Synthesis and characterization of bis[bis(pentafluoroethyl)phosphinyl]imides, M(+)N[(C2F5)2P(O)]2(-), M = H, Na, K, Cs, Ag, Me4N

A convenient synthesis and a full characterization of the strong acid bis[bis(pentafluoroethyl)phosphinyl]imide and some of its salts M (+)N[(C 2F 5) 2P(O)] 2 (-), M = Na, K, Cs, Ag, Me 4N, are presented. Their thermal (mp, T dec.) and spectroscopic (IR, Raman, NMR) properties are discussed. A single crystal structure of [Me 4N][N{P(O)(C 2F 5) 2} 2] has been obtained, and the structural parameters of the anion are compared with the results of quantum-chemical calculations. The observed properties are comparable to those of bis((trifluoromethyl)sulfonyl)imide and their derivatives.     

Enthalpies of formation of gas-phase N3, N3-, N5+, and N5- from Ab initio molecular orbital theory, stability predictions for N5(+)N3(-) and N5(+)N5(-), and experimental evidence for the instability of N5(+)N3(-)

Ab initio molecular orbital theory has been used to calculate accurate enthalpies of formation and adiabatic electron affinities or ionization potentials for N3, N3-, N5+, and N5- from total atomization energies. The calculated heats of formation of the gas-phase molecules/ions at 0 K are DeltaHf(N3(2Pi)) = 109.2, DeltaHf(N3-(1sigma+)) = 47.4, DeltaHf(N5-(1A1')) = 62.3, and DeltaHf(N5+(1A1)) = 353.3 kcal/mol with an estimated error bar of +/-1 kcal/mol. For comparison purposes, the error in the calculated bond energy for N2 is 0.72 kcal/mol. Born-Haber cycle calculations, using estimated lattice energies and the adiabatic ionization potentials of the anions and electron affinities of the cations, enable reliable stability predictions for the hypothetical N5(+)N3(-) and N5(+)N5(-) salts. The calculations show that neither salt can be stabilized and that both should decompose spontaneously into N3 radicals and N2. This conclusion was experimentally confirmed for the N5(+)N3(-) salt by low-temperature metathetical reactions between N5SbF6 and alkali metal azides in different solvents, resulting in violent reactions with spontaneous nitrogen evolution. It is emphasized that one needs to use adiabatic ionization potentials and electron affinities instead of vertical potentials and affinities for salt stability predictions when the formed radicals are not vibrationally stable. This is the case for the N5 radicals where the energy difference between vertical and adiabatic potentials amounts to about 100 kcal/mol per N5.     

Enantiospecific synthesis of (+)-N(a)-methylpericyclivine and (-)-N(a)-methylakuammidine as well as the ring-A oxygenated natural products, (+)-10-methoxy N(a)-methylpericyclivine and 10-hydroxy N(a)-methylpericyclivine

[reaction: see text] The first enantiospecific, regiospecific total synthesis of the enantiomers of N(a)-methylpericyclivine and N(a)-methylakuammidine as well as the ring-A oxygenated natural products (+)-10-methoxy N(a)-methylpericyclivine and 10-hydroxy N(a)-methylpericyclivine was achieved. The lactones (see 19, 22, and 25) are key to the formation of the beta-axial methyl ester moiety.     

The first synthesis of (-)-asperpentyn and efficient syntheses of (+)-harveynone, (+)-epiepoformin and (-)-theobroxide

A generally applicable strategy for the synthesis of a range of polyoxygenated cyclohexane natural products has been developed. The enantioselective syntheses of (-)-theobroxide, a polyoxygenated cyclohexane natural compound with potent growth inducing properties in potato microtubers has been achieved via a 1,2 O-silyl migration between trans-hydroxyl groups and a remote hydroxyl directed epoxidation of an enone derived from quinic acid. A thus derived alpha-iodoenone was subjected to Stille coupling with tetramethylstannane to afford the first title compound. A similar strategy enabled a route to the complete asymmetric synthesis of the acetylenic phytotoxin (+)-harveynone. By selective reduction of (-)-theobroxide, (+)-epiepoformin was also prepared in enantiopure form and similarly, stereoselective reduction of (+)-harveynone completed the first enantioselective synthesis of (-)-asperpentyn, another natural compound with antimicrobial activity.     

