Palladium(II) chloride complexes of bis(pyrazolyl)cyclotriphosphazenes

Reactions of the bis(3,5-dimethylpyrazolyl)cyclotriphosphazene derivatives gem-N3P3(MeNCH(2)CH(2)O)(2)(dmp)(2) (1) and nongeminal cis-N3P3(OPh)(4)(dmp)(2) (2) with PdCl2 afford complexes of the type [PdCl2.(L)] (L = 1 or 2). In these complexes, the phosphazenes act as bidentate NN-donor ligands with the two pyrazolyl pyridinic nitrogen atoms bonded to the metal, thus forming a six- and an eight-membered chelate ring, respectively. The structures of 2 and [PdCl2.(2)] (4) have been confirmed by single-crystal X-ray diffraction. Crystal data for 2: a = 16.759(2) Angstrom, b = 10.788(3) Angstrom, c = 19.635(9) Angstrom, beta = 101.61(3)degrees, P2(1/c), Z = 4, R = 0.038 for 4688 reflections with F > 5 sigma(F). Crystal data for 4: a = 9.701(3) Angstrom, b = 24.853(4) Angstrom, c = 15.794(4) Angstrom, beta = 101.46(2)degrees, P2(1/n), Z = 4, R = 0.030 for 5416 reflections with F > 5 sigma(F).

Stereochemical properties and x-ray structure of a water-soluble diastereomeric (arene)ruthenium(II) Schiff-base complex: [Ru(.eta.-MeC6H4Pri-p)(H2O)(L*)](ClO4), containing a weakly bound aqua ligand [HL* = (S)-(.alpha.-methylbenzyl)salicylaldimine]

An air-stable and water-soluble diastereomeric half-sandwich ruthenium(I1) complex, [Ru(s-MeCsH4Pr'-p)(H*O)-(L*)] (C104) (l), has been isolated and structurally characterized [HL* = (27)-(a methylbenzyl)salicylaldimine,2-HOC6H4CH-NCHMePhI. Complex 1, Czd-I3oNO&lRu, crystallizes in the noncentric triclinic space group P1 with a = 9.885(1) A, b = 10.185(1) A, c = 14.187(2) A, a = 110.32(1)', 6 = 102.17(1)', y = 102.41(1)O, V=1243( 1) A3, and 2 = 2. The X-ray structure shows the presence of two diastereomers in a 1:l ratio having RR,,,SCand SR,,,&c onfigurations. The Ru-OHz bond distances are considerably long, and the values for RR, - a~n d SRu-1isomers are 2.1 19(5) and 2.203(5) A, respectively. The aqua complex (1) exists as a single diastereomer in solution,and it forms stable adducts with P-, N-, and halide-donor ligands. The stereochemical changes associated with adduct-forming reactions follow an inversion order: PPhs >> P(OMe)3 > pyridine bases >> halides (I, Br, Cl) >H20.

Studies of phosphazenes. Part 34. group 6 metal carbonyl complexes of bis(pyrazolyl)cyclotriphosphazenes

Reactions of the bis(3,5-dimethylpyrazol-1-yl)cyclotriphosphazenes gem-N3P3Ph4(C3HN2Me2)2 (L1) and N3P3(MeNCH2CH2O)2(C3HN2Me2)2 (L2) with [M(CO)6] (M = Mo or W) afford complexes of the type [M(CO)3L] (L = L1 or L2), which have been characterised by IR and NMR spectroscopic data. The structures of [Mo(CO)3L1], [W(CO)3L2] and the ligand L2 have been determined by single-crystal X-ray diffraction. The phosphazenes act as novel tridentate NNN-donor ligands with two pyrazolyl nitrogen atoms and one phosphazene ring nitrogen atom bonded to the metal atom

The first bis(phosphine) monoxide (BPMO) complexes of copper(I)

Copper(l) complexes of bis(phosphine) monoxide ligands, bis(diphenylphosphino)ethane monoxide (dppeo) and bis(diphenylphosphino)methane monoxide (dppmo) have been prepared and characterized. One of the complexes with dppeo was characterized by X-ray crystal structure analysis confirming Cu(I) coordination to hard and soft donors. The stability of these complexes in solution was probed via spectroscopic and electrochemical studies. Copper(I) is more readily oxidized in the presence of the hard 0 donor ligands. In solution, they readily exchange the hard donor O, for soft ligands. Although copper(l) prefers soft ligands and is more stable towards oxidation in their presence, it coordinates to hard donors when there is electrostatic or an entropy driven advantage. (C) 2002 Elsevier Science Ltd. All rights reserved.

