Synthesis, structure, and electrochemistry of di- and zerovalent nickel, palladium, and platinum monomers and dimers derived from an enantiopure (S,S)-tetra(tertiary phosphine)

The ligand (S,S)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (S,S)-tetraphos, reacts with hexa(aqua)nickel(II) chloride in the presence of trimethylsilyl triflate (TMSOTf) in dichloromethane to give the yellow square-planar complex [Ni{(R,R)-tetraphos}](OTf)2, which has been crystallographically characterized as the square-pyramidal, acetonitrile adduct [Ni(NCMe){(R,R)-tetraphos}]OTf. Cyclic voltammograms of the nickel(II) complex in dichloromethane and acetonitrile at 20 degrees C showed two reduction processes at negative potentials with oxidative (E(p)(ox)) and reductive (E(p)(red)) peak separations similar to those observed for ferrocene/ferrocenium under identical conditions, suggesting two one-electron steps. The cyclic voltammetric data for the divalent nickel complex in acetonitrile at temperatures below -20 degrees C were interpreted according to reversible coordination of acetonitrile to the nickel(I) and nickel(0) complexes. The divalent palladium and platinum complexes [M{(R,R)-tetraphos}](PF6)2 and [M2{(R,R)-tetraphos}2](OTf)4 have been prepared. The reduction potentials for the complexes [M{(R,R)-tetraphos}](PF6)2 increase in the order nickel(II) < palladium(II) < platinum(II). The reaction of (S,S)-tetraphos with bis(cycloocta-1,5-diene)nickel(0) in benzene affords orange [Ni{(R,R)-tetraphos}], which slowly rearranges into the thermodynamically more stable, yellow, double-stranded helicate [Ni2{(R,R)-tetraphos}2]; the crystal structures of both complexes have been determined. The reactions of (S,S)-tetraphos with [M(PPh3)4] in toluene (M = Pd) or benzene (M = Pt) furnish the double-stranded helicates [M2{(R,R)-tetraphos}2]; the palladium complex crystallizes from hot benzene as the 2-benzene solvate and was structurally characterized by X-ray crystallography. In each of the three zerovalent complexes, the coordinated (R,R)-tetraphos stereospecifically generates tetrahedral M(PP)2 stereocenters of M configuration.     

Synthesis, characterization, and materials chemistry of Group 4 silylimides

This paper focuses on the development of potential single source precursors for M-N-Si (M = Ti, Zr or Hf) thin films. The titanium, zirconium, and hafnium silylimides (Me(2)N)(2)MNSiR(1)R(2)R(3) [R(1) = R(2) = R(3) = Ph, M = Ti(1), Zr (2), Hf (3); R(1) = R(2) = R(3) = Et, M = Ti (4), Zr (5), Hf (6); R(1) = R(2) = Me, R(3) = (t)Bu, M = Ti (7), Zr (8), Hf (9); R(1) = R(2) = R(3) = NMe(2), M = Ti (10), Zr (11), Hf (12)] have been synthesized by the reaction of M(NMe(2))(4) and R(3)R(2)R(1)SiNH(2). All compounds are notably sensitive to air and moisture. Compounds 1, 2, 4, and 7-10 have been structurally characterized, and all are dimeric, with the general formula [M(NMe(2))(2)(μ-NSiR(3))](2), in which the μ(2)-NSiR(3) groups bridges two four-coordinate metal centers. The hafnium compound 3 possesses the same basic dimeric structure but shows additional incorporation of liberated HNMe(2) bonded to one metal. Compounds 11 and 12 are also both dimeric but also incorporate additional μ(2)-NMe(2) groups, which bridge Si and either Zr or Hf metal centers in the solid state. The Zr and Hf metal centers are both five-coordinated in these species. Aerosol-assisted CVD (AA-CVD) using 4-7 and 9-12 as precursors generates amorphous films containing M, N, Si, C, and O; the films are dominated by MO(2) with smaller contributions from MN, MC and MSiON based on XPS binding energies.     

