Synthetic regulators of carotenoid biosynthesis in Citrus paradisi

The ability of 16 amines to induce carotenoid biosynthesis in Marsh seedless grapefruit is correlated with the octanol-water partition coefficient and the Hammett constants. The compounds fall into three series: p-RC₆H₄COOCH₂CH₂NEt₂ (R = H, NH₂, CN, NO₂, MeO, Me, tert-Bu, F, Cl, Br), p-RC₆H₄CH₂NEt₂ (R = H, Me, NO₂), and RC₆H₄OCH₂CH₂NEt₂ (R = o-Me, m-Me, p-Me). Total carotene content increased up to 12-fold. Lycopene, not normally accumulated, became a major pigment. The benzoates caused up to a 24-fold increase in the β-carotene content. Except for the larger accumulation of cyclic carotenes, the mode of action of these amines appears to be similar to that of 2-(4-chlorophenylthio triethylamine hydrochloride.     

Potential multifunctional anti-cancer metal complexes. I. Synthesis and x-ray structural studies of some dinuclear rhodium(II) carboxylate complexes with diamine-substituted acridine ligands in terminal coordination positions

The preparations are reported of [Rh(RCO₂)₂L]₂ [where R = CH₃, C₂H₅, and CH₃OCH₂; L = 6-chloro-2-methoxy-9-[2(NR′₂)ethyl]aminoacridine (R′ = H, CH₃)]. X-ray structural studies have been carried out on two of the compounds [ R = C₂H₅, R′ = H, (1); R = CH₃, R′ = CH₃, (2)]. Compound 1 is monoclinic, space group C2/c, with a = 20.864(11), b = 15.736(4), c = 14.402(4) Å, β = 93.14(4)°, V = 4721 ų, and Z = 4; 2 is monoclinic, space group P2₁/n, a = 8.861(2), b = 23.089(10), c = 12.014(2) Å, β = 105.84(2)°, V = 2365 ų, and Z = 2. Both compounds comprise the standard dinuclear rhodium(II) carboxylate unit with the substituted acridine ligands coordinated to rhodium in the axial positions, via the NH₂ group nitrogen in 1 and the N(CH₃)₂ nitrogen in 2.The dimethyl substitution on the tertiary amine group in 2, and an associated conformational change in the diamine chain, result in an increased separation of the acridine ligand from the metal centre. There is a pronounced acridine base stacking in 1 but not in 2.     

Photolytic CO-substitution reaction of organoiron thiocarboxylate derivatives CpFe(CO)2SCOR (R=alkyl, aryl) with diphosphines (Ph2P(CH2)nPPh2) (n=1-6): X-ray crystal structure of [CpFe(dppm)SCO(3,5-(NO2)2C6H3)]

The photolytic CO-substitution reaction of the organoiron thiocarboxylate complexes CpFe(CO)₂SCOR (R=CH₃, 2-CH₃C₆H₄, 2-NO₂C₆H₄, 4-NO₂C₆H₄, 3,5-(NO₂)₂C₆H₃) with diphosphines (Ph₂P(CH₂)_nPPh₂) [n=1 (dppm), n=2 (dppe), n=3 (dpppr), n=4 (dppb), n=5 (dppp), n=6 (dpph)] at room temperature using 1:2 (metal-ligand) molar ratio afforded exclusively the disubstituted complexes CpFe(Ph₂P(CH₂)_nPPh₂)SCOR when n=1, 2 and 3 and the monosubstituted analogs CpFe(CO)(Ph₂P(CH₂)_nPPh₂)SCOR when n=4, 5 and 6. This reaction was found to be strongly influenced by the backbone length of the diphosphine ligand, the nature of the R group of the thiocarboxylate moiety and the metal-ligand molar ratios. The crystal structure of CpFe(dppm)SCO(3,5-(NO₂)₂C₆H₃) was determined.     

