Synthesis of P-Chiral [ 18 O]-Labeled Isotopomeric Oligo(deoxyribonucleoside Phosphorothioate)s and Phosphates

Diastereomerically pure, isotopically labeled 5'- O -DMT-nucleoside-3'- O -(2-thio-4,4-"spiro"-pentamethylene-1,3,2-[ 18 O]oxathiaphospholane)s and -(2-oxo-4,4-"spiro"-pentamethylene-1,3,2-[ 18 O]oxathiaphospholane)s suitable for stereocontrolled synthesis of P-chiral oligonucleotide [ 18 O]phosphorothioates and [ 18 O]phosphates were synthesized. Obtained in that way "chimeric" oligonucleotide d[A PO A PS-Rp,Sp A PS-Rp , Sp A PS-Rp C PS(18O)-Rp G PS-Rp T PS-Rp T PS-Rp,Sp T PO T] was used for determination of the stereochemistry of hydrolysis by endonuclease from Serratia marcescens .     

Nucleophilic participation in the transition state for human thymidine phosphorylase

Recombinant human thymidine phosphorylase catalyzes the reaction of arsenate with thymidine to form thymine and 2-deoxyribose 1-arsenate, which rapidly decomposes to 2-deoxyribose and inorganic arsenate. The transition-state structure of this reaction was determined using kinetic isotope effect analysis followed by computer modeling. Experimental kinetic isotope effects were determined at physiological pH and 37 degrees C. The extent of forward commitment to catalysis was determined by pulse-chase experiments to be 0.70%. The intrinsic kinetic isotope effects for [1'-(3)H]-, [2'R-(3)H]-, [2'S-(3)H]-, [4'-(3)H]-, [5'-(3)H]-, [1'-(14)C]-, and [1-(15)N]-thymidines were determined to be 0.989 +/- 0.002, 0.974 +/- 0.002, 1.036 +/- 0.002, 1.020 +/- 0.003, 1.061 +/- 0.003, 1.139 +/- 0.005, and 1.022 +/- 0.005, respectively. A computer-generated model, based on density functional electronic structure calculations, was fit to the experimental isotope effect. The structure of the transition state confirms that human thymidine phosphorylase proceeds through an S(N)2-like transition state with bond orders of 0.50 to the thymine leaving group and 0.33 to the attacking oxygen nucleophile. The reaction differs from the dissociative transition states previously reported for N-ribosyl transferases and is the first demonstration of a nucleophilic transition state for an N-ribosyl transferase. The large primary (14)C isotope effect of 1.139 can occur only in nucleophilic displacements and is the largest (14)C primary isotope effect reported for an enzymatic reaction. A transition state structure with substantial bond order to the attacking nucleophile and leaving group is confirmed by the slightly inverse 1'-(3)H isotope effect, demonstrating that the transition state is compressed by the impinging steric bulk of the nucleophile and leaving group.     

Stereodefined synthesis of O3'-labeled uracil nucleosides. 3'-[(17)O]-2'-Azido-2'-deoxyuridine 5'-diphosphate as a probe for the mechanism of inactivation of ribonucleotide reductases

Thermolysis of a 2'-[(16)O]-O-benzoyl-[(17)O]-5'-O-(tert-butyldimethylsilyl)-O(2),3'-cyclouridine derivative gave the more stable 3'-[(17)O]-O-benzoyl-[(16)O]- 5'-O-(tert-butyldimethylsilyl)-O(2),2'-cyclouridine isomer, which was converted into 3'-[(17)O]-2'-azido-2'-deoxyuridine by deprotection and nucleophilic ring opening at C2' with lithium azide. The 5'-diphosphate was prepared by nucleophilic displacement of the 5'-O-tosyl group with tris(tetrabutylammonium) hydrogen pyrophosphate. Model reactions gave (16)O and (18)O isotopomers, and base-promoted hydrolysis of an O(2),2'-cyclonucleoside gave stereodefined access to 3'-[(18)O]-1-(beta-D-arabinofuranosyl)uracil. Inactivation of ribonucleoside diphosphate reductase with 2'-azido-2'-deoxynucleotides results in appearance of EPR signals for a nitrogen-centered radical derived from azide, and 3'-[(17)O]-2'-azido-2'-deoxyuridine 5'-diphosphate provides an isotopomer to perturb EPR spectra in a predictable manner.     

