Luminescent lanthanide complexes with liquid crystalline properties

Lewis-base adducts of tris( β-diketonato)lanthanide(III) complexes were prepared, where the β-diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β-diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature.     

Synthesis and characterization of oxo-bridged, trinuclear, six-coordinate mixed-carboxylato complexes of chromium (III)

Mixed-carboxylato β-diketonato complexes of chromium (III) (R=C₁₃H₂₇, C₁₅H₃₁ or C₁₇H₃₅ and L=CH₃OH) [Cr₃O(OOCR)₃(dike)₃L₃]⁺ have been synthesized by enforced substitution reactions of [Cr₃O(OOCCH₃)₇(H₂O)] first with straight chain fatty acids (myristic, palmitic or stearic acid) and then with β-diketones (Hβ-dike) like acetylacetone(Hacac) or benzoylacetone(Hbzac) in toluene under reflux. These are new type of oxo-bridged chromium(III) complexes in which one ligand is a fatty acid while the other one is a β-diketone. The complexes were characterized by elemental analyses, spectral (infrared, electronic, FAB mass and powder XRD) studies, molar conductance and magnetic susceptibility measurements. Bridging coordination modes for both carboxylate and β-diketonate anions were indicated by presence of ν_asym(Cr₃O) vibrations in the infrared spectra. Trinuclear nature of the complexes and their structural features have been discussed on the basis of physicochemical studies.     

Beta-aryl eliminations from Rh(I) iminyl complexes

beta-Aryl eliminations from a series of iminyl complexes to form rhodium aryl complexes and free nitriles are reported. Iminyl complexes [Rh(PEt3)3(N=CArAr')] were prepared from [Rh(COE)Cl]2, PEt3, LiN(SiMe3)2, and the imines HN=CArAr'. One example of these complexes was characterized by X-ray diffraction. Heating of these complexes in cyclohexane generated the rhodium aryl complexes and free nitriles in high yields; heating in benzene formed the same products in slightly lower yields. Complexes with varied aryl groups on the imine were studied to assess the migratory aptitudes of the aryl groups. Migration of the o-anisyl group occurred much faster than migration of a phenyl group; migration of a phenyl group occurred slightly faster than migration of the more electron-rich p-anisyl group; and migration of a phenyl group occurred slightly faster than migration of the more hindered o-tolyl group. Kinetic studies showed that the reaction was inverse first-order in the concentration of added phosphine and zero-order in added nitrile. These results show that the beta-aryl elimination most likely occurs by dissociation of phosphine from the starting complex and carbon-carbon bond cleavage of the resulting 14-electron intermediate.     

Synthesis and characterization of chiral iron carbonyl complexes from imine ligands with carbohydrates and amino acids as substituents

Imine ligands derived from 6-amino-6-desoxy-1,2,3-O-trimethyl--d-glucopyranose or from various amino acid esters react with Fe₂(CO)₉ to give chiral iron carbonyl complexes. Derivatives produced from benzaldehyde react via a C–H activation reaction in ortho-position with respect to the exocyclic imine substituent followed by an intramolecular hydrogen transfer reaction of the activated hydrogen towards the former imine carbon atom. The molecular structure of the diiron hexacarbonyl complexes of benzylideneamino-l-phenylalanine ethyl ester and benzylideneamino-l-methionine methyl ester were characterized by means of X-ray structure determinations. Imines produced from cinnamaldehyde upon reaction with Fe₂(CO)₉ produce mononuclear iron tricarbonyl complexes with the imine ligand being coordinated in a η⁴-fashion.     

Photophysical properties of novel fluorescent poly(oxyethylene phosphate) tris(β-diketonate) europium (III) complexes

In the present study, photophysical properties of fluorescent poly(oxyethylene phosphate) tris(β-diketonate) europium (III) complexes have been studied by means of stationary and time-resolved fluorescence spectroscopy (in ethanol at room temperature). The luminescent quantum yields and efficiency for the energy transfer from β-diketonate ligands to Eu(III) ion have been determined for the studied complexes by using diffusion-enhanced fluorescence resonance energy transfer. Obtained results show effect of the polymer ligands upon photophysical properties of the complexes and a relation has been established with length of the oxyethylene spacer between two phosphonate groups. The Förster radiuses of the synthesized compounds with SulfoRhodamine 101 as acceptor have been calculated. Measured distances between molecules of the donors and acceptor at identical acceptor/donor molar ratios have been illustrated the difference in structure of the ternary and polymer complexes in solution even at low concentration.     

