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A series of lithium complexes with trianionic bis(trityl)/aryloxide ligands were prepared by triple deprotonation of phenols with two ortho-diarylmethyl substituents. Transmetalation with one of the lithium complexes via salt metathesis resulted in the synthesis of corresponding Mg and Zn complexes, which showed distinct coordination stoichiometry and structures. The metal complexes were characterized by multi-nuclear NMR, UV–vis, and infrared spectroscopy. Additionally, the redox property of a trilithium compound was investigated by electrochemical methods. X-ray crystallography revealed that the new bis(trityl)/aryloxide ligands could simultaneously bind to two nearby metal centers both in chelating κ2-O,C fashion, making themselves rare examples of tridentate binucleating alkyl/aryloxo scaffolds.

Copper(II) nitrate complexes of 2-(((2-((2-aminoethyl)amino)ethyl)imino)methyl)phenol, 2-(((2-((2-aminoethyl)amino)ethyl)imino)methyl)-4,6-dichlorophenol, 2-(((2-(piperazin-1-yl)ethyl)imino)methyl)phenol and (2,4-di-tert-butyl-6-(((2-(piperazin-1-yl)ethyl)imino)methyl)phenol, as well as a copper(II) acetate complex of 2-(((2-(piperidin-1-yl)ethyl)imino)methyl)phenol, have been prepared and characterized by X-ray diffraction studies. In combination with benzyl alcohol, all complexes are active in rac-lactide polymerization at 140 °C in molten monomer to provide moderately heterotactic polylactic acid. Most complexes showed complicated reaction kinetics, indicative of two interconverting active species. Molecular weight control was poor and a strong tendency toward intramolecular transesterification led to oligomeric products. There was no indication that the basic site of the ligand is participating in the polymerization reaction by deprotonation of the alcohol nucleophile.

A series of ClRe(CO)3-containing complexes with 1-methyl-1H-benzo[d]imidazol-2-yl)quinoline (Me-QuBIm), 1-benzyl-1H-benzo[d]imidazol-2-yl)quinoline (Bn-QuBIm), and 2-(1-(4-methoxybenzyl)-1H-benzo[d]imidazol-2-yl)quinoline (OMeBn-QuBIm) ligands were prepared and characterized. Each complex was characterized using 1H and 13C NMR, infrared, UV–vis, and fluorescence spectroscopies, and cyclic voltammetry. The physical properties of each complex are similar to the parent ClRe(CO)3(2-(1H-benzo[d]imidazol-2-yl)quinoline) complex. However, the electrochemical behavior is distinct from the parent, showing reversible voltammograms and poor CO2 reduction activity. Addition of K+ or Mg2+ as Lewis acids modestly increases catalytic currents, but at large overpotentials. The work presented here is consistent with a mechanism that involves rhenium reduction and deprotonation of imidazole and benzimidazole prior to CO2 reduction electrocatalysis.

Theoretical investigation has been conducted into the mechanism for the Ag(I)/PhI(OTFA)2-catalyzed 1,4-radical aryl migration from carbon center to nitrogen center in sulfonamides by using density functional theory (DFT). The calculations show that 11 elementary reactions compose the whole catalytic reaction, which includes the deprotonation, the oxidation of Ag(I) intermediate to Ag(II) intermediate, the formation of nitrogen radical, the 1,4-radical aryl migration, the oxidation of benzyl radical to benzyl cation, etc. The difference between sulfonamides and other amides in the deprotonation process accounts for the experimental phenomenon that only the sulfonamides perform the deprotonation and subsequent 1,4-radical aryl migrations. Moreover, migrations of this kind proceed via a five-membered spirocyclic radical intermediate and favor the electron-rich phenyl group.

Pseudo-first-order rate constants for the polymerization of rac-lactide with dimeric (nacnacBnCu(μ-OiPr))2 (nacnacBn = deprotonated N,N′-dibenzyl-2-amino-4-imino-pent-2-ene), 1, in acetonitrile, THF, dichloromethane, and toluene are kobs = 2.4(1), 5.3(5), 3.6–4.4, and 10(1) min−1, respectively (25 °C, 1.0 mmol L−1 1). A bimodal polymer molecular weight distribution is obtained in toluene, narrow polydispersities of 1.1 for THF and acetonitrile. Under the same conditions (25 °C, 1.0 mmol L−1 1, CH2Cl2), 1 polymerizes β-butyrolactone, ε-caprolactone, and δ-valerolactone with rate constants of kobs = 3.0(1) × 10−2, 1.2–2.7 × 10−2, and 0.11(1) min−1, respectively. Homopolymers showed narrow polydispersities of approximately 1.1. Sequential addition polymerizations showed evidence for transesterification if β-butyrolactone or ε-caprolactone is introduced after a lactide block.

Deamination of adenine is one of several forms of premutagenic lesions occurring in DNA. In the present study, mechanisms for the deamination reaction of adenine with OH−/nH2O (n = 0, 1, 2, 3) and 3H2O were investigated. HF/6-31G(d), B3LYP/6-31G(d), MP2/6-31G(d), and B3LYP/6-31+G(d) levels of theory were employed to search for and optimize all geometries. Energies were calculated at the G3MP2B3 and CBS-QB3 levels of theory. The effect of solvent (water) was computed using the polarizable continuum model (PCM). Intrinsic reaction coordinate (IRC) calculations were performed for all transition states. Five pathways were investigated for the deamination reaction of adenine with OH−/nH2O and 3H2O. The first four pathways (A–D) are initiated by deprotonation at the amino group of adenine by OH−, while pathway E is initiated by tautomerization of adenine. For all pathways the next two steps involve formation of a tetrahedral intermediate followed by dissociation to products via a 1,3-proton shift. Deamination with a single OH− has a high activation barrier (190 kJ mol−1 using the G3MP2B3 level) for the rate-determining step. The addition of one water molecule reduces this barrier by 68 kJ mol−1 at the G3MP2B3 level. Adding additional water molecules decreases the overall activation energy of the reaction, but the effect becomes smaller with each additional water molecule. The most plausible mechanism is pathway E, the deamination reaction of adenine with 3H2O, with an overall G3MP2B3 activation energy of 139 and 137 kJ mol−1 for the gas phase and PCM, respectively. This barrier is lower than that for the deamination with OH−/3H2O by 6 and 2 kJ mol−1 for the gas phase and PCM, respectively.

The potential energy surface of l-homoselenocysteine (HSEC) has been explored through the use of B3LYP/6-311+G(d,p) calculations. In this survey, seventy-seven different conformers have been located. These local minima can be classified in four groups, A–D. Structures A, B, and D are stabilized by intramolecular hydrogen bonds (IMHBs) with the amino group acting as the hydrogen bond (HB) donor and the carbonyl group (structures A and D) or the hydroxyl group (structure B) as HB acceptors. The structures in set C present an IMHB with the amino group acting as the HB acceptor and the hydroxyl group as the HB donor. The stability order decreases in the following order: A > B > C > D. From their relative stabilities it can be concluded that only three of these conformers, namely A1, A4, and A5, would exist in the gas phase at room temperature. The most stable deprotonated form corresponds to a Se-deprotated species stabilized by a strong IMHB between the hydroxyl group and the Se atom. However, a direct deprotonation of the most stable neutrals lead to O-deprotonated species, which eventually isomerize to yield the global minimum. Hence, we can conclude that, quite unexpectedly, HSEC behaves as a Se acid in the gas phase, its intrinsic acidity being 1374 kJ mol–1at the B3LYP/6-311++G(3df,2p) level of theory. The most stable protonated forms are systematically the N-protonated ones, the global minimum being a structure stabilized through an IMHB involving the protonated amino group as the HB donor and the SeH group as the HB acceptor. The calculated gas-phase proton affinity (PA) at the B3LYP/6-311++G(3df,2p) level of theory is 930 kJ mol–1.

