Singlet methylene kinetics: Direct measurements of removal rates of ã1A1 and b̃1B1 CH2 and CD2

Rate constants for collisional removal of ã¹A₁ and b?¹B₁ CH₂ and CD₂ have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH₂(ã¹A₁) removal by He, Ne, Ar, Kr, Xe, N₂, H₂, O₂, CO and CH₄, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10^?12 cm³ molecule^?1 s^?1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD₂(ã¹A₁) by the rare gases. The rate determining step in removal by the rare gases and N₂ is thought to be singlet—triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH₂(b?¹B₁) and three Σ vibronic levels of CD₂(b?¹B₁) have been measured and found to lie in the range 2.5–6.0 μs, and collisional quenching rates for CH₂(b?¹B₁) are found to be of the order of the gas kinetic collisional frequency.     

Collisional quenching of K* (4p2p) and K* (5p2p by H2O,CF4, and CH4

Rate constants are reported for collisional quenching of K^* (4p^2p and K^* (5p^2p) by H₂O, CF₄ and CH₄. The K^* (4p^2p or K^*(5p^2p) is produced by photodissociation of K1 vapor at 2450 Å or 1925 Å, respectively. As for Na^* (3p^2p, H₂O, CF₄, and CH₄ are very inefficient at quenching K^* (4p^2p); however, they are very efficient at quenching K^* (5p^2p).     

Binuclear ruthenium complexes of fluorous phosphine ligands: Synthesis, properties, and biphasic catalytic activity. Crystal structure of [Ru(μ-O2CMe)(CO)2P(CH2CH2(CF2)5CF3)3]2

The fluorocarbon soluble, binuclear ruthenium(I) complexes [Ru(μ-O₂CMe)(CO)₂L^F]₂, where L^F is the perfluoroalkyl substituted tertiary phosphine, P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃, or P(CH₂CH₂(CF₂)₅CF₃)₃, were synthesized and partition coefficients for the complexes in fluorocarbon/hydrocarbon biphases were determined. Catalytic hydrogenation of acetophenone to 1-phenylethanol in benzotrifluoride at 105 °C occured in the presence of either [Ru(μ-O₂CMe)(CO)₂P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃]₂ (1) or [Ru(μ-O₂CMe)(CO)₂P(CH₂CH₂(CF₂)₅CF₃)₃]₂ (2). The X-ray crystal structure of [Ru(μ-O₂CMe)(CO)₂P(CH₂CH₂(CF₂)₅CF₃)₃]₂ was determined. The compound exhibited discrete regions of fluorous and non-fluorous packing.     

New types of asymmetrical bromonium salts [RF(RF′)Br]Y where RF and/or RF′ represent perfluorinated aryl, alkenyl, and alkynyl groups

A series of previously unknown asymmetrical fluorinated bis(aryl)bromonium, alkenyl(aryl)bromonium, and alkynyl(aryl)bromonium salts was prepared by reactions of C₆F₅BrF₂ or 4-CF₃C₆H₄BrF₂ with aryl group transfer reagents Ar′SiF₃ (Ar′ = C₆F₅, 4-FC₆H₄, C₆H₅) or perfluoroorganyl group transfer reagents R_F′BF₂ (R_F = C₆F₅, trans-CF₃CFCF, C₃F₇C≡C) preferentially in weakly coordinating solvents (CCl₃F, CCl₂FCClF₂, CH₂Cl₂, CF₃CH₂CHF₂ (PFP), CF₃CH₂CF₂CH₃ (PFB)). The presence of the base MeCN and the influence of the adducts R_F′BF₂·NCMe (R_F = C₆F₅, CF₃C≡C) on reactions aside to bromonium salt formation are discussed. Reactions of C₆F₅BrF₂ with Alk_F′BF₂ in PFP gave mainly C₆F₅Br and Alk_F′F (Alk_F′ = C₆F₁₃, C₆F₁₃CH₂CH₂), presumably, deriving from the unstable salts [C₆F₅(Alk_F′)Br]Y (Y = [Alk_F′BF₃]⁻). Prototypical reactivities of selected bromonium salts were investigated with the nucleophile I^-and the electrophile H⁺. [4-CF₃C₆H₄(C₆F₅)Br][BF₄] showed the conversion into 4-CF₃C₆H₄Br and C₆F₅I when reacted with [Bu₄N]I in MeCN. Perfluoroalkynylbromonium salts [C_nF_2n+1C≡C(R_F)Br][BF₄] slowly added HF when dissolved in aHF and formed [Z-C_nF_2n+1CFCH(R_F)Br][BF₄].     

