NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

Photo-degradation studies on Di-η5-Cyclopentadienyldimethylvanadium,Di-η5-Cyclopentadienylmethylvanadium,Di-η5-Cyclopentadienyldimethylniobium,and some deuterated analogs

The photolysis of alkyl metallocene derivatives of vanadium and niobium in hydrocarbon solvents results in cleavage of the carbon—metal σ-bond. In the cases of (η⁵-C₅H₅)₂VCH₃ and (η⁵-C₅H₅)₂Nb(CH₃)₂, only methane (>99%) is produced photochemically. (η⁵-C₅H₅)₂V(CH₃)₂, prepared on a convenient new synthesis from (η⁵-C₅H₅)₂VCl₂ and methyllithium in toluene, degrades under photochemical conditions to yield both methane and ethane in a 2 : 1 ratio. The ethane arises from intra- and intermolecular methyl dimerization. Deuterium labeling studies have shown that the methyl group, the cyclopentadienyl ring, and the solvent are all sources of hydrogen in the formation of methane in these photolyses. The extent to which each source participates in the hydrogen abstraction process cannot be quantitatively determined because of the influence of an isotope effect. Chemical reactions with carbon monoxide during the photolyses give low yields of (η⁵-C₅H₅)V(CO)₄ from (η⁵-C₅H₅)₂VCH₃ or (η⁵-C₅H₅)₂V(CH₃)₂, and of (η⁵-C₅H₅)₂Nb(CO)CH₃ from (η⁵-C₅H₅)₂Nb(CH₃)₂.     

2,2-diphenyl-2λ5-phospha-phenalenyl-und 2,2-dimethyl-2λ5-phospha-indenyl-lithium

From the reaction of 1,8-bis(bromomethyl)naphthalene with diphenyl(trimethylsilyl)phosphine a cyclic phosphonium salt IX is formed which can be rearranged with (CH₃)₃PCH₂ to yield the cyclic ylide X. Its metallation with t-butyllithium gives 2,2-diphenyl-2λ⁵-phospha-phenalenyl-lithium XI. The anion of XI cannot be seen as a delocalized phospha-phenalenyl π-system but rather as a phosphonium-bis-ylide similar to the diphenylphosphonium-bis-benzylide.From 1,2-bis(chloromethyl)benzene and (C₆H₅)₂PSi(CH₃)₃ or from 1,2-bis(chloromagnesiummethyl)benzene and CH₃PCl₂, followed by quaternization using CH₃Br, cyclic phosphonium salts (XII and XV, respectively) can also be obtained, which may again be rearranged to form the ylides XIII or XVI. XVI gives with (CH₃)₃CLi 2,2-dimethyl-2λ⁵-phospha-indenyl-lithium XVII, containing a dimethyl-phosphonium-bis-ylide anion (“isophosphindolyl-lithium”).     

A rate constant for CH2(3B1) + CH3

Triplet methylene, CH₂(³B₁), and methyl radicals were produced by flash photolysis of a mixture of ketene and azomethane. A computer fit of the product ratios, using the known rate constants for CH₂ + CH₂, and CH₃ + CH₃, requires a rate constant of 5.0 × 10^?11 cm³ molecule^?1s^?1 for the reaction CH₂ + CH₃ ? C₂H₄ + H.     

2-Phosphinothioyl- and 2-phosphinoylethylcyclopentadienyl zirconium and titanium complexes. Crystal structure of [η5:η1-C5H4CH2CH2P(O)Ph2]TiCl3

The intracomplex conversion of (2-diphenylphosphanoethyl)cyclopentadienyl zirconium and titanium complexes into the corresponding 2-phosphinothioyl and 2-phosphinoyl derivatives, viz., (η⁵-C₅H₅)[η ⁵-C₅H₄CH₂CH₂P(S)Ph₂]ZrCl₂, [η⁵-C₅H₄CH₂CH₂P(S)Ph₂]ZrCl₃, [η⁵:η¹C₅H₄CH₂CH₂P(O)Ph₂]ZrCl₃·THF, and [η⁵:η ¹-C₅H₄CH₂CH₂P(O)Ph₂]TiCl₃ (7), was performed. The NMR spectroscopy data revealed the following order of the coordination ability of the functional groups with respect to the Zr center: Ph₂P=O > Ph₂P > Ph₂P=S. An analogous order was found for the monodentate ligands (Ph₃P=O > Ph₃P > Ph₃P=S) with respect to (η⁵-C₅H₅)ZrCl₃. The molecular structure of complex 7 was established by X-ray diffraction analysis. Coordination of the Ph₂P=O group to the titanium atom was found retained both in the crystalline state and solution.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 116–122, January, 2005.     