Dihydrogen generation from amine/boranes: synthesis, FT-ICR, and computational studies

A Fourier transform ion cyclotron resonance spectrometry (FT-ICR) study of the gas-phase protonation of ammonia-borane and sixteen amine/boranes R(1)R(2)R(3)N-BH(3) (including six compounds synthesized for the first time) has shown that, without exception, the protonation of amine/boranes leads to the formation of dihydrogen. The structural effects on the experimental energetic thresholds of this reaction were determined experimentally. The most likely intermediate and the observed final species (besides H(2)) are R(1)R(2)R(3)N-BH(4)(+) and R(1)R(2)R(3)N-BH(2)(+), respectively. Isotopic substitution allowed the reaction mechanism to be ascertained. Computational analyses ([MP2/6-311+G(d,p)] level) of the thermodynamic stabilities of the R(1)R(2)R(3)N-BH(3) adducts, the acidities of the proton sources required for dihydrogen formation, and the structural effects on these processes were performed. It was further found that the family of R(1)R(2)R(3)N-BH(4)(+) ions is characterized by a three-center, two-electron bond between B and a loosely bound H(2) molecule. Unexpected features of some R(1)R(2)R(3)N-BH(4)(+) ions were found. This information allowed the properties of amine/boranes most suitable for dihydrogen generation and storage to be determined.     

Studies on the constituents of Broussonetia species VIII. Four new pyrrolidine alkaloids, broussonetines R, S, T, and V and a new pyrroline alkaloid, broussonetine U, from Broussonetia kazinoki Sieb

Four new pyrrolidine alkaloids, broussonetines R, S, T, and V and a new pyrroline alkaloid, broussonetine U were isolated from the branches of Broussonetia kazinoki SIEB. (Moraceae) in low yield. Broussonetines R, S and T were formulated as (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(1R)-1-hydroxy-3-[6-(4-hydroxybutyl)-cyclohexy-2-on-1(6)-enyllpropyl] pyrrolidine (1), (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(1R,10S)-1,10,13-trihydroxytridecyl] pyrrolidine (2), (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(1R,5S)-1,5, 13-trihydroxy-10-oxo-tridecyl] pyrrolidine (3). And broussonetines U and V were proposed to be (2S,3S,4S)-2-hydroxymethyl-3, 4-dihydroxy-5-(9-oxo-13-hydroxytridecyl)-5-pyrroline (4), (2R,3S,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(E)-9-oxo-13-hydroxy-3-tridecenyl] pyrrolidine (5), respectively, by spectroscopic and chemical methods.     

Hydrocarbon-Soluble Mercuracarborands: Syntheses, Halide Complexes, and Supramolecular Chemistry

The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) ?, b = 18.19(1) ?, c = 13.61(1) ?, beta = 113.74(2) degrees, V = 6568 ?(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) ?, b = 21.12(2) ?, c = 20.96(2) ?, beta = 97.87(2) degrees, V = 5600 ?(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) ?, c = 21.666(2) ?, V = 10098 ?(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) ?, b = 13.013(1) ?, c = 15.867(2) ?, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 ?(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution.     

Mixing behavior of the biosurfactant, rhamnolipid, with a conventional anionic surfactant, sodium dodecyl benzene sulfonate