The application of computational chemistry to studies in geochemistry is increasingly becoming invaluable in explaining experimentally observed trends for surface interactions of pollutants with sorbents ubiquitous in the environment. We report computational results on factors that affect the force constant of AsOx bonds in As(V)-containing compounds relevant to geochemical environments. Geometries, atomic charges, and stretching frequencies of –AsOxHx–1 (x = 2– 4) moieties in these molecules were calculated using semi-empirical methods (PM3) and density functional theory (B3LYP) for both isolated (gas phase) molecules and hydrated complexes in which the molecules are surrounded by four water molecules. We found that the number of organic substituents has a relatively smaller effect on the force constant of AsOx bonds than protonation. The increase in resonance effect with deprotonation causes As–O bond lengths to increase, and the decrease in resonance in fully deprotonated species with increasing organic substitution causes As–O bond lengths to decrease. In the absence of the resonance effect in fully protonated species, As–O bond lengths increase with more organic substituents. Also, increasing organic substitution causes the charge on the central arsenic atom to decrease. Charges on oxygen atoms in As–OH bonds are more sensitive to deprotonation than to resonance relative to other oxygen atoms in As–O bonds. As expected, frequencies of ν(AsOx) show an inverse relationship with As–O bond lengths upon deprotonation and organic substitution. Our results have implication for the interpretation of infrared and X-ray absorption spectra of adsorbed As(V)-containing compounds.

A new family of rhodium-diene based complexes has been developed that incorporates an N-heterocyclic carbene ligand with an N-donor tether. The ligand is denoted Mes[CNH] 2 (where Mes[CNH] is 2,4,6-Me3C6H2NC3H2NCH2CH2NH-2,4,6-Me3C6H2) and Mes[CN] for the amido form. The synthesis of the Mes[CNH] ligand involves reaction of N-mesitylimidazole with 2-chloroethyl-N-mesitylamine under melt conditions, followed by deprotonation with KN(SiMe3)2. The reaction of Mes[CNH] with [(diene)RhCl]2 results in the formation of the monodentate complexes, Mes[CNH]Rh(diene)Cl (where diene = 1,5-cyclooctadiene (COD): 3a; diene = 2,5-norbornadiene (NBD): 3b). Bidentate variants could be isolated as either a neutral species, Mes[CN]Rh(diene) 4a–4b, via deprotonation, or an ionic analogue such as [Mes[CNH]Rh(diene)]BF4 5a–5b by reaction with NaBF4. Compounds 4–5 are the first examples of rhodium compounds that contained a bidentate NHC ligand with a pendant amino or amido donor. Complexes 3–5 were characterized fully and the solid-state single crystal X-ray structures of 3a, 4a, and 5b are discussed. The utility of these complexes as catalyst precursors for hydrogenation reactions was examined and it was determined that these systems are not significantly more active than colloidal rhodium when parallel reactions were run. Various methods of transfer hydrogenations were also investigated with 3a, which did not yield an appreciable conversion of either benzophenone or N-benzylideneaniline as substrates.Key words: rhodium, N-heterocyclic carbene, catalysis, hydrogenation.

A detailed study of the lithium dialkylamide induced deprotonation of β,β-disubstituted α,β-unsaturated amides is presented. The preferential γ-Z-deprotonation and stereochemical outcome of substituents on the γ-Z carbon atom are rationalized in terms of a cyclic eight-membered transition state, which is supported by DFT calculations. Analogous deprotonations on cyclohexylidenecarboxamides reveal a delicate balance of the preference for the eight-membered cyclic transition state with the effects of existing substituents on the ring and the intervention of a twist-boat transition state.Key words: dienolate, amide, deprotonation mechanism, transition state, enolization, regioselectivity, stereoselectivity.

The Claisen-like condensation of a series of 1-arylacetyl-6-acetyl-3,4,7,8-tetramethylglycolurils (Ar = Ph, p-OMeC6H4, and p-ClC6H4) was studied in preparative experiments and by analysis of kinetic data. The reactions proceeded in virtually quantitative yield and were highly regioselective: the corresponding N-(2′-aryl-3′-ketobutanoyl)-3,4,7,8-tetramethylglycolurils were obtained in all cases, with none of the 4′-aryl regioisomers being detected. Clean bimolecular kinetics were observed for each conversion using UV spectroscopy. Reaction rates followed the order Ar = p-OMeC6H4 < Ph < p-ClC6H4. The results are explained by a mechanism in which the deprotonation of the substrates is rate-limiting; thus, deprotonation of the arylacetyl groups is favoured. The ensuing enolate reacts rapidly in the C–C bond-forming step.Key words: glycoluril, biomimetic, Claisen condensation, regioselectivity, kinetics, mechanism, substituent effects.

Deprotonation of Me3SiNP(t-Bu)2Me with BuLi generates [Me3SiNP(t-Bu)2CH2Li] (1), which reacts with (Me2SiCl)2O to give the new siloxyl-bis(phosphinimine) ligand [Me3SiNP(t-Bu)2CH2SiMe2]2O (2). This ligand reacts with 1 or 2 equiv. of CpTiCl3 to give [CpTiCl2NP(t-Bu)2CH2SiMe2OCH2SiMe2P(t-Bu)2NSiMe3] (3) and [CpTiCl2NP(t-Bu)2CH2SiMe2]2O (4), similar to the species [CpNbCl3NP(t-Bu)2CH2SiMe2]2O (5) and [CpTiCl2NP(t-Bu)2(µ-O-(CH2SiMe2)2)- P(t-Bu)2NCpNbCl3] (6). Subsequent alkylations of these metal-halide derivatives afforded the analogous permethylated analogs 7–10, respectively. Reaction of 8 with B(C6F5)3 generates [(CpTiMe2NP(t-Bu)2CH2SiMe2)(CpTiMeNP(t-Bu)2CH2SiMe2)O][MeB(C6F5)] (11). Benzylation of 4 give the species [CpTiBz2NP(t-Bu)2CH2SiMe2]2O (12), which reacts subsequently with NC(2,6-Me2C6H3) to give a 1:1 mixture of the diastereoisomers of [CpTiBz(N=C(CH2Ph)(2,6-Me2C6H3))NP(t-Bu)2CH2SiMe2]2O 13a and 13b. These synthetic routes are described and the implications considered. X-ray structural data for compounds 2, 4, 8, and 10 are reported.Key words: phosphinimide ligands, bimetallic species, heterobimetallic compounds.

