Hybrid scorpionate/cyclopentadienyl titanium and zirconium complexes with alkoxide and imido ligands

The reactivity of hybrid scorpionate/cyclopentadienyl ligand-containing trichloride zirconium complexes [ZrCl₃(bpzcp)] (1) [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] and [ZrCl₃(bpztcp)] (2) [bpztcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl] toward several lithium alkoxides has been carried out. Thus, alkoxide-containing complexes [ZrCl₂(OR)(bpzcp)] (R = Me, 3; Et, 4; ⁱPr, 5; (R)-2-Bu, 6), [ZrCl₂(OR)(bpztcp)] (R = Me, 7; Et, 8; ⁱPr, 9; (R)-2-Bu, 10) and [Zr(OR)₃(bpztcp)] (R = Et, 11; ⁱPr, 12) were prepared by deprotonation of the appropriate alcohol group with BuⁿLi followed by reaction with 1 or 2. In addition, the imido-complex [Ti(N^tBu)Cl(bpztcp)(py)] (13) were also prepared. The structures of these complexes have been proposed on basis of spectroscopic and DFT methods.     

Ruthenium complexes containing tertiary phosphines and imidazole or 2,2′-bipyridine ligands

Complexes RuCl₃(PPh₃)L₂ (L = MeIm (1a, Im (1b)) and [RuCl₂(PPh₃)₂(bipy)]Cl·4H₂O (2) have been synthesized via the ruthenium(III) precursor RuCl₃(PPh₃)₂ (DMA), and characterized, including an X-ray structural analysis for 1a (MeIm = N-methylimidazole, Im = imidazole, bipy = 2,2′-bipyridyl, and DMA = N, N′-dimethylacetamide). Crystals of 1a are monoclinic, space group P2₁/n, A = 10.5491(5), B = 20.4934(9), C = 12.8285(4) Å, β = 90.166(4)°, Z = 4. The structure, which reveals a mer configuration for the chlorides, and cis-methylimidazoles, was solved by conventional heavy atom methods and was refined by full-matrix least-square procedures to R = 0.041 and R_w = 0.042 for 3328 reflections with I 3σ(I). From the RuCl₂(PPh₃)₃ precursor, the ruthenium(II) complexes RuCl₂(PPh₃)₂L₂ and [RuCl(PPh₃)L₄]Cl have been made (L = Im or MeIm), while [RuCl(dppb)Im₃]Cl has been made from [RuCl₂(dppb)]₂(μ-dppb) (dppb = Ph₂P(CH₂)₄PPh₂).     

The reactions of nitrogen trichloride with some tertiary phosphines

Nitrogen trichloride reacts with trimethyl-, triethyl-, tri-n-butyl-, and triphenylphosphine to yield dichlorophosphoranes of the general formula R₃PCl₂ plus dinitrogen. Nitrogen trichloride reacts with phosphorus trichloride to yield phosphorus pentachloride plus dinitrogen. Chloramine reacts with phosphorus trichloride to yield a mixture of dichlorophosphazene trimer and tetramer.     

Some interactions of L-DOPA and its related compounds with glutamate receptors

L-DOPA is probably a transmitter and/or modulator in the central nervous system (1). L-DOPA methyl ester (DOPA ME) is a competitive L-DOPA antagonist. However, it remains to be clarified whether there exist L-DOPAergic receptors. In Xenopus laevis oocytes injected with rat brain poly(A)+ RNA, L-DOPA induced small inward currents with ED50 of 2.2 mM at a holding potential of -70 mV. The currents were abolished by kynurenic acid or CNQX. Similar L-DOPA-currents were seen in oocytes co-injected with AMPA receptors, GluRs1,2,3 and 4. In brain membrane preparations, L-DOPA inhibited specific binding of [3H]-AMPA with IC50 of 260 microM. This inhibition was not modified by 200 microM ascorbic acid, an antioxidant. L-DOPA did not inhibit binding of [3H]-ligands of MK-801, kainate, DCKA and CGP39653. DOPA ME and L-DOPA cyclohexyl ester, a novel, potent and competitive antagonist (2), inhibited specific binding of [3H]-MK-801 with respective IC50 of 1 and 0.68 mM, but elicited no effect on that of the other [3H]-ligands. With low affinities, L-DOPA acts on AMPA receptors, while competitive antagonists act on NMDA ion channel domain. L-DOPAergic agonist and antagonist may not interact on ionotropic glutamate receptors. DOPA ME-sensitive L-DOPA recognition sites (1) seem to differ from glutamate receptors.     

Reactions of 2-thiopyridone rhodium(III) complexes with tertiary phosphines

The rhodium(III) complexes containing 2-thiopyridone (pySH) and its conjugate anion 2-thiopyridonato (pyS) as the only ligands, [Rh(pyS)₂(pySH)₂]Cl, [Rh(pyS)₃(pySH)], and [Rh(pyS)₃], react with the tertiary phosphines PMe₂Ph, PPh₃, Ph₂PCH₂PPh₂ (dppm), and Ph₂PCH₂CH₂PPh₂ (dppe) to give mixed pyS/tertiary phosphine complexes of the type [Rh(pyS)₃L], [Rh(pyS)₃L₂], and [Rh(pyS)₂L₂]ClO₄ where L represents a single phosphorus donor atom. These compounds were characterized mainly by ¹H and ³¹P NMR spectroscopy.     