The use of small angle neutron scattering, SANS, neutron reflectivity, NR, and surface tension to study the mixing properties of the biosurfactant rhamnolipid with a conventional anionic surfactant, sodium dodecyl 6-benzene sulfonate, LAS, is reported. The monorhamnose rhamnolipid, R1, mixes close to ideally with LAS at the air-water interface, whereas for mixtures of LAS with the dirhamnose rhamnolipid, R2, the LAS strongly partitions to the air-water interface relative to R2, probably because of the steric hindrance of the larger R2 headgroup. These trends in the binary mixtures are also reflected in the ternary R1/R2/LAS mixtures. However, for these ternary mixtures, there is also a pronounced synergy in the total adsorption, which reaches a maximum for a LAS/rhamnolipid mole ratio of about 0.6 and a R1/R2 mol ratio of about 0.5, an effect which is not observed in the binary mixtures. In solution, the R1/LAS mixtures form relatively small globular micelles, L(1), at low surfactant concentrations (<20 mM), more planar structures (lamellar, L(α), unilamellar/multilamellar vesicles, ulv/mlv) are formed at higher surfactant concentrations for R1 and LAS rich compositions, and a large mixed phase (L(α)/L(1) and L(1)/L(α)) region forms at intermediate surfactant compositions. In contrast, for the R2/LAS mixtures, the higher preferred curvature of R2 dominates the phase behavior. The predominant microstructure is in the form of small globular micelles, except for solution compositions rich in LAS (>80 mol % LAS) where more planar structures are formed. For the ternary mixtures, there is an evolution in the resulting phase behavior from one dominated by L(1) (R2 rich) to one dominated by planar structures, L(α), (R1, LAS rich), and which strongly depends upon the LAS/rhamnolipid and R1/R2 mole ratio.     

Synthesis of zirconium, hafnium, and tantalum complexes with sterically demanding hydrazide ligands

The bulky hydrazine t-BuN(H)NMe2 was synthesized via hydrazone and t-BuN(H)N(H)Me intermediates as the major component in a 90:5:5 mixture consisting of t-BuN(H)NMe2, t-BuN(Me)N(H)Me, and t-BuN(Me)NMe2. Reacting the mixture with n-BuLi followed by distillation and fractional crystallization led to the isolation of the ligand precursor LiN(t-Bu)NMe2. Lithium hydrazides, LiN(R)NMe2, were reacted with metal chlorides to afford the hydrazide complexes M(N(Et)NMe2)4 (M = Zr or Hf), MCl(N(R)NMe2)3 (M = Zr, R = i-Pr or t-Bu; M = Hf, R = t-Bu), and TaCl3(N(i-Pr)NMe2)2. The X-ray crystal structures of [LiN(i-Pr)NMe2]4, [LiN(t-Bu)NMe2.THF]2, ZrCl(N(R)NMe2)3 (R = i-Pr or t-Bu), and TaCl3(N(i-Pr)NMe2)2 were determined. The structural analyses revealed that the hydrazide ligands in ZrCl(N(R)NMe2)3 (R = i-Pr or t-Bu) and TaCl3(N(i-Pr)NMe2)2 are eta2 coordinated.     

Generation of secondary, tertiary, and quaternary centers by geminal disubstitution of carbonyl oxygens

Methods for replacing the carbonyl oxygen by two new substituents (C=O→CR(1)R(2)) are discussed in this Minireview, whereby R may be H, NR(2), alkyl, allyl, benzyl, vinyl, alkynyl, aryl, heteroaryl, or acyl groups. The most frequently used starting materials for geminal disubstitution with the formation of two C-C bonds (R(1),R(2)≠H, NR(2)) are amides and thioamides, which react with organometallic nucleophiles R-M (M=Li, MgX, CeX(2), TiX(3), ZrX(3)) to give tertiary sec- and tert-alkylamines. Quaternary centers can be built directly from ketones by treatment with Me(3)Al, MeTiCl(3), or Me(2)TiCl(2) (R(1)R(2)C=O→R(1)R(2)CMe(2)). The scope and limitations of the various methods and mechanistic models are briefly discussed. The remarkable variety and diversity of structures thus accessible are demonstrated by numerous examples.     

