I3C NMR Research Articles

Synthesis, characterization and in vitro DNA binding studies of tin(IV) complexes of tert-butyl 1-(2-hydroxy-1-phenylethylamino)-3-methyl-1-oxobutan-2-yl carbamate

Tin(IV) complexes 1( a and b) and 2( a and b) of valine derived peptide derivatives were synthesized and characterized on the basis of elemental analysis, IR, 1H, 13C, 119Sn NMR, ESI-MS spectra and molar conductance measurements. The C–Sn–C angle was estimated from I3C and 1H NMR data 1 J( 119Sn, I3C) = 623 Hz; solution 2 J( 119Sn, 1H) = 93.04 Hz to be 149.9°. In vitro binding studies of complexes 1 and 2 under physiological conditions at room temperature with CT-DNA were carried out employing UV–visible, fluorescence, circular dichroism and viscometric studies. The binding affinity of the complexes was quantified by calculating the K b values and it follows the order 2a > 1a > 2b > 1b. To further examine the specific mode of binding, the interaction of complexes 2( a and b) were carried out with 5′GMP and 5′TMP by using absorption and NMR ( 1H, 31P) spectroscopy. The supercoiled pBR322 plasmid DNA cleavage activity of the complexes was ascertained by gel electrophoresis assay. The complexes cleave supercoiled pBR322 plasmid DNA efficiently into its nicked form at micromolar concentrations.

Isolation and Characterization of Badge Hydrolysis Products

Heating a suspension of Bisphenol A diglycidyl ether (BADGE) in 20 : 80 tetrahydrofuran/water at 70°C and subsequent passage of the resulting solution through C18 columns allowed isolation and purification to > 97% of each of the two hydrolysis products 2-[4-(2,3-dihydroxypropoxy) phenyl]-2-[4-(2,3-epoxypropoxy)phenyl]propane (1HP) and 2,2-bis[4-(2,3-dihydroxypropoxy)phenyl] propane (2HP), which were characterized by UV, IR, 1H and I3C NMR spectroscopy and mass spectrometry.

Synthesis and Characterization of Mixed- Ligand Complexes of Cu(I) Containing Halides, Triphenylstibine and Triphenylbismuthine, N,N-Dimethyl-N′-Phenylthiourea (Dmpth), N,N-Dibutyl-N′-Phenylthiourea (dbptH) and 1,3-thiazolidine-2-thione (tzdtH)

The triphenylstibine and bismuthine complexes [Cu(EPh3)(LH)2X] (LH = N, N-dimethyl-N′-phenylthiourea) (dmptH), N, N-dibutyl-N′-phenylthiourea (dbptH) or 1, 3-thiazolidine-2-thione (tzdtH); E = Sb or Bi; X = Cl, Br or I have been prepared and characterized on the basis of analytical, IR. electronic (UV-Vis), 1H and I3C NMR, FAB mass and conductivity measurements. In all cases there is a distorted tetrahedral environment around Cu(I) and the ligand (LH) binds through the thionc sulphur atom to copper(1). This is confirmed by FTIR spectra of the complexes. The complexes show v(Cu-Sb) in the range 180–195 cm−1.

THE SYNTHESIS AND CHARACTERIZATION OF 10,11-BIS(HYDROXYIMINO)-4,8,12,17-TETRAAZA 1,2,19,20-O-DICYCLO-HEXYLIDENEOCTACOSENE AND SOME TRANSITION METAL COMPLEXES

In this study, a novel dioxime 10,1l-bis(hydroxyimino)-4,8,12,17-tetraaza-1,2,19,20-O-di-cyclohexylideneoctacosene (LH2) has been synthesized starting from 1,2-O-cyclohexylidene-4-aza-8-aminooctane, which has been prepared from the l-chloro-2,3-O-cyclohexylidene, and dichloroglyoxime. The structure of this vic-dioxime has been determined as the (E, Z) form according to 1H NMR, I3C NMR and IR data. Mononuclear complexes with a metal to ligand ratio of 1:2, except for UO2(VI), have been isolated with Co(III), Co(II), Cu(II) and Ni(II) salts. The metal to ligand ratio of the uranyl complex is 1:1 and it has a dimeric structure. Attempts to prepare trinuclear complexes of the ligand with Co(III), Co(II), Cu(II) and Ni(II), failed. The structure of the ligand and its complexes is proposed from elemental analyses, IR, UV-VIS, 13C and 1H NMR spectra, magnetic susceptibility measurements, thermogravimetric analyses (TGA) and differential thermal analyses (DTA).