Transition-state analysis of S. pneumoniae 5'-methylthioadenosine nucleosidase

Kinetic isotope effects (KIEs) and computer modeling are used to approximate the transition state of S. pneumoniae 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN). Experimental KIEs were measured and corrected for a small forward commitment factor. Intrinsic KIEs were obtained for [1'-3H], [1'-14C], [2'-3H], [4'-3H], [5'-3H(2)], [9-15N] and [Me-3H(3)] MTAs. The intrinsic KIEs suggest an SN1 transition state with no covalent participation of the adenine or the water nucleophile. The transition state was modeled as a stable ribooxacarbenium ion intermediate and was constrained to fit the intrinsic KIEs. The isotope effects predicted a 3-endo conformation for the ribosyl oxacarbenium-ion corresponding to H1'-C1'-C2'-H2' dihedral angle of 70 degrees. Ab initio Hartree-Fock and DFT calculations were performed to study the effect of polarization of ribosyl hydroxyls, torsional angles, and the effect of base orientation on isotope effects. Calculations suggest that the 4'-3H KIE arises from hyperconjugation between the lonepair (n(p)) of O4' and the sigma* (C4'-H4') antibonding orbital owing to polarization of the 3'-hydroxyl by Glu174. A [methyl-3H(3)] KIE is due to hyperconjugation between np of sulfur and sigma* of methyl C-H bonds. The van der Waal contacts increase the 1'-3H KIE because of induced dipole-dipole interactions. The 1'-3H KIE is also influenced by the torsion angles of adjacent atoms and by polarization of the 2'-hydroxyl. Changing the virtual solvent (dielectric constant) does not influence the isotope effects. Unlike most N-ribosyltransferases, N7 of the leaving group adenine is not protonated at the transition state of S. pneumoniae MTAN. This feature differentiates the S. pneumoniae and E. coli transition states and explains the 10(3)-fold decrease in the catalytic efficiency of S. pneumoniae MTAN relative to that from E. coli.     

Conformational equilibrium isotope effects in glucose by (13)C NMR spectroscopy and computational studies.

Anomeric equilibrium isotope effects for dissolved sugars are required preludes to understanding isotope effects for these molecules bound to enzymes. This paper presents a full molecule study of the alpha- and beta-anomeric forms of D-glucopyranose in water using deuterium conformational equilibrium isotope effects (CEIE). Using 1D (13)C NMR, we have found deuterium isotope effects of 1.043 +/- 0.004, 1.027 +/- 0.005, 1.027 +/- 0.004, 1.001 +/- 0.003, 1.036 +/- 0.004, and 0.998 +/- 0.004 on the equilibrium constant, (H/D)K(beta/alpha), in [1-(2)H]-, [2-(2)H]-, [3-(2)H]-, [4-(2)H]-, [5-(2)H]-, and [6,6'-(2)H(2)]-labeled sugars, respectively. A computational study of the anomeric equilibrium in glucose using semiempirical and ab initio methods yields values that correlate well with experiment. Natural bond orbital (NBO) analysis of glucose and dihedral rotational equilibrium isotope effects in 2-propanol strongly imply a hyperconjugative mechanism for the isotope effects at H1 and H2. We conclude that the isotope effect at H1 is due to n(p) --> sigma* hyperconjugative transfer from O5 to the axial C1--H1 bond in beta-glucose, while this transfer makes no contribution to the isotope effect at H5. The isotope effect at H2 is due to rotational restriction of OH2 at 160 degrees in the alpha form and 60 degrees in the beta-sugar, with concomitant differences in n --> sigma* hyperconjugative transfer from O2 to CH2. The isotope effects on H3 and H5 result primarily from syn-diaxial steric repulsion between these and the axial anomeric hydroxyl oxygen in alpha-glucose. Therefore, intramolecular effects play an important role in isotopic perturbation of the anomeric equilibrium. The possible role of intermolecular effects is discussed in the context of recent molecular dynamics studies on aqueous glucose.     

