Several lanthanide chelates of the fluorochloroalkyl β-diketones Ln(CF2ClCOCHCOR)3 ·nH2O were prepared (2, Ln=Eu; 2a, R=C(CH3)3, n=0; 2b, R=C6F5, n=0; 2c, R=CF2Cl, n=2. 3, Ln=Pr; 3a, R=C (CH3)3, n=0; 3b, R=C6F5, n=l; 3c, R=CF2Cl, n=2. 4, Ln=La, R=C6H5, n=0) and the NMR shift data of compounds 2 and 3 had been determined using alcohols, ether, ketones and amine as substrates. With alcohol, ether and ketone, compounds 2 induces shifts similar to that induced by Eu (fod)3. However due to the high solubility of the chelates in non-polar organic solvents such as CHCl3 and CCl4 and the absence of 1H signal from compounds 2b and 2c, their application as a series of new 1H NMR shift reagents seems promising. 相似文献
The lanthanide chelates of (l)-2, 2-dimethyl-6-trifluoromethyl-7-oxa-6, 8, 8, 9, 9, 10, 10, 10-octafluoro-3, 5-decanedione, Ln [(l)-CF3CF2CF2OCF (CF3) COCHCOC (CH3)3]3 (l-3a, Ln=Eu; 3b, Ln=Pr), are useful as 1H NMR shift reagents for direct determination of enantiomeric composition of enantiomorphous alcohols, ketones and amines. With these substrates, l-3a induces shift difference similar to that induced by Eu(facam)3 and Eu(hfbc)3. However, due to the higher solubility of the chelates l-3a and l-3b in nonpolar organic solvent such as CHCl3, CCl4 and only one 1H signal from l-3a and l-3b is observed, their application as the new chiral shift reagents seems promising. The spectral nonequivalence is also observed for dimethylsulfoxide in the presence of l-3a. 相似文献
The protonation constants of 2‐[4,7,10‐tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic acid (H7DOA3P) and of the complexes [Ln(DOA3P)]4? (Ln=Ce, Pr, Sm, Eu, and Yb) have been determined by multinuclear NMR spectroscopy in the range pD 2–13.8, without control of ionic strength. Seven out of eleven protonation steps were detected (pK =13.66, 12.11, 7.19, 6.15, 5.77, 2.99, and 1.99), and the values found compare well with the ones recently determined by potentiometry for H7DOA3P, and for other related ligands. The overall basicity of H7DOA3P is higher than that of H4DOTA and trans‐H6DO2A2P but lower than that of H8DOTP. Based on multinuclear‐NMR spectroscopy, the protonation sequence for H7DOA3P was also tentatively assigned. Three protonation constants (pKMHL, pKMH2L, and pKMH3L) were determined for the lanthanide complexes, and the values found are relatively high, although lower than the protonation constants of the related ligand (pK , pK , and pK ), indicating that the coordinated phosphonate groups in these complexes are protonated. The acid‐assisted dissociation of [Ln(DOA3P)]4? (Ln=Ce, Eu), in the region cH+=0.05–3.00 mol dm?3 and at different temperatures (25–60°), indicated that they have slightly the same kinetic inertness, being the [Eu(H2O)9]3+ aqua ion the final product for europium. The rates of complex formation for [Ln(DOA3P)]4? (Ln=Ce, Eu) were studied by UV/VIS spectroscopy in the pH range 5.6–6.8. The reaction intermediate [Eu(DOA3P)]* as ‘out‐of‐cage’ complex contains four H2O molecules, while the final product, [Eu(DOA3P)]4?, does not contain any H2O molecule, as proved by steady‐state/time‐resolved luminescence spectroscopy. 相似文献