Association phenomena: IV. Catalysis of the ionization of dihydroxyacetone phosphate by monofunctional,difunctional, and trifunctional amines

The rate of the ionization of dihydroxyacetone phosphate (DHAP) has been measured in the presence of (a) simple monofunctional primary, secondary, and tertiary amines, (b) monoprotonated diamines, and (c) monoprotonated N-[N′-(arylalkyl)aminoalkyl]guanidines of the general structure Ar(CH₂)_mNH(CH₂)_nNC(NH₂)₂ in which the aryl groups are phenyl, 2-pyridyl, and 4-pyridyl, the values of m are 1, 2, and 3, and the values of n are 2 and 3. Evidence for bifunctional catalysis by several diamines has been obtained, but evidence is marginal for trifunctional catalysis by the guanidinium compounds in which the guanidinium moiety interacts electrostatically with the phosphate of DHAP, the secondary amino group forms an iminium bond with the carbonyl group of DHAP, and the 2-pyridyl moiety abstracts the a-proton of DHAP to generate the carbanion. Although the guanidinium compounds are uniformly better catalysts than their simpler analogs, only compound 7 catalyzes the ionization of DHAP at a rate slightly faster than would be predicted on the basis of its pK_a value.     

Chiroptical properties of diastereomeric five-coordinate Pt(II)–olefin complexes. Molecular structure of [PtCl2{(S,S)-(E)-CNCHCHCN}(R,R)-{C6H5CH(CH3)N(CH3)CH2}2]·C6H6

The chiroptical properties of five-coordinate diastereomeric complexes of general formula [PtCl₂(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂{olefin}], with olefin ligands having electron-withdrawing substituents, have been investigated. The sign of CD bands in the 28 000–30 000 cm⁻¹ region appears to be correlated to the absolute configuration of the prochiral coordinated alkene. Single-crystal X-ray diffraction structure determination has been performed on the single diastereomer [PtCl₂(E-but-2-enedinitrile)(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂]· C₆H₆. The compound crystallizes in the monoclinic space group C2 with a = 17.842(2), b = 8.466(1), c = 10.464(1) Å, β = 109.34(1)°, Z = 2. The number of observed reflections was 1943 and the final R and R_w values were 0.020 and 0.028 respectively. Trigonal-bipyramidal geometry is observed around the Pt atom, with the two Cl atoms in axial positions. The unsaturated ligand lies in the equatorial plane disclosing S,S absolute configuration.     

Complexes of the fac-{Re(CO)3} core with tridentate ligands derived from arylpiperazines

Arylpiperazines, XC₆H₄N(CH₂CH₂)₂NH, are readily alkylated to give the N-alkylpiperazines of the type XC₆H₄N(CH₂CH₂)₂N(CH₂)_nNH₂. The amine functions of these derivatives are in turn easily subjected to mono- or dialkylation to provide potentially tridentate ligands of the types XC₆H₄N(CH₂CH₂)₂N(CH₂)_nN(H)(CH₂Y) and XC₆H₄N(CH₂CH₂)₂N(CH₂)_nN(CH₂Y)(CH₂Z), respectively. The latter class of dialkylated derivatives may be symmetrically (Y=Z) or unsymmetrically (Y ≠ Z) substituted. The donor groups Y and Z of this study include pyridine, imidazole, methyl-imidazole, thiazole, carboxylate and thiolate.The reactions of these ligands with [NEt₄]₂[Re(CO)₃Br₃] yield complexes of the type [Re(CO)₃{(YCH₂)N(H)(CH₂)_n(H)_xN(CH₂CH₂)₂N(H)_yC₆H₄X}]ⁿ and [Re(CO)₃{(ZCH₂)(YCH₂)N(CH₂)_n(H)_xN(CH₂CH₂)₂N(H)_yC₆H₄X}]ⁿ where the molecular charge n (0, +1, or +2) depends on the nature of the donor groups Y and Z (whether neutral or anionic or a combination of neutral and anionic) and on the degree of protonation of the piperazine unit (x=0 or 1; y=0 or 1). This variety of tridentate chelators provides complexes with fac-{Re(CO)₃N₃}, {Re(CO)₃N₂O}, {Re(CO)₃NO₂}, {Re(CO)₃N₂S} and {Re(CO)₃NS₂} coordination geometries. The structures of the model compound [Re(CO)₃{(CH₃N₂C₃H₂CH₂)N(H)CH₂CH₂-piperidine}]Br · H₂O, [Re(CO)₃{(CH₃N₂C₃H₂CH₂)N(H)CH₂CH₂-Fphenpip}]Br, [Re(CO)₃{(NC₅H₄CH₂)N(H)CH₂CH₂-Fphenpip}]Br, [Re(CO)₃{(O₂CCH₂)₂NCH₂CH₂CH₂-CH₃OphenpipH}] · xCH₃OH (x≈0.875), [Re(CO)₃{(NC₅H₄CH₂)₂NCH₂CH₂CH₂-CH₃OphenpipH}]Br₂ · 2CH₂Cl₂ · H₂O and [Re(CO)₃{(CH₃N₂C₃H₂CH₂)(O₂CCH₂)NCH₂CH₂CH₂-CH₃OphenpipH₂}]BrCl · 1.5CH₃OH · H₂O are discussed (phenpip: phenylpiperazine, -C₆H₄N(CH₂CH₂)₂N-).     