Structural, electrochemical, and spectroscopic characterization of a redox pair of sulfite-based polyoxotungstates: alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-

The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr4N)4{alpha-[W18O54(SO3)2]}.2CH3CN and the one-electron reduced form (Pr4N)5{alpha-[W18O54(SO3)2]}.2CH3CN has been achieved. alpha-[W18O54(SO3)2]5- was obtained as a Pr4N+ salt by reducing the "Trojan Horse" [W18O56(SO3)2(H2O)2]8- cluster via a template orientation transformation. Acetonitrile solutions of pure alpha-[W18O54(SO3)2]5- also were prepared electrochemically by one-electron bulk reductive electrolysis of alpha-[W18O54(SO3)2]4-. Cyclic voltammetry of alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5- in CH3CN (0.1 M Hx4NClO4) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten-oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH3CN exhibit the expected sign and magnitude of the steady-state limiting current values for the alpha-[W18O54(SO3)2]4-/5-/6- series and confirm the existence of a stable one-electron reduced species, alpha-[W18O54(SO3)2]5-. Employment of the Randles-Sevcik (cyclic voltammetry) and Levich (rotating disk electrode) equations at a glassy carbon electrode (d=3 mm) enable diffusion coefficient values of 3.7 and 3.8x10(-6) cm2 s-1 to be obtained for alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-, respectively. The tungsten polyoxometalates are highly photoactive, since measurable photocurrents and color changes are detected for both species upon irradiation with white light. EPR spectra obtained from both acetonitrile solution and solid samples, down to temperatures as low as 2.3 K, of the chemically and electrochemically prepared one-electron reduced species provided evidence that the unpaired electron in alpha-[W18O54(SO3)2]5- is delocalized over a number of atoms in the polyoxometalate structure, even at very low temperatures.     

Synthesis of analogues of (-)-cytisine for in vivo studies of nicotinic receptors using positron emission tomography

[formula: see text] 9-Substituted analogues of (-)-cytisine were synthesized in high yields via palladium-mediated couplings of either 9-(-)-bromocytisine and organostannanes or 9-(-)-trimethylstannylcytisine and fluorobromobenzene. The protection of the amine with a nitroso group and the use of PdCl2(PPh3)2 to carry out the Stille reaction allowed the rapid synthesis of 9-(4'-[18F]fluorophenyl)cytisine (18F: t1/2 = 109.7 min), a new promising radioligand (radiochemical yield: 10% from [18F]KF, 150 min, four steps) for positron emission tomography studies of alpha 4 beta 2 nicotinic receptors.     

Platinum complexes of dibenzo[1,2]dithiin, dibenzo[1,2]dithiin oxides and related polyaromatic hydrocarbon ligands

The synthesis of platinum bisphosphine complexes of biphenyl- 2,2'-dichalcogenates and the oxides of dibenzo[1,2]dithiin and related ligand systems by oxidative addition to [Pt(PPh(3))(4)] is reported. We also describe the synthesis of a new compound, dibenzothiophen-4-yldiselenide and its simple platinum complex (obtained by oxidative addition). All complexes have been fully characterised, principally by using multinuclear NMR spectroscopy and in six cases by means of single-crystal X-ray diffraction studies. The majority are simple S/S or Se/Se complexes, however the addition of dibenzo[1,2]dithiin trioxide to [Pt(PPh(3))(4)] gives a bimetallic system, [Pt[2-[S(O)],2'-[S(O)(2)]-biphen}(PPh(3))](2), containing a central Pt(2)S(2)O(2) core in which the ligand behaves as a tridentate S,S,O donor.     