Synthesis and properties of pentamethylmetallocene derivatives Cp*MCp (M = Ru, Fe). Crystal structure of the salt [CpRuC5Me4CH2+OC6H2(NO2)3-]

Photolysis of a solution of Cp*RuCp (1) in CF₃CO₂H generates salt [CpRu(C₅Me₄CH₂)]-(O₂CCF₃)(2 • O₂CCF₃). The reaction of compound 1 with oleum at 20 °C through the intermediate dication [η⁵-(CH₂C₅Me₄)Ru(μ:η⁵,ν⁵-C₅H₄C₅H₅)Ru(C₅Me₄CH₂)-η⁶]²⁺ leads to the triply charged cation η⁷CH₂)₂C₅Me₃Ru(μη⁵,η⁵-C₅H₄C₅H₄)Ru(C₅Me₄CH₂)-η⁶]³⁺. Synthesis of pentamethylmetallocene derivatives CpMC₅Me₄X (M = Ru, Fe; X = CHO, CH₂OH, CH₂An) has been accomplished. The reactions of 1-hydroxymethyl-2,3,4,5-tetramethylruthenocene with acids CF₃CO₂H, HBF₄, CF₃CO₂H/NaB[C₆H₃(CF₃)₂]₄, and picric acid C₆H₂(NO₂)₃OH afforded salts 2•X (X = CF₃CO₂, BF₄, B[C₆H₃(CF₃)₂]₄), and (2,3,4,5-tetram ethylruthenocenyl)methyl picrate [CpRu(C₅Me₄CH₂)-η⁶][(C₆H₂(NO₂)₃O] (2•C₆H₂(NO₂)₃O). Structure of the latter was characterized by single crystal X-ray diffraction.     

The reaction of boron trihalides with CF3Sn(CH3)3 in the presence of trimethylamine

The reaction of CF₃Sn(CH₃)₃ with BCl₃ and BBr₃ in the presence of trimethylamine has been investigated. The volatile adducts CF₂XBF₂·N(CH₃)₃ (X = F, Cl and Br) have been isolated from the complex reaction mixture while the anions BF^?₄, CF₂XBF^?₃, CF₃BF₂CF₂X^? and (CF₂X)₂BF^?₂ have been identified in the residue. [(CH₃)₃NH][CF₂ClBF₃] has been isolated. The formation of the CF₂XB derivatives is likely to occur via CF₂ insertion, which is promoted by the presence of N(CH₃)₃. NMR, IR, Raman and mass spectra of the novel fluoromethyl borane derivatives are reported.     

Photodissociation of alkyl bromides

The branching ratios for the production of Br(4²P_{$\text{1}\text{2}$}) following the broadband flash photolysis of the alkyl bromides, CH₃Br and C₂H₅Br, and the perfluorinated molecules, CF₃Br, C₂F₅ Br and n-C₃F₇ Br, have been determined using time-resolved atomic absorption spectroscopy. The production of electronically excited bromine atoms is shown to be inefficient in the case of the alkyl bromides while the perfluorinated molecules yield decreasing amounts of Br(4²P_{$\text{1}\text{2}$}) as the molecular complexity increases, i.e., CF₃Br > C₂F₅Br > C₃F₅Br > C₃F₇. It is also shown that the hydrogenated bromides deactive electronically excited atoms almost two orders of magnitude faster than do the perfluorinated bromides.     