Allylic interactions in organometallics: probing Electronic structure in (η5-C5H5)Fe(CO)2R,R = CH3, η1-C3H5, η1-C5H5.

The He(I) photoelectron spectra of (η⁵-C₅H₅)Fe(CO)₂R, where R = CH₃, η¹-C₃H₅ and η¹-C₅H₅, have been recorded. The lowest lying ion states result from ionization of molecular orbitals with large Fe 3d character; these move to lower anergy when R places double bonds in an allylic relationship to the metal atom. The cyclic voltammetric oxidation potential correlates well with the energies of the lowest ion states. A significant interaction between olefin π orbitals and the allylic metal center is proposed.     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Actinide-centered cyclometalation chemistry. An unusually distorted thorium bishydrocarbyl: Thp[η5-(CH3)5C5]2CH2Si(CH3)3]2

The crystal and molecular structure of the complex Th[η⁵-(CH₃)₅C₅]₂[CH₂-Si(CH₃)₃]₂, which undergoes facile intramolecular cyclometalation to the thoracyclobutane Th[η⁵-(CH₃)₅C₅]₂(CH₂)₂Si(CH₃)₂, is reported. While the Th[η⁵-(CH₃)₅C₅]₂ ligation is unexceptional, the Th[CH₂Si(CH₃)₃]₂ fragment is highly unsymmetrical having Th-C (corresponding angle Th-C-Si) 2.51(1) Å (132.0(6)°) and 2.46(1) Å (148.0(7)°). This conformation, which appears to result from severe intramolecular non-bonded contacts, allows a methyl hydrogen atom of one CH₂Si(CH₃)₃ ligand to approach within ca. 2.3 Å of the α-carbon atom of the other CH₂Si(CH₃)₃ ligand.     

CH3O(X̄ 2E) production from 266 nm photolysis of methyl nitrite and reaction with NO

The CH₃O(X? ²E) radical produced by the 266 nm photolysis of CH₃ONO is characterized by laser induced fluorescence. Using a flowing gas cell the reaction rate of CH₃O(X? ²E) with NO is measured to be (2.08 ± 0.12) × 10^?11 cm³ s^?1 based upon disappearance of CH₃O and appearance of HNO detected by laser induced fluorescence. Upper limits for CH₃O reactions with CH₄, CO, N₂O, NH₃, CH₃OH, (CH₃)₃CH and CH₂CHCH₂CH₃ are reported. These reactions are all too slow to measure under our experimental conditions.     

Structure, 31P and 13C chemical shift anisotrophy of (CH3)3P, (CH3)3PO, (CH3)3PS and (CH3)3PSe as determined by liquid crystal NMR spectroscopy

The ¹³P and ¹³C spectra of the triply ¹³C labelled molecules (CH₃)₃P, (CH₃)₃PO, (CH₃)₃PS and (CH₃)₃PSe oriented in a nematic phase are reported. The CPC bond angles have been measured. The ¹³P chemical shift tensor shows a large anisotropy except in the case of (CH₃)₃P. The abnormal large value observed for the PSe bond length suggests a large anisotropy of the ¹J(PSe) spin coupling.     

