Electrophilic radiofluorination of aryltrimethylsilanes as a general route to 18F-labeled aryl fluorides

The reactions of a variety of aryltrimethylsilanes with elemental fluorine and acetyl hypofluorite have been studied with the aim of developing a general method for labeling aromatic compounds with fluorine-18. Extensive ¹⁸F incorporation into the aromatic ring of the selected aryltrimethylsilanes was invariably observed, leading to the ipso (¹⁸F-for-Si) electrophilic substitution products together with variable yields of other (¹⁸F-for-H) electrophilic substitution products. The relative extent of the ¹⁸F substitution processes [(C-Si/C-H)subst.] is found to depend largely upon the substituent group on the aromatic ring of the substrate, the leaving moiety, and the radiofluorination procedure used. The utility of aryltrimethylsilyl derivatives as precursors for the rapid synthesis of high specific activity of ¹⁸F-labeled radiopharmaceuticals is discussed.     

Synthesis and some reactions of the stable vinyl cation stabilized by the 3-η5-cyclopentadienyl-η5-(3)-1,2-dicarbollyliron(II)-1 group

An individual vinyl cation in the form of a zwitterion stabilized by the 3-η⁵-C₅H₅Fe¹¹-η⁵-(3)-1,2-C₂B₉$\text{H}$₁₀-1 group has been produced for the first time, and its reactions with nucleophilic agents have been studied. Deprotonation yielding an acetylene derivative is the main reaction in the interaction of the vinyl cation with MeLi, NaBH₄ and C₅H₅N.     

The mechanism of biomolecular methyl transfer in a methyl aminoalkanesulfonate. application of 18o isotope shifts in 13cmr spectra of sulfonic esters.

¹³Cmr spectra show complete absence of scrambling of an ¹⁸O label in $\text{1}$$\text{a}$ recovered after partial conversion to $\text{2}$$\text{a}$ thereby precluding an $\text{0}$-methylation mechanism for the bimolecular formation of $\text{2}$$\text{a}$ from $\text{1}$$\text{a}$.     

Fluorination of aromatic compounds with F2 and acetyl hypofluorite: synthesis of 18F-aryl fluorides by cleavage of aryl-tin bonds [1]

Elemental fluorine and acetyl hypofluorite, labeled with ¹⁸F, were added to eight simple aryl-tin derivatives. Both reagents gave good radiochemical yields of labeled aryl fluorides. Overall, acetyl hypofluorite gave more consistent yields (～70%), while F₂ gave more variable yields (54% – 95%).     

Energy transfer processes in reactions of He(2 3S) and Ne(3P0,2) with CS2

A comparative spectroscopic study in the visible and ultraviolet ranges was conducted on the flowing afterglows resulting from the reactions of He(2 ³S) and Ne(³P_0,2) metastables with CS₂. Penning ionization was found to be the predominant energy transfer process. However, electron—ion recombination within the afterglows constitutes a major secondary process and gives rise to the most intense emitting system, CS(A ¹ Π → X ¹Σ⁺). Both afterglows were found to produce the CS⁺₂($\text{B}$²Σ⁺_u-$\text{X}$²Π_g), CS⁺₂($\text{A}$²Π_u-$\text{X}$²Π_g) and CS(a ³Π-X ¹Σ⁺) emission systems as well as some atomic sulfur emission lines. Some intensity differences were observed and are interpreted in terms of energetics and the formation mechanisms of the emitting species. A moderately strong CS⁺(A ²Π_i-X ²Σ⁺) emission system was also observed in the ehlium afterglow. In addition, a weak, sharp group of bands in the 390–420 nm range in the helium afterglow has been determined to be due to the presence of a small amount of He⁺ ions. This group of bands consists of two overlapping emission systems and are identified as CS(B ¹Σ⁺ → A ¹Π) and CS⁺(B ²Σ⁺ → A ²Π_i).     