The first solid phase synthesis of pincer palladium complexes

Both dimeric μ-chlorine bridged and monomeric bidentate Pd(II) complexes with SCN hybrid pincer-type ligands, bearing thiophosphoryl group and imine moiety of the benzothiazole ring as coordination arms, formed in the reaction with (PhCN)(2)PdCl(2) under kinetic control (20 °C, dichloromethane solution) were readily converted into the corresponding SCN pincer complexes via solid phase synthesis (neat, 200 °C, 15 min). The synthesis of pincer complexes can be performed also by heating (200 °C, 5 min) of a homogeneous mixture of the initial reactants, namely, the ligand and (PhCN)(2)PdCl(2), obtained by manual grinding in a mortar. The efficacy of solid phase approaches is comparable with the analogous synthesis in solutions under severe conditions.     

Photochemically initiated oxidative carbon-carbon bond-cleavage reactivity in chlorodiketonate Ni(II) complexes

Three mononuclear Ni(II) complexes containing a 2-chloro-1,3-diketonate ligand and supported by the 6-Ph(2)TPA chelate, as well as analogues that lack the 2-chloro substituent on the β-diketonate ligand, have been prepared and characterized. Upon irradiation at 350 nm under aerobic conditions, complexes containing the 2-chloro-substituted ligands undergo reactions to generate products resulting from oxidative cleavage, α-cleavage, and radical-derived reactions involving the 2-chloro-1,3-diketonate ligand. Mechanistic studies suggest that the oxidative cleavage reactivity, which leads to the production of carboxylic acids, is a result of the formation of superoxide, which occurs through reaction of reduced nickel complexes with O(2). The presence of the 2-chloro substituent was found to be a prerequisite for oxidative carbon-carbon bond-cleavage reactivity, as complexes lacking this functional group did not undergo these reactions following prolonged irradiation. The approach toward investigating the oxidative reactivity of metal β-diketonate species outlined herein has yielded results of relevance to the proposed mechanistic pathways of metalloenzyme-catalyzed β-diketonate oxidative cleavage reactions.     

Extraction chromatography of palladium and platinum complexes with nitroso-R-salt

The retention of palladium and platinum complexes with nitroso-R-salt on silica gel treated with Aliquat 336 has been investigated. The complexation of platinum with nitroso-R-salt (NRS) requires heating of H₂PtCl₆ with an excess of NRS at 100°. The affinity of the complexes for an Aliquat 336 stationary phase increases in the following order: PdCl₄²⁻ ˜ Pt-NRS < PtCl₆²⁻ Pd-NRS. The complexes of palladium and platinum can be separated by column chromatography on silica treated with Aliquat 336 and eluted with 0.25M perchloric acid (Pt) and 1M perchloric acid (Pd).     

Acyl complexes of molybdenum: structural and reactivity studies

The following structural peculiarities of the agostic acyl structure ₂R) (R = H, SiMe₃) and some characteristic chemical reactivity of the M-η²-acyl and iminoacyl linkage are described. (i) A structural comparison of the bonding parameters within three agostic acetyl Mo complexes containing the dithioacid ligand, indicates that the agostic interaction strengthens upon increasing the electron-releasing properties of the S-chelating ligand. (ii) The acyl-xanthate complex Mo(C(O)Me)(S₂COR)(CO)(PMe₃)₂ undergoes loss of a sulfur atom from the coordinated xanthate and coupling with the acyl ligand to form complexes containing coordinated alkoxythiocarbonyl and monothioacetate ligands. The latter can be metathetically replaced by KS₂COR. (iii) Upon heating at 70°C η²-acyl-dicarbonyl bispirazolilborate complexes of molybdenum of the type Mo(H₂B(pz^*)₂)(η²-C(O)Me)(CO)₂(PMe₃) (pz^* = 3,5-dimethyl-pyrazol-1-yl) yield functionalized acyl ligands derived from the stereo- and regioselective intramolecular addition of one of the B---H bonds of the H₂B(pz^*)₂ group across the C=O moiety of the η²-acyl group. (iv) The η²-acyl-isocyanide complexes {Mo}(η²-C(O)R)(CNR′) ({Mo} = Mo(H₂B(pz^*)₂)(CO)(PMe₃)) undergo irreversible thermal isomerization to the corresponding η²-iminoacyl-carbonyl derivatives {MO}(η²-C(NR′)R)(CO). This isomerization reaction follows first-order kinetics.     