Cobalt(II), nickel(II), copper(II), and two cobalt(III) complexes of a new dianionic ligand, bqb, [H2bqb = N,N'-bis(2-quinolinecarboxamide)-1,2-benzene] have been synthesized and characterized by elemental analyses, IR, and 1H NMR spectroscopy. The crystal and molecular structures of the [Ni(bqb)] (2) and [N(n-Bu)4][CoIII(bqb)(N3)2] (5) complexes were determined by X-ray crystallography. Complex 2 crystallizes in the monoclinic space group C2/c with a distorted square-planar structure including two short Ni–N (1.848 Å) and two long Ni–N (1.958 Å) bonds. The structure consists of sheets formed in the plane parallel to the b axis and diagonal to vectors a and c by intermolecular hydrogen bonds. Complex 5 crystallizes in the monoclinic space group C2 with a distorted octahedral structure. The [N(n-Bu)4]+ ion is disordered at the C3A and C4A atoms of one Bu. The IR and 1H NMR spectra of the complexes are also discussed.Key words: N4-dianionic amido ligand (bqb), (bqb) complexes of Co(II), Ni(II), Cu(II), and Co(III), azide, cyanide, X-ray crystal structures.

The utility of (–)-sparteine-mediated directed ortho metalation (DoM) has been investigated in stereoselective preparation of planar chiral ferrocenes derived from 1,1′-N,N,N′,N′-tetraisopropylferrocenedicarboxamide (5). In the synthesis of C2-symmetric analogs of 5, the protocol (base, solvent, and two-step DoM) was found to be crucial for obtaining high enantio- and diastereo-selectivities of the products. A variety of highly enantioenriched mono and doubly functionalized derivatives of 5 have been synthesized. The synthetic applications of these compounds as chiral ligands in asymmetric alkylation of aldehydes and asymmetric palladium-catalyzed allylic substitutions have been demonstrated.Key words: directed ortho metalation, stereoselective deprotonation, ferrocene ligands, asymmetric catalysis.

The coordination chemistry of bis(di-ortho-tolylphosphino)methane (dotpm) has been studied. It is an excellent chelating ligand and a range of low-valent mononuclear complexes have been prepared; cis-[M(CO)4(η2-dotpm)] (M = Cr, Mo, W; 1–3), [CpRuCl(η2-dotpm)] (4), and cis-[MX2(η2-dotpm)] (M = Pt, X = Cl, Br, I; 5a–5c, M = Pd, X = Cl; 6). The backbone protons are relatively acidic and can be deprotonated using n-BuLi or LiN(SiMe3)2. Subsequent alkylation by RX (X = halogen; R = Me, Et, CH2Ph) affords cis-[M(CO)4(η2-Rdotpm)] (M = Cr, Mo, W, R = Me; 7–9, M = Mo, W, R = Et, CH2Ph; 12–15), [CpRuCl(η2-Medotpm)] (10), and cis-[PtI2(η2-Medotpm)] (11). Thermolysis of cis-[Mo(CO)4(η2-Medotpm)] (8) yields what is believed to be the coordinately and electronically unsaturated complex [Mo(CO)3(η2-Medotpm)] (16), suggesting that derivatives of dotpm (cone angle 194°) are bulky enough to stabilize a 16-electron complex. Crystal structures of 2, 3, 7–9, 13, and 14 have been determined (diphosphine bite angles ranging from 66.58(3)° to 70.96(5)°.Key words: diphosphine, transition metal, bulky, carbonyl, ortho-tolyl.

A number of chiral secondary amines attached to Merrifield resin or to noncrosslinked (soluble) polystyrene support were synthesized. The corresponding lithium amides, generated from these amines by treatment with BuLi, react with tropinone, a model symmetrical ketone, to give the corresponding enolates enantioselectively (ee up to 75%). The enolates were trapped either as the corresponding aldol adducts by a reaction with benzaldehyde or as ring-opening products in a reaction with a chloroformate.Key words: chiral lithium amides, polymer-supported reagents, deprotonation, enolates, tropinone.

Treatment of Cl2Si(NH-t-Bu)2 (6a) with t-BuNH2 in boiling toluene yields trisamino(chloro)silane ClSi(NH-t-Bu)3 (7); formation of the tetraaminosilane Si(NH-t-Bu)4 is not observed. The reaction of SiCl4 with 4 equiv. of LiNHR produces the corresponding tetraaminosilanes Si(NHR)4 (2a, R = i-Pr; 2b, R = t-Bu; 2c, R = p-tol) in good yields. When the sterically demanding adamantyl derivative LiHNAd is employed, only disubstitution occurs to form Cl2Si(NHAd)2 (6b). Oxidation of the dimeric imidosilicates {Li3[Si(NR)3(NHR)]·THF}2 (3a, R = i-Pr; 3b, R = t-Bu) with 1 mol of iodine produces the persistent radicals {Li2[Si(NR)3(NHR)]·LiI·3THF}·, which, on the basis of EPR spectra, exist as SiN3Li3I cubes in solution. The spirocyclic tetraimidosilicate monoanion radical {[(THF)2Li(µ-Nnaph)2Si(µ-Nnaph)2Li(THF)2]}–· (10) is formed upon oxidation of the tetralithiated species {Li4[Si(Nnaph)4]·4Et2O} (1) and {[Li(12-crown-4)]2[(Et2O)2Li(µ-Nnaph)2Si(µ-Nnaph)2Li(Et2O)2]} (8) with iodine. The spectroscopic characterization of hexa(amino)disiloxane (t-BuNH)3SiOSi(NH-t-Bu)3 (14) formed from the reaction of Cl3SiOSiCl3 with 6 equiv. of LiNH-t-Bu is discussed. Key words: imido ligands, silicate, radicals, EPR spectra, lithium.

The oxidation of diarylmethanes is a multistep process involving initial formation of a radical cation, deprotonation of the radical cation to the radical, and oxidation of the radical to the carbocation. The dynamics and ef- ficiency of the last two steps in this process, namely deprotonation and oxidation, in acidic zeolites and non-acid zeolites are examined in the present work as a function of the acidity of the diarylmethane radical cations and the oxi- dation potential of the diarylmethyl radicals. Our results indicate that rate constants for deprotonation strongly depend on the acidity of the radical cations, but not on the composition of the zeolites. In addition, oxidation of the radicals to the diarylmethyl cations is strongly dependent on both the oxidation potential of the radicals and the oxidizing ability of the zeolite. This dependence allows oxidation potentials of the zeolites to be estimated. Resume : L'oxydation de diarylmethanes est un processus en plusieurs etapes qui implique la formation initiale d'un cation radical, une deprotonation du cation radical et une oxydation du radical en carbocation. On a etudie la dyna- mique et l'efficacite des deux dernieres etapes de ce processus, soit la deprotonation et l'oxydation, dans des zeolites acides et des zeolites non acides, en fonction de l'acidite des cations radicaux diarylmethanes et du potentiel d'oxydation des radicaux diarylmethyles. Les resultats obtenus indiquent que les constantes de vitesse pour la deproto- nation dependent fortement de l'acidite des cations radicaux, mais pas sur la composition des zeolites. De plus, l'oxydation des radicaux en cations diarylmethyles est fortement dependante a la fois sur le potentiel d'oxydation des radicaux et sur l'habilite des zeolites a oxyder. Cette dependance permet d'evaluer les potentiels d'oxydation des zeo- lites. Mots cles : cations radicaux, carbocations, zeolites, photolyse eclair au laser. (Traduit par la Redaction) Shea et al. 1648