NMR kinetic study of ligand exchange on a (µ-oxo)bis(µ-acetato)diruthenium(III) complex. A special kinetic case of introduction of a more labile ligand

We have prepared the new [Ru2(μ-O)(μ-O2CCH3)2(4-pic)6](PF6)2 complex and followed the kinetics of exchange of the 4-picoline ligands, trans to the oxo bridge, with dimethyl sulfoxide (DMSO-d6) by 1H NMR at 30, 40, 50, and 60 °C. The 1H NMR spectra of this complex in DMSO gradually change in the acetyl methyl region as solvent substitution of the 4-picoline trans to the oxo bridge takes place. This substitution is in accordance with the lability of the ligands trans to the RuIII-O-RuIII bridge in this kind of complex. The kinetic data fit in a series of double reversible reactions, pseudo first order in the forward direction and second order in the reverse direction, with ΔH≠ = 115, 105, 116, and 106 kJ mol−1 and ΔS≠ = 35.7, 17.2, 38.8, and 16.9 JK−1 mol−1 associated with k1, k−1, k2, and k−2 rate constants, respectively.[Formula: see text]A, B and C stand for the nonexchanged, monoexchanged, and diexchanged complexes, respectively. The large ΔH≠ and positive ΔS≠ values agree with the dissociative nature of the mechanism in both forward and reverse reactions. The differences in 1H and I3C NMR chemical shifts of the three complexes are explained in terms of the effect of the ligand exchange on the N—Ru bond lengths and the geometry of the dimetal core. It is evident from our data that the exchange on one metallic site modifies the reactivity at the other site in this kind of dinuclear complex. Keywords: diruthenium complex, variable temperature NMR, ligand exchange kinetics.

Monoacylglycerols alter the lipid composition and molecular mobility of phosphatidylcholine bilayers: 13C NMR evidence of dynamic lipid remodeling

The physical effects of monoacylglycerols (MAG) in small unilamellar vesicles composed of phosphatidyl-choline (PC), triolein, cholesterol, and varying amounts of monopalmitin and monoolein were studied by 13C-NMR. The signal to noise ratio of the carbonyls of PC and triolein were enhanced by the addition of 1,2-di-[1-13C]palmitoylphosphatidylcholine and tri-[1-13C]oleoylglycerol. The linewidths of the carbonyl-13C, choline methyl, olefinic carbon, and terminal methyl resonances were measured digitally from vesicles with 0 to 42 mol % of MAG. Significant increases in the linewidth of carbonyl (P < 0.05), olefinic and terminal methyl carbons (P < 0.01) of vesicles containing 42 mol % monopalmitin indicated that these groups experienced restricted molecular mobility at high monopalmitin concentrations. However, more striking was the apparent displacement of triolein from the surface environment of PC bilayers to an oil-like environment in systems containing only 8 mol % monopalmitin. Displacement of triolein from the surface by monoolein occurred only above 15 mol %. Thus, saturated and monounsaturated monoacylglycerols, natural products of lipoprotein metabolism, dynamically alter both the lipid composition and molecular mobility of lipoprotein surfaces in distinct ways.