Synthesis, structure and reactivity of palladium(II) complexes of chiral N-heterocyclic carbene-imine and -amine hybrid ligands

The synthesis and structures of chiral N-heterocyclic carbene (NHC)-N-donor complexes of silver(I) and palladium(II) are reported. The X-ray structure of an NHC-imine silver(I) complex [((nPr)CN(CHPh))AgBr](2) exhibits an Ag(2)Br(2) dimer motif where the imine group is not coordinated to the silver atom. Reaction between 2 and [PdCl(2)(MeCN)(2)] gives the palladium(II) complex [(kappa(2)-(nPr)CN(CHPh))PdCl(2)](3) that contains a chelating NHC-imine ligand as shown by single-crystal X-ray diffraction. Slow hydrolysis of related complexes [(kappa(2)-(nPr)CN(CHPh))PdCl(2)](3) and [(kappa(2)-((Ph)(2)CH)CN(CHPh))PdCl(2)](4) using triethylammonium chloride and water lead to the precipitation of single crystals of insoluble NHC-amino palladium(II) complexes [(kappa(2)-(nPr)CN(H(2)))PdCl(2)](6) and [(kappa(2)-((Ph)(2)CH)CN(H(2)))PdCl(2)](7), respectively. In the solid state, complexes 6 and 7 both exhibit intermolecular hydrogen bonding between chlorine and an amino-hydrogen atom resulting in an infinite chain structure. Substitution of an amino hydrogen for an ethyl group gives the soluble complex [(kappa(2)-(iPr)CN((H)Et))PdCl(2)](12). Reaction between two equivalents of 2 and [PdCl(2)(MeCN)(2)] gives the di-NHC complex [(kappa(1)-(nPr)CN(CHPh))(2)PdCl(2)](5) that does not contain a coordinated imine as shown by single crystal X-ray diffraction. Conproportionation between 5 and an equivalent of [PdCl(2)(MeCN)(2)] to does not occur at temperatures up to 100 degrees C in CD(3)CN.     

Cycloadditions and annulations of transition metal carbene complexes

The synthetic aspects of several reactions from the multifaceted chemistry of Fischer carbene complexes are examined. Their benzannulation reactions with acetylenes are utilized in the synthesis of anthracyclinones via two approaches which differ by beginning at opposite ends of the molecule with either an aryl or an alkenyl substituted chromium carbene complex. The latter has been employed in a formal synthesis of daunomycinone. The Diels-Alder reactions of ,β-acetylenic chromium carbene complexes provide for a facile entry into substituted cyclohexenyl chromium carbene complexes that are subsequently employed in benzannulation reactions. These tandem cycloaddition/annulation reactions are incorporated into model studies for the synthesis of anthracyclinones and wentilactone A. Their potential is also demonstrated for coupling to yet a third reaction of organochromium compounds ; aromatic nucleophilic substitutions on arene chromium tricarbonyl complexes. The annulations of β,β-disubstituted alkenyl complexes provides for a regio- and stereoselective synthesis of 2,4-cyclohexadienones under neutral conditions at near ambient temperatures.     

Vapour phase chemistry of oxovanadium iv β-diketonates

A series of fluorinated and one non-fluorinated β-diketonate complexes of oxovanadium IV have been prepared, their gas phase IR spectra examined, vapour pressures determined and their vapour phase thermal decomposition investigated. Decomposition of the fluorinated complexes occurred according to the overall reaction scheme VO(β-diket)₂»VOF₂ + Furanone. The furanones C₅HF₅O₂, C₅H₄F₂O₂ and C₈H₁₀F₂O₂ were isolated and identified. The non-fluorinated complex gave the parent diketone and a vanadium oxide as its principal products.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated dipalladium–dioxygen complexes

The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η²–O₂) and Pd(η²–O₂)₂, dinuclear palladium–dioxygen complexes: Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η²–O₂), Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η²–O₂)(Ng)₂, Pd₂(η²–O₂)(Ng)₂ and Pd₂(η²–O₂)₂(Ng)₂ (NgAr or Xe) complexes isolated in solid argon.     