Recent work has focused on developing Raman spectroscopy as a noninvasive probe of DNA interactions with solvents, intercalants, proteins, and other ligands. Here, we report the Raman spectra of thymine in eight solvents and thymidine in nine solvents obtained with visible excitation. Raman spectra under acidic, neutral, and basic conditions were also obtained of both thymine and thymidine. Changes in both the frequencies and intensities of several of the vibrational bands in the 800–1800 cm–1 region are observed. No evidence of deprotonation in the different solvents is observed for either thymine or thymidine. Correlations of the observed frequency shifts of specific vibrational modes with characteristic properties of the solvent for both thymine and thymidine show a significant correlation with acceptor and donor numbers, measures of the hydrogen-bonding ability of the solvent, in both thymine and thymidine. These results are interpreted in terms of hydrogen-bonding interactions between the N-H protons of the thymine base and lone pairs of electrons on the solvent molecules and between the solvent hydrogens and lone pairs on C=O sites. The solvent-dependent intensity in vibrational bands of thymine between 1500 and 1800 cm–1 indicates a strong interaction between thymine and solvent at the C=O and N-H sites that leads to separation of the C=O stretches from the C=C stretch. The intensity variations with solvent were much smaller for thymidine than for thymine, perhaps as a result of replacing the N1 proton by the sugar. These results suggest that Raman spectroscopy is uniquely sensitive to specific interactions of thymine and thymidine with their environment.Key words: Raman spectroscopy, thymine, thymidine, solvent effects, hydrogen bonding.

The outer-sphere oxidation of the nickel(II) complex of the deprotonated pendant-arm macrocycle, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate, [NiL1(OH2)]+ by bis-(1,4,7-triazacyclononane)nickel(III), [Ni(tacn)2]3+ has been studied in aqueous perchlorate media. The reaction displays reversible second-order behaviour and the kinetic study reveals the forward and reverse rate constants for the reaction: [Formula: see text] The kinetics show the forward reaction to be acid dependent, a feature that is attributed to protonation of the acetato group of the nickel(II) complex. Using Marcus theory, the self-exchange rate for the [NiL1(OH2)]+/2+ couple has been calculated. The nickel(II/III) electron transfer is a reversible one electron process with E° = 1.04 V (vs. S.H.E.). The formation of the authentic nickel(III) product has been confirmed by esr spectroscopy. The kinetics of reduction of the [NiL1(OH2)]2+ species by Fe2+(aq) exhibits a second-order rate law, the reaction being independent of acid. Using the calculated self-exchange rate for the nickel complex, its reaction with Fe2+(aq) has been examined in terms of an inner- versus outer-sphere mechanism. Key words: nickel(III), pendant-arm macrocycles, hexaaquairon(II), outer sphere, kinetics, Marcus theory.

5,10,15-Tri(4-hydroxyphenyl)-20-(4-hexadecyloxyphenyl)porphyrin (P) was solubilized in sodium dodecyl sulfate (SDS) micelle solutions. Taking advantage of the protonation and deprotonation properties of the amphiphilic porphyrin allowed the study of the pH-controlled transfer process of P in SDS micelle by means of UV–vis and fluorescence spectra. In neutral SDS micelle, P may be protonated and located at the outer surface of the micelle. In mildly basic conditions the hydrophilic ability of P decreases and the porphyrin moiety may transfer to the inner layer of SDS micelle. In strong basic conditions the porphyrin may transfer back to the outer aqueous surface of the micelle. The kinetic study of the porphyrin complexed with Cu(II) shows that the metalation rate of P could be controlled by changing the pH.Key words: porphyrin, location, metalation, sodium dodecyl sulfate, micelle.

The dilithiated boraamidinate complexes {Li2[RB(N-t-Bu)2]}2 (1a, R = Ph; 1b, R = t-Bu), prepared by the reaction of B[N(H)-t-Bu]3 with three equivalents of LiR, are shown by X-ray crystallography to have dimeric structures consisting of a distorted Li4N4 cube capped on two opposite faces by RB units. Reactions of 1a with TeCl4 or PX3 (X = Cl, Br) yielded complexes PhB(μ-N-t-Bu)2TeCl2 (2) and PhB(μ-N-t-Bu)2PX (4a, X = Cl; 4b, X = Br), respectively. The structures of 2 and 4b were determined by X-ray crystallography. In the solid state, complex 2 forms a dimer with weak Te···Cl contacts (3.2411(6) Å). Complex 4b is monomeric with a P—Br bond length of 2.3047(11) Å. The reactions of 2 and 4a with the appropriate amounts of Li[N(H)-t-Bu] produce the monomeric tellurium imide PhB(μ-N-t-Bu)2Te=N-t-Bu and the amido derivative PhB(μ-N-t-Bu)2PN(H)-t-Bu (4c), respectively. The X-ray structure of 4c was determined. Deprotonation of 4c with n-BuLi produces the dimeric monolithium derivative {Li[PhB(μ-N-t-Bu)2PN-t-Bu]}2 (5), which was shown by X-ray crystallography to have a centrosymmetric structure with a central transoid Li2N2 ring.Key words: boraamidinates, lithium, tellurium, phosphorus, X-ray structures.

Enantioselective deprotonation of 8-thiabicyclo[3.2.1]octan-3-one (1) with chiral lithium amides, followed by reactions with electrophiles affords sulfur analogs of tropane alkaloids of pyranotropane family. Thus, deprotonation of 1 with (S)-N-(diphenyl)methyl-1-phenylethylamine (11d), followed by the reaction of the resulting nonracemic enolate with benzaldehyde gives the corresponding aldol product as one diastereoisomer (exo, threo) and in high enanatiomeric purity (95% ee). Trimethylsilyl chloride, acetic anhydride, and acyl cyanides react readily with the lithium enolate to give the corresponding derivatives of 1, however common alkylating agents fail to provide C-alkylated products. The reaction with acyl cyanides derived from α,β-unsaturated carboxylic acids (e.g., cinnamoyl cyanide) can be utilized in synthesis of thia-analogs of tropane alkaloids physoperuvine and isobellendine (13, 15).Key words: enantioselective deprotonation, tropane alkaloids.

The hexahydridobis(phosphine)rhenate anions, [ReH6(PR3)2]- (PR3 = PCy3, P-i-Pr3, PPh3, PMe3) were generated by potassium hydride deprotonation of the neutral heptahydride conjugate acids (ReH7(PR3)2), isolated as their [K(18-crown-6)]+ and [K(1,10-diaza-18-crown-6)]+ salts, and characterized by NMR and IR spectroscopy and elemental analyses. Structures from single crystal X-ray diffraction were obtained for the [K(1,10-diaza-18-crown-6)]+salts and these indicate the presence of short protonic—hydridic bonds involving the hydrides of the anions and the proton donor NH moieties of the cations. The structure of [K(1,10-diaza-18-crown-6)][ReH6(P-i-Pr3)2] adopts a one-dimensional zigzag chain with alternating cations and anions connected and held together by inter-ion N-H···Hx-Re interactions (x = 1 or 2). Short distances between the NH protons of the cations and hydrides of the anion ranging from 1.6 to 1.9 Å are estimated for this complex. A different kind of chain structure is observed for [K(1,10-diaza-18-crown-6)][ReH6(PMe3)2] in which the combined effects of inter-ion protonic—hydridic bonding (N-H···Hx-Re) and inter-ion electrostatic interactions (ReH-x···K+···H-xRe), result in one-dimensional networks of alternating cations and anions, with the metals and hydrides occupying the interior and the organic moieties of the phosphine ligands and crown ether lining the exterior of cylindrical supramolecular assemblies. A combination of intra- and inter-ion protonic-hydridic and intra-ion-pair electrostatic interactions in [K(1,10-diaza-18-crown-6)][ReH6(PPh3)2] result in the formation of discrete two-dimensional {[K(1,10-diaza-18-crown-6)][ReH6(PPh3)2]}4 tetramers. The PCy3 salt is disordered but appears to consist of isolated 1:1 ion pairs containing strong intra-ion-pair NH···HRe bonding. The solid-state IR spectra of the [K(1,10-diaza-18-crown-6)]+ salts show low-frequency shifts for the NH bands relative to [K(1,10-diaza-18-crown-6)][BPh4], and perturbed Re-H bands relative to those in the [K(18-crown-6)]+ salts. The magnitude of ΔνNH is related to the basicity of the anion as indicated by the pKαTHF of the conjugate acid form (ReH7(PR3)2), which increases as PPh3 < < PMe3 < P-i-Pr3 < PCy3. Solution 1H NMR, NOE, and T1 relaxation measurements of [K(1,10-diaza-18-crown-6)][ReH6(PPh3)2] indicate that these interactions also persist in toluene solutions of this compound.Key words: rhenium, hydride, phosphine, hydrogen bonding, self-assembly.