Hammett Correlation in the Accelerated Formation of 2,3-Diphenylquinoxalines in Nebulizer Microdroplets

The accelerated formation of 2,3-diphenylquinoxalines in microdroplets generated in a nebulizer has been investigated by competition experiments in which equimolar quantities of 1,2-phenylenediamine, C₆H₄(NH₂)₂, and a 4-substituted homologue, XC₆H₃(NH₂)₂ [X = F, Cl, Br, CH₃, CH₃O, CO₂CH₃, CF₃, CN or NO₂], or a 4,5-disubstituted homologue, X₂C₆H₂(NH₂)₂ [X = F, Cl, Br, or CH₃], compete to condense with benzil, (C₆H₅CO)₂. Electron-donating substituents (X = CH₃ and CH₃O) accelerate the reaction; in contrast, electron-attracting substituents (X = F, Cl, Br and particularly CO₂CH₃, CN, CF₃ and NO₂) retard it. A structure–reactivity relationship in the form of a Hammett correlation has been found by analyzing the ratio of 2,3-diphenylquinoxaline and the corresponding substituted-2,3-diphenylquinoxaline, giving a ρ value of −0.96, thus confirming that the electron density in the aromatic ring of the phenylenediamine component is reduced in the rate-limiting step in this accelerated condensation. This correlation shows that the phenylenediamine acts as a nucleophile in the reaction.     

Cationic iridium complexes of the Xantphos ligand. Flexible coordination modes and the isolation of the hydride insertion product with an alkene

Reaction of the Ir(I)-Xantphos complex [Ir(κ²-Xantphos)(COD)][BAr^F₄] (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Ar^F = C₆H₃(CF₃)₂) with H₂ in acetone or CH₂Cl₂/MeCN affords the Ir(III)-hydrido complexes [Ir(κ³-Xantphos)(H)₂(L)][BAr^F₄], L = acetone or MeCN, whereas in non-coordinating CH₂Cl₂ solvent dimeric [Ir(κ³-Xantphos)(H)(μ-H)]₂[BAr^F₄]₂ is formed. A common intermediate in these reactions that invokes a (σ, η²-C₈H₁₃) ligand is reported. Addition of excess tert-butylethene (tbe) to [Ir(κ³-Xantphos)(H)₂(MeCN)][BAr^F₄] results in insertion of a hydride into the alkene to form [Ir(κ³-Xantphos)(MeCN)(CH₂CH₂C(CH₃)₃)(H)][BAr^F₄], an Ir(III) alkyl-hydrido-Xantphos complex. This reaction is reversible, and heating (80 °C) results in the reformation of [Ir(κ³-Xantphos)(H)₂(MeCN)][BAr^F₄] and tbe. These complexes have been characterised by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. They show variable coordination modes of the Xantphos ligand: cis-κ²-P,P, fac-κ³-P,O,P and mer-κ³-P,O,P with the later coordination mode like that found in related PNP-pincer complexes.     

Kinetics of O(1D) reactions with bromocarbons

The rate coefficients for the removal of O(¹D) by reaction with the following seven bromocarbons were measured using time-resolved vacuum UV atomic resonance fluorescence detection of O(³P): CH₃Br, CH₂Br₂, CHBr₃, CF₃Br (Halon-1301), CF₂Br₂ (Halon-1202), CF₂ClBr (Halon-1211), and CF₂BrCF₂Br (Halon-2402). The branching ratios for the quenching of O(¹D) to O(³P) by the above molecules were also determined. From these measurements, the rate coefficients for reactive and nonreactive loss of O(¹D) were calculated. These results are discussed in terms of their atmospheric relevance and trends in reactivity of O(¹D) with hydrocarbons upon halogen substitution. © 1993 John Wiley & Sons, Inc.     

