N,N′-diisopropylcarbodiimide (ⁱPrNCNⁱPr) with H₂N(CH₂)₃NH₂ and (C₅H₅)₃Ln, give (C₅H₅)₂Ln[H₂N(CH₂)₃NC(NHⁱPr) NⁱPr)] in high yields, indicating that the N–H bonds of one NH₂ group readily add to the CN double bonds of carbodiimide and one cyclopentadienyl group is eliminated to construct a novel amino-tethered guanidinate anionic ligand [H₂N(CH₂)₃N C(NHⁱPr)NⁱPr)]⁻.     

Preparation of high-temperature stable SiBCN fibers from tailored single source polyborosilazanes

Bulk SiBCN ceramics derived from polyborosilazanes of the type [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H; C₂H₄ = CHCH₃, CH₂CH₂) exhibit an exceptional structural stability at high temperature. Therefore, such quaternary systems are of great scientific and technical interest as fibrous reinforcements intended for high-temperature applications. In this context, the design of novel polyborosilazanes, which display properties tailored for the preparation of SiBCN fibers, is studied. Boron-modified polysilazanes of the type [B(C₂H₄SiRNCH₃)₃]_n (1b, R = CH₃; 2b, R = H) are prepared via aminolysis of the tris(dichlorosilylethyl)boranes B(C₂H₄SiRCl₂)₃ (1, R = CH₃; 2, R = H). It is shown that the functionalisation of the precursors with NCH₃ units improves their processability (i.e. solubility) compared to that of their ammonolysed analogs [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H). In addition to the influence of the NCH₃ units, the presence of the SiCH₃ functions in such polymers offers the best potential for the preparation of fibers by melt-spinning. As-spun fibers are then converted under controlled atmosphere into high-temperature stable SiBCN fibers according to the polymer-derived ceramic route.     

Schiff pentadentate ligands based on an [ON2O2] core displaying structural isomerism and their coordination to dibutyltin moieties

Two tin compounds [Sn(ⁿBu)₂(Lⁿ)], where L¹{O(C₆H₄-2-NC(H)C₆H₄-2′-O)₂}^2 − and L²{O(C₆H₄-2-C(H)NC₆H₄-2′-O)₂}^2 − enclosing five electron donors in an [ON₂O₂] core, were synthesized and structurally characterized by infrared and NMR spectroscopy and by single crystal X-ray crystallographic studies at room temperature. The hepta-coordinate geometry around the Sn centers is achieved through the bonding of two monodentate n-butyl groups and the coordination of the pentadentate Lⁿ ligands, where the [ON₂O₂] core is forming a pentagonal base. The two types of oxygen atoms displayed different bonding situations around the Sn atom. DFT calculations with Gaussian 09 using PBEPBE/6-31G**/SDD level were carried out for both compounds. The topological analysis indicated that bond critical points are present along the SnO_ether direction.     

Tetra(o-phenyldiazo-p-methylphenoxy)silane – A silicon complex with a fourfold capped-tetrahedral [4+4] coordination sphere

2-Hydroxy-5-methylazobenzene (HO–C₆H₃-p-Me-o-NN–C₆H₅, 1) reacts with SiCl₄ in the presence of triethylamine to yield the [4+4]-coordinate silicon complex 2 [Si(O–C₆H₃-p-Me-o-NN–C₆H₅)₄]. Its molecular structure has been determined by X-ray crystallography, and 2 represents the first structurally characterized Si-complex bearing o-diazophenoxy ligands. ²⁹Si NMR data suggest that the capped tetrahedral coordination sphere of the Si-atom is retained in solution. Even the difluorocompound 3 [F₂Si(O–C₆H₃-p-Me-o-NN–C₆H₅)₂] still exhibits a tetracoordinate Si-atom, whereas 4 [F₂B(O–C₆H₃-p-Me-o-NN–C₆H₅)], the byproduct of the formation of 3 from 2, bears a bidentate chelating o-phenyldiazo-p-methylphenoxy ligand.     

Thermally stable pseudo-third-generation Grubbs ruthenium catalysts with pyridine–phosphinimine ligand

The ligand precursors 2-(R₃PN)CH₂Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl₂(CHPh)(Py)₂(H₂IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl₂(CHPh)(PyCH₂(NPR₃))(H₂IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.     

Activity of Mo(II) allylic complexes supported in MCM-41 as oxidation catalysts precursors

[Mo(η³-C₃H₅)X(CO)₂(NCCH₃)₂] (X = Br, 1a; X = Cl, 1b) complexes reacted with the bidentate ligand RNC(Ph)–C(Ph)NR, R = (CH₂)₂CH₃ (DAB, 2) affording [Mo(η³-C₃H₅)X(CO)₂(DAB)] (X = Br, 4a; X = Cl, 4b), which were characterized by elemental analysis, FTIR and ¹H and ¹³C NMR spectroscopy. The modified silylated ligand RNC(Ph)C(Ph)NR, R = (CH₂)₃Si(OCH₂CH₃)₃ (DAB–Si, 3), was used to immobilize the two complexes in MCM-41 (MCM) mesoporous silica. The new materials were characterized by powder X-ray diffraction, N₂ adsorption analysis, FTIR and ²⁹Si and ¹³C CPMAS solid state NMR spectroscopy. Both the materials and the complexes were tested in the oxidation of cyclooctene and styrene and behaved as active catalyst precursors for cyclooctene and styrene epoxidation with TBHP (t-butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs. Although the homogeneous systems reach 100% conversion of cyclooctene and slightly less for styrene, the loss of catalytic activity in the heterogeneous systems is small, with a 98% conversion of styrene achieved by the chloride containing material.     