Rare gas molecular ions: Formation of XeF+ by ion-molecule reactions in Xe and NF3 and evidence for radiative deactivation of Xe+ (2P12)

The formation of the XeF⁺ ion by ion-molecule reaction has been observed in an ionized mixture of Xe and NF₃ by ion cyclotron resonance mass spectrometry. The excited ²P_{$\text{1}\text{2}$} state of the xenon ion has unambiguously been identified as the major precursor by photoionization mass spectrometry. The NF⁺₃ ion makes an additional minor contribution. Evidence suggests that the excited ²P_{$\text{1}\text{2}$} xenon ion radiatively decays to the ²P_{$\text{3}\text{2}$} ground state on the time scale of the experiment. The transition probability deduced for this dipole forbidden emission, 18 ± 4 s^?1, is in good agreement with the theoretical value of 21 s^?1 for the sum of the magnetic dipole and electric quadrupole transition rates.     

Electric moments,polarizabilities and hyperpolarizabilities for BH(X1Σ+ and CH+ (X1Σ+)

The electric moments and static polarizabilities of BH(1σ²2σ²3σ², X¹Σ⁺) and CH⁺ (1σ²2σ²3σ², X¹Σ⁺) were calculated at the experimental internuclear separation in the LCAO SCF MO approximation. Most of the molecular properties reported in this paper for BH and CH⁺ appear for the first time and should be close to the Hartree—Fock limit. All tensors up to the fourth rank have been included in this study. The isotropy and anisotropy of the α, β and γ tensors are, in atomic units. $\text{α}$ = 22.71, Δα = ?0.26, $\text{β}$ = 55.1, Δβ = ?183.7, $\text{γ}$ = 12428, Δ₁γ = 37895, Δ₂γ = 25120 for BH and $\text{α}$ = 7.73, Δα = 0.39, $\text{β}$ = ?12.4, Δβ = ?11.7, $\text{γ}$ = 344, Δ₁γ = 1515, Δ₂γ = 750 for CH⁺.     

Contiguous concerted participation in the rearrangement of anti-tricyclo[4.2.1.1.2,5]deca-3,7,-diene-9,10-diol,a highly hindered system.

The acid catalysed peclppangement of anti-tricyclo[4.1.1.^2,5]deca-3,7-diene-9, 10-diol ($\text{1a}$) to $\text{2a}$ is shown to proceed through concommitant electrophilic and nucleophilic attack on an alkene by an incipient carbonium ion and the rernaining alcohol function.     

General approach for the synthesis of polyquinenes via the weiss reaction. Preparation of the chiral tetracyclo [6.6.0.01,5.08,12]tetradecane-3,6,10,13,-tetraene

The aldol approach to construct the tetracyclic polyquinane skeleton of $\text{12}$, followed by hydroboration and the HMPA mediated dehydration of four hydroxyl groups has resulted in the facile synthesis of the chiral polyquinene, tetracyclo[6.6.0.0^1,5.0^8,12]-tetradecane-3,6,10,13-tetraene $\text{2}$. This method completely avoids the troublesome fragmentation reactions earlier encountered when the strained tetraone $\text{9}$ was reacted with nucleophilic reagents.     

Reaction of some tertiary phosphines and phosphites with [Co(η5-C5H5)(S2C2{CN}2)]

Reaction of the 16 electron monomer [Co(η⁵-C₅H₅)(S₂C₂{CN}₂)] with various tertiary phosphines and phosphites (L) gives readily the 18 electron monomers [Co(η⁵-C₅H₅)(S₂C₂{CN}₂)L] which for L = P(OR)₃ have J($\text{P}$C₅$\text{H}$₅) ca. 6 Hz but J($\text{P}$C₅$\text{H}$₅) = 0 for L = PR₃.     

Yield of I(2Psol:12) in the photodissociation of CH2I2

The production of I(²P_{$\text{1}\text{2}$}) in the photolysis of CH₂I₂ has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm^?1 correlate with I(²P_{$\text{3}\text{2}$}) whilst those at 34700 and 40100 cm^?1, which correlate with I(²P_{$\text{1}\text{2}$}), give final ²P_{$\text{3}\text{2}$}/²P_{$\text{1}\text{2}$} ratios of 1.75 and 1.1, respectively, after curve crossing.     