Proton and Carbon Chemical Shift Assignment and Solution-State Conformation of the Macrocyclic Ring in the Macrolide Antibiotic Tylosin in Aprotic Solvents

Tylosin is a 16-membered macrolide antibiotic, composed of a substituted lactone (tylonolide), an amino sugar (mycaminose) and two neutral sugars (mycinose and mycarose' (Scheme 1). It is produced on an industrial scale and is widely used as a feed additive and as a therapeutic agent in the treatment of mycoplasmosis in poultry and livestock. An advantage of this antibiotic is that it does not cause resistance because it is not used in human medicine.' The exact molecular structure of tylosin (molecular mass 916) together with the principal assignment of its I3C NMR spectrum was established in 1975 based on the analysis and identification of the products of mild acid hydrolysis3 and on 13C NMR data for related subs t a n c e ~ . ~ The crystal structure and the absolute configuration of protynolide,' a 16-membered lactone

Ethereal Solvation of Lithium Hexamethyldisilazide: Unexpected Relationships of Solvation Number, Solvation Energy, and Aggregation State

Li, 15N, and I3C NMR spectroscopic studies of 6Li-15N labeled lithium hexamethyldisilazide ((6Li,'5N)- LiHMDS) are reported. Mono-, di-, and mixed-solvated dimers are characterized in the limit of slow solvent exchange for a variety of ethereal ligands including the following: tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHl3 2,2-dimethyltetrahydrofuran (2,2-Me2THF), diethyl ether (EtzO), tert-butyl methyl ether (r-BuOMe), n-butyl methyl ether (n-BuOMe), tetrahydropyran (THP), methyl isopropyl ether (i-PrOMe), and trimethylene oxide (oxetane). The ligand exchange is too fast to observe bound and free diisopropyl ether (i-PrZO), tert-amyl methyl ether (Me2(Et)COMe), and 2,2,5,5-tetramethyltetrahydrofuran (2,2,5,5-Me4THF). Exclusively dissociative ligand substitu- tions occur at low ligand concentrations for all ligands except oxetane. Relative free energies and enthalpies of LiHMDS dimer solvation determined for eight ethereal ligands show an approximate inverse correlation of binding energy and ligand steric demand. Mixed solvation is found to be non-cooperative showing there exists little communication between the two lithium sites on the dimer. The different ethereal solvents display a widely varying propensity to cause formation of LiHMDS monomer. The often-cited correlation of reduced aggregation state with increasing strength of the lithium-solvent interaction receives no support whatsoever. The measured free energies of aggregation display a considerable solvent dependence that is traced to solvent-independent enthalpies of aggregation and solvent-dependent entropies of aggregation. LiHMDS monomer solvation numbers derive from solvent- concentration-dependent monomer:dimer proportions. Moderately hindered ethereal solvents afford LiHMDS monomers in trisolvated forms ((MesSi)zNLiS3) whereas THF and oxetane appear to afford considerable concentrations of five-coordinate tetrasolvates ((Me3Si)zNLiS4), The complex relationship between solvation energy and observable aggregation state is discussed in light of solvent-amide and solvent-solvent interactions on both the monomer and the dimer, the combined contributions of solvation enthalpy and entropy, and the complicating intervention of variable solvation numbers.

Neural Network Prediction of Carbon-13 NMR Chemical Shifts of Alkanes

Three-layer feed-forward neural networks for the prediction of I3C NMR chemical shifts of alkanes through nine carbon atoms are used. Carbon atoms in alkanes are determined by 13 descriptors that correspond to the so-called embedding frequencies of rooted subtrees. These descriptors are equal to numbers of appearance of smaller structural skeletons composed of two through five carbon atoms. It is demonstrated that the used descriptors offer a very useful formal tool for the proper and adequate description of environment of carbon atoms in alkanes. Neural networks with different numbers of hidden neurons have been examined. Best results are given by the neural network composed of three hidden neurons. Simultaneous calculations carried out by the standard linear regression analysis are compared with our neural network calculations.