Effets electroniques en stereochimie—II : Reduction asymetrique de benzophenones substituees

The asymmetric reduction of benzophenones p-X-C₆H₄-CO-C₆H₅ (X = CH₃, OCH₃, Br, CF₃) and p-CF₃-C₆H₄-CO-C₆H₄-p'-Z (Z = CH₃, Br) by chiral Grignard reagents p-Y-C₆H₄-CH(C₂H₅)CH₂MgCl (Y = OCH₃, CF₃) gives benzhydrols of optical purities which can reach 37%. The absolute configuration of the alcohol depends on the nature of substituents. The substituent effect is discussed through donor-acceptor interactions between the aromatic nuclei in the diastereoisomeric transition states.     

Phosphonium Salts of 1,8‐Bis(diphenylphosphino)naphthalene: Molecular Structures and NMR‐spectroscopic Studies

A representative series of diphosphine monophosphonium salts [1‐Ph₂P(C₁₀H₆)‐8‐PRPh₂]⁺X^– ( 2 b : R = H, X = CF₃SO₃; 4 : R = Me, X = CF₃SO₃; 5 : R = C₆H₅CH₂ = Bn, X = Br) has been prepared by treatment of 1,8‐bis(diphenylphosphino)naphthalene (dppn, 1 ) with stoichiometric amounts of HSO₃CF₃ or CH₃SO₃CF₃ in CH₂Cl₂ at +20 °C and with C₆H₅CH₂Br in toluene at +80 °C. Their X‐ray crystal structures show that there is no evidence for dative P → P⁺ interactions. Instead, steric repulsion deflects the substituent groups to opposite faces of the naphthalene plane [splay angles: +11.4° ( 2 b ), +13.6° ( 4 ); +16.7° ( 5 )]. In solution 2 b , 4 , and 5 were dynamic according to ³¹P, ¹³C, and ¹H NMR spectroscopy. The fluxionality of 2 b involves rapid intramolecular proton exchange between the two phosphorus atoms, which slows down at low temperature, whereas the dynamic behaviour of 4 and 5 is interpreted in terms of hindered rotation of the bulky RPh₂P⁺ groups (R = Me or Bn) about the P–C(naphthyl) bond. Treatment of 1,8‐bis(diphenylphosphoryl)naphthalene (dppnO₂, 6 ) with HSO₃CF₃ gave the protonated bis(phosphine oxide), as the triflate salt, dppnO₂H⁺ CF₃SO₃^– ( 7 ). The X‐ray structure analysis of 7 revealed a highly strained molecule (P1…P2 365.5 pm) in which the P=O bonds point to the same face of the naphthalene plane to accommodate the proton. All isolated compounds were characterised by a combination of ³¹P, ¹H, and ¹³C NMR spectroscopy, IR spectroscopy ( 7 ), mass spectrometry and elemental analysis.     

Investigation of pharmacophore and antipharmacophore features of certain dimethyltin(IV) complexes of flexible N‐protected amino acids and fluorinated β‐diketone/β‐diketones

A set of pentacoordinated dimethyltin(IV) complexes of flexible N‐protected amino acids and fluorinated β‐diketone/β‐diketones was screened for their antibacterial activity against Pseudomonas aeruginosa , Staphylococcus aureus and Streptomyces griseus . These pentacoordinated complexes of the type Me₂SnAB (where : R = CH(CH₃)C₂H₅, A₁H; CH₂CH(CH₃)₂, A₂H; CH(CH₃)₂, A₃H; CH₂C₆H₅, A₄H; and BH = R'C(O)CH₂C(O)R″: R′ = C₆H₅, R″ = CF₃, B₁H; R′ = R″ = CH₃, B₂H; R′ = C₆H₅, R″ = CH₃, B₃H; R′ = R″ = C₆H₅, B₄H) were generated by the reactions of dimethyltin(IV) dichloride with sodium salts of flexible N‐protected amino acids (ANa) and fluorinated β‐diketone/β‐diketones (BNa) in 1:1:1 molar ratio in refluxing dry benzene solution. Plausible structures of these complexes were elucidated on the basis of physicochemical and spectral studies. ¹¹⁹Sn NMR spectral data revealed the presence of pentacoordinated tin centres in these dimethyltin(IV) complexes.     