Comparison of reactivity of Ar(3Po) and Ar(3P2) metastable states. Products of quenching by some halogen-containing compounds

Vacuum UV emission from the products of quenching ofAr(³P_o) and Ar(³P₂) by several reagents has been compared. The large differences suggest that Ar(³P_o) and Ar(³P₂) preferentially yield respectively the D($\text{1}\text{2}$) and B($\text{1}\text{2}$) excited states of ArBr^★ or ArCl^★, which show specific, but very different, predissociation patterns.     

Interactions magnétiques dans des groupements binucléaires [Fe2O7]8− au sein de Na8Fe2O7

The magnetic interaction in the structural units [Fe₂O₇]^8?, built of two corner-sharing FeO₄ tetrahedra, in Na₈Fe₂O₇ ($\text{Na}{}_2\text{O}\text{Fe}{}_2\text{O}{}_3\text{=}\text{4}\text{1}$) has been studied by magnetic susceptibility measurements (4.2–500 K). An exchange integral $\text{J}\text{K}{}_{\mathrm{<mtext>B</mtext>}}$ of ?37 K is obtained by comparison of the experimental values and the calculated ones using a Heisenberg-Dirac-Van Vleck-type Hamiltonian ? = $\text{?2J}\text{S}\text{?}{}_1\text{S}\text{?}{}_2$. The hypothesis of magnetically isolated [Fe₂O₇]^8? groups is corroborated by Mössbauer spectroscopy between 1.5 and 77 K. The susceptibility measurements of the solid solutions Na₈Fe_2?xM_xO₇ (M = Al, Ga; 0 ≤ x ≤ 0.2 for Al; 0 ≤ x ≤ 2 for Ga) leads to the same conclusion of the existence of isolated Fe³⁺Fe³⁺ pairs in Na₈Fe₂O₇. The type of substitution of Fe by Al or Ga is determined; homonuclear Fe³⁺Fe³⁺ and M³⁺M³⁺ pairs and heteronuclear Fe³⁺M³⁺ pairs are formed.     

X-ray molecular structure of the 1:1 adduct of [FeH(CO)4]− and dimethyl acetylenedicarboxylate. η3-[trans-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate

The crystal structure of a bis(triphenylphosphine)iminium salt of the 1:1 adduct of [FeH(CO)₄]^? and dimethyl acetylenecarboxylate has been determined from three-dimensional X-ray data collected by the counter method. Single crystals belong to the triclinic space space group P$\text{1}$, with two units of [C₃₆H₃₀NP₂]⁺[C₁₀H₇FeO₈]^? in a cell of dimensions: $\text{a}$ = 13.918(2), $\text{b}$ = 15.669(5), $\text{c}$ = 9.909(2) Å, $\text{α}$ = 91.22(3), $\text{β}$ = 94.83(2), and $\text{γ}$ = 77.62(2)°. The structure was refined to a conventional $\text{R}$ of 0.068 for 5373 observed

reflections. The resulting structure indicates that the complex anion is η³-[$\text{trans}$-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate, the coordination around the iron atom being described as a considerably distorted trigonal bipyramid. A comparison of the present structure with the structures of related complexes suggests that the η³-acryloyl portion is best represented as an intermediate of (η³-allyl) with the oxygen atom and (η²-olefin + η¹-acyl). The short Fe-C(acyl) length of 1.897(5) Å implies an enhanced back-donation of electrons from the iron atom to the acyl group.     