The nickel(II) complex of the deprotonated pendant-arm macrocycle 5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetate (L2)2–has been structurally characterized by X-ray crystallography. The Ni(II)L2complex crystallizes in the monoclinic system, space group P21/c, with a = 12.981(8), b = 16.474(6), c = 14.262(7) Å and β = 98.81(4)°. The complex shows a distorted cis-geometry about the metal centre, the macrocyclic ligand being folded about a N-Ni-N axis, with the pendant arms coordinated cis to one another. The Ni(II)L1(where (L1)2–is meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetate) and Ni(II)L2complexes undergo reversible one-electron oxidation, with redox potentials of 0.717 and 0.766 V (vs. S.H.E.), respectively. Chemical oxidation of the complexes by peroxodisulfate obey overall second-order rate laws. Enthalpies and entropies of activation for Ni(II)L1are 38 ± 3 kJ mol–1and -106 ± 9 J K–1mol-1; and for Ni(II)L2the corresponding values are 41 ± 5 kJ mol–1and –126 ± 15 J K-1mol-1. Outer-sphere oxidation of Ni(II)L1by bis-(triazacyclononane)nickel(III) ([Ni(III)(tacn)2]3+) has been studied, and a self-exchange rate constant for the [Ni(II)L1]0/+system has been estimated at 55 mol–1dm3s–1.Key words: peroxodisulfate, nickel(II), dicarboxylato-pendant arm macrocycles, bis-(triazacyclononane)nickel(III), self-exchange rate.

One-dimensional diffusive phosphate transport in a porous cation-exchange resin model system was investigated to examine the effect of exchangeable Al on the movement of phosphate. This study presumes that Al interacts with phosphate and H+ is produced as a result of deprotonation of H2PO4−. The production of H+ due to interactions between positively charged Al ions and phosphate ions was confirmed by measuring the pH change during the titration of phosphate by aluminum or aluminum by phosphate ions. A set of cylindrical wax columns packed with: (A) a mixture of sand and solid Al2O3, (B) a mixture of sand and Al3+-saturated cation-exchange resin, (C) a mixture of sand, solid Al2O3, and Al3+-saturated cation-exchange resin, and (D) sand as a control was used. A 0.2-g sample of 32P-KH2PO4 was applied on the surface of the mixture in each column simulating one-dimensional diffusion from an instantaneous planar source into a semi-finite system. Retardation of phosphate transport by exchangeable Al3+ was characterized by lowering of pH. Phosphate transport was not retarded in the presence of solid Al2O3 alone. Phosphate movement was further retarded in the presence of exchangeable Al3+ with solid Al2O3. Under this situation, H+ ion produced from precipitation reactions dissolved solid Al2O3, giving rise to more Al3+ in solution. Aluminum ion in the solution phase moved towards the site where phosphate was precipitated. From a mass balance of P, a slight amount of P was not recovered in the system whose pH was kept around 2.0 or below, indicating a probable formation of K-taranakite. Either K-taranakite or K2Al5H7(PO4)8−14H2O was identified as a final precipitation product from a series of titration experiments. However, at least two unidentified morphologically different amorphous aluminum phosphates were observed. Key words: Aluminum, cation-exchange, phosphate, precipitation, retardation, transport

The 3-deoxy-D-erythro-hexos-2-ulose bis(thiosemicarbazone) (LH2) acts as a tetradentate ligand with S2N2 donor sites to form a copper(II) chelate (Cu(II)L). The Cu K-edge X-ray absorption spectra analysis of a powdered sample revealed a square-planar S2N2 local coordination geometry with average Cu—N and Cu—S distances of 1.92 and 2.33 Å. The EXAFS and XANES spectra and the structural parameters of a DMF solution sample indicate the retention of the square-planar local structure of the Cu(II)S2N2 chromophore upon dissolution. Semiempirical PM3 calculations indicate that the structure of Cu(II)L with the copper(II) ion bound to the S2N2 donor set disposed in a square-planar geometry is the most favorable one (with the highest |ΔHf |). The formation constant (log Kf = 20.65 ± 0.06) of the neutral [CuL] species was calculated in 30% v/v dioxane-water and the protonation and deprotonation constants determined.Key words: bis(thiosemicarbazone), copper(II), chelate, structure, stability constant.

We have prepared a number of complexes of the type cis-MoO2L2 where L represents a hydroxypyronato or hydroxypyridinonato ligand. Both the maltol (3-hydroxy-2-methyl-4-pyrone, Hma) and kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone, Hka) complexes, cis-MoO2(ma)2 (1) and cis-MoO2(ka)2 (2), have been characterized by X-ray diffraction studies. The pyrone ligands are bound to molybdenum in a cis bidentate fashion via the deprotonated hydroxyl groups and the ketone moieties. Crystals of 1 are orthorhombic, a = 12.107 (1), b = 8.6169 (8), c = 16.472 (1) Å, Z = 4, space group Pca21, and those of 2 are monoclinic, a = 8.4591 (5), b = 16.3453 (10), c = 10.2954 (7) Å, β = 103.0320 (10)°, Z = 4, space group P21/c. Hydroxypyridinone molybdenum complexes have been prepared for both maltol and kojic acid derivatives with the substituents Me, n-Pr, CH2Ph, Ph at the ring nitrogen. Crystals of the 3-hydroxy-2-methyl-1-phenyl-4-pyridinone (Hppp) derivative, MoO2(ppp)2 (9), are monoclinic, a = 10.9476 (6), b = 13.5353 (9), c = 17.4877 (10) Å, β = 93.465 (4)°, Z = 4, space group P21/n. Initial investigations into the effects molybdenum compounds have on diabetic hearts are presented. Both Na2MoO4 (used as a control) and 1 were effective in lowering blood glucose and free fatty acid levels. Diabetic rats treated with molybdate showed significant improvements in postischemic cardiac function.Key words: molybdenum, hydroxypyrones, hydroxypyridinones, heart function.