Advances in Trifluoromethylating Phosphorus Compounds

Abstract

The System CF₃I/Me₃P is re-investigated and Me₂PCF₃, Me₄P⁺γ, (CF₃)₂PMe₃, Me₃PI₂, [Me₃(CF₃)P]⁺γ are found as products. Using CF₃Br/P(NEt₂)₃ the phosphines R¹ ₂PCF₃ and R¹P(CF₃)₂ (e.g. R¹ = Me, iPr, NEt₂) can be obtained which are precursors either for phosphoranes (e.g. 1,2λ⁵σ⁵-oxaphosphetanes) or phosphonium salts (e.g. [R¹ ₂(Me)PCF₃]⁺X^? or [R¹(Me)P(CF₃)₂X^?]. The latter are deprotonated to furnish methylene phosphoranes R¹ ₂(CH₂=)PCF₃ or R¹(CH₂=)P(CF₃)₂, reactive synthons. From CF₃Br/P(NEt₂)₃/P(OPh)₃ the phosphine P(CF₃)₃ is available, which turned out to be a potent electrophile. Amido phospites ROP(NEt₂)₂ and halides R²X (R²=CCl₂CF₃, X=Cl; R²=CF=CFCF₃, X=F; R²=C₆F₅, X=Br, I; R²=C(CF₃)₃, X=Br; R²=SCF₃, X=CF₃) undergo an ARBUZOV reaction.     

Formation of association ions in the photoionization of alkyl halides

The methyl and ethyl chlorides and bromides, as well as methyl iodide, were photoionized in the vacuum ultraviolet at 300 K in a mass spectrometer over the pressure range 0.5 to approximately 100 millitorr. Under these conditions, stabilized parent ion dimers are found in CH₃Br, CH₃I, and C₂H₅Br, but not in the chlorides. Lower limits for the dissociative lifetimes of the ion–molecule collision complexes were estimated and are as follows: (CH₃Br)₂⁺, 1.6 μs; (CH₃I)₂⁺, 1.9 μs; and (C₂H₅Br)₂⁺, 5.4 μs. An increase in photon energy (internal energy content of the reactant ion) decreases the dissociative lifetime of the collision complex in CH₃I.     

Mercury-photosensitized luminescence of NH3 and ND3 at low pressure

The mercury-photosensitized luminescence of ammonia has been investigated at low pressures. The emission spectrum with [ND₃] = 0.005 torr consisted of two peaks at 305 and 340 nm. The 305 nm band was assigned to the complex in the higher electronic state which correlates with Hg(³P₁). At limiting zero pressure, the complex formation in the higher state predominates, while the 340 nm band is in the ascendant at higher pressure. Results obtained in the presence of third-bodies, M = C₂H₆, CH₄, CF₄, N₂, and Ne have been also reported.     