Ditopic tris(2-mercaptoimidazol-1-yl)borate ligands and their coordination behavior toward [Ru(p-cymene)]

The ditopic tris(2-mercaptoimidazol-1-yl)borate ligand K₂[(mt^Et)₃B-B(mt^Et)₃] cannot be prepared from B₂(NMe₂)₄/4 Hmt^Et/2 Kmt^Et, because the stable intramolecular diadduct (mt^Et)B(μ-mt^Et)₂B(mt^Et) is generated instead (Hmt^Et = 2-mercapto-1-ethylimidazole). Introduction of a meta- or para-phenylene spacer between the two boron atoms precludes the 2-mercaptoimidazol-1-yl groups from adopting a bridging position so that the potassium salts K₂[(mt^Et)₃B-(m-C₆H₄)-B(mt^Et)₃] and K₂[(mt^Et)₃B-(p-C₆H₄)-B(mt^Et)₃] become readily accessible. These ligands react with [(p-cym)RuCl₂]₂ to give the dinuclear Ru^II complexes [(p-cym)Ru(mt^Et)₃B-(m-C₆H₄)-B(mt^Et)₃Ru(p-cym)]Cl₂ and [(p-cym)Ru(mt^Et)₃B-(p-C₆H₄)-B(mt^Et)₃Ru(p-cym)]Cl₂ (p-cym = p-cymene). After the exchange of the Cl⁻ counterions for [PF₆]⁻, both complexes have been crystallized and structurally characterized by X-ray diffraction.     

Design and synthesis of cholecystokinin-4 dipeptide analogues with anxiolytic and anxiogenic activities

A new series of dipeptide analogues of the general formula Ph(CH₂) _n CO-NH(CH₂) _m CO-Trp-NH₂ (n = 1, 3–5; m = 1–3) was designed based on the structure of the endogenous tetrapeptide cholescystokinin-4 (CCK-4) and the topochemical Shemyakin-Ovchinnikov-Ivanov principle. The L-tryptophan derivatives exhibited anxiolytic properties and the D-tryptophan derivatives, anxiogenic properties. The dipeptide Ph(CH₂)₅CO-Gly-L-Trp-NH₂ (GB-115) with the activity in rats of 0.05–0.2 mg/kg after oral and intraperitoneal administration was chosen for further studies as a promising anxiolytic agent.     

The effect of some oligo-amines and -guanidines on membrane permeability in higher plants