Synthesis of an osmafuran from photochemical hydrolysis of OsCl2(CHC(PPh3)C(O)-η2-CHCH2)(PPh3)2

The η²-alkene coordinated α,β-unsaturated ketone complex Os(CHC(PPh₃)C(O)-η²-CHCH₂)Cl₂(PPh₃)₂ (3) is very stable even at elevated temperature due to the strong steric hindrance effect of PPh₃ ligands. However, compound 3 in a chloroform solution can be almost quantitatively converted into the corresponding osmafuran [OsCl(CO)(PPh₃)₂(CHC(PPh₃)C(CH₃)O)]Cl (6) via hydrolysis of the η²-coordinated olefin under photochemical conditions. Osmafuran 6 has been characterized by single crystal X-ray diffraction analysis, NMR spectroscopy and elemental analysis data. The UV-induced reaction provides a new highly efficient method for preparation of osmafurans by hydrolysis of η²-α,β-unsaturated ketone complexes.     

Polymerizable inorganic–organic hybrid: Syntheses and structures of mono-lacunary Dawson polyoxometalate-based olefin-containing organosilyl derivatives

Three olefin-containing organosilyl derivatives supported on the mono-lacunary Dawson polyoxometalate (POM), [α₂-P₂W₁₇O₆₁{(RSi)₂O}]⁶⁻ (R = {CH₂C(CH₃)COO(CH₂)₃}, {CH₂CHCOO(CH₂)₃} and {CH₂CH}), as Me₂NH₂ salts, which can act as precursors for the immobilization of the POMs in polymer networks, were obtained by the 2:1 molar ratio reaction of the organosilyl precursor RSi(OCH₃)₃ with K₁₀[α₂-P₂W₁₇O₆₁] · 19H₂O in acidic MeOH/H₂O mixed solutions. X-ray crystallography revealed that the two organic chains connected through an –Si–O–Si– bond were grafted onto the mono-lacunary site of the POM. The four-coordination of each Si atom was attained with the bridging oxygen atom, the terminal organic group R in the organosilyl group, and 2 of the 4 oxygen atoms in the mono-lacunary site of the POM.     

Synthesis,spectroscopic and structural aspects of triphenylantimony(V) complex with internally functionalized acetylferroceneoxime: Crystal and molecular structures of [C5H5FeC5H4C(CH3)NO]2SbPh3 and C5H5FeC5H4C(CH3)NOH

Triorganoantimony(V) complex (C₅H₅FeC₅H₄C(CH₃)NO)₂SbPh₃ (1) has been prepared by the reaction of Ph₃SbCl₂ with acetylferroceneoxime C₅H₅FeC₅H₄C(CH₃)NOH (2) in 1:2 molar ratio in anhydrous toluene. The complexes have been characterized by elemental analyses, IR and NMR (¹H and ¹³C) spectroscopic studies, and biologic activity was measured. And crystal structures of 1, 2 were reported. The coordination geometry around the antimony atom in 1 was slightly distorted trigonal bipyramidal with the carbon atoms of the SbPh₃ unit in equatorial positions and the two oxygen atoms of the oxime group occupying axial positions. The free oxime was clearly hydrogen bonded (H–N 2.10 Å/2.04 Å in 2) to essentially form a dimer.     

Novel push–pull butadienes derived from 1,1-diaryl-2-propyn-1-ols and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione: Synthesis,absorption spectra and solvatochromic behaviour

Butadiene dyes were synthesized by the catalytic C–C coupling of 1,1-diaryl-2-propyn-1-ols with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione. The reaction, which was promoted by the 16e⁻ (η³-allyl)-ruthenium(II) complex [Ru(η³-2-C₃H₄Me)(CO)(dppf)][SbF₆], involved the Meyer–Schuster rearrangement of the aromatic alkynol and subsequent aldol-type condensation of the resulting enal with the fluorinated β-dicarbonyl compound. The absorption spectra of the dyes, as well as their solvatochromic behaviour, were studied; the structure of (4-C₆H₄OMe)₂CCH–CHC(COCF₃)₂ was unambiguously confirmed by means of single-crystal X-ray diffraction.     