Rhenium and technetium complexes with N,N-dialkyl-N'-benzoylthioureas

N,N-Dialkyl-N'-benzoylthioureas, HR(1)R(2)btu, react under single deprotonation and form air-stable chelate complexes with common rhenium or technetium complexes such as (NBu(4))[MOCl(4)] (M = Re, Tc) or [ReOCl(3)(PPh(3))(2)]. Compositions and molecular structures of the products are strongly dependent on the precursors used and the reaction conditions applied. Reactions with [ReOCl(3)(PPh(3))(2)] in CH(2)Cl(2) give complexes of the general formula [ReOCl(2)(R(1)R(2)btu)(PPh(3))] (3), with the benzoyl oxygen atom of the chelating benzoylthiourea being trans to the oxo ligand, and/or Re(III) complexes of the composition [ReCl(2)(R(1)R(2)btu)(PPh(3))(2)] (4) with the PPh(3) ligands in trans positions to each other. In polar solvents such as MeOH, EtOH or acetone, corresponding reactions without addition of a supporting base only result in intractable brown solutions, from which no crystalline complexes could be isolated. The addition of NEt(3), however, allows the isolation of the bis-chelates [ReOCl(R(1)R(2)btu)(2)] (1) in good yields. In this type of complex, one of the chelating R(1)R(2)btu- ligands coordinates equatorially, while the second occupies the position trans to the oxo ligand with its oxygen atom. The latter compounds can also be prepared from (NBu(4))[ReOCl(4)] in MeOH when no base is added, while the addition of NEt(3) results in the formation of [ReO(OMe)(R(1)R(2)btu)(2)] (5) complexes with the methoxo ligand trans to O(2-). Compounds of the type 5 can alternatively be prepared by heating 1 in MeOH with addition of NEt(3). A reversible conversion of 5 into oxo-bridged dimers of the composition [{ReO(R(1)R(1)btu)(2)}(2)O] (6) is observed in water-containing solvents. Starting from (NBu(4))[TcOCl(4)], a series of technetium complexes of the type [TcOCl(R(1)R(2)btu)(2)] (2) could be prepared. The structures of such compounds are similar to those of the rhenium analogues 1. Reduction of 2 with PPh(3) in CH(2)Cl(2) gives Tc(III) complexes of the composition [TcCl(R(1)R(2)btu)(2)(PPh(3))] (7) having the chloro and PPh(3) ligands in cis positions. When this reaction is performed in the presence of excess chelating ligand, the Tc(III) tris-chelates [Tc(R(1)R(2)btu)(3)] (8) are formed.     

Studies on the constituents of Broussonetia species. VII. Four new pyrrolidine alkaloids, broussonetines M, O, P, and Q, as inhibitors of glycosidase, from Broussonetia kazinoki SIEB

Four new pyrrolidine alkaloids, broussonetines M, O, P, and Q, were isolated from the branches of Broussonetia kazinoki SIEB, (Moraceae). Broussonetines M, O, P, and Q were formulated as (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(10S)-10,13-dihydroxy-tri decyl]pyrrolidine (1), (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(E)9-oxo-13-hydroxy-3- tridecenyl]pyrrolidine (2), (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(E)10-oxo-13-hydroxy-3-++ +tridecenyl]pyrrolidine (3), and (2R,3S,4R,5R)-2-hydroxymethyl-3-hydroxy-4-(beta-D-glucopyranosyloxy++ +)-5-[10-oxo-13-(beta-D-glucopyranosyloxy)tridecyl]pyrrolidine (4) respectively, by spectroscopic and chemical methods. 1-4 inhibited beta-glucosidase, beta-galactosidase and beta-mannosidase.     

Aluminacyclopropene: syntheses, characterization, and reactivity toward terminal alkynes