The effect of a series of oligo-amines and -guanidines on the membranes of higher plants has been tested by measuring the efflux of betacyanin from beet root discs, and the loss of total ions from beet root and swede discs, beet and spinach leaf discs and apple cells in suspension culture. All of the naturally occurring di- and polyamines tested showed relatively little toxicity. Betacyanin efflux from beet root discs was reduced by diamines [NH₂(CH₂)_xNH₂] up to x = 10 or less. Ion efflux was minimal at x = 7. Within the triamine series [NH₂(CH₂)_xNH(CH₂)₃NH₂] for x = 8 or less, betacyanin efflux was reduced or unaffected, although total ion loss was increased by the triamines when x = 4 or more and especially by the longer chain amines (to x = 10). Similar behaviour was found in the tetra-amine series [NH₂(CH₂)₃NH(CH₂)_xNH(CH₂)₃NH₂] with betacyanin efflux reduced for x = 2–4 (spermine). Although spermine potentiated the toxicity effects of Guazatine {[NH₂C(NH)NH(CH₂)₈]₂NH} and Dodine [NH₂C(NH)NH(CH₂)₁₁,Me] in beet root discs, spermine and calcium ions reduced the ion efflux caused by these toxic guanidines and also by Synthalin B [NH₂C(NH)NH(CH₂)₁₂NHC(NH)NH₂] in swede discs, spinach leaves and apple cells. No significant reversal of ion loss was detected with putrescine, cadaverine or spermidine in swede discs. In the homologous series of monoguanidines [NH₂C(NH)NH(CH₂)_x?1Me] for x up to 18, greatest toxicity was shown for x = 10 and 11 in both betacyanin loss and total ion efflux in beet root discs. Greatest ion efflux from the apple cell suspension was found with x = 11 and 12. In the homologous series of diguanidines [NH₂C(NH)NH(CH₂),NHC(NH)NH₂] for x = 2–12 greatest toxicity was shown for x = 12 (the longest chain tested) in beet root and in the efflux of ions from apple cell suspension. Technical Guazatine was considerably more phytotoxic than pure Guazatine in all systems tested. p-Chloromercuribenzoate (p-CMB) potentiates the loss of betacyanin and total ions caused by Guazatine, Synthalin B, and Dodine in beet root discs. This effect of p-CMB is reversed by subsequent incubation in cysteine or mercaptoethanol, prior to treatment with the guanidines.     

Preparations and properties of tripodal and linear tetradentate N,S-Donor ligands and their complexes containing the MoO22+core

New linear and tripodal tetradentate ligands, LH₂, are reported and their syntheses are described. The new linear ligands L = HSCH₂CH₂SCH₂CH₂NRCH₂CR₂SH, R = H, CH₃) and the new tripodal ligands N(CH₂CH₂SH)₂CH₂Z, Z = CH₂NH₂, CH₂N(CH₃)₂, CH₂N(C₂H₅)₂, CH₂SCH₃ and CO₂^- were synthesized. The known linear ligands HSCH₂CH₂NCH₃(CH₂)_nNCH₃CH₂CH₂SH (n = 2, 3) and HSCR₂CH₂NHCH₂CH₂NHCH₂CR₂SH (R = H, CH₃) were also utilized. These ligands react with MoO₂(acac)₂ in CH₃OH to yield MoO₂L complexes in high yield. Infra-red and ¹H nmr spectra provide evidence to supplement X-ray crystallographic results reported elsewhere for selected numbers of the series. Octahedral structures with cis MoO₂²⁺ groupings are assigned. Solution ¹H nmr studies are consistent with a trans placement of the two thiolate donors in agreement with the X-ray studies.     

Raman spectra and conformations of n-hexadecynoic fatty acids and their potassium salts

Raman spectra of n-hexadecynoic fatty acids, CH₃(CH₂)_m?2C  C(CH₂)_n?2COOH (with n = 4, 6, 7, 8 and 12, m + n = 16) and their potassium salts were recorded and assigned. The skeletal optical mode (SOM) regions were analysed on using the dispersion curve of the ν₄ (stretch) vibrations of saturated fatty acids. The localised vibrations of the carboxyl- and methyl-terminated sections of the hydrocarbon chains were assigned to the phase differences δ = kπ/m and kπ/n (k = 1, 2, …), respectively. Evidence for a ν₄ vibration with δ = π/2m was found. The materials were found to be resistant to chemical decomposition under laser illumination.     