Deprotonation of cyclohexene oxide, 1, by lithium (S)-2-(1-pyrrolidinylmethyl)pyrrolidide, 2-Li, on changing the solvent from tetrahydrofuran (THF) to, for example, 2,5-dimethyltetrahydrofuran (DMTHF) or diethyl ether (DEE) has been shown to yield, besides the lithium alkoxide of 2-cyclohexene-1-ol, 3-Li, the lithium alkoxide of the homoallylic alcohol 3-cyclohexene-1-ol, 4-Li. It was shown that compound 4-Li is formed from 3-Li. No such rearrangement has been observed in THF. We have now shown that the solvent-induced isomerization of the lithium alkoxide of (S)-3-methyl-2-cyclohexene-1-ol, (S)-5-Li, catalyzed by 2-Li to the lithium alkoxide of (S)-3-methyl-3-cyclohexene-1-ol, (S)-6-Li, is 100% stereospecific. Furthermore, deuterium-labeling experiments suggest that the rearrangement of the proton is close to 100% intramolecular.Key words: 1,3-proton transfer, chiral lithium amide, intramolecular, solvent-induced isomerization, stereospecific.

The ionization of a series of 7-(4′-X anilino) 4-nitrobenzofurazans (4H) (X = NO2, CN, CO2Me, F, H, Me, OMe) to give the conjugate amide anions 4− has been studied by 1H and 13C NMR in Me2SO-d6. Concomitantly, their acidity (pKa) has been measured spectrophotometrically in a H2O–Me2SO mixture with a molar fraction [Formula: see text] Although the measured pKa values for the whole series of compounds 4H lie in a relatively narrow range (6.40, X = NO2/7.98, X = OMe), they reveal that each derivative is about 3 times more acidic than the similarly X-substituted 2,4,6-trinitrodiphenylamines. These results, together with an analysis of substituent effects on the proton and carbon chemical shifts [Formula: see text] and the related deprotonation parameters (Δδ), which are specially significant for H6, C4, C6, and C7, emphasize the very strong electron-withdrawing character of the 4-nitrobenzofurazanyl moiety. In addition, the observation of nice linear correlations of the type [Formula: see text] has enabled us to control and sometimes to firmly assign the various chemical shifts. Keywords: 7-anilino 4-nitrobenzofurazans, acidities, 1H and 13C NMR deprotonation shifts, water – dimethyl sulfoxide mixtures.

The equilibrium reactions between deprotonated D-lactobionic acid (4-O-β-D-galactopyranosyl-D-gluconic acid) and cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and mercury(II) have been studied by potentiometric and spectrophotometric methods in aqueous solution. All measurements have been carried out at a temperature of 20.0 ± 0.1 °C and at an ionic strength of 0.100 M (NaNO3) with the corresponding stability constants calculated by applying computational methods. The interactions between the proposed cations with deprotonated D-lactobionic acid were compared with those corresponding to D-gluconic acid. Compounds of type: Co(C12H21O12)2•2H2O•C2H5OH, Ni(C12H21O12)2•2H2O•C2H5OH, Cu(C12H21O12)2•2H2O•C2H5OH, Zn(C12H21O12)2•2H2O•C2H5OH, and Cd(C12H21O12)2•2H2O•0.5C2H5OH have been isolated. These metal–sugar salts were characterized by elemental, thermogravimetric, and susceptibility analyses and FT-IR, UV–visible absorption, diffuse reflectance, and 13C NMR spectroscopies. Keywords: D-lactobionate, metal complexes, equilibrium constants, potentiometry, solid state studies.

Manganese and cadmium complexes of singly and doubly deprotonated 2,3-pyrazinedicarboxylic acid (pyzdcH2) have been prepared and studied. Crystal data: [H3O]2χ[Mn(pyzdc)2]x, 1, monoclinic, C2/c (no. 15), a = 14.472(1) Å, b = 8.475(2) Å, c = 13.0771(9) Å, β = 114.753(4)°,Z = 4; [H3O]2x[Cd(pyzdc)2]x, 2, monoclinic, C2/c (no. 15),a = 14.4857(9) Å, b = 8.502(1) Å, c = 14.9803(7) Å, β = 126.951(2)°, Z = 4; [Mn(pyzdc)(H2O)2]x•2xH2O, 3, monoclinic, P21/c (no. 14), a = 6.5523(7) Å, b = 7.6702(7) Å, c = 20.5815(6) Å, β = 93.605(5)°, Z = 4; [Cd(pyzdc)(H2O)3]x•xH2O,4, monoclinic, Cc (no. 9), a = 6.088(1) Å, b = 11.5410(9) Å, c = 15.0624(7) Å, β = 96.532(8)°, Z = 4. The structures were solved by Patterson (1,4) or direct (2,3) methods and were refined by full-matrix least-squares procedures to R = 0.036, 0.025, 0.034, and 0.022 (Rw = 0.032, 0.025, 0.036, and 0.023) for 2825, 4961, 1672, and 2641 reflections with I ≥ 3σ(F2), respectively. The structures of 1 and 2 consist of extended anionic chains of metal ions that are linked by double-bridging pyzdc2−groups, with electrical neutrality maintained by the presence of H3O+ cations in the lattice. In 3 double chains of manganese ions are cross-linked by pyzdc2− ligands forming a "ladder-like" motif. The structure of 4 consists of extended chains of cadmium ions in which single pyzdc2− groups bridge metal centres. Magnetic susceptibility studies indicate, at most, only weak antiferromagnetic exchange in 1 but moderately strong antiferromagnetic interactions in 3, mediated by bridging carboxylate groups (J = −0.27 cm−1). Key words: extended chains, manganese, cadmium, 2,3-pyrazinedicarboxylates, X-ray structures, antiferromagnetism.

A series of five, structurally related, substituted 2-phenyl-benzopyrylium (flavylium) salts were synthesized and characterized by NMR, absorption, and fluorescence techniques. Their hydration and deprotonation constants were obtained through thermodynamic and relaxation kinetic methods. Metallic complexation with the two compounds possessing a catechol group and its effect on the fluorescence intensity was also studied. The ground state properties of the five pigments are correlated with the theoretical data collected through AM1 molecular orbital calculations. Key words: naphthoflavylium synthesis, hydration and deprotonation constants, fluorescence, metallic complexation, molecular orbital calculations.