Excitation of XeF* by reactions of XeF2 with Ar(3P0,2),Kr(3P2) and Xe(3P2)

The reactions of the lowest metastable states of Ar, Kr and Xe with XeF₂ were studied in a flowing afterglow apparatus; XeF emission (from D²Π_{$\text{1}\text{2}$} and B ²Π⁺ states) was observed in all cases. The total rate constants (cm³ molecule^?1 s^?1) for XeF^* formation were determined as 75 × 10^?11 ? Xe(³P₂);64 × 10^?11 ? Kr(³P₂) and 20 × 10^?11 ? Ar(³P_0,2). The reactions of Ar(³P_0,2) and Kr(³P₂) with XeF₂ also gave ArF^* and KrF^*, respectively. Analysis of these emissions indicates that at least two different mechanisms are operative: reactive quenching by the ionic—covalent curve-crossing mechanism and excitation transfer. The Ar(³P_0,2 + XeF₂ reaction is a sufficiently strong source of XeF(D—X) emission that the main features of the XeF(D²Π_{$\text{1}\text{2}$} ? X²Σ⁺) system could be photographed and tentative assignments of these vibrational bands are given. The XeF(D → B) emission could not be observed and the ratio of the D—X versus the D—B transition probability must be > 1000 : 1.     

Single-crystal growth and structure determination of Ag16I12P2O7

Single crystals of the fast-ion conductor Ag₁₆I₁₂P₂O₇ were prepared and their structure ($\text{P6}\text{mcc}\text{, a = 12.054, c = 7.504}$ Å) was determined by X-ray diffraction (r = 0.08). The I atoms form a close-packed array leaving channels occupied by P₂O^4?₇ ions running along the c axis. The Ag atoms are disordered over four different types of site with occupation numbers ranging from 0.12 to 0.52. Each Ag⁺ ion coordination polyhedron shares several faces with adjacent polyhedra providing ready paths for Ag⁺ ion conduction.     

Kinetic spectroscopy in the far vacuum ultraviolet. Part I: Detection of (2p5) 2P32,12 fluorine atoms using atomic resonance spectrometry in the wavelength range 95–98 nm

A new experimental system for atomic resonance spectrometry at λ < 105 nm in a discharge-flow system is described. The spectrum of a fluorine resonance lamp has been studied, and possible precursors for the 2p⁴ 3s excited F atoms formed are suggested. Ground state (2p⁵²P_{$\text{3}\text{2}$}) and J-excited ²P_{$\text{1}\text{2}$} F atoms have been detected for the first time in resonance absorption and fluorescence using the first resonance transitions with wavelengths between 95.2 and 97.8 nm. Preliminary measurements (using both ⁴P-²P and ²P-²P lines) of the variations with concentration of absorption intensity by ground state F ²P_{$\text{3}\text{2}$} and by J-excited F ²P_{$\text{1}\text{2}$} atoms are reported; F atom concentrations were measured using a titration method based on the rapid reaction, F + Cl₂ → FCl + Cl.     

Selected fluorescence and dissociation lifetimes on N2O+ in its Ã(2Σ+),000 and 100 states

Radiative and radiationless lifetimes together with the quantum yield towards fluorescence of individual vibronic states of molecular ions can be determined by threshold electron—fluorescence photon coincidence measurements. This method is here applied to the X?²Π_{$\text{3}\text{2,1,2}$} and òΣ⁺ states of N₂O⁺ which were also studied by high resolution photoionization resonance spectroscopy.     

Structure des ions [C4H7O]+ obtenus par fragmentations du [1-methylcyclobutanol]

The mass spectra of metastable molecular and fragment ions demonstrate that the loss of CH₃^. from [1-methylcyclobutanol]^.+ leads competitively to three different ions: $\text{a}$ = protonated cyclobutanone; $\text{b}$ = [n-C₃H₇CO]⁺ and $\text{c}$ = protonated methylvinylketone.     

The synthesis and crystal and molecular structure of H3(μ-η2-C6H4)(μ-η2-HC3NC6H5)Os3(CO)8

The complex H₃(μ-η²-C₆H₄) (μ-η²-HC₃NC₆H₅)Os₃(CO)₈ has been synthesized and characterized by IR, ¹H NMR and X-ray crystal structure analyses. The compound contains a $\text{dihapto}$-benzyne ligand bridging one edge of a triangular cluster of osmium atoms and a $\text{dihapto}$-formimidoyl ligand bridging a different edge on the opposite face of the cluster from the benzyne ligand.