Sodium perfluoroalkanesulfinate, RFSO2Na [RF?Cl(CF2)4, 1a; CF3(CF2)5, 1b; Cl(CF3)6, 1c] reacted with bromine in aqueous solution to give the corresponding sulfonyl bromide RFSO2Br (2a-2c) and in acetonitrile or acetic acid, to form perfluoroalkyl bromide RFBr (3a-3c). Heating in acetonitrile at 80°C, 2a-2c were converted smoothly into 3a-3c. However, reaction of sodium α,α-dichloropolyfluoroalkanesulfinate RCCl2SO2Na (R?CF3, Cl(CF2)n, n=2, 4, 6, 5a-5d) with bromine in aqueous solution gave directly the corresponding bromoalkanes 1-bromo-1,1-dichloropolyfluoroalkane RCCl2Br (6a-6d). In aqueous potassium iodide solution, 1a-1c, 5a and 5b also reacted with iodine to form the corresponding iodo-polyfluoroalkane 4a-4c, 7a and 7b directly. 6a and 7a underwent free radical addition to alkene readily in the presence of free radical initiator and reacted with Na2S2O4 in the usual way to form α,α-dichloropolyfluoroethane sulfinate (5a). 5a was stable in strong acid, but reacted with strong base to yield 10. 5a was oxidised by hydrogen peroxide to the sulfonate 11 and reduced by zinc in dilute acid to from the α-chloro sulfinate 12. 相似文献
Eu(fod)3-, Yb(fod)3- and Pr(fod)3-induced chemical shifts of the ‘thioaldehydic’ protons in enethial ligands complexed to a cobalt cyclopentadienyl group are unusually large and in the same direction (10–30 ppm downfield per mole of shift reagent per mole of substrate). The shifts of the protons induced by Eu(fod)3 and Pr(fod)3 in the enethial ligands show an alternation in sign on proceeding away from the sulfur atom. In contrast to the results with the fod reagents, the ytterbium and lanthanum shift reagents Yb(thd)3 and La(thd)3 caused only small shifts of protons in the 2-phenylpropenethial ligand. No induced shifts with the Eu or Pr reagents were observed for a cyclopentadienyl cobalt complex of dithioglyoxal. The induced shifts in these enethial complexes may be caused by varying blends of complex formation, contact and pseudocontact shifts. Caution is advised in assigning origins to lanthanide induced shifts in such organometallic systems. 相似文献
The 1H NMR spectra of several symmetrical diphenyls, having two unlike substituents on the ortho positions of each aromatic ring, were determined in the presence of Eu(fod)3 and of Pr(fod)3. The lanthanide induced shifts were used to establish the more probable conformation of the molecules, as deduced from computer calculations assuming pseudocontact interactions. It was found that the two like groups are in opposite conformation and that the inter-ring angles are in the order of 15–35°. 相似文献
Novel complexes [(C5Me5)2Ln][B(C6F5)4] (Ln = Pr, Nd, or Gd) were prepared, which in combination with iBu3Al efficiently induce highly 1,4‐cis‐specific polymerization of butadiene. The activity of the Gd complex/iBu3Al system is high enough to exhibit good catalytic activity even at low temperature. Polymerization at −78 °C gave polybutadiene with nearly perfect 1,4‐cis microstructure (>99.9%) with sharp molecular weight distribution (Mw/Mn = 1.45) and in reasonable yield.