Complexes of singly and doubly deprotonated 2,3-pyrazinedicarboxylic acid (pyzdcH2) have been prepared and studied. Crystal data: [Ni(pyzdcH)2(H2O)2], 1, monoclinic, P21/n, a = 9.2897(8) Å, b = 7.6931(8) Å, c = 10.1044(9) Å, β = 93.378(7)°,Z = 2; [Cu(pyzdcH)2]x•2xH2O, 2, monoclinic, P21/n, a = 6.598(1) Å, b = 14.198(2) Å, c = 8.586(2) Å, β = 97.65(2)°, Z = 2;• [Co(pyzdc)(H2O)2]x•2xH2O, 3, monoclinic, C2/c, a = 12.5777(9) Å, b = 7.5191(9) Å, c = 11.839(1) Å, β = 110.754(4)°, Z = 4; [Ni(pyzdc)(H2O)2]x•2xH2O, 4, monoclinic, C2/c, a = 12.4772(7)Å, b = 7.452(1) Å, c = 11.9166(5) Å, β = 112.302(2)°, Z = 4; [Cu(pyzdc)(H2O)2]x•2xH2O, 5, monoclinic, C2/c, a = 12.784(2) Å, b = 7.527(2) Å, c = 12.323(2) Å, β = 116.150(2)°, Z = 4. The structures were solved by Patterson (1), direct (2, 3), or isomorphous replacement methods (4 and 5 are isomorphous with 3) and were refined by full-matrix least-squares procedures to R = 0.028, 0.030, 0.029, 0.030, and 0.030 (Rw = 0.026, 0.029, 0.027, 0.025, and 0.027) for 1894, 1694, 2476, 1867, and 1412 reflections with I ≥ 3σ(F2), respectively. The structure of 1 consists of monometallic [Ni(pyzdcH)2(H2O)2] units linked by hydrogen-bonding interactions in a three-dimensional network. In 2 extended chains of copper ions are linked by double-bridging pyzdcH− groups while 3, 4, and 5 have structures in which pyzdc2− ligands bridge metal centers to form extended linear chains. Magnetic susceptibility studies reveal antiferromagnetic interactions in 1, 2, 3, 4, and 6 (6 is Cu(pyzdc)). The magnitude of exchange (−zJ = 0.033 cm−1 for 1 and −J = 0.11, 0.74, 0.049, and 1.14 cm−1 for 2, 3, 4, and 6, respectively) is discussed in terms of the structures and d-electron configurations involved. Key words: metal 2,3-pyrazinedicarboxylates, synthesis, X-ray structure, antiferromagnetism.

Thermodynamic data of proton dissociation of 75 organic acids belonging to four classes (protonated amines, aliphatic carboxylic acids, benzoic acids, phenols) have been processed by multivariate chemometric techniques. The variables consist of conventional thermodynamic quantities (Gibbs function, enthalpy, entropy) and of partial components of these quantities (internal and external, electrostatic and nonelectrostatic components). The above data refer to the aqueous medium, at 25 °C and I = 0 mol dm−3. The Gibbs function of deprotonation in the gas phase and the Hammett σ constant have also been considered. Multivariate techniques include Principal Component Analysis, Factor Analysis, and feature selection. Factor Analysis and related concepts have proved to be useful in defining the causes of differences in acid strengths and their respective importance. Keywords: acid dissociation data, chemometrics of; chemometrics of acid dissociation data; factor analysis of acid dissociation data; principal component analysis of acid dissociation data; thermodynamics of acid dissociation.

A general synthetic route to 2-alkyl- and 2,2-dialkyl-1,3-dioxan-5-ones, using tris(hydroxymethyl)-nitromethane as the starting material, is described. Deprotonation of these compounds was studied. It was established that these dioxanones could be deprotonated with LDA; however, the reduction of the carbonyl group via a hydride transfer from LDA, giving the corresponding dioxanols, often competed with deprotonation. The reduction could be minimized by using Corey's internal quench procedure to form silyl enol ethers and was less pronounced in 2,2-dialkyldioxanones (ketals) than in 2-alkyldioxanones (acetals). Self-aldol products were observed when dioxanone lithium enolates were quenched with H2O. Addition reactions of lithium enolates of dioxanones to aldehydes were threo-selective as predicted by the Zimmerman–Traxler model. Dioxanones having two different alkyl groups at the 2-position were deprotonated enantioselectively by chiral lithium amide bases with enantiomeric excess (ee) of up to 70%. Keywords: 1,3-dioxan-5-ones, enantioselective deprotonation, chiral lithium amides.

Transition-metal-bound imidazoles are suitable models for evaluating the roles of metal ions in biomolecules having the imidazole moiety and similar heterocyclic residues as part of their structure. Such studies provide useful insights into metal–biomolecule interactions in biological systems, especially when the lability of the metal–ligand bond is substantially reduced, such that the identity of the metal–ligand complex is preserved during the course of the reaction under investigation. The present paper reports on a kinetic study of tritium exchange from the C(2) position of the imidazole moiety in the substitution-inert complex cations [Co(NH3)5[2-3H]-imidazole]3+ (1) and [Co(NH3)5-1-methyl-[2-3H]-imidazole]3+ (2). Rate–pH profiles have been determined in aqueous solution at 60 °C. Both substrates are believed to react through rate-determining attack of hydroxide ion (kM+ pathway) at C(2)-T. Dissection of the kinetic data reveals an additional pathway for 1 consequent upon deprotonation of its pyrrole-like N-H(T) to yield 3, which is then attacked by hydroxide at C(2) (kM pathway). The ratio kM+/kM = 103 that is obtained is in accord with the expected reduced reactivity of 3. Comparison of the present data with those reported for a variety of heterocyclic substrates shows that the order of reactivity, protonated [Formula: see text] metal ion coordinated [Formula: see text] neutral form of substrates, prevails. The superiority of the proton over metal ions in catalyzing isotopic hydrogen exchange is attributed to its larger ground state acidifying effect coupled with the greater transition state stabilization it affords, relative to metal ions. The exchange reaction of 3 via the kM pathway is the first example of a reactive anionic species in which the negative charge is located α to the exchanging C-H. Keywords: tritium exchange, cobalt (III)-coordinated imidazoles.

The kinetics of NaOD-catalyzed H/D exchange (enolization) at C3 α to the carbonyl group of bicyclo[2.2.2]octane-2,5-dione (1) and bicyclo[2.2.2]octane-2,6-dione (2) have been studied in 60:40 (v/v) dioxane–D2O at 25.0 °C. The second-order rate constants for exchange are (9.7 ± 1.5) × 10−1 and (3.4 ± 1.2) × 10−5 L mol−1 s−1 for 1 and 2, respectively. Thus, 1, exchanges 76 times faster than bicyclo[2.2.2]octan-2-one (3) (k = (1.27 ± 0.02) × 10−2 L mol−1 s−1), but the 2,6-dione 2 unexpectedly is much less reactive (2.7 × 10−3) than the monoketone. Unlike the large exo selectivity of 658 observed in the case of bicyclo[2.2.1]heptan-2-one, small and opposite selectivities, exo (1.2) for 1 and endo (2.1) for 2, are found for the isomeric [2.2.2] ketones. The results indicate that the incipient enolate of 1 is stabilized by a polar effect of the β carbonyl group at C5, not by homoconjugation. The source of the surprising low reactivity of 2 is unknown at this stage. The small diastereoselectivities, exo (1.2) for 1 and endo (2.1) for 2, correlate with relative energies of the diastereomeric pyramidal enolates calculated with AM1. Keywords: enolization, bicyclo[2.2.2]octane-2,5-dione, bicyclo[2.2.2]octane-2,6-dione, AM1, thermodynamic acidities.

The deprotonation constants of uridine (K1 and K2), thymidine (K1 and K2), cytidine (K1 and K2), guanosine (K1, K2, and K3), and xanthosine (K1, K2, and K3) have been obtained in water from EMF measurements of Harned-Ehler type cells comprising H2 and Ag-AgI electrodes at different temperatures. The pK values were substituted in the temperature equation: pK = AT−1 + B + CT and A, B, and C were obtained by the method of least squares. Related thermodynamic quantities viz. ΔG0, TΔS0, and ΔH0 were obtained from coefficients A, B, and C of the respective nucleosides. Keywords: deprotonation energetics, uridine, thymidine, cytidine, guanosine, xanthosine.