Chiral Metal Complexes. 27. Stereoselectivity in the synthesis and reaction of coordinated aminomalonic acid derivatives

The synthesis is reported of a series of ternary cationic complexes of general form [Co(R,Rpicchxn)(ARMA)⁺ (where picchxn is the N₄ tetradentate N,N′-di(2-picolyl)-1,2-diaminocyclohexane and ARMA is a bidentate α-substituted-α-aminomalonate dianion). The aminomalonic acid (NH₂· C(COOH)₂·R) derivatives investigated have R = -CH₃ (AMMAH₂), -CH₂·CH₃ (AEMAH₂), -CH₂· CH₂·CH₃ (APMAH₂), -CH₂·(CH₂)₂·CH₃ (ABuTMAH₂, -CH₂·C₆H₅ (ABMAH₂), -CH₂·(p-C₆H₄)· C(CH₃)₃ (ABuBMAH₂) and -CH₂·C₁₀H₇ (ANMAH₂). The isomeric species in the complex products have been separated using cation exchange chromatography and each isomer has been characterized using NMR and circular dichroism techniques. In each synthesis the major isomeric product obtained has a Λ-β₁ topology. However, where ARMAH₂ possesses a lengthy alkyl sidechain trace amounts of Δ-α-[Co(R,R-picchxn)(ARMA)]⁺ isomers have been observed during the synthetic reactions. This unusual isomeric form readily undergoes inversion of its absolute configuration in DMSO solution to yield the more thermodynamically stable Λ-β₁-[Co(R,R-picchxn()R-ARMA)]⁺ species stereospecifically.In the case of Λ-β₁-[Co(R,R,-pichxn)(S-APMA)]ClO₄·2NaClO₄·5H₂O the crystal structure has been determined. The compound crystallises in the orthorhombic space group P2₁2₁2₁, with a = 10.056(3),b = 16.475(7),c = 23.370(7)Å and Z = 4. The structure was refined to R = 0.079 for 4460 non-zero reflexions, and confirms the absolute configuration of each chiral centre to be consistent with the NMR and circular dichroism interpretations.The decar☐ylation of these chelate ARMAH₂ derivatives under acid conditions leads to corresponding complexes containing mixtures of coordinated R-andS-α-aminoacids in various ratios. This ratio has been determined in each case, and factors which may influence the degree of chiral induction observed are discussed.     

Structural and magnetic characteristics of tetramethylammonium tetrahalogenoferrates(III)

A series of tetramethylammonium tetrahalogenoferrates(III), [FeBr_4−nCl_n]⁻ (n = 0, 1, 3, 4), of general formula [(CH₃)₄N][FeBr_4−nCl_n], have been synthesized. The crystal and molecular structures of [(CH₃)₄N][FeCl₄] were determined. The compound is isostructural with its [FeBr_4−nCl_n]⁻ (n = 0, 1, 3, 4) analogues. Magnetic measurements of the powdered samples of [(CH₃)₄N][FeBr_4−nCl_n] gave negative values of the Weiss constant, which suggest antiferromagnetic coupling. The strength of the antiferromagnetic interactions strongly depends on the kind of halide ligands in the coordination sphere of iron(III) and increases with an increasing number of the bromide anions.     

Antitubercular activity of α,ω-diaminoalkanes,H2N(CH2)nNH2

A series of 11 α,ω-diaminoalkanes, (H₂N(CH₂)_nNH₂, n = 2–12) have been evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv. Compounds, (H₂N(CH₂)_nNH₂, n = 9–12), exhibited a very good activities in the range 2.50–3.12 μg/mL, which can be compared with that of the first line drug, ethambutol (3.12 μg/mL). These results and a preliminary QSAR study can be considered an important start point for the rational design of new leads for anti-TB compounds.     

Structural comparison of octahedral MoO22+ complexes of bidentate and linear tetradentate N,S-donor ligands