Reactions of LAl with ethyne, mono- and disubstituted alkynes, and diyne to aluminacyclopropene LAl[eta2-C2(R1)(R2)] ((L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3); R1 = R2 = H, (1); R1 = H, R2 = Ph, (2); R1 = R2 = Me, (3); R1 = SiMe3, R2 = C[triple bond]CSiMe3, (4)) are reported. Compounds 1 and 2 were obtained in equimolar quantities of the starting materials at low temperature. The amount of C2H2 was controlled by removing an excess of C2H2 in the range from -78 to -50 degrees C. Compound 4 can be alternatively prepared by the substitution reaction of LAl[eta2-C2(SiMe3)2] with Me3SiC[triple bond]CC[triple bond]CSiMe3 or by the reductive coupling reaction of LAlI2 with potassium in the presence of Me3SiC[triple bond]CC[triple bond]CSiMe3. The reaction of LAl with excess C2H2 and PhC[triple bond]CH (<1:2) afforded the respective alkenylalkynylaluminum compounds LAl(CH=CH2)(C[triple bond]CH) (5) and LAl(CH=CHPh)(C[triple bond]CPh) (6). The reaction of LAl(eta2-C2Ph2) with C2H2 and PhC[triple bond]CH yielded LAl(CPh=CHPh)(C[triple bond]CH) (7) and LAl(CPh=CHPh)(C[triple bond]CPh) (8), respectively. Rationally, the formation of 5 (or 6) may proceed through the corresponding precursor 1 (or 2). The theoretical studies based on DFT calculations show that an interaction between the Al(I) center and the C[triple bond]C unit needs almost no activation energy. Within the AlC2 ring the computational Al-C bond order of ca. 1 suggests an Al-C sigma bond and therefore less pi electron delocalization over the AlC2 ring. The computed Al-eta2-C2 bond dissociation energies (155-82.6 kJ/mol) indicate a remarkable reactivity of aluminacyclopropene species. Finally, the 1H NMR spectroscopy monitored reaction of LAl(eta2-C2Ph2) and PhC[triple bond]CH in toluene-d8 may reveal an acetylenic hydrogen migration process.     

Enzymatic resolution, desymmetrization, and dynamic kinetic asymmetric transformation of 1,3-cycloalkanediols

An efficient desymmetrization of cis-1,3-cyclohexanediol to (1S,3R)-3-(acetoxy)-1-cyclohexanol ((R,S)-2a) was performed via Candida antarctica lipase B (CALB)-catalyzed transesterification, in high yield (up to 93%) and excellent enantioselectivity (ee's up to >99.5%). (R,R)-Diacetate ((R,R)-3a) was obtained in a DYKAT process at room temperature from (1S,3R)-3-acetoxy-1-cyclohexanol ((R,S)-2a), in a high trans/cis ratio (91:9) and in excellent enantioselectivity of >99%. Metal- and enzyme-catalyzed dynamic transformation of cis/trans-1,3-cyclohexanediol using PS-C gave a high diastereoselectivity for cis-diacetate (cis/trans = 97:3). The (1R,3S)-3-acetoxy-1-cyclohexanol (ent-(R,S)-2a) was obtained from cis-diacetate by CALB-catalyzed hydrolysis in an excellent yield (97%) and selectivity (>99% ee). By deuterium labeling it was shown that intramolecular acyl migration does not occur in the transformation of cis-monoacetate to the cis-diacetate.     

Reactions of Li- and Yb-coordinated N,N'-bis(trimethylsilyl)-beta-diketiminates: one- and two-electron reductions, deprotonation, and C-N bond cleavage

The synthesis and characterisation of novel Li and Yb complexes is reported, in which the monoanionic beta-diketiminato ligand has been (i) reduced (SET or 2 [times] SET), (ii) deprotonated, or (iii) C-N bond-cleaved. Reduction of the lithium beta-diketiminate Li(L(R,R'))[L(R,R')= N(SiMe(3))C(R)CHC(R')N(SiMe(3))] with Li metal gave the dilithium derivative [Li(tmen)(mu-L(R,R'))Li(OEt(2))](R = R'= Ph; or, R = Ph, R[prime or minute]= Bu(t)). When excess of Li was used the dimeric trilithium [small beta]-diketiminate [Li(3)(L(R,R[prime or minute]))(tmen)](2)(, R = R'= C(6)H(4)Bu(t)-4 = Ar) was obtained. Similar reduction of [Yb(L(R,R'))(2)Cl] gave [Yb[(mu-L(R,R'))Li(thf)](2)](, R = R[prime or minute]= Ph; or, R = R'= C(6)H(4)Ph-4 = Dph). Use of the Yb-naphthalene complex instead of Li in the reaction with [Yb(L(Ph,Ph))(2)] led to the polynuclear Yb clusters [Yb(3)(L(Ph,Ph))(3)(thf)], [Yb(3)(L(Ph,Ph))(2)(dme)(2)], or [Yb(5)(L(Ph,Ph))(L(1))(L(2))(L(3))(thf)(4)] [L(1)= N(SiMe(3))C(Ph)CHC(Ph)N(SiMe(2)CH(2)), L(2)= NC(Ph)CHC(Ph)H, L(3)= N(SiMe(2)CH(2))] depending on the reaction conditions and stoichiometry. The structures of the crystalline complexes 4, 6x21/2(hexane), 5(C(6)D(6)), and have been determined by X-ray crystallography (and have been published).     