Structures and dissociation channels of protonated mixed clusters around a small magic number: infrared spectroscopy of ((CH3)3N)n-H(+)-H2O (n = 1-3)

The magic number behavior of ((CH(3))(3)N)(n)-H(+)-H(2)O clusters at n = 3 is investigated by applying infrared spectroscopy to the clusters of n = 1-3. Structures of these clusters are determined in conjunction with density functional theory calculations. Dissociation channels upon infrared excitation are also measured, and their correlation with the cluster structures is examined. It is demonstrated that the magic number cluster has a closed-shell structure, in which the water moiety is surrounded by three (CH(3))(3)N molecules. The ion core (protonated site) of the clusters is found to be (CH(3))(3)NH(+) for n = 1-3, but coexistence of an isomer of the H(3)O(+) ion core cannot be ruled out for n = 3. Large rearrangement of the cluster structures of n = 2 and 3 before dissociation, which has been suggested in the mass spectrometric studies, is confirmed on the basis of the structure determination by infrared spectroscopy.     

Tris(dimethylamino)oxosulfonium difluorotrimethylsilicate, (Me(2)N)(3)SO(+)Me(3)SiF(2)(-) (TAOS Fluoride)

In the OSF(4)/Me(2)NSiMe(3) system besides the long known Me(2)NS(O)F(3) only the trisubstituted derivative is isolated as (Me(2)N)(3)SO(+)Me(3)SiF(2)(-) (3). Similar to (Me(2)N)(3)S(+)Me(3)SiF(2)(-) compound 3 is an excellent fluoride ion donor. With AsF(5) and HF the corresponding hexafluoroarsenate (Me(2)N)(3)SO(+)AsF(6)(-) (4) and the hydrogen bifluoride (Me(2)N)(3)SO(+)HF(2)(-) (5) are formed in almost quantitative yield. X-ray structure determinations of 3-5 surprisingly showed two different types of structures for the cation. In 3 and 5 this cation has C(3) symmetry, while in the hexafluoroarsenate 4 a (Me(2)N)(3)S(+)-like structure with C(s)() symmetry is determined. The experimental results for (Me(2)N)(3)SO(+) and (Me(2)N)(3)S(+) are compared with theoretical calculations for these cations and their isoelectronic neutral counterparts, the phosphorus amides (Me(2)N)(3)PO and (Me(2)N)(3)P, respectively.     

Magnitudes and chemical consequences of R(3)N(+)-C-H...O[double bond]C hydrogen bonding

The magnitude of the stabilizing interaction between an aliphatic C[bond]H bond attached to an ammonium nitrogen and a carbonyl oxygen was evaluated by ab initio calculations at the MP2/6-311++G** level of theory. Attractive R(3)N(+)-C-H...O[double bond]C interactions play an important role in supramolecular recognition and various types of stereoselective catalysis. Our calculations show that R(3)N(+)-C-H...O[double bond]C is the strongest hydrogen bond of the C-H...O type known to date. Such hydrogen bonds remain as stabilizing interactions even in water for amide acceptors.     

Structural study on 2,2'-(methylimino)bis(N,N-dioctylacetamide) complex with Re(VII)O4- and Tc(VII)O4- by 1H NMR, EXAFS, and IR spectroscopy

The structures of the complex of 2,2'-(methylimino)bis(N,N-dioctylacetamide) (MIDOA) with M(VII)O(4)(-) (M = Re and Tc), which were prepared by liquid-liquid solvent extraction, were investigated by using (1)H nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS), and infrared (IR) spectroscopy. The (1)H NMR spectra of the complex of MIDOA with Re(VII)O(4)(-) prepared in the organic solution suggest the transfer of a proton from aqueous to organic solution and the formation of the H(+)MIDOA ion. The EXAFS spectra of the complexes of H(+)MIDOA with Re(VII)O(4)(-) and Tc(VII)O(4)(-) show only the M-O coordination of the aquo complexes, suggesting that the chemical state of M(VII)O(4)(-) was unchanged during the extraction process. The results from (1)H NMR and EXAFS, therefore, provide evidence of M(VII)O(4)(-)···H(+)MIDOA complex formation in the organic solution. The IR spectra of Re(VII)O(4)(-)···H(+)MIDOA and Tc(VII)O(4)(-)···H(+)MIDOA were analyzed based on the structures and the IR spectra that were calculated at the B3LYP/cc-pVDZ level. Comparison of the observed and calculated IR spectra demonstrates that an intramolecular hydrogen bond is formed in H(+)MIDOA, and the M(VII)O(4)(-) ion interacts with H(+)MIDOA through multiple C-H(n)···O hydrogen bonds.     