Enzymic preparation of dioxygen-18 labelled leukotriene E4 and its use in quantitative gas chromatography-mass spectrometry.

A simple and rapid method is described for the preparation of a stable isotope oxygen-18 labelled leukotriene E4 (LTE4). Oxygen-18 labelling of LTE4 methyl ester in oxygen-18 water catalysed by a pig liver esterase resulted in the incorporation of two oxygen-18 atoms in the carboxylic group of LTE4 to the extent of 89.8% ([18O2]LTE4) and one oxygen-18 atom to the extent of 9.4% ([16O18O]LTE4), with only 0.7% remaining unchanged ([16O2]LTE4). [18O2]LTE4 was found not to back-exchange following incubation in acidified urine (pH 4.0) at 4 degrees C for up to 20 h. [18O2]LTE4 was demonstrated to be a useful internal standard in a method for the quantitative determination of LTE4 in human urine involving high-performance liquid chromatography and gas chromatography with negative-ion chemical ionization tandem mass spectrometry: the concentration of LTE4 in a 24-h urine sample of a healthy subject was determined to be 68.1 pg/ml.     

Asymmetric synthesis of the putative structure of (-)-oryzoxymycin

[reaction: see text] A short asymmetric synthesis of (2'S,5R,6R)-2'-[6-amino-5-hydroxy-1,3-cyclohexadiene-1-carbonyloxy]propionic acid, the enantiomer of the reported structure of (+)-oryzoxymycin is described. The reported spectral data does not match that obtained for synthetic "oryzoxymycin".     

Distance dependence of electron transfer in rigid,cofacially compressed,pi-stacked porphyrin-bridge-quinone systems

The electron-transfer (ET) dynamics of a series of unusually rigid pi-stacked porphyrin-quinone (P-Q) systems, in which sub-van der Waals interplanar distances separate juxtaposed porphyryl, aromatic bridge, and quinonyl components of these assemblies, are reported. The photoinduced charge separation (CS) and thermal charge recombination (CR) ET reactions of [5-[8'-(2',5'-benzoquinonyl)-1'-naphthyl]-10,20-diphenylporphinato]zinc(II) (1a-Zn), [5-[8'-(4'-[8'"-(2'"',5'"'-benzoquinonyl)-1'"-naphthyl]-1'-phenyl)-1'-naphthyl]-10,20-diphenylporphinato]zinc(II) (2a-Zn), and [5-(8'-[4'-(8'"-[4'"'-(8'"-[2'"',5'"'-benzoquinonyl]-1'"-naphthyl)-1'"'-phenyl]-1'"-naphthyl)-1'-phenyl]-1'-naphthyl)-10,20-diphenylporphinato]zinc(II) (3a-Zn) in CH(2)Cl(2) were investigated by pump-probe transient absorption spectroscopy. Analyses of these data show that the phenomenological ET distance dependence (beta) for both the CS and CR reactions in these systems is soft (beta(CS) = 0.43 A(-1); beta(CR) = 0.35 +/- 0.16 A(-1)). This work demonstrates that simple aromatic building blocks such as benzene, which are characterized by highly stabilized filled molecular orbitals and large HOMO-LUMO gaps, can provide substantial D-A electronic coupling when organized within a pi-stacked structural motif that features a modest degree of arene-arene interplanar compression.     