Untersuchungen zum reaktiven verhalten von (CF3)2PPH2 und (CF3)2AsPH2

Cleavage of the E-P bond in compounds of the type (CF₃)₂EPh₂(E = P, As) is achieved by polar [HBr, (CF₃)₂EI, (CH₃)₃SnH, (CF₃)₂AsH] and non-polar [Br₂, Mn₂(CO)₁₀] substances. Exchange reactions are possible with (CF₃₄)E₂ and P₂F₄ leading to the unsymmetrical compounds (CF₃)₂PPF₂, (CF₃)₂AsPF₂, (CF₃)₂PAs(CF₃)₂, F₂PPH₂, (CF₃)₂AsPH₂. The reaction of (CF₃)₂PPH₂ with Mn₂(CO)₁₀ gives the new binuclear complex Mn₂(CO)₈PH₂P(CF₃)₂ and Mn₂(CO)₈[P(CF₃)₂]₂. The hitherto unknown compound (CF₃)₂AsPF₂ is obtained by the reaction of (CF₃)₂AsPH₂ with P₂F₄. Adducts of (CF₃)₂PPH₂ with B₂H₆ and (CH₃)₃N, respectively, are discussed. Investigation of the reaction route and characterization of most of the reaction product is based on ¹H and ¹⁹F NMR spectral data.     

Improved synthesis of cyclic and polymeric phosphazenes based on facile chlorine substitution with phenols promoted by cesium carbonate

In this report we describe a very convenient synthetic method for the preparation in high yields and purity of cyclic [N₃P₃(OCH₂CF₃)₆] and [N₃P₃(OC₆H₄R)₆] (R = Br, CN, CHO, COC₆H₅, COCH₃, H, OCH₃), and polymeric [NP(OC₆H₄R)₂]_n (R = Br, CHO, COC₆H₅, H, Bu^t) phosphazenes from the direct reaction of the trimer [N₃P₃Cl₆] or the high polymer [NPCl₂]_n and the alcohol HO CH₂CF₃ or the para-substituted phenols HO C₆H₄R, using Cs₂CO₃ as proton abstractor and acetone or tetrahydrofuran as solvent.     

Binuclear ruthenium complexes of fluorous phosphine ligands: Synthesis, properties, and biphasic catalytic activity. Crystal structure of [Ru(μ-O2CMe)(CO)2P(CH2CH2(CF2)5CF3)3]2

The fluorocarbon soluble, binuclear ruthenium(I) complexes [Ru(μ-O₂CMe)(CO)₂L^F]₂, where L^F is the perfluoroalkyl substituted tertiary phosphine, P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃, or P(CH₂CH₂(CF₂)₅CF₃)₃, were synthesized and partition coefficients for the complexes in fluorocarbon/hydrocarbon biphases were determined. Catalytic hydrogenation of acetophenone to 1-phenylethanol in benzotrifluoride at 105 °C occured in the presence of either [Ru(μ-O₂CMe)(CO)₂P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃]₂ (1) or [Ru(μ-O₂CMe)(CO)₂P(CH₂CH₂(CF₂)₅CF₃)₃]₂ (2). The X-ray crystal structure of [Ru(μ-O₂CMe)(CO)₂P(CH₂CH₂(CF₂)₅CF₃)₃]₂ was determined. The compound exhibited discrete regions of fluorous and non-fluorous packing.     

The collisional behaviour of the spin orbit states of the lead atom,Pb(63P1,2), studied by time-resolved attenuation of atomic resonance radiation

A kinetic study of lead atoms in the spin orbit states, Pb(6³P₁) and Pb Pb(6³P₂), 0.969 and 1.320 eV, respectively, above the 6³P₀ ground state, has been carried out by atomic absorption spectroscopy. The electronically excited lead atoms were generated by the pulsed irradiation of lead tetraethyl and monitored photoelectrically by time-resolved attenuation of resonance radiation. The decay of the two atomic states has been studied in the presence of He, Ar, H₂, D₂, N₂, O₂, CO, NO, CO₂, N₂O, CH₄, C₂H₄, C₂H₂ CF₄, SF₆, and PbEt₄, and rate constants for the collisional quenching by these gases are reported. The resulting data are compared with those for the deactivation of other atomic spin orbit states of comparable energy. In general, the higher energy state, Pb(6³P₂), is found to be deactivated more rapidly. It would appear that the magnitude of the electronic energy to be transferred on collision governs the rates of quenching, at least where a weak interaction potential is involved, and that for most gases, deactivation of Pb(6³P₂) proceeds via Pb(6³P₁).