Self-assembled ZnO nanoparticles on ZnO microsheet: ultrafast synthesis and tunable photoluminescence properties

We report on the tunable photoluminescence characteristics of porous ZnO microsheets fabricated within 1-5 min of microwave irradiation in the presence of a capping agent such as citric acid, and mixture of citric acid with polyvinylpyrrolidone (PVP). The UV emission intensity reduces to 60% and visible emission increases tenfold when the molar concentration of citric acid is doubled. Further diminution of the intensity of UV emission (25%) is observed when PVP is mixed with citric acid. The addition of nitrogen donor ligands to the parent precursor leads to a red shift in the visible luminescence. The deep level emission covers the entire visible spectrum and gives an impression of white light emission from these ZnO samples. The detailed luminescence mechanism of our ZnO samples is described with the help of a band diagram constructed by using the theoretical models that describe the formation energy of the defect energy levels within the energy band structure. Oxygen vacancies play the key role in the variation of the green luminescence in the ZnO microsheets. Our research findings provide an insight that it is possible to retain the microstructure and simultaneously introduce defects into ZnO. The growth of the ZnO microsheets may be due to the self assembly of the fine sheets formed during the initial stage of nucleation.

Contrasting Electronic Requirements for C-H Binding and C-H Activation in d(6) Half-Sandwich Complexes of Rhenium and Tungsten

A computational study of the interaction half-sandwich metal fragments (metal=Re/W, electron count=d(6)), containing linear nitrosyl (NO+), carbon monoxide (CO), trifluorophosphine (PF3), N-heterocyclic carbene (NHC) ligands with alkanes are conducted using density functional theory employing the hybrid meta-GGA functional (M06). Electron deficiency on the metal increases with the ligand in the order NHC < CO < PF3 < NO+. Electron-withdrawing ligands like NO+ lead to more stable alkane complexes than NHC, a strong electron donor. Energy decomposition analysis shows that stabilization is due to orbital interaction involving charge transfer from the alkane to the metal. Reactivity and dynamics of the alkane fragment are facilitated by electron donors on the metal. These results match most of the experimental results known for CO and PF3 complexes. The study suggests activation of alkane in metal complexes to be facile with strong donor ligands like NHC. (C) 2015 Wiley Periodicals, Inc.

Design, Synthesis, and Study of Novel Platforms for Iron-N2 Chemistry and Photoinduced, Copper-mediated C-N Bond Formation

Several new ligand platforms designed to support iron dinitrogen chemistry have been developed. First, we report Fe complexes of a tris(phosphino)alkyl (CP^iPr₃) ligand featuring an axial carbon donor intended to conceptually model the interstitial carbide atom of the nitrogenase iron-molybdenum cofactor (FeMoco). It is established that in this scaffold, the iron center binds dinitrogen trans to the C_alkyl anchor in three structurally characterized oxidation states. Fe-C_alkyl lengthening is observed upon reduction, reflective of significant ionic character in the Fe-C_alkyl interaction. The anionic (CP^iPr₃)FeN₂^- species can be functionalized by a silyl electrophile to generate (CP^iPr₃)Fe-N₂SiR₃. This species also functions as a modest catalyst for the reduction of N₂ to NH₃. Next, we introduce a new binucleating ligand scaffold that supports an Fe(μ-SAr)Fe diiron subunit that coordinates dinitrogen (N₂-Fe(μ-SAr)Fe-N₂) across at least three oxidation states (Fe^IIFe^II, Fe^IIFe^I, and Fe^IFe^I). Despite the sulfur-rich coordination environment of iron in FeMoco, synthetic examples of transition metal model complexes that bind N₂ and also feature sulfur donor ligands remain scarce; these complexes thus represent an unusual series of low-valent diiron complexes featuring thiolate and dinitrogen ligands. The (N₂-Fe(μ-SAr)Fe-N₂) system undergoes reduction of the bound N₂ to produce NH₃ (~50% yield) and can efficiently catalyze the disproportionation of N₂H₄ to NH₃ and N₂. The present scaffold also supports dinitrogen binding concomitant with hydride as a co-ligand. Next, inspired by the importance of secondary-sphere interactions in many metalloenzymes, we present complexes of iron in two new ligand scaffolds ([SiP^NMe₃] and [SiP^iPr₂P^NMe]) that incorporate hydrogen-bond acceptors (tertiary amines) which engage in interactions with nitrogenous substrates bound to the iron center (NH₃ and N₂H₄). Cation binding is also facilitated in anionic Fe(0)-N₂ complexes. While Fe-N₂ complexes of a related ligand ([SiP^iPr₃]) lacking hydrogen-bond acceptors produce a substantial amount of ammonia when treated with acid and reductant, the presence of the pendant amines instead facilitates the formation of metal hydride species.