Stereoselective syntheses of (+)-goniodiol, (-)-8-epigoniodiol,and (+)-9-deoxygoniopypyrone via alkoxyallylboration and ring-closing metathesis

A convenient synthesis of (+)-goniodiol, (-)-8-epigoniodiol, and (+)-9-deoxygoniopypyrone has been developed via asymmetric alkoxyallylboration and ring-closing metathesis pathways.     

On the gas-phase Co(+)-mediated oxidation of ethane by N2O: a mechanistic study

The potential energy surface (PES) corresponding to the Co(+)-mediated oxidation of ethane by N(2)O has been investigated by using density functional theory (DFT). After initial N(2)O reduction by Co(+) to CoO(+), ethane oxidation by the nascent oxide involves C-H activation followed by two possible pathways, i.e., C-O coupling accounting for ethanol, Co(+)-mediated β-H shift giving the energetically favorable product of CoC(2)H(4)(+) + H(2)O, with minor CoOH(2)(+) + C(2)H(4). CoC(2)H(4)(+) could react with another N(2)O to yield (C(2)H(4))Co(+)O, which could subsequently undergo a cyclization mechanism accounting for acetaldehyde and oxirane and/or a direct H-abstraction mechansim for ethenol. Loss of oxirane and ethenol is hampered by respective endothermicity and high kinetics barrier, whereas acetaldehyde elimination is much energetically favorable. CoOH(2)(+) could facilely react with N(2)O to form OCoOH(2)(+), rather than Co(OH)(2)(+) or CoO(+).     

Solvation-induced cluster anion core switching from NNO2(-)(N2O)n-1 to O(-)(N2O)n

We report a photoelectron imaging study of the [O(N(2)O)(n)](-), 0or=4 (and up to at least n=9) signatures of an O(-) core are predominantly observed. Photofragmentation studies at 355 nm support these results.     

A Convenient Synthesis of (R)-(+)-Perillaldehyde

A short and efficient synthesis of the commercially unavailable (R)-(+) isomer of perillaldehyde from (+)-limonene oxide has been developed.     

Enantioselective syntheses of (-)- and (+)-monomorine I

A concise enantioselective total synthesis of unnatural (-)-monomorine I has been achieved starting from lactam 2 in 54% overall yield. Natural (+)-monomorine I was also synthesized.     

Asymmetric synthesis of (-)-7-epiaustraline and (+)-1,7-diepiaustraline

A diastereoselective and modular approach to the synthesis of the 3-hydroxymethyl-2,3,5,6,7,7a-hexahydro-1H-pyrrolizine-1,2,7-triol structure, characteristic of several natural pyrrolizidine natural products, has been developed. This approach culminated in the synthesis of (-)-7-epiaustraline and (+)-1,7-diepiaustraline. The oxazolidinone group has been found to be a useful protecting group in the RCM reaction and, as part of a pyrrolo[1,2-c]oxazol-3-one ring system, has functioned as a stereo- and regio-directing group in a key diastereoselective cis-dihydroxylation reaction and a regioselective nucleophilic ring-opening of a S,S-dioxo-dioxathiole.     

Asymmetric total synthesis of (-)-spirofungin A and (+)-spirofungin B

[chemical reaction: see text]. The stereocontrolled total synthesis of (-)-spirofungin A (1) and (+)-spirofungin B (2a), polyketide-type antibiotics having various antifungal activities, has been achieved employing the Weinreb amide 8, the alkyne 9, and the vinyl boronate 5 readily available from the common intermediate 10. The first synthesis proceeded with a longest linear sequence of 31 steps, affording (-)-1 and (+)-2a in 7.9% and 5.2% overall yields, respectively.     