Furfuroxides of lanthanum,praseodymium, neodymium,and samarium

Ln(R)₃, Ln(R)₂(OPrⁱ), and Ln(R)(OPrⁱ)₂ (where Ln = La, Pr, Nd, and Sm; R = deprotonated furfuryl alcohol, RH) were prepared from lanthanide isopropoxide and furfuryl alcohol in 1:3, 1:2 and 1:1 stoichiometric ratios respectively in anhydrous benzene under reflux. Ln(R)₂-(OPrⁱ) and Ln(R)(OPrⁱ)₂ were also obtained at room temperature. The isopropoxy group(s) of these derivatives were replaced by tertiary butoxy group(s) during the alcohol exchange reactions with tertiary butanol. All these derivatives are soluble in benzene except the tertiary butoxy derivatives which are only sparingly soluble. However, they become insoluble on standing. These furfuroxides did not distil at ～300°C/10² torr but decomposed. Isopropoxy/butoxy furfuroxides were characterized by the elemental analysis and also by estimating the liberated isopropanol. The i.r. spectra of Ln(R)₃ clearly supports the presence of furfuroxide groups in these derivatives.     

Enantioselective synthesis of piperidine,indolizidine, and quinolizidine alkaloids from a phenylglycinol-derived delta-lactam

Starting from a common lactam, (3R,8aS)-5-oxo-3-phenyl-2,3,6,7,8,8a-hexahydro-5H-oxazolo[3,2-a]pyridine (1), or its enantiomer, the enantioselective synthesis of 2-alkylpiperidines and cis- and trans-2,6-dialkylpiperidines is reported. The potential of this approach is illustrated by the synthesis of the piperidine alkaloids (R)-coniine, (2R,6S)-dihydropinidine, (2R,6R)-lupetidine, and (2R,6R)-solenopsin A, the indolizidine alkaloids (5R,8aR)-indolizidine 167B and (3R,5S,8aS)-monomorine I, and the nonnatural base (4R,9aS)-4-methylquinolizidine.     

Low-melting, low-viscous, hydrophobic ionic liquids: aliphatic quaternary ammonium salts with perfluoroalkyltrifluoroborates

A novel class of low-melting, hydrophobic ionic liquids based on relatively small aliphatic quaternary ammonium cations ([R(1)R(2)R(3)NR](+), wherein R(1), R(2), R(3) = CH(3) or C(2)H(5), R = n-C(3)H(7), n-C(4)H(9), CH(2)CH(2)OCH(3)) and perfluoroalkyltrifluoroborate anions ([R(F)BF(3)](-), R(F) = CF(3), C(2)F(5), n-C(3)F(7), n-C(4)F(9)) have been prepared and characterized. The important physicochemical and electrochemical properties of these salts, including melting point, glass transition, viscosity, density, ionic conductivity, thermal and electrochemical stability, have been determined and comparatively studied with those based on the corresponding [BF(4)](-) and [(CF(3)SO(2))(2)N](-) salts. The influence of the structure variation in the quaternary ammonium cation and perfluoroalkyltrifluoroborate ([R(F)BF(3)](-)) anion on the above physicochemical properties is discussed. Most of these salts are liquids at 25 degrees C and exhibit low viscosities (58-210 cP at 25 degrees C) and moderate conductivities (1.1-3.8 mS cm(-1)). The electrochemical windows of these salts are much larger than those of the corresponding 1,3-dialkyimidazolium salts. Additionally, a number of [R(F)BF(3)](-) salts exhibit plastic crystal behavior.     