The development of polar discotic metallomesogens Vanadyl 1,3-diketonate complexes

Abstract

The dependence of mesomorphism of 1,3-diketonate vanadium-oxo (vanadyl) complexes on the number of side chains was investigated. These complexes have a large dipole normal to the disc plane and are under investigation in an effort to generate discotic phases with polar order. Relatively complex phase behaviour is observed when the vanadyl 1,3-diketonate complexes are appended with four phenyl groups with two octyloxy or decyloxy side chains each for a total of eight side chains. These complexities are most likely related to the order/disorder associated with the polar vanadyl group. Vanadyl 1,3-diketonate complexes with four side chains were prepared by replacement of two of the phenyl groups with methyl or trifluoromethyl groups, and these complexes displayed only crystal phases. Complexes with two trialkyloxy phenyls and two dialkyloxy phenyls were synthesized and found to display a very stable D_hd phase. The presence of additional alkyloxy groups was found also to promote a linear chain structure, (i.e. ??V?O??V?O??), in the crystal phase.     

Novel hemi-labile pyridyl-imine palladium complexes: Synthesis, molecular structures and reactions with ethylene

Ligands (2-pyridyl-2-furylmethyl)imine, (L1), (2-pyridyl-2-thiophenemethyl)imine (L2), and (2-pyridyl-2-thiopheneethyl)imine (L3) were synthesized by condensation reactions and obtained in good yields. Reactions of L1-L3 with either [PdClMe(cod)] or [PdCl₂(cod)] gave the corresponding monometallic palladium(II) complexes 1-5 in very good yields. Molecular structures of complexes 1, 4 and 5 indicated that the ligands are bidentate and coordinate to the palladium metal through the imine and pyridine nitrogen atoms. When complexes 3-5 were treated with NaBAr₄, cationic species, 3a, 4a, and 5a were produced which catalyzed polymerization of ethylene though with very low activities. ¹H NMR spectroscopy studies showed that these cationic species were very stable in solution. DFT calculations showed high ethylene coordination barriers to the cationic species 3a, 4a and 5a.     

Syntheses of complexes containing substituted 4-ethynylquinolines or 1-azabuta-1,3-dienes by addition of imines to a cationic butatrienylidene-ruthenium complex

Reactions of [Ru(=C=C=C=CH₂)(PR₃)₂Cp]⁺ (R=Ph or OMe) with arylimines ArN=CH(C₆H₄R) afford either substituted quinolines, Ru{CCC₉H₄RN(Ar)}(PR₃)₂Cp, by attack of the terminal carbon of the butatrienylidene ligand at the imine carbon, followed by C---C bond formation between the ortho carbon of the N-aryl group and C_γ of the unsaturated carbene, or 1-azabuta-1,3-dienyl complexes, formed by cycloaddition of the N=CH group to C_γ=C_δ of the carbene, followed by opening of the resulting four-membered ring. Some product dependence on the nature of the substituents in the N- and C-aryl groups is found. The N atoms in the products are strongly basic, being readily protonated, methylated or aurated. The molecular structures of nine complexes are reported, together with that of a new modification of RuCl{P(OMe)₃}₂Cp.     

Tris(difluoro and trifluorobutane-2,4-dionato) gallium(III) and indium(III) complexes

Eight tris(β-diketonate)gallium(III) and seven tris(β-diketonate)-indium(III) complexes M(RCOCH-COR′)₃, with R′being difluoromethyl and trifluoromethyl substituents and R′ being methyl, phenyl, aryl, 2′-naphthyl and 2′-thienyl substituents have been studied by nuclear magnetic resonance spectroscopy. The complexes are all nonrigid (fluxional) and their ¹⁹F NMR spectra show four resonances in the nonexchanging regions due to cis and trans isomers. A variable low temperature study of these complexes was done for the gallium chelates and activation parameters are calculated. The indium complexes all have nonexchanging regions below ?100°C. The ¹³C NMR data on the complexes are also reported.     