A series of derivatives of 4-hydroxycyclohexanone (1a–g) with the hydroxy group protected as a silyl ether (1a, b), ether (1d, g), an acetal (1c), or an ester (1e, f) were deprotonated with chiral, optically pure, lithium amides 3–9. The resulting non-racemic enolates were trapped as enol acetates. The enantioselectivity of deprotonation was up to 74% ee.

The protonation/deprotonation constants for uracil (U) (pK1 and pK2), thymine (T) (pK1) and cytosine (C) (pK1 and pK2) in water have been determined from emf measurements of Harned–Ehler type cells comprising H2 and Ag–AgI electrodes at five equidistant temperatures ranging from 15–35 °C. The pKa values were fitted in the temperature equation pKa = AT−1 + B + CT by the method of least squares and the standard free energies (ΔG0), entropies (ΔS0), and enthalpies (ΔH0) of protonation/deprotonation processes in water were evaluated using the values of the coefficients A, B, and C of the respective acids. The second step deprotonation constant for T was determined using precise spectrophotometric method. The results have been duly compared with the existing literature data and are also shown to derive important reflections on the sites of protonation/deprotonation in the light of pK values of some acids and bases of comparable functional groups and especially the entropies of protonation/deprotonation of the key DNA–RNA base molecules.

The kinetics of the azo coupling of eight para-substituted benzenediazonium tetrafluoroborates 2a–h with indole and its 1-, 2-,and 3-methyl derivatives 1a–d, respectively, were studied in acetonitrile at 25 °C under pseudo-first-order conditions. The relation k1(obs) = k2[diazonium salt] was found applicable in all cases. The logarithms of the rate constants k2 for each reaction series were correlated by the Hammett equation. A plot of the values of the reaction constant, ρ, obtained against the acidity constants pKa of 1a–d gave a straight line: ρ = 2.97 – 0.15 pKa. These results indicate that the azo-coupling reactions of indoles 1a–d follow one general mechanism involving rate-limiting initial electrophilic attack at the 3-position for all four compounds, contrary to the previous conclusion of Jackson and Lynch that the final deprotonation step is rate limiting.

The rates of deprotonation of several β-keto esters in basic aqueous solution are elevated by α- and β-cyclodextrin (α- and β-CD). In most cases saturation kinetics are observed that indicate fairly strong binding of the esters to the CDs (Kd = 0.22–11 mM); catalytic ratios (kc/ku) are in the range 1.9–17. For esters of the form RCO-CH2COOEt with both α- and β-CD the values of Kd and kc/ku show little sensitivity to the acyl group, RCO (R = Me, Et, Pr, i-Pr), and for 2-carboethoxycyclopentanone, a cyclic analogue, these parameters are similar. In contrast, for R-COCH2CO-OR′ (R = Me or Et; R′ = Me, Et, allyl) there is a marked dependence of the parameters on the alkoxyl group, OR′. These results suggest that the β-keto esters studied bind to the CDs with their alkoxyl groups in the CD cavity and that the catalysis ensues from the complexes thus formed. Variations in two other kinetic parameters, k2 = kc/Kd (substrate selectivity) and KTS = ku/k2 (apparent constant for dissociation of CD from the transition state) support this interpretation. Apparent second-order rate constants for the reaction of the esters with neutral CD (k2 = kc/Kd) are 1900–360 000 M−1 s−1 (at pH ≈ 10), whereas for hydroxide ion attack on ethyl acetoacetate kOH = 5500 M−1 s−1. Assuming the pKas of the CDs are 12.2 and 12.3, deprotonation of the esters by the CD anions has rate constants of 105 to 5 × 107 M−1 s−1. Thus, binding of the β-keto esters in the CD cavities, adjacent to a basic oxyanion site, enhances the reactivity of the CD anions towards these weak carbon acids by at least 2–4 orders of magnitude.

The acido-basic behavior of 4-acylamino-4H-1,2,4-triazoles and of the related structures, 4-acylamino-4H-1,2,4-triazolium salts, 4-acylamino-1,2,4-triazoline-3-thiones, and 4-acylamino-1,2,4-triazolin-3-ones, has been compared. Among the triazolium salts examined, the 1-carboxymethyl-4-phenylacetylamino derivative has been selected as a particular triazolium salt bearing two acidic centres, a carboxylic acid group and an exocyclic amide group. This compound has been isolated in three different ionic forms corresponding to different protonation and deprotonation states of the molecule. For these compounds, IR, NMR, and X-ray data were compared and the preferential localization site of the labile proton on the betainic intermediate structure has been discussed. Taking into account that deprotonation of the amide function of 4-acylamino-4H-1,2,4-triazolium salts may introduce a negative pole in the proximity of the strong electrophilic carbon atom in the 2-position of the ring, reactivity of different triazolium salts toward the nucleophilic addition of the hydride ion has been compared. In particular, 4-acylamino-4H-1,2,4-triazolium salts free of alkyl substituent on the amide nitrogen failed to give the corresponding 4-acylamino-Δ2-1,2,4-triazolines after reaction with the hydride ion, while, under the same conditions, the 4-N-methyl derivatives were transformed into this unusual ring system in good yields. In this case, no decrease of reactivity toward the nucleophilic agent was observed since, as a result of the N-al-kylation, no deprotonation of the amide group can occur in these alkaline experimental conditions.

The pKa values for the deprotonation of a series of 4-(X-phenylsulfonylmethyl)pyridines (6) (pKa = 19.89 (X = H); ρ = 3.0) were determined in aqueous dimethyl sulfoxide solutions at 25 °C using the H0q acidity function. The pKa values were also measured for the corresponding series of N-mefhyl 4-(X-phenylsulfonylmethyl)pyridinium cations (2) (pKa = 11.27 (X = H); ρ = 1.45) and also for a series of N-(X-benzyl) 4-phenylsulfonylmethylpyridinium cations (7) (pKa = 10.70 (X = H); ρ = 0.65) in aqueous solution (ionic strength 0.1 at 25 °C). Comparison of the substituent effects upon the pKa values of the sulfonyl-activated carbon acids 2, 6, and 7 with the substituent effects upon the pKa values of the corresponding three series of ketones gives insight into the electron-density distribution in the carbanionic conjugate bases of sulfone and ketone carbon acids. Extrapolation of a linear free energy relationship between the pKa values of neutral sulfones and ketones allows the estimation of pKa = 28.7 for the deprotonation of methyl phenyl sulfone in aqueous solution.

Tropinone (6) was deprotonated with lithium diisopropylamide and with chiral lithium amides (18–24) and the resulting enolates (two enantiomers) were treated with electrophiles. The aldol reaction with benzaldehyde and deuteration were both diastereoselective. The former yielded only one isomer (exo, anti) of the aldol 8a; the latter proceeded from the exo face. This selectivity permitted us to probe the deprotonation of tropinone with lithium amides; it was concluded that the reaction involves predominantly the exo axial protons. The reaction of tropinone enolate with ethyl chloroformate led, via a ring opening, to the cycloheptenone derivative 9. The reaction with methyl cyanoformate yielded, in the presence of silver acetate and acetic acid, the β-ketoester 8b; however, in the absence of these additives, and especially when 12-crown-4 was added to the enolate, a ring opening leading to the pyrrolidine derivative 10 occurred instead. Deprotonation of tropinone with chiral lithium amides proceeded with modest enantioselectivity. A synthesis of non-racemic anhydroecgonine via this strategy allowed establishing the absolute stereochemistry of deprotonation.