The structures of MoO₂[NH₂C(CH₃)₂CH₂S]₂ and MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] have been determined using X-ray diffraction intensity data collected by counter techniques. MoO₂[NH₂C(CH₃)₂CH₂S]₂ crystallizes in space group Pbca with a = 11.234(3), b = 11.822(3) and c = 20.179(5) Å, V = 2680(2) ų and Z = 8. Its structure is derived from octahedral coordination with cis oxo groups [MoO = 1.705(3) and 1.705(3)], trans thiolate donors cis to the oxo groups [MoS = 2.416(1) and 2.402(1) and N donors trans to oxo [MoN = 2.325(3) and 2.385(4) Å]. MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] crystallizes in the space group P2₁/c with a = 10.798(5), b = 6.911(2), c = 20.333(9) Å, β = 95.20°, V = 1511(2) Å₃ and Z = 4. Its structure is very similar to that of MoO₂[NH₂C(CH₃)₂CH₂S]₂ with MoO = 1.714(2) and 1.710(2), MoS = 2.415(1) and 2.404(1) and MoN = 2.316(3) and 2.362(3). The small differences in the geometries of the two compounds are attributed to the constraints of the extra chelate ring in the complex with the tetradentate ligand. The structures in this paper stand in contrast to those reported for complexes of similar ligands wherein steric hindrance produces complexes with a skew trapezoidal bipyramidal structure.     

Copper N2S2 Schiff base macrocycles: The effect of structure on redox potential

A series of bis-salicylidene based N₂S₂ copper macrocycles were prepared, structurally characterised and subjected to electrochemical analysis. The aim was to investigate the effects of length of polymethylene chains between either the imine donors or the sulfur donors on redox state and potential of the metal. The complexes structurally characterised had either distorted square planar or tetrahedral geometries depending on their oxidation state (Cu²⁺ or Cu⁺, respectively), and the N–(CH₂)_n–N bridge was found to be most critical moiety in determining the redox potential and oxidation state of the copper macrocycles, with relatively little change in these properties caused by lengthening the S–(CH₂)_n–S bridge from two to three carbons. In fact, a weakness was observed in the complexes at the sulfur donor, as further lengthening of the S–(CH₂)_n–S methylene bridge to four carbons caused fission of the carbon–sulfur bond to give dimeric rings and supramolecular assemblies. Cu⁺ complexes could be oxidised to Cu²⁺ by tert-butylhydroperoxide, with a corresponding change in the spectrophotometric properties, and likewise Cu²⁺ complexes could be reduced to Cu⁺ by treatment with β-mercaptoethylamine. However, repeated redox cycles appeared to compromise the stability of the macrocycles, most probably by a competing oxidation of the ligand. Thus the copper N₂S₂ macrocycles show potential as redox sensors, but further development is required to improve their performance in a biochemical environment.     

The coordination chemistry of bidentate tellurium ligands. I. Complexes of palladium,platinum, and mercury with large chelate rings

Complexes formed from the reaction of palladium(II) and platinum(II) halides with (p-EtO·C₆H₄)Te(CH₂)_nTe(C₆H₄OEt-p) (Lⁿ, n = 6, 7, 8, 9, 10) are reported together with data for some mercury(II) complexes, [HgLⁿCl₂] which are used for comparative purposes. The compounds [MLⁿX₂] (M  Pd, Pt; n = 7, 8 (Pt only), 9, 10; X  Cl, Br) have molecular weights in molten naphthalene which fluctuate about the monomer value. [ML⁶X₂] (M  Pd, Pt; X  Cl, Br) are totally insoluble and are believed to be polymeric. The palladium(II) complexes have trans dichloro groups whereas the platinum compounds show cis dichloro groups in the solid state.¹³C NMR spectra are valuable to confirm the coordination of the ligand; the methylene resonance of the TeCH₂ group undergoes a 19–20 ppm downfield shift on coordination. ¹²⁵Te NMR spectra of the Pd(II) and Pt(II) complexes show two broad resonances the chemical shifts of which imply the presence of cis and trans isomers in CDCl₃ solution. A more detailed variable temperature high field study of [PtL⁸Cl₂] (¹²⁵Te and ¹⁹⁵Pt NMR) reveals a complex solution chemistry involving at least two cis and two trans species. The temperature range over which the solution is stable (−10 to 70 °C) is insufficient to allow a totally unambiguous interpretation but a model based on monomer ⇍ dimer equilibria provides a self consistent interpretation.     