Additionally, we present the development and mechanistic study of copper-mediated and copper-catalyzed photoinduced C-N bond forming reactions. Irradiation of a copper-amido complex, ((m-tol)₃P)₂Cu(carbazolide), in the presence of aryl halides furnishes N-phenylcarbazole under mild conditions. The mechanism likely proceeds via single-electron transfer from an excited state of the copper complex to the aryl halide, generating an aryl radical. An array of experimental data are consistent with a radical intermediate, including a cyclization/stereochemical investigation and a reactivity study, providing the first substantial experimental support for the viability of a radical pathway for Ullmann C-N bond formation. The copper complex can also be used as a precatalyst for Ullmann C-N couplings. We also disclose further study of catalytic C_alkyl-N couplings using a CuI precatalyst, and discuss the likely role of [Cu(carbazolide)₂]^- and [Cu(carbazolide)₃]^- species as intermediates in these reactions.

Finally, we report a series of four-coordinate, pseudotetrahedral P₃Fe^II-X complexes supported by tris(phosphine)borate ([PhBP₃Fe^R]^-) and phosphiniminato X-type ligands (-N=PR'₃) that in combination tune the spin-crossover behavior of the system. Low-coordinate transition metal complexes such as these that undergo reversible spin-crossover remain rare, and the spin equilibria of these systems have been studied in detail by a suite of spectroscopic techniques.

Near-infrared luminescent properties and natural lifetime calculation of a novel Er3+ complex

in this communication, a novel Er3+ complex Er(PT)(3)TPPO [PT = 1-phenyl-3-methyl-4-tert-butylbenzoyl-5-pyrazolone, TPPO = triphenyl phosphine oxide] is successfully synthesized and characterized by elemental analysis and single-crystal X-ray diffraction. Its optical properties and the energy transfer process from the ligand PT to the Er3+ ion are investigated, the typical near-infrared (NIR) luminescence (centered at around 1530 nm) is attributed to the I-4(13/2) -> I-4(15/2) transition of Er3+ ion which results from the efficient energy transfer from PT to Er3+ ion (an antenna effect). The wider full width at half maximum (78 nm) peaked at 1530 nm in the emission spectrum and the Judd-Ofelt theory calculation on the radiative properties suggest that Er(PT)(3)TPPO should be a promising candidate for tunable lasers and planar optical amplifiers.

Methyleneimidazoline Complexes of Iridium, Rhodium, and Palladium from Selective C(sp(3))-H Bond Activation

Palladium, iridium, and rhodium complexes of 2-methyleneimidazolines have been synthesized by selective phosphine-assisted activation of the 2-methyl C-H bonds in 2-methylimidazolium compounds. Metallacycles of various sizes were obtained in the reaction of phosphine-tethered 2-methylimidazolium compounds and [{M(cod)X}(2)] (M = Rh or Ir cod = 1,5-cyclooctadiene: X = alkoxyl or Cl). representative complexes were characterized by X-ray crystallography. The selectivity for aliphatic C(sp(3))H versus aromatic C(sp(2))H activation could be adjusted by means of the steric bulk of the OR ligand, whereby a bulky, OR group favors activation of the 2-methyl C(sp(3))-H bond. Experimental results confirmed that a methyl C-H activation product (a seven-membered iridacycle) is the kinetic product, while the aryl C-H activation product (a six-membered iridacycle) is the thermodynamic product.

Synthesis of iminophosphine and phosphinoiminol cyclometallated Pt (II) and Pt (IV) chloro complexes and studies into their biological and photophysical properties

This thesis focuses on the synthesis and analysis of novel chloride based platinum complexes derived from iminophosphine and phosphinoamide ligands, along with studies on their reactivity towards substitution and oxidation reactions. Also explored here are the potential applications of these complexes for biological and luminescent purposes. Chapter one provides an extensive overview of platinum coordination chemistry with examples of various mixed donor ligands along with the history of platinum anticancer therapy. It also looks at metals in medicine, both for biological functions as well as for therapeutic purposes and gives a background to some other applications for platinum complexes. Chapter two outlines the design and synthetic strategies employed for the development of novel platinum (II) chloride complexes from iminophosphine and phosphinoamide ligands. Also reported is the cyclometallation of these complexes to form stable tridentate mixed donor platinum (II) compounds. In Chapter three the development of a direct method for displacing a chloride from a platinum metal centre with a desired phosphine is reported. Numerous methods for successful oxidation of the platinum (II) complexes will also be explored, leading to novel platinum (IV) complexes being reported here also. The importance of stabilisation of the displaced anion, chloride, by the solvent system will also be discussed in this chapter. Chapter four investigates the reactivity of the platinum (II) complexes towards two different biomolecules to form novel platinum bio-adducts. The potential application of the platinum (II) cyclometallates as chemotherapeutics will also be explored here using in-vitro cancer cell testing. Finally, luminescence studies are also reported here for the ligands and platinum complexes reported in chapter two and three to investigate potential applications in this field also. Chapter five provides a final conclusion and an overall summary of the entire project as well as identifying key areas for future work.