Extreme electronic modulation of the cofacial porphyrin structural motif

The synthesis, electrochemistry, and optical spectroscopy of an extensive series of cofacial bis[(porphinato)zinc(II)] compounds are reported. These species were synthesized using sequential palladium-catalyzed cross-coupling and cobalt-mediated [2+2+2] cycloaddition reactions. This modular methodology enables facile control of the nature of macrocycle-to-macrocycle connectivity and allows unprecedented modulation of the redox properties of face-to-face porphyrin species. We report the synthesis of 5,6-bis[(5',5'-10',20'-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (1), 5,6-bis[(2'-5',10',15',20'-tetraphenylporphinato)zinc(II)]indane (2), 5-([2'-5',10',15',20'-tetraphenylporphinato]zinc(II))-6-[(5"-10',20'-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (3), 5-([2'-5',10',15',20'-tetrakis(trifluoromethyl)porphinato]zinc(II))-6-[(5' '-10' ',20' '-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (4), 5-(2'-5',10',15',20'-[tetrakis(trifluoromethyl)porphinato]zinc(II))-6-[(2'-5',10',15',20'-tetraphenylporphinato)zinc(II)]indane (5), 5,6-bis([2'-5',15'-diphenyl-10',20'-(trifluoromethyl)porphinato]zinc(II))indane (6), and 5,6-bis([2'-5',10',15',20'-tetrakis(trifluoromethyl)porphinato]zinc(II))indane (7); 4-7 define the first examples of cofacial bis[(porphinato)metal] compounds in which sigma-electron-withdrawing perfluoroalkyl groups serve as macrocycle substituents, while 2, 6, and 7 constitute the first such structures that possess a beta-to-beta linkage topology. Cyclic voltammetric studies show that the electrochemically determined HOMO and LUMO energy levels of these cofacial bis(porphinato) complexes can be lowered by 780 and 945 mV, respectively, relative to the archetypal members of this class of compounds; importantly, these orbital energy levels can be modulated over well-defined increments throughout these wide potentiometric domains. Analyses of these cofacial bis[(porphinato)metal] potentiometric data, in terms of the absolute and relative frontier orbital energies of their constituent [porphinato]zinc(II) building blocks, as well as the nature of macrocycle-to-macrocycle connectivity, provide predictive electronic structural models that rationalize the redox behavior of these species.     

Synthesis of [5'-13C]ribonucleosides and 2'-deoxy[5'-13C]ribonucleosides

The present efficient synthesis of [5'-13C]ribonucleosides and 2'-deoxy[5'-13C]ribonucleosides is characterized by the synthesis of the D-[5-13C]ribose derivative as an intermediate via the Wittig reaction of 4-aldehydo-D-erythrose dialkyl acetals with Ph3P13CH3I-BuLi to introduce the 13C label at the 5-position of a pentose. This was followed by the highly diastereoselective osmium dihydroxylation for the preparation of 2,3-di-O-benzyl-D-[5-13C]ribose dialkyl acetal and the cyclization from D-[5-13C]ribose dialkyl acetal derivatives to the alkyl D-[5-13C]ribofuranoside derivative by the use of LiBF(4). The obtained D-[5-13C]ribose derivative was converted into [5'-13C]ribonucleosides and subsequently into the corresponding 2'-deoxynucleosides.     

Phosphoramidites of Chiral (Rp)-and (Sp)-Configurated d(T[P-18O]-A): Synthesis,Configurational Assignment,and Use as Dimer Blocks in Oligonucleotide Synthesis

The N,N-diisopropylphosphoramidites 10a and 10b of appropriately protected chiral diastereoisomers of d(T[P-¹⁸O]-A) ( 8a and 8b , resp.), chiral by virtue of the isotope ¹⁸O at the P-atom, have been synthesized. The ¹⁸O-isotope was incorporated by oxidation of the phosphite triester 3 with H₂[¹⁸O]/I₂. Separation of the diastereoisomers was accomplished by flash chromatography of the O-3′-deprotected phosphate triesters 5a/b . The absolute configuration at the chiral P-atom was deduced from the methylation products of the fully deprotected diastereoisomers 8a and 8b . Phosphinylation of 5a and 5b yielded the configurationally pure phosphoramidites 10a and 10b , respectively, which were then employed in solid-phase synthesis to yield the self-complementary oligomers d(G-A-G-T-(R_p)-[P-¹⁸O]-A-C-T-C) ( 13 ) and d(G-A-G-T-(S_P)-[P-¹⁸O]-A-C-T-C) ( 14 ), respectively.     