(Arene)cyclopentadienylchromium Chemistry. Synthesis, EPR, NMR, and Cyclic Voltammetry of Neutral Compounds and Their Monocations

The unsymmetric sandwich compounds Cp*Cr(arene) (arene = benzene (3, benzene-d6, (3ds), toluene (4, toluenedg, (4&), ethylbenzene (5), mesitylene (6) , ethylmesitylene (7), hexamethylbenzene (8)) were synthesized from [Cp*CrC12]* in yields up to 75% by applying three procedures. Two reaction pathways could be substantiated by NMR measurements and cyclic voltammetry. For comparison CpCr(C&) (1) and Cp'Cr(C&) (2) (cp' = CH3C5b) were also made in low yield. Well-resolved EPR spectra in liquid and solid solutions were obtained below -120 C, while 'H and I3C NMR spectra could be recorded at 25 C and above. From the spectroscopic results a 2Al (eZ4, al I ) ground state was deduced; its bearing on the electron and nuclear relaxation was analyzed. Appreciable spin density was found on the ligands; in the ligand n orbitals the spin is negative, more spin sits on the arene than on Cp(*), and the n orbitals dominating the delocalization are antisymmetric. Cyclic voltammetry showed 3, 6, and 8 to undergo quasi-reversible electron transfers to [Cp*Cr(arene)]and [Cp*Cr(arene)]+, while the oxidation to the dication was followed by chemical reaction. The hitherto unknown sandwich type [Cp(*)Cr(arene)]+ could be synthesized in the case of 3+, 6+, and 8' as [PF6]and partly as [B(C&)4]-, I-, [Cp*CrC13]-, and [Cp*CrI3]salts. The 'H and I3C NMR spectra proved that the monocations are paramagnetic having most probably a 3E* (e23, all) ground state. Negative spin density was found in the ligand n system so that these cations are potential building blocks in ferromagnetic donor-acceptor stacks.

Alkene and Carbon Monoxide Insertion Reactions of Nitrogen-Coordinated Monoorganopalladium(II) Complexes: The Stepwise Construction of Alternating Copolymers of CO and Alkenes on a Palladium(II) Center

The stepwise synthesis of a palladium(II) bod N-N = N,N,”,”-tetramethylethylenediamine (tmeda) or 2,2’-bipyridyl (bpy)). The bpy-coordinated acetyl complexes (4a-c) show an unexpected isomerization reaction of the groups around the metal center for which thermodynamic parameters have been determined. A mechanism for the isomerization is proposed. The ionic complexes [Pd(COMe)(MeCN)(N-N)]OTf (5, 6; OTf = trifluoromethanesulfonate), obtained in situ from reaction of 2a-c and 4a-c with AgOTf, react with a number of alkenes. Nonstrained alkenes do insert, but decomposition (probably involving B-elimination) is fast. Alkenes containing potential donor groups do not insert at all. Only in the case of strained alkenes like norbomene and its derivatives were the insertion products isolated and fully characterized by I3C NMR, IR, and X-ray analysis. Crystals of the dicyclopentadiene insertion product [Pd(C1$I12COMe)(bpy)]OTf (8c) are monoclinic, space group P21/n, a = 8.3086(4) A, b = 15.3894(6) A, c = 18.1479(9) A, B = 99.98(1)’, V = 2285.36(19) A3, Z = 4, R = 0.042 (wR = 0.034). Here, the alkene insertion has occurred in cis,exo fashion on the norbomene-type alkene moiety, indicating this reaction to be both stereoand chemoselective. The molecular structure shows that the acyl group is coordinated to the metal. Products resulting from a second CO insertion into the Pd-C bond of 8a, i.e. PdX(COC7HloCOMe)(bpy) (X = C1 (12a) or I (12b)), were formed in the presence of a large excess of a sodium halide salt. Reaction of 12a,b with AgOTf and norbomene gave the alkyl complex [P~(C~HI~COC~HI~COM~)(~~~)]OT~ (Ua). Norbomadiene was inserted similarly. Attempted recrystallization of the insertion product of 5-norbomene-endu2,3-dicarboxylic anhydride (13c) gave the alkyl complex 8a. This is the first example of a reversible alkene insertion reaction on an isolated palladium complex. Addition of CO and excess NaI (20 equiv) to 13a gave the neutral acyl complex P~I(COC~H~~COC~HI~COM~)(~~~) (14), the first isolated and fully characterized CO/alkene oligomer still connected to the palladium(I1) catalytic site. Crystals are triclinic, space group P i with a = 10.128(2) A, b = 11.655(2) A, c = 13.633(2) A, a = 109.89(1)’, /3 = 100.58(1)0, y = 92.92(2)’, V = 1476.3(4) A3, Z = 2 and R = 0.044 (wR = 0.057). Norbomadiene also reacts with 2 equiv. of 5 or 6 to give the homoligated dinuclear complexes [(N-N)P~((C~H~)(COM~)~-~,~}P~(N-N)](OT~)Z with -N = tmeda (9) or bpy (10). Crystals of 9 are orthorhombic, space group P212121, a = 11.176(3) A, b = 11.362(1) A, c = 30.394(3) A, V = 3859(1) A3, Z = 4, wR2 = 0.124, R = 0.049. In this complex a double alkene insertion reaction has taken place involving both alkene functionalities of a dialkene: 9 is symmetrically substituted with the Pd atoms at opposite (trans) positions.