Syntheses and X-ray structures of a series of V2S4(RCS2)4 (R=alkoxy, dialkylamino) complexes

A simple synthetic procedure leading to the V₂(S₂)₂(RCS₂)₄ species (R=Et₂N (1), cyclo-C₄H₈N (2), n-Bu₂N (3), EtO (4), i-PrO (5)) has been developed. X-ray structures of 3 and 5 have been reported, featuring the centrosymmetric molecules with VV distances 2.850(3) Å for 3 and 2.838(2) Å for 5.The FAB mass spectra were recorded. In all cases molecular peaks are observed. Fragmentation patterns are discussed.     

Synthesis and coordination chemistry of tripodal dialkyl[1,2-bis(diethylcarbamoyl)ethyl]phosphonates with lanthanide nitrates

Trifunctional dialkyl [1,2-bis(diethylcarbamoyl)- ethyl] phosphonates, (RO)₂P(O)CH[C(O)N(C₂H₅)₂]- [CH₂C(O)N(C₂H₅)₂] R  CH₃, C₂H₅, i-C₃H₇, n-C₆H₁₃ were prepared from the respective sodium salts, Na[(RO)₂P(O)CHC(O)N(C₂H₅)₂] and N,N- diethylchloroacetamide, and they were characterized by elemental analysis, mass, infrared and NMR spectroscopy. The molecular structure of (i-C₃H₇O)₂- P(O)CH[C(O)N(C₂H₅)₂][CH₂C(O)N(C₂H₅)₂] was determined by single crystal X-ray diffraction analysis and found to crystallize in the monoclinic space group P2₁/c with a=15.589(6), b=9.783(4), c= 16.283(7) Å, β = 110.90(3)°, Z = 4 and V= 2320(2) ų. The structure was solved by direct methods and blocked least-squares refinement converged with Rf = 5.7% and R_wF= 4.4% on 2266 unique data with F>4σ(F). Important bond distances include PO 1.459(3) Å, CHCO 1.228(3) Å and CHCH₂CO 1.223(3) Å. The coordination chemistry of the ligand with several lanthanides was examined, and the structure of the complex Gd(NO₃)₃{[(i-C₃H₇O)₂P(O)CH[C(O)N(C₂H₅)₂][CH₂C(O)N(C₂H₅)₂]}₂·H₂O was determined. The complex crystallized in the monoclinic space group P2₁/n with a = 13.524(5), b = 22.033(4), c = 19.604(4) Å β = 106.22(2)°, Z = 4 and V= 5609(3) ų. The structure was solved by heavy atom techniques and blocked least-squares refinement converged with R_F = 5.9% and R_wF = 4.1% on 5275 reflections with F > 4σ(F). Both trifunctional ligands were found to bond to Gd(III) through only the phosphoryl oxygen atoms. The remainder of the Gd coordination sphere was composed of three bidentate nitrate oxygen atoms and an oxygen bonded water molecule. Several important bond distances include GdO(phosphoryl)_av = 2.343(5) Å, GdO(nitrate)_av = 2.475(7) Å, GdO(water) = 2.354(5) Å, PO(phosphoryl)_av = 1.467(6) Å, CHCO_av = 1.242(10) Å and CHCH₂CO_av = 1.209(11) Å.     

Asymmetric binuclear titanocenes linked by alkyl benzyl ethers: Synthesis, characterization and use as catalysts for ethylene polymerization

A series of novel asymmetric binuclear titanocenes linked with alkyl benzyl ethers p-[(C₅H₅TiCl₂)C₅H₄CH₂]C₆H₄O(CH₂)_n[C₅H₄(TiCl₂C₅H₅)] (n = 2-5) (13-16) have been synthesized by treating p-(LiC₅H₄CH₂)C₆H₄O(CH₂)_n(C₅H₄Li) (n = 2-5) (9-12) with C₅H₅TiCl₃. The new complexes have been characterized by elemental analysis and NMR spectra. Their catalytic activity for ethylene polymerization was investigated in the presence of aluminoxane (MAO). The results show that 13-16 are efficient catalysts for producing polyethylene (PE) with a broad molecular weight distribution (MWD). Their catalytic activity is highly dependent on the length of the alkyl chain and the polymerization conditions. A longer alkyl chain increases the catalytic activity, whereas the molecular weight of the produced polyethylene decreases.