Structural characterization of several cadmium halides with N-donor ligands

Five cadmium halides with N-donor ligands were synthesized under the hydrothermal conditions and characterized by X-ray single-crystal diffraction. The isostructural [CdX₂(2,2′-bpy)] (X = I 1, Br 2, bpy = bipyridine) (1) possess 3-D supramolecular network structures based on 1-D zigzag-type CdX₂ chains extended by bpy molecules via non-covalent C-H?X hydrogen-bonded interactions. The 3-D porous [CdBr₂(pip)] (pip = piperazine) (3) is formed through a linkage of 1-D zigzag-type CdBr₂ chains by pip bridges. The heteronuclear dimetal-iodo cluster [Cu(phen)₂CdI₄] (phen = phenanthroline) (4) consists of a trigonal bipyramidal Cu(II) center and a tetrahedral Cd(II) center linked by a μ₂-I bridge. The ionic [Co(dien)₂][CdI₄] (dien = diethylenetriamine) (5) comprises an octahedral cation and a tetrahedral anion.     

New pyridyl modified phosphines: Synthesis and late transition-metal coordination studies

Using a phosphorus based Mannich condensation reaction the new pyridylphosphines {5-Ph₂PCH₂N(H)}C₅H₃(2-Cl)N (1-Cl) and {2-Ph₂PCH₂N(H)}C₅H₃(5-Br)N (1-Br) have been synthesised in good yields (60% and 88%, respectively) from Ph₂PCH₂OH and the appropriate aminopyridine. The ligands 1-Cl and 1-Br display variable coordination modes depending on the choice of late transition-metal complex used. Hence P-monodentate coordination has been observed for the mononuclear complexes AuCl(1-Cl) (2), AuCl(1-Br) (3), RuCl₂(p-cymene)(1-Cl) (4), RuCl₂(p-cymene)(1-Br) (5), RhCl₂(Cp^∗)(1-Cl) (6), RhCl₂(Cp^∗)(1-Br) (7), IrCl₂(Cp^∗)(1-Cl) (8), IrCl₂(Cp^∗)(1′-Cl) (8′), IrCl₂(Cp^∗)(1-Br) (9), cis-/trans-PdCl₂(1-Cl)₂ (10), cis-/trans-PdCl₂(1-Br)₂ (11), cis-PtCl₂(1-Cl)₂ (12) and cis-PtCl₂(1-Br)₂ (13). Reaction of Pd(Me)Cl(cod) (cod = cycloocta-1,5-diene) with either 1 equiv. of 1-Br or the known pyridylphosphines 1′-Cl, 1-OH or 1-H gave the P/N-chelate complexes Pd(Me)Cl(1-Br-1-H) (14)-(17). All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 4, 5, 10 and 16 · (CH₃)₂SO have been elucidated by single crystal X-ray crystallography. A crystal structure of the dinuclear metallocycle trans,trans-[PdCl₂{μ-P/N-{Ph₂PCH₂N(H)}C₅H₄N}]₂ · CHCl₃, 18 · CHCl₃, has also been determined. Here 1-H bridges, using both P and pyridyl N donors, two dichloropalladium centres affording a 12-membered ring with the PdCl₂ units adopting a head-to-tail arrangement.     

Organoiridium compounds with bidentate phosphines as highly regioselective catalysts for alkynes cyclotrimerization

The iridium derivatives HIr(cod)(L-L) (cod=1,5-cyclooctadiene; L-L=Ph₂PCH₂PPh₂ (dppm); Ph₂P(CH₂)₂PPh₂ (dppe); Ph₂P(CH₂)₃PPh₂ (dppp); Ph₂P(CH₂)₄PPh₂ (dppb); o-C₆H₄(PPh₂)₂; Cy₂P(CH₂)₂PCy₂ (dcpe); o-Me₂NC₆H₄PPh₂ (P-NMe₂)) and Ir(OMe)(cod)(dppe-F) (dppe-F=(C₆F₅)₂P(CH₂)₂P(C₆F₅)₂) are active catalysts for the cyclotrimerization of phenylacetylene and substituted derivatives. The nature of the phosphine ligand has a pronounced effect on catalytic activity and selectivity of the reactions: in some cases (L-L=dcpe, dppe-F) mixtures of oligomerization and polymerization products are obtained, in others only cyclomerization is observed, with regioselectivities as high as 100% of the 1,2,4-trisubstituted benzenes in the reactions catalyzed by HIr(cod)(dppm). The observed regioselectivity is discussed in terms of preferential formation of one of the possible metallacyclic intermediates of the catalytic reaction.     