Novel Contrast Agents for Magnetic Resonance Imaging. Synthesis and Characterization of the Ligand BOPTA and Its Ln(III) Complexes (Ln = Gd, La, Lu). X-ray Structure of Disodium (TPS-9-145337286-C-S)-[4-Carboxy-5,8,11-tris(carboxymethyl)-1-phenyl-2-oxa- 5,8,11-triazatridecan-13-oato(5-)]gadolinate(2-) in a Mixture with Its Enantiomer

The syntheses of the ligand BOPTA, (4-carboxy-5,8,1 l-tris(carboxymethyl)-l-pheny1-2-oxa-5,8,1 l-triazatridecan13-oic acid; benic acid) and its Gd(III), La(III), and Lu(1U) complexes are reported. Protonation constants for BOPTA have been determined by potentiometry, and the microscopic protonation sequence has been investigated by 'H NMR. The results obtained together with the value of the Gd-BOPTA2- stability constant (log KML = 22.59) show that the complexing properties of the ligand, in comparison with DTPA, are little affected by the presence of the benzyloxymethyl residue in the structure. The solid state structure of Gd-BOPTA disodium salt [C22H2&01 I (H~O)Gd]Na2~/2H20 was determined in a single-crystal X-ray diffraction study. The structure consists of [C22H2a3011(H20)Gdl2- anions, sodium cations, and water molecules; the space group is Pi (Z = 2), with a = 9.083(6) A, b = 9.469(2) A, c = 16.698(6) A, a = 102.22(3), = 92.48(4)', y = 102.26(3), V = 1366(1) A3, and d = 1.84 g/mL. The gadolinium ion adopts a nine-coordinate geometry, which is best described as a distorted tricapped trigonal prism. Eight coordinating sites are occupied by the ligand (three nitrogen atoms and five carboxylate oxygens), and the ninth site is occupied by the oxygen atom of a water molecule. Relaxation studies have shown that in solution also Gd-BOPTA2- has one water molecule directly coordinated to the metal ion. 139La NMR studies on the La-BOPTA2- complex have further supported the view that such complexes maintain in solution the same kind of coordination as found in the solid state for Gd-BOPTA disodium salt. I3C NMR spectra of the diamagnetic La- and Lu-BOPTA2- complexes at various temperatures are consistent with the presence of two couples of isomers interconverting through a dynamic process. Such a process has previously been reported for the parent Ln-DTPA2- complexes.