(+)-Rimocidin synthetic studies. Construction of an advanced C(1-18) polyol fragment

[structure: see text] The synthesis of an appropriately functionalized advanced C(1-18) polyol fragment of the mycosamine-glycosylated polyene macrolide, (+)-rimocidin (1), has been achieved in a highly efficient manner. Highlights of the strategy include the S(N)2/S(N)2' addition of dithiane anions to vinyl epoxides and the multicomponent linchpin union of 2-TBS-1,3-dithiane with two advanced epoxides.     

Dissociative recombination study of N(3) (+): cross section and branching fraction measurements

We report an investigation into the dissociative recombination of the azide radical cation, N(3) (+). The reaction rate constant has been measured to be 6.47 x 10(-7) cm(3) s(-1) at room temperature. This value is smaller than those reported earlier for the ion-electron neutralization of N(3) (+) at nitrogen atmospheric pressure. A strong propensity to dissociate through the N(2)+N channel has been observed.     

Total synthesis of natural (+)-sesbanimide a and (-)-sesbanimide b

The first total synthesis of natural (+)-sesbanimide A (1) and (-)-sesbanimide B (2), potent antitumor alkaloids isolated from the seeds of the leguminous plant, Sesbania drummondii, has been accomplished starting from D-(+)-xylose. This total synthesis involves efficient construction of the optically active AB-ring system from D-(+)-xylose, introduction of the C₅-unit into the AB-ring system in a form of exo-methylene-γ-lactone, and elaboration of the labile C-ring system at the last stage of the synthesis. The absolute configurations of natural 1 and 2 could be obviously established by our total synthesis.     

A kinetic study of the reactions of Fe+ with N2O, N2, O2, CO2 and H2O, and the ligand-switching reactions Fe+.X + Y --> Fe+.Y + X (X = N2, O2, CO2; Y = O2, H2O)

A series of reactions involving Fe(+) ions were studied by the pulsed laser ablation of an iron target, with detection of ions by quadrupole mass spectrometry at the downstream end of a fast flow tube. The reactions of Fe(+) with N(2)O, N(2) and O(2) were studied in order to benchmark this new technique. Extending measurements of the rate coefficient for Fe(+) + N(2)O from 773 K to 185 K shows that the reaction exhibits marked non-Arrhenius behaviour, which appears to be explained by excitation of the N(2)O bending vibrational modes. The recombination of Fe(+) with CO(2) and H(2)O in He was then studied over a range of pressure and temperature. The data were fitted by RRKM theory combined with ab initio quantum calculations on Fe(+).CO(2) and Fe(+).H(2)O, yielding the following results (120-400 K and 0-10(3) Torr). For Fe(+) + CO(2): k(rec,0) = 1.0 x 10(-29) (T/300 K)(-2.31) cm(6) molecule(-2) s(-1); k(rec,infinity) = 8.1 x 10(-10) cm(3) molecule(-1) s(-1). For Fe(+) + H(2)O: k(rec,0) = 5.3 x 10(-29) (T/300 K)(-2.02) cm(6) molecule(-2) s(-1); k(rec,infinity) = 2.1 x 10(-9) (T/300 K)(-0.41) cm(3) molecule(-1) s(-1). The uncertainty in these rate coefficients is determined using a Monte Carlo procedure. A series of exothermic ligand-switching reactions were also studied at 294 K: k(Fe(+).N(2) + O(2)) = (3.17 +/- 0.41) x 10(-10), k(Fe(+).CO(2) + O(2)) = (2.16 +/- 0.35) x 10(-10), k(Fe(+).N(2) + H(2)O) = (1.25 +/- 0.14) x 10(-9) and k(Fe(+).O(2) + H(2)O) = (8.79 +/- 1.30) x 10(-10) cm(3) molecule(-1) s(-1), which are all between 36 and 52% of their theoretical upper limits calculated from long-range capture theory. Finally, the role of these reactions in the chemistry of meteor-ablated iron in the upper atmosphere is discussed. The removal rates of Fe(+) by N(2), O(2), CO(2) and H(2)O at 90 km altitude are approximately 0.1, 0.07, 3 x 10(-4) and 1 x 10(-6) s(-1), respectively. The initially formed Fe(+).N(2) and Fe(+).O(2) are converted into the H(2)O complex at approximately 0.05 s(-1). Fe(+).H(2)O should therefore be the most abundant single-ligand Fe(+) complex in the mesosphere below 90 km.