Mononuclear rhodium and iridium compounds with pyridyl-pyrazole ligands

Neutral [MCl(L₂)(Hpzpy)], [M(L₂)(pzpy)] and cationic [M(L₂)(Hpzpy)]CF₃SO₃ rhodium(I) or iridium(I) complexes [M = Rh or Ir; L₂ = diolefin or (CO)₂; pzpy = 3-(2-pyridyl)pyrazolate] have been prepared; the pzpy and Hpzpy ligands coordinate to the metal as bidentate chelate groups through one pyrazole nitrogen and the pyridine nitrogen atom. The reactivity of these complexes towards oxidative addition reactions of halogens, methyl iodide or triflic acid and towards displacement reactions has been studied. The neutral and cationic iridium(I) complexes are modest catalysts for the hydrosilylation of phenylacetylene with triethylsilane at 60 °C. The complexes have been characterised by analytical and spectroscopic data; their configuration has been confirmed by COSY and NOESY experiments and the molecular structure of [Rh(COD)(Mepzpy)(PPh₃)]CF₃SO₃ has been established by an X-ray diffraction study.     

Aluminium reactions with polygalacturonate and related organic ligands

Aluminium (Al), in inorganic monomeric forms, has been recognised as a limiting factor for root growth in many acid soils. Plant tolerance to Al may be achieved by the detoxification (complexation) of Al by organic ligands present in the rhizosphere. The Al-complexing ability of seven organic ligands, citric, oxalic, gluconic, glucuronic, mucic, galacturonic and polygalacturonic (pectin) acids, was investigated. The proportion of organically-complexed Al was determined using colorimetric methods based on differences in reaction rate with pyrocatechol violet or aluminon. The colorimetric methods confirmed that citric acid forms a strong complex with Al at pH 4.2. In contrast, pectin and related organic ligands weakly complexed Al in acidic conditions. In an additional study, the Al-binding ability of pectin and Ca-pectate was compared at a biologically significant concentration of 32 µM Al. Only 29% of free Al remained in solution in the presence of Ca-pectate, while 54% remained when pectin was present. This suggests that Ca-pectate, rather than pectin, is responsible for binding Al in root cell walls and consequently plays an important role in Al toxicity to plants. Root growth of mungbean (Vigna radiata (L.) Wilczek) confirmed differences in the ability of citrate, oxalate and galacturonate to complex Al.     

Influence of dodecyltrimethylammonium halides on interaction of phenyltin compounds with model membranes

The effects were studied of dodecyltrimethylammonium chloride (DTAC), dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium iodide (DTAI) on thermotropic phase behaviour of phosphatidylcholine bilayers, as well as on 1H NMR and 31P NMR spectra, in the presence of diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT). The obtained results indicate that in the presence of the surfactant studied the interaction of phenyltin compounds with model membranes was changed and the changes depended on the kind of the counterion. The surfactants studied (especially DTAC) decrease the ability of phenyltin compounds to induce structural changes in the bilayer. It is suggested that DTAB, and especially DTAC, prevent DPhT induced interdigitated phase formation as well as formation of an inverted hexagonal phase (H(II)) in the case of TPhT/DPPC liposomes.     

Titanium, zirconium and hafnium halide complexes of trithioether and triselenoether ligands

The reaction of TiX₄(X=Cl or Br) with the tripodal ligands MeC(CH₂SMe)₃ or MeC(CH₂SeMe)₃, (L³) in anhydrous n-hexane or CH₂Cl₂ produced the extremely moisture sensitive complexes [TiX₄(L³)]. These were characterised by microanalysis, IR, UV-Vis and variable temperature ¹H,¹³C{¹H} and ⁷⁷Se NMR spectroscopy. The NMR studies showed that in solution in CH₂Cl₂ the complexes contain L³ bound as bidentates, and that pyramidal inversion and exchange between the free and coordinated chalcogen donors is rapid at room temperature. Ligand dissociation/exchange increases TiCl₄<TiBr₄ and MeC(CH₂SMe)₃<MeC(CH₂SeMe)₃ and attempts to isolate TiI₄ analogues were unsuccessful. The reactions of [MCl₄(Me₂S)₂] (M=Zr or Hf) with (L³) in anhydrous CH₂Cl₂ produces white or cream 7-coordinate [MCl₄(L³)], which are insoluble in chlorocarbon solvents. The reactions of TiX₄ (X=Cl, Br or I) with the trithia-macrocycles [9]aneS₃ and [10]aneS₃ produced [TiX₃([n]aneS₃)]X, whilst reaction of TiCl_4, SbCl₅ and [9]aneS₃ in anhydrous CH₂Cl₂ gave [TiCl₃([9]aneS₃)]SbCl₆. Spectroscopic studies suggest these macrocyclic compounds contain 6-coordinate cations, [TiX₃([n]aneS₃)]⁺ (n=9 or 10) but with Zr and Hf the complexes [MCl₄([n]aneS₃)] are 7-coordinate and neutral.