The classic Wells-Dawson polyoxometalate, K6[alpha-P2W18O62].14H2O. Answering an 88 year-old question: what is its preferred, optimum synthesis?

The 88-year-old problem of developing a preferred, optimized synthesis of the prototype Wells-Dawson polyoxometalate, K6[alpha-P2W18O62].14H2O, is addressed herein. Specifically, six published syntheses of K6[alpha-P2W18O62].14H2O are listed and discussed, with emphasis given to the two most recent syntheses, Nadjo and co-workers' 2004 synthesis and a 1997 Inorganic Syntheses procedure by Droege, Randall, Finke et al. (hereafter D-R-F). For the starting experiment, the synthesis by Nadjo and co-workers was repeated. Next, the D-R-F synthesis and then the earlier (1984) synthesis in Droege's Ph.D. thesis were repeated and reinvestigated. The results demonstrate that the Nadjo synthesis produces over 200 g of high alpha-isomer purity (> or =97% by (31)P NMR) K6[alpha-P 2W18O62].14H2O in four steps over 8 days in 93% yield in our hands. A recrystallization step added as part of this work (for a total of five steps over 12 days) produces an increase in purity (>99%) with a concomitant loss of 8% yield (i.e., 85% overall yield) for the Nadjo-plus-recrystallization synthesis. Next, the D-R-F Inorganic Syntheses procedure was reinvestigated to determine the cause of "failed syntheses" occasionally encountered in our laboratories, the most recent and worst example to date being when one of us (C.R.G.) found 150 g of K10[alpha2-P 2W17O61] as an undesired side product when, as it turns out, the D-R-F Inorganic Syntheses procedure is followed rather than the earlier Droege synthesis. Specifically, it is shown that the problem in the Inorganic Syntheses procedure is that it ambiguously says to add 210 mL of HCl until a pH of 3-4 is reached when, in fact, it takes only 130-150 mL of HCL to reach a pH 3-4. Adding the full 210 mL of HCl ensures that a pH <2 is reached, as is required to produce isomerically pure K6[alpha-P 2W18O62].14H2O from the K 10[alpha 2-P 2W 17O 61] intermediate. The result is K6[alpha-P2W18O62].14H2O in five steps over 10 days in 82% yield and > or =97% purity. A table is provided comparing the details of the two best syntheses as reported herein: the Nadjo-plus-recrystallization synthesis and the D-R-F synthesis (with sufficient added HCl/proper pH control). That table makes apparent that the Nadjo-plus-recrystallization synthesis is improved on the basis of its better atom economy, its slightly higher product yields (85% vs 82%), slightly better purity (>99% vs >97%), and its comparable time (2 days shorter without recrystallization but 2 days longer with recrystallization) in comparison to the D-R-F synthesis with proper pH <2 control. Perhaps most importantly, some take-home messages concerning polyoxometalate synthesis illustrated by the iterative, 88 year-old quest to the best K6[alpha-P 2W18O62].14H2O synthesis are summarized and briefly discussed.     

Mononuclear, five-coordinate lanthanide amido and aryloxide complexes bearing tetradentate (N2O2) Schiff bases