Theoretical investigation of the molecular structure,vibrational spectra,and molecular docking of tramadol using density functional theory

The optimized molecular structures, harmonic vibrational wavenumbers, and the corresponding vibrational assignments of (1S,2S)-tramadol and (1R,2R)-tramadol are computationally examined using the B3LYP density functional theory method together with the standard 6–311++G(d,p) and def2-TVZP basis sets. The optimized structures show that phenolic rings of both 1R,2R and 1S,2S tramadol adopt planar geometry, which are slightly distorted due to the substitution at the meta-position; and the six-membered cyclohexane adopts a slightly distorted chair conformation. The 1S,2S enantiomer is energetically more favorable than 1R,2R with the energy differences of 1.32 and 1.03 kcal/mol obtained at B3LYP/6–311++G(d,p) and B3LYP/Def2-TVZP levels, respectively. The analysis of the binding pocket in the silico molecular docking with the m-opioid receptor shows that it originated two clusters with the 1S,2S enantiomer and one cluster with the 1R,2R enantiomer of tramadol. The results point to a more stable complex of the m-opioid receptor with the 1R,2R enantiomer of tramadol.     

Structure, conformation, stereodynamics, dimer formation, and absolute configuration of axially chiral atropisomers of hindered biphenyl carbinols

NMR spectra of biphenyl derivatives bearing a single CR2OH substituent in the ortho position indicate that they exist as sp (more stable) and ap (less stable) conformers, due to the restricted rotation about the Ar-CR2OH bond. When R = Et (compound 2) the corresponding rotation barrier was determined (7.5 kcal mol-1) by line shape simulation of the low-temperature NMR spectra. Introduction of the prochiral i-Pr group in the position 3' of a biphenyl with the CMe2OH substituent in the position 2 (4) allowed the determination of the enantiomerization barrier (due to the Ar-Ar bond rotation) for the stereolabile axially chiral atropisomers (13.95 kcal mol(-1)). DFT computations of these barriers were all in agreement with the experiments. Biphenyls bearing two CR2OH groups in the 2,2' positions were found to exist as configurationally stable atropisomers: when R = Me (7) they were separated by enantioselective HPLC and the absolute configuration assigned on the basis of the corresponding CD spectra. In solution, compounds 6 (R = H) and 7 (R = Me) were found to originate a dimer, due to H-bond interactions between two enantiomers. In the case of 7, the free energy of activation (9.5 kcal mol-1) for the exchange of the monomer with the dimer could be measured, for the first time, by dynamic NMR. The conformational preferences, predicted by computations for the biphenyls with two CR2OH substituents in the 2,2' positions, were confirmed by X-ray diffraction in the case of R = H (6), R = Me (7), and R = i-Pr (9).     

Selective photochemistry at stereogenic metal and ligand centers of cis-[Ru(diphosphine)2(H)2]: preparative, NMR, solid state, and laser flash studies