Catalytic reactions of dioxygen with ethane and methane on platinum clusters: Mechanistic connections,site requirements,and consequences of chemisorbed oxygen

C₂H₆ reactions with O₂ only form CO₂ and H₂O on dispersed Pt clusters at 0.2–28 O₂/C₂H₆ reactant ratios and 723–913 K without detectable formation of partial oxidation products. Kinetic and isotopic data, measured under conditions of strict kinetic control, show that CH₄ and C₂H₆ reactions involve similar elementary steps and kinetic regimes. These kinetic regimes exhibit different rate equations, kinetic isotope effects and structure sensitivity, and transitions among regimes are dictated by the prevalent coverages of chemisorbed oxygen (O^*). At O₂/C₂H₆ ratios that lead to O^*-saturated surfaces, kinetically-relevant CH bond activation steps involve O^*O^* pairs and transition states with radical-like alkyls. As oxygen vacancies (¹) emerge with decreasing O₂/alkane ratios, alkyl groups at transition states are effectively stabilized by vacancy sites and CH bond activation occurs preferentially at O^** site pairs. Measured kinetic isotope effects and the catalytic consequences of Pt cluster size are consistent with a monotonic transition in the kinetically-relevant step from CH bond activation on O^*O^* site pairs, to CH bond activation on O^** site pairs, to O₂ dissociation on ^** site pairs as O^* coverage decrease for both C₂H₆ and CH₄ reactants. When CH bond activation limits rates, turnover rates increase with increasing Pt cluster size for both alkanes because coordinatively unsaturated corner and edge atoms prevalent in small clusters lead to more strongly-bound and less-reactive O^* species and lower densities of vacancy sites at nearly saturated cluster surfaces. In contrast, the highly exothermic and barrierless nature of O₂ activation steps on uncovered clusters leads to similar turnover rates on Pt clusters with 1.8–8.5 nm diameter when this step becomes kinetically-relevant at low O₂/alkane ratios. Turnover rates and the O₂/alkane ratios required for transitions among kinetic regimes differ significantly between CH₄ and C₂H₆ reactants, because of the different CH bond energies, strength of alkylO^* interactions, and O₂ consumption stoichiometries for these two molecules. Vacancies emerge at higher O₂/alkane ratios for C₂H₆ than for CH₄ reactants, because their weaker CH bonds lead to faster scavenging of O^* and to lower O^* coverages, which are set by the kinetic coupling between CH and OO activation steps. The elementary steps, kinetic regimes, and mechanistic analogies reported here for C₂H₆ and CH₄ reactions with O₂ are consistent with all rate and isotopic data, with their differences in CH bond energies and in alkyl binding, and with the catalytic consequences of surface coordination and cluster size. The rigorous mechanistic interpretation of these seemingly complex kinetic data and cluster size effects provides useful kinetic guidance for larger alkanes and other catalytic surfaces based on the thermodynamic properties of these molecules and on the effects of metal identity and surface coordination on oxygen binding and reactivity.     

Bridge-splitting of trans-[PtCl2(η2-CH2CH2)]2 by weak nucleophiles: Crystal and molecular structure of trans-[PtCl2(η2-CH2CH2)(MeCN)]

Bridge-splitting of trans-[PtCl₂(η²-CH₂CH₂)]₂, 1, by L in dichloromethane yields trans-[PtCl₂(η²-CH₂CH₂)(L)] (L = THF, 2, or MeCN, 3) with bridge-splitting equilibrium constants of 0.0289 ± 0.0007 and 3601 ± 215 mol^?1 dm³, respectively, as determined by UV/Vis measurements. The reaction of 3 in MeCN with Cl^? is essentially quantitative. The crystal structure of trans-[PtCl₂(η²-CH₂CH₂)(CH₃CN)] is reported.     

Aspartic acid in a new role: Synthesis and application of a pH-responsive cyclopolymer containing residues of the amino acid

The reaction between diallylamine and dimethyl maleate afforded the Michael addition product dimethyl N,N-diallylaspartate [(CH₂CH–CH₂)₂NCH(CO₂Me)CH₂CO₂Me] I, which upon treatment with dry HCl and ester hydrolysis with aqueous HCl gave its hydrochloride salt [(CH₂CH–CH₂)₂NH⁺CH(CO₂Me)CH₂CO₂Me Cl⁻] II and N,N-diallylaspartic acid hydrochloride [(CH₂CH–CH₂)₂NH⁺CH(CO₂H)CH₂CO₂H Cl⁻] III, respectively. The new monomers II and III underwent cyclopolymerization to give, respectively, cationic polyelectrolytes (CPEs) poly(II) and poly(III). Under the influence of pH, triprotic acid (+) poly(III) was equilibrated to water-insoluble diprotic polyzwitterionic acid (±) IV, water-soluble monoprotic poly(zwitterion–anion) (± −) V, and its conjugate base polydianion (=) VI. The protonation constants of the carboxyl group and trivalent nitrogen in VI have been determined. A 20-ppm concentration of IV is effective in inhibiting the precipitation of CaSO₄ from its supersaturated solution with an ≈ 100% scale inhibition efficiency for a duration of 50 h at 40 °C. The aqueous two-phase systems (ATPSs) of VI and polyoxyethylene have been studied. The transformation of water-soluble VI to insoluble IV makes it a recycling ATPS as it can be recycled by precipitation at a lower pH.