Two monomeric, five-coordinate lanthanide complexes, [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]samarium[2,6-bis(tert-butyl)-4-methylphenoxide] and [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]erbium[2,6-bis(tert-butyl)-4-methylphenoxide], were isolated from the reactions of 2,6-bis(tert-butyl)-4-methylphenol with [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]lanthanide[bis(trimethylsilyl)amido] (lanthanide = Er(3+) and Sm(3+)). The purified phenoxides were recovered in excellent yields and analytical purity, and the reactions proceeded cleanly without Schiff-base degradation or cluster formation. Analogously, [bis-3,3'-(1,3-propanediyldiimino)-1-phenyl-2-butene-1-onato]erbium[bis(trimethylsilyl)amido] was also directly converted to [bis-3,3'-(1,3-propanediyldiimino)-1-phenyl-2-butene-1-onato]erbium[2,6-bis(tert-butyl)-4-methylphenoxide]; however, a less sterically demanding alcohol (i.e., ethanol) yielded a neutral trinuclear oxo alkoxide species with each dianionic Schiff base asymmetrically bridging through micro-oxo interactions. In this polynuclear cluster, each symmetry-related, seven-coordinate erbium(III) ion exhibits monocapped trigonal prismatic geometry, which assembles by sharing triangular capped faces. Single-crystal X-ray diffraction revealed square-pyramidal metal coordination in each five-coordinate lanthanide ion with varied S(4) ruffling of the "square base" donor atoms and the six-membered propylene diamine chelate ring adopting the boat conformation. To contrast the effect of subtle ligand changes, we also report the synthesis and characterization of [bis-5,5'-(2,2-dimethyl-1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]samarium[bis(trimethylsilyl)amido], having gem-dimethyl substituents appended to the propylene bridge central carbon. The six-membered diamine chelate ring in this compound adopts the chair conformation without metal-hydrocarbon interaction. Also presented are qualitative activity observations and polymerization data for the polymerization of rac-lactide and epsilon-caprolactone using the five-coordinate lanthanide amidos and phenoxides.     

Synthesis and characterization of benzoxazine-functionalized amine bridged bis(phenolate) lanthanide complexes and their application in the ring-opening polymerization of cyclic esters

The synthesis and structures of lanthanide complexes supported by benzoxazine-functionalized amine bridged bis(phenolate) ligand 6,6'-(2-(8-tert-butyl-6-methyl-2H-benzo[e][1,3]oxazin-3(4H)-yl)ethylazanediyl)bis(methylene)bis(2-tert-butyl-4-methylphenolato) (L(2-)) are described. Salt metathesis reaction between lanthanide trichloride and 2 eq of LNa(2) in THF at room temperature afforded the corresponding "ate" complexes [L(2)LnNa(THF)(2)] (Ln[double bond, length as m-dash]Y (1), Nd (2), Er (3), Yb (4)). Further treatment of the product with 18-crown-6 afforded discrete ion-pair complexes [L(2)Ln][(18-crown-6)Na(THF)(2)] (Ln[double bond, length as m-dash]Y (5), Yb (6)). The single-crystal structural analyses of 1 and 3-6 revealed that the lanthanide cation and the sodium cation were bridged by two phenolate oxygen atoms in complexes 1, 3 and 4, while in complexes 5 and 6, the anion comprises a lanthanide cation coordinated by two L(2-) and the cation is comprised of a sodium cation surrounded by an 18-crown-6 and two THF molecules. These complexes were found to exhibit distinct activities towards the ring-opening polymerization of ε-caprolactone and l-lactide.     

双核Cd(Ⅱ)配合物[Cd2(C22H14N4)2Cl2(N3)2]2·H2O的合成与晶体结构

A dinuclear Cd(Ⅱ) complex [Cdz (N3)2LzCl2]2·H2O (1) [L=4'-(4-eyanophenyl)-2,2':6',2"-terpyridine]was synthesized by reaction of ligand L with CdCl2 and NaN3 using solvothermal method and its structure was determined by X-ray crystal structure analysis. The structure indicates that the complex crystallizes in monoclinic, space group C2/c with a=1.644 5(16) nm, b=1.441 9(12) nm, c=1.9181(18) nm,β=100.349(11)°. V=4474(7) nm3, Z=2, Dc=1.570Mg·m-3,μ=1.120 mm-l, F(000)=2 100, and final R1=0.039 3, wR2=0.0811. The result shows a Cd(Ⅱ) ion was sixcoordinated by a tridentate 4'-(4-cyanophenyl)-2,2' :6',2"-terpyridine ligand and one bridging nitrogen atom of the azide group in the basal position and an chloride atom and the other bridging nitrogen atom of the azide group in the axialone, to form a distorted octahedral-pyramidal geometry. CCDC: 673291.