ORTEP drawing of 2b . Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2). 相似文献
Six α, β, β-trifluorostyrenes with the following substituents, viz., p-MeO, p-Me, m-Me, p-Cl, m-Cl, and m-CF3, were synthesized by the reaction of the corresponding Grignard reagents with tetrafluoroethylene in tetrahydrofuran. Similarly, α-and β-trifluoroethenylnaphthalenes were prepared. The substituent electronic effects on the 19F-NMR parameters were investigated for the trifluorostyrenes (I). Linear correlations between the Hammett σ constants and the following 19F-NMR parameters were established, namely, chemical shifts δ. (F1) and δ (F2), coupling constants J12, differences of chemical shifts Δδ3-1 (δ (F3)—δ(f1) or Δδ3-2. The results are consistent with previous expectations based on the simple concept of “distorted π-electron clouds”. Facts are presented which indicate that the Δδ3-1 (or Δδ3-2) values may serve as empirical measures of the degree of polarization of the π bonds of these fluoroolefins. 相似文献
It is shown that the complexation of the (R)-MTPA (α-methoxy-α-trifluoromethyl-α-phenylacetic acid) ester of cis-4-tert-butylcyclohexanol with Eu(fod)3 is very similar to that of the corresponding trans-ester and ketones with Eu(fod)3. Further evidence is provided that the MTPA moiety exists as two different rotamers. The LIS technique, used as a tool for structure and conformation elucidation, was found by means of a Monte Carlo error analysis not to be dependent on small experimental errors. 相似文献
Enantiomerically pure triflones R1CH(R2)SO2CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3SSCF3. The deprotonation of RCH(Me)SO2CF3 (R=CH2Ph, iHex) with nBuLi with the formation of salts [RC(Me)? SO2CF3]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2CF3 group of (S)‐MeOCH2C(Me)(CH2Ph)SO2CF3 (95 % ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2C(Me)(CH2Ph)Et of 96 % ee. Racemization of salts [R1C(R2)SO2CF3]Li follows first‐order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a Cα? S bond rotation as the rate‐determining step. Lithium α‐(S)‐trifluoromethyl‐ and α‐(S)‐nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α‐(S)‐tert‐butylsulfonyl carbanion salts. Whereas [PhCH2C(Me)SO2tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half‐life of racemization at ?105 °C of 2.4 h, that of [PhCH2C(Me)SO2CF3]Li at ?78 °C is 30 d. DNMR spectroscopy of amides (PhCH2)2NSO2CF3 and (PhCH2)N(Ph)SO2CF3 gave N? S rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2C(Ph)SO2R]M (M=Li, K, NBu4; R=CF3, tBu) shows for both salts a confinement of the negative charge mainly to the Cα atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2C(Ph)SO2CF3]Li? L }2 ( L =2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH2C(Ph)SO2CF3]NBu4 have the typical chiral Cα? S conformation of α‐sulfonyl carbanions, planar Cα atoms, and short Cα? S bonds. Ab initio calculations of [MeC(Ph)SO2tBu]? and [MeC(Ph)SO2CF3]? showed for the fluorinated carbanion stronger nC→σ* and nO→σ* interactions and a weaker benzylic stabilization. According to natural bond orbital (NBO) calculations of [R1C(R2)SO2R]? (R=tBu, CF3) the nC→σ*S? R interaction is much stronger for R=CF3. Ab initio calculations gave for [MeC(Ph)SO2tBu]Li ? 2 Me2O an O,Li,Cα contact ion pair (CIP) and for [MeC(Ph)SO2CF3]Li ? 2 Me2O an O,Li,O CIP. According to cryoscopy, [PhCH2C(Ph)SO2CF3]Li, [iHexC(Me)SO2CF3]Li, and [PhCH2C(Ph)SO2CF3]NBu4 predominantly form monomers in tetrahydrofuran (THF) at ?108 °C. The NMR spectroscopic data of salts [R1(R2)SO2R3]Li (R3=tBu, CF3) indicate that the dominating monomeric CIPs are devoid of Cα? Li bonds. 相似文献