Synthesis and decomposition of neutral palladium(IV) complexes containing fac-PdMe2R groups, including reductive elimination by η-propenylpalladium(IV) complexes to form η-propenylpalladium(II) species

Oxidative addition of ethyl iodide to PdMe₂(2,2′-bipyridyl) in (CD₃)₂CO gives the unstable “PdIMe₂Et(bpy)”, which undergoes reductive elimination to form PdIR(bpy) (R = Me, Et), ethane, and propane. Ethene and palladium metal are also formed, and are attributed to decomposition of PdIEt(bpy) via β-elimination. Similar results are obtained with n-propyl iodide, although a palladium(IV) intermediate was not detected, but CH₂=CHCH₂X (X = Br, I) and PhCH=CHCH₂Br give isolable complexes fac-PdXMe₂(CH₂CH=CHR)(L₂) (R = H, Ph; L₂ = bpy, phen). The propenyl complexes decompose at ambient temperature to form ethane, a trace of PdXMe(L₂), and mixtures of [Pd(η³-C₃H₅)(L₂)]X and [Pd(η³-C₃H₅)(L₂)]-[Pd(η³-C₃H₅)X₂]; for fac-PdBrMe₂(CH₂CH=CH₂)(bpy) the major palladium(II) product is [Pd(η³-C₃H₅)(bpy)]Br.     

Synthesis and structural characterization of binuclear palladium(II) complexes of salicylaldimine dithiosemicarbazones

A series of binuclear palladium(II) salicylaldiminato dithiosemicarbazone complexes have been synthesized and characterized. The palladium complexes were obtained by the reaction of various ethylene- and phenylene-bridged dithiosemicarbazones with Pd(PPh₃)₂Cl₂. The free salicylaldimine ligands and their palladium complexes were characterized by NMR and IR spectroscopies, ESI-mass spectrometry, elemental analyses and for two representative complexes also by X-ray diffraction. In both metal complexes, the solid-state structures show the two palladium centers to be coordinated in a slightly distorted square-planar geometry, which gives rise in each case to five- and six-membered chelate rings. The salicylaldimine thiosemicarbazone ligands coordinate to palladium in a tridentate manner, through the phenolic oxygen, imine nitrogen and thiolate sulfur atoms.     

Observation and identification of the catalytically active species of bis(phenoxy-imine) group 4 transition metal complexes for olefin polymerization using 1H NMR spectroscopy

Solution structures of bis(phenoxy-imine) group 4 transition metal complexes (FI Catalysts) were investigated using ¹H NMR spectroscopy. At least two isomers exist in equilibrium for FI Catalysts precursors, bis[N-(3-tert-butylsalicylidene)anilinato]zirconium(IV) dichloride ( 1 ), and bis[N-(3,5-dicumylsalicylidene)anilinato]zirconium(IV) dichloride ( 2 ), while bis[N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato]titanium(IV) dichloride ( 3 ) exhibits only one isomer under the conditions examined. Upon activation with MAO, all FI Catalysts ( 1-3 ) generate two species at ambient temperature judging from some key signals in the ¹H NMR. When temperature is raised (up to 75°C), one species ( 1a-3a ) converts irreversibly to the other species ( 1b-3b ). The resulting species, 1b-3b , are stereochemically rigid, in contrast to precursors 1 and 2 . Species 3b , derived from a living FI Catalyst, exhibited virtually no reactivity toward olefin insertion. The imine protons of species 1b-3b are temperature and solvent polarity sensitive. Two possibilities are proposed for the assignment of species 1b-3b, i) heterobinuclear complexes of group 4 metal and alkylaluminum with methyl and/or chlorine as bridging groups and ii) phenoxy-imine ligated aluminum complexes whose ligands are transferred from the group 4 metal. The latter is more probable from the separate synthesis of LAlMe₂ (L: phenoxy-imine ligand). When 3 was activated with MAO in the presence of olefins, a new imine signal was observed. This species ( 3c for ethylene and 3d for propylene) is thermally more robust than 3a toward transformation to 3b and assignable to the living propagating species.