Three ruthenium complexes Λ-[cis-Ru((R,R)-Me-BPE)(2)(H)(2)] Λ-R,R-Ru1H(2), Δ-[cis-Ru((S,S)-Me-DuPHOS)(2)(H)(2)] Δ-S,S-Ru2H(2), and Λ-[cis-Ru((R,R)-Me-DuPHOS)(2)(H)(2)] Λ-R,R-Ru2H(2) (1 = (Me-BPE)(2), 2 = (Me-DuPHOS)(2)) were characterized by multinuclear NMR and CD spectroscopy in solution and by X-ray crystallography. The chiral ligands allow the full control of stereochemistry and enable mechanistic studies not otherwise available. Oxidative addition of E-H bonds (E = H, B, Si, C) was studied by steady state and laser flash photolysis in the presence of substrates. Steady state photolysis shows formation of single products with one stereoisomer. Solid state structures and circular dichroism spectra reveal a change in configuration at ruthenium for some Δ-S,S-Ru2H(2)/Λ-R,R-Ru2H(2) photoproducts from Λ to Δ (or vice versa) while the configuration for Λ-R,R-Ru1H(2) products remains unchanged as Λ. The X-ray structure of silyl hydride photoproducts suggests a residual H(1)···Si(1) interaction for Δ-[cis-Ru((R,R)-Me-DuPHOS)(2)(Et(2)SiH)(H)] and Δ-[cis-Ru((R,R)-Me-DuPHOS)(2)(PhSiH(2))(H)] but not for their Ru(R,R-BPE)(2) analogues. Molecular structures were also determined for Λ-[cis-Ru((R,R)-Me-BPE)(2)(Bpin)(H)], Λ-[Ru((S,S)-Me-DuPHOS)(2)(η(2)-C(2)H(4))], Δ-[Ru((R,R)-Me-DuPHOS)(2)(η(2)-C(2)H(4))], and trans-[Ru((R,R)-Me-DuPHOS)(2)(C(6)F(5))(H)]. In situ laser photolysis in the presence of p-H(2) generates hyperpolarized NMR spectra because of magnetically inequivalent hydrides; these experiments and low temperature photolysis with D(2) reveal that the loss of hydride ligands is concerted. The reaction intermediates [Ru(DuPHOS)(2)] and [Ru(BPE)(2)] were detected by laser flash photolysis and have spectra consistent with approximate square-planar Ru(0) structures. The rates of their reactions with H(2), D(2), HBpin, and PhSiH(3) were measured by transient kinetics. Rate constants are significantly faster for [Ru(BPE)(2)] than for [Ru(DuPHOS)(2)] and follow the substrate order H(2) > D(2) > PhSiH(3) > HBpin.     

Dipole and quadrupole moment functions of the hydrogen halides HF, HCl, HBr, and HI: a Hirshfeld interpretation

The dipole and quadrupole moment functions of the hydrogen halides are calculated using a large polarized basis and correlated wavefunctions and compared to experiment and previous calculations. These functions are analyzed in terms of local moments constructed using the Hirshfeld method. The dipole moment is the sum of the functions q(H)R+mu(H) and mu(X) with q(H) being the charge on the hydrogen atom, R the internuclear separation, mu(H) and mu(X) the atomic dipoles on the hydrogen and halogen atoms. We find that q(H)R+mu(H) is always positive and has a maximum at bond lengths larger than the equilibrium. In HF, mu(F) is slightly positive at the maximum in q(H)R+mu(H) and has little effect on the resultant maximum in the dipole moment function (DMF). mu(Cl), mu(Br), and mu(I), on the other hand, are increasingly more negative at the maximum of q(H)R+mu(H) and have a profound effect on the width of the maximum of the resulting DMF, successively broadening it and completely eliminating it at HI. The quadrupole moment function (QMF) (with the halogen as origin) is given by Theta(HX)=Theta(HX) (proto)+deltaTheta(X)+deltaTheta(H)+2mu(H)R+q(H)R(2), where Theta(HX) (proto) is the quadrupole moment of the separated atoms (the halogen in this instance) and deltaTheta(X)+deltaTheta(H) the change in the in situ quadrupole moments of the halogen and hydrogen atoms. The maximum in the QMF and its slope at equilibrium are determined essentially by 2mu(H)R+q(H)R(2), which is known once the DMF is known. deltaTheta(X)+deltaTheta(H) is always negative while Theta(HX) (proto) is positive, so one can approximate the molecular quadrupole moment to within 10% as Theta(HX)>Theta(HX) (proto)+2mu(H)R+q(H)R(2).