2-Azetidinones which carry a proton each on C-3 and C-4 often pose a problem in the correct assignment of the resonances due to these protons; titanium tetrachloride has been shown to be an effective and reliable n.m.r. shift reagent to differentiate between these two protons on the basis of their different sensitivities to this reagent. A few compounds were also studied with Eu(fod)3 and Pr(fod)3 for the sake of confirmation. 相似文献
A detailed investigation of the reactions of PhSO2CF2H and PhSO2CH2F with (E)‐chalcone (=(E)‐1,3‐diphenylprop‐2‐en‐1‐one) at low temperatures revealed that these two reactions were kinetically controlled, and the ratios of 1,2‐ vs. 1,4‐adducts, which did not change much over time at these temperatures, reflect the relative rates of the two reaction pathways. The controlled experiments of converting the PhSO2CF2‐ and PhSO2CHF‐substituted 1,2‐adducts to 1,4‐adducts showed that these isomerizations are not favored due to the low stability and hard‐soft nature of PhSO2CF and PhSO2CHF? anions. Moreover, taking advantage of the remarkable stability and softness of (PhSO2)2CF? anion, an efficient thermodynamically controlled isomerization of (PhSO2)2CF‐substituted 1,2‐adduct to 1,4‐adduct was achieved for the first time. 相似文献
1‐Allyl‐2,4,7‐trimethyl‐1 H‐indene ( 1 ) and 1‐(3‐buten‐1‐yl)‐4,7‐dimethyl‐1 H‐indene ( 2 ), which are to prepare from (2,4,7‐trimethylindenyl)lithium and allyl chloride or from (4,7‐dimethylindenyl)lithium and 4‐bromo‐1‐butene, react with n‐butyllithium yielding (1‐allyl‐2,4,7‐trimethylindenyl)lithium [LiL ( 1 a )] or [1‐(3‐buten‐1‐yl)‐4,7‐dimethylindenyl]lithium [LiL′ ( 2 a )], respectively. The reactions of the trichlorides of gadolinium, erbium, yttrium, lutetium, and ytterbium with 1 a or 2 a (mole ratio 1 : 2) in THF produce the bis(indenyl)lanthanide chloride complexes L2LnCl(THF) [Ln = Gd ( 1 b ), Er ( 1 c )], LLnCl(THF) [Y ( 2 d ), Lu ( 2 e )], or LYb(μ‐Cl)2Li(THF)2 ( 2 f ), whereas the trichlorides of the comparatively large samarium and lanthanum ions react with different molar amounts of 2 a in THF exclusively with formation of the tris(indenyl) complexes LSm ( 2 g ) or LLa(μ‐Cl)Li(Et2O)3 ( 2 h ), respectively. All new compounds were characterized by elemental analyses, mass spectrometry, and the diamagnetic compounds 2 d , 2 e and 2 h also by 1H and 13C{1H}‐NMR spectroscopy. The single crystal X‐ray structural analyses of 1 c , 2 f , 2 g and 2 h demonstrate that the alkenyl groups of the indenyl side chains are not coordinated to the lanthanide atoms. 相似文献
Uncatalyzed cycloaddition of α-alkoxycarbonylnitrones 1 with vinyl ethers 7 gave mixtures of cis- and trans-cycloadducts 8, whereas Eu(fod)3-catalyzed cycloaddition of 1 with 7 gave the trans-cycloadducts trans-8 in a highly stereoselective manner. NMR studies indicated that Eu(fod)3 selectively activated (Z)-nitrones (Z)-1 in E,Z-equilibrium mixtures of nitrones 1. In contrast, the reaction of 1 with allyl alcohols 12 in the presence of Eu(fod)3 resulted in sequential transesterification and intramolecular cycloaddition to give intramolecular cycloadducts 13. 相似文献
The equimolar mixtures of typical lanthanide shift reagents such as Eu(fod)3, Pr(fod)3 or Yb(fod)3 with silver trifluoroacetate, previously used to induce paramagnetic shifts in the 1H NMR spectra of alkenes, have been successfully applied to simple aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes. In benzene and p-xylene the signals of all the aromatic protons are shifted identically. In other substituted benzenes the magnitude of the induced shift depends on the distance between the proton and the substituents. In addition, the different behaviour of the signals of the methyl groups in meta-and para-xylene on the addition of the complex shift reagent allows the quantitative analysis of the two xylenes in their mixtures. 相似文献