Synthesis of Gold–Silver Luminescent Honeycomb Aggregates by Both Solvent-Based and Solvent-Free Methods

Heterometallic clusters with strong luminescence have been synthesized (see picture: Au(CCPh)2 yellow-red, Ag2 blue, O red) from the metalloligand unit [Au(CCPh)PPh3] (yellow/red bars) by using both standard solvent-based and solvent-free reactions. The aggregates are stabilized only by acetylide–metal or metal–metal interactions, and their nuclearity is controlled through the addition of different donor ligands.

Structural and Spectral Investigations of Transition Metal Complexes Of Di-2-Pyridyl Ketone N (4), N (4)-Disubstituted Thiosemicarbazones

The study deals with structural and spectral investigations of transition metal complexes of di-2-pyridyl ketone N(4),N(4)-disubstituted thiosemicarbazones. The main objective and scope of the work deals with di-2-pyridyl ketone N(4),N(4)-disubstituted thiosemicarbazones are quardridentate NNNS donor ligands. To chosen this ligand for study because, the ligands are prepared and characterized for the first time, since there are two pyridyl nitorgens, dimmers and polymers of complexes may result leading to interesting structural aspects. The work includes the preparation of the thiosemicarbzones and their structural and spectral studies, synthesis and spectral characterization of complexes of copper(II),,nickel(II),manganese(II), dioxovanadium(V),cobalt(III),zinc(II),cadmium(II) of the ligand HL, synthesis and spectral characterization of complexes of copper(II),manganese(II), of the ligand HL and the development of X-ray quality crystals and its X-ray diffraction studies. The structural characterization techniques are elemental analysis, conductivity measurements, magnetic measurements, electronic spectroscopy, H NMR spectroscopy, Infrared spectroscopy and X-ray crystallography.

Molybdenum eta(3)-allyl dicarbonyl complexes as a new class of precursors for highly reactive epoxidation catalysts with tert-butyl hydroperoxide

New Mo(II) diimine derivatives of [Mo(q (3)allyl)X(CO)(2)(CH3CN)(2)] (allyl = C3H5 and C5H5O; X = Cl, Br) were prepared, and [MO(eta(3)-C3H5)Cl(CO)(2)(BIAN)] (BIAN = 1,4-(4-chloro)phenyl-2,3-naphthalene-diazabutadiene) (7) was structurally characterized by single-crystal X-ray diffraction. This complex adopted an equatorial-axial arrangement of the bidentate ligand (axial isomer), in contrast with the precursors, found as the equatorial isomer in the solid and fluxional in solution. The new complexes of the type [Mo(eta(3)-allyl)X(CO)(2)(N-N)l (N-N is a bidentate chelating dinitrogen ligand) were tested for the catalytic epoxidation of cyclooctene using tert-butyl hydroperoxide as oxidant. All catalytic systems were 100% selective toward epoxide formation. While their turnover frequencies paralleled those of related Mo(eta) carbonyl compounds or Mo(VI) compounds bearing similar N-donor ligands, they exhibited similar olefin conversions in consecutive catalytic runs. The acetonitrile precursors were generally more active than the diimine complexes, and the chloro derivatives more active than the bromo ones. Combined vibrational and NMR spectroscopy and computational studies (DFT) were used to investigate the nature of the molybdenum species formed in the catalytic system with [Mo(eta(3)-C3H5)Cl(CO)(2){1,4-(2,6-dimethyl)phenyl-2.3-dimethyldiazabuta diene}] (4) and to propose that the resulting species may be dimeric bearing oxide bridges.

A hexadecanuclear copper(I)-copper(II) mixed-valence compound: structure, magnetic properties, intervalence charge transfer, EPR, and NMR

Hexadecanuclear copper mixed-valence complex 2 containing 10 Cu-II, centers and 6 Cu-I centers was isolated with N,O donor ligands. From the X-ray crystal structure, 2 was found to contain a centrosymmetric dimeric cation - each monomeric unit composed of eight copper centers. It displays a very broad and weak intervalence charge-transfer band around 1100 nm at room temperature in the solid state. Variable-temperature magnetic susceptibility measurements indicate an S = 1/2 ground state for half of 2, explicitly, each Cu-8 moiety has a g value around 2.26. Complex 2 was examined by NMR spectroscopy at room temperature in solution and by EPR at low temperature; the data indicates that the valence is delocalized in 2 at room temperature but localized at low temperature. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Stabilisation of two Cu(I)-amino N bonds in presence of imino N's

Two structurally characterised examples of air stable Cu-1 (amino N)(2)(imino N)(2) chromophores having a Cu(II/I) potential of 0.01-0.19 V vs SCE in CH2Cl2 are provided using two tetradentate N-donor ligands.