Methyl Halide Reactions on Multifunctional Metal-Exchanged Zeolite Catalysts

Proximal sites consisting of a divalent metal cation as a hydroxide and/or oxide and an anion site in the zeolite framework are very active for the conversion of methyl halides to ethylene. These studies further support the effects of zeolite framework and halide leaving-group stability reported previously (J. Am. Chem. SOC. 1993,115,4732-4741) and demonstrate multiple roles for divalent metal sites. Whereas the basic zeolite CsX converted methyl iodide to hydrocarbons at temperatures as low as 498 K, this reaction commenced at 248 K on the multifunctional catalyst ZnX. The orders of activity Zn2+ > Cd2+ and Mgz+ > Ba2+ suggest that Lewis acidity is one of these roles. Zeolite CuY is very selective for ethylene formation. These reactions were studied by in situ 13C solid-state NMR, by in situ FT’IR spectroscopy with a flow cell, and with conventional flow reactors. The active sites of ZnZSM-5 were also probed with IH solid-stateNMR. The first intermediate is a framework-bound methoxy group. The I3C NMR and FTIR properties of this species have been correlated, and it is shown that this species is very similar or identical to that observed during methanol to gasoline chemistry. A detailed mechanism is proposed for the reaction of methyl halides on Zn and Mg zeolites that includes several explicit roles for the metal.

Synthesis of heterobimetallic allene complexes

The first dinuclear complex containing a four-electron p-q2,q2allene ligand was synthesized from the reaction of allene with [Cp(C0)2M0]2 (Cp = q5-C5H5) and was reported in 1977.1 Thereafter, a number of complexes of this type were prepared,2 notably by photolysis of dinuclear complexes with a bridging cyclopropylidene ligand.2b,c Several dinuclear and trinuclear metal complexes containing allenyl ligands in various bonding modes have been prepared by initially using a propargyl ligand as a t em~la t e .~ Despite these and other report^,^ methods that lead to formation of a heterodinuclar p-q2,q2-allene complex are still l a~k ing .~ In exploring the chemistry of a tungsten @-(chlorocarbony1)allylic complex Cp(C0)2W(q3-CH2C(COCl)CH2) (la)? we prepared several dinuclear complexes by replacing the C1 atom with another metal group and found photolysis of such complexes provided a systematic approach to the dinuclear p+,q2allene complexes. Herein, we report several complexes synthesized via this approach and their characterization. The reaction of Cp(CO)2W(q3-CH2C(COCl)CH2) (la)6 with CP(CO)~Win THF resulted in the formation of a homonuclear complex Cp( CO) 2W [ p-q3,q1-CH2C( CO)CH2] W(C0) 3Cp (2a). Heteronuclear analogues Cp(C0)2M(p-q3,q1-CH2C(CO)CH2)M’ (2b, M = Mo, M’ = W(CO)3Cp; 2c, M = W, M‘ = Fe(C0)zCp; 2d, M = W, M’ = Re(CO)5) were prepared similarly. However, attempts to prepare similar complexes using the Cp(C0)3Moanion were unsuccessful. We believe that metal anions with weak nucleophilicity7 may not be applicable for the preparation of 2 employing this synthetic strategy. On the basis of the EAN rule, the two metal centers in 2 bridged by a p-q3,q’-/3-carbonylallylic ligand should have no M-M bond. Complexes 2 were characterized through a combination of microanalytical data and IR, IH NMR, and I3C NMR spectroscopy.8 For example, in the ‘H NMR spectrum of 2a at room temperature, the two inequivalent Cp groups displayed a sharp resonance and a broad resonance and the allylic syn and anti protons appeared as two broad resonances at 6 2.76 and 1.38, respectively. These broad resonances are due to the fluxional behavior of the endo and exo configurations of the allylic group. At 240 K, the two broad resonances at 6 2.76 and 1.38 of 2a were resolved into two sets of allylic protons at 6 2.78, 1.16 and 2.68, 1.58,8 assignable to those of the endo and exo isomers, respectively. Photolysis of complexes 2a-c with UV irradiation in benzene resulted in the loss of two CO ligands and afforded the dinuclear

SpecInfo: An integrated spectroscopic information system

and 6000 NMR spectra of other nuclei (I9F, 15N, I7O, 31P), Several other types of spectra are planned to be included in SpecInfo for future releases. The online database offers many different access capabilities to the factual data, and some illustrative examples are discussed in this paper. In addition, there are four special programs available in the SpecInfo system in dealing with 13C NMR data: CHESS for a search of identical or similar chemical structures, COUPCAL for the calculation of coupling constants, GETSPEC for a similarity research of 13C NMR spectra, and SPECAL for the estimation of a I3C NMR spectrum from a query structure. In addition, there is a spectrum editor (EDSPEC) available to support the building of spectral queries. At the online host STN International, the SpecInfo system is embedded in a cluster of chemical databases, and it is possible to navigate through this system using the various substance registry numbers connecting the different databases. Finally, some future development plants for SpecInfo are presented.

Complexation of Zn(II) ion with macrocyclic ligands containing nitrogen-oxygen donors

Abstract

EFFECTS OF HYDROTREATING COKER LIGHT GAS OIL ON FUEL QUALITY

ABSTRACT Coker light gas oil (LGO) derived from Athabasca bitumen was hydrotreated in a fixed bed reactor using two commercial NiO-MoO3/Al203 catalysts. The effect of temperature on product quality was investigated in a pilot plant between 330 and 390 °C at 12.4 MPa, space velocity of 0.5 Ir1 and 700 liter of hydrogen per liter of coker LGO (L/L). The product quality was monitored by I3C NMR spectroscopy, elemental analysis, density and distillation techniques. The data showed that coker LGO can be hydrotreated using nickel-molybdenum catalysts at 350 °C, 0.5 h1, 12.4 MPa and 700 L/L to meet the diesel product specifications, namely, 0.5 wt % sulfur, 20% aromatics and cetane index of 40. The cetane index improvement and aromatic saturation, which are affected by thermodynamic equilibrium at temperature higher than 370 °C, could reach 29 and 86% respectively. The cetane improvement was attributed to aromatic saturation and hydrocracking with hydrogen consumption ranging from 215-340 L/L. The Ketjenfine KF-...

Synthesis, multinuclear NMR, and solution conformation of (η5-indenyl)CoIRfL complexes (L = CO, P-donor)

The preparation, spectroscopic characterization, and conformational analysis of a series of Co(III) indenyl complexes, (C9H7)CoIRfL (Rf = C3F7, C6F13, L = CO, P-donor), 2–8, are described. I3C and 1H NMR parameters are consistent with a slightly distorted -η5-C9H7 coordination. 1H nuclear Overhauser effect difference (nOed) spectra indicate a preferred solution conformation in which the perfluoroalkyl group is trans to the C3a—C7a ring junction.

Carbon-13 NMR study and observation of restricted phenyl rotation in the cobalt alkyne complex Co2(CO)6(.mu.-PhC.tplbond.CH)

We have recently reported the application of I3C NMR relaxation time analysis to investigate the phenyl group internal rotation in benzylidyne- and phosphinidene-capped metal carbonyl clusters2-6 with the goal of elucidating the factors affecting electronic interactions between the aryl ring and molecular skeleton. The experimental results have ranged from unhindered phenyl group rotation in Co,(CO)g(p3-CPh) (1) to complete immobility in Co4(CO)lo(cc4-PPh)~ (2) and CpzCo~(r-CO)(CO)3(cc3-CPh) (3). The arrested ring rotation observed in the latter complex was attributed to a strong electronic interaction between the bridging carbonyl's T* orbital and the phenyl a system through the metal 2e and carbynyl 2p orbitals. The same phenomenon has been observed by Stoneet al.' in their low-temperatureNMR

Déplacements homolytiques intramoléculaires. 19. Stéréochimie de la décomposition induite de peroxydes insaturés conduisant à la formation d'hétérocycles à trois et quatre chaînons

Homolytic decomposition induced by addition of dichloromethyl radicals to β- and γ-unsaturated peroxides having a substituent on the chain linking the unsaturation and the peroxide function was studied. The stereochemistry of the heterocycles produced was determined by I3C NMR and the stereoselectivity of intramolecular homolytic substitution on the peroxidic bond discussed. Key words: unsaturated peroxides, homolytic intramolecular substitutions, radical additions, oxygenated heterocycles.