Synthesis of 1,1′-di-t-butylstannocene and its reaction with trifluoroborane. The crystal and molecular structure of η5-(CH3)3CC5H4Sn+BF4−

The reaction of Li(CH₃)₃CC₅H₄ with SnCl₂ in THF affords 1,1′-di-t-butylstannocene in 78% yield as an air-sensitive oil. ¹H and ¹³C NMR spectra are consistent with a pentahapto-structure. Mössbauer parameters of the stannocene and its trimethylsilyl counterpart match closely those of known stannocenes and neither compound appears to undergo oligomerization. The reaction of 1,1′-di-t-butylstannocene with BF₃ in CH₂Cl₂ affords η⁵-(CH₃)₃CC₅H₄Sn⁺ BF₄^? and other uncharacterized product(s) thought to involve tetracoordinate tin. The structure of η⁵-(CH₃)₃CC₅H₄Sn⁺ BF₄^? was determined by single crystal X-ray diffraction (orthorhombic,Pbcn, (T 25°C), a 18.423(3), b 11.723(1), c 11.044(2) Å, Z Å, m.p. 95–96°C, colorless, Mo-K_α, R = 0.043).     

35Cl Nqr spectroscopy of the [PO2Cl2]− and POCl3 groups in Me(PO2Cl2)2·2D (Me = Mg,Ca, Mn; D = POCl3,CH3COOC2H5,CH3COCH3)

³⁵Cl NQR spectra of dichlorophosphates Me(PO₂Cl₂)₂ · 2D (Me = Mg, Ca, Mn; D = CH₃COOC₂H₅, CH₃COCH₃, POCl₃) are studied in the temperature range 77 ? T (K) ? 305. It is shown that the three compounds with CH₃COOC₂H₅ as donor are isomorphic at 77 K, the crystal structure of Mn(PO₂Cl₂)₂· 2CH₃COOC₂H₅. The structure of Mg(PO₂Cl₂)_2^?· 2CH₃COCH₃ and of Mg(PO₂Cl₂)₂ · 2POCl₃ probably consists of infinite chains as found for Mn(PO₂Cl₂)₂· 2CH₃COOC₂H₅. Mg(PO₂Cl₂)₂· 2CH₃COOC₂H₅ shows phase transformations and a complicated dynamical behaviour leading to strong deviations from a Bayertype NQR function v = f(T). The donor capacity of POCl₃ in Mg(PO₂Cl₂)₂· 2POCl₃ is comparable with the donor strength in AsCl₃ · POCl₃ · A d_π-p_π overlap of the P-O bond influences the P-Cl bond.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Temperature-programmed desorption/pulse surface reaction (tpd/tpsr) studies of CH4, C2H6, C2H4, and CO over a cobalt/MWNTs catalyst

Summary Temperature-programmed desorption (TPD) of CH₄, C₂H₆, C₂H₄, and CO and temperature-programmed pulse surface reactions (TPSR) of CH₄, C₂H₆, C₂H₄, CO, and CO/H₂ over a Co/MWNTs catalyst have been investigated. The TPD results indicated that CH₄ and C₂H₆ mainly exist as physisorbed species on the Co/MWNTs catalyst surface, whilst C₂H₄ and CO exist as both physisorbed and chemisorbed species. The TPSR results indicated that CH₄ and C₂H₆ do not undergo reaction between room temperature and 450^oC. Pulsed C₂H₄ can be transformed into CH₄ at 400 ^oC whilst pulsed CO can be transformed into CO₂ at 100 or 150^oC. In gaseous mixtures of CO and H₂ containing excess CO, the products of pulsed reaction were CH₃CHO and CH₃OH. When the ratio of CO and H₂ was 1:2, pulsed CO and H₂ were transformed into CH₃CHO, CH₃OH and CH₄. In H₂ gas flow, pulsed CO was transformed into a mixture of CH₃CHO and CH₄ between 200 and 250^oC and was transformed into CH₄ only above 250^oC.     

Freezing Point of Mixtures of C6H6 with C6D6 or 13C6H6 and of CH3COOH with CH3COOD or CD3COOD

The freezing points of mixtures of benzene, C₆H₆, with one of its isotopes, C₆D₆ and ¹³C₆H₆, and those of acetic acid CH₃COOH with its isotopes, CH₃COOD and CD₃COOD, were measured as functions of the molal concentrations of C₆D₆ and ¹³C₆H₆, CH₃COOD and CD₃COOD, respectively. They changed linearly or non-linearly with increasing molal concentration of C₆D₆ and ¹³C₆H₆, CH₃COOD, and CD₃COOD, respectively. These findings confirm Kiyosawas previous conclusion drawn from experiments on the freezing points of mixtures of H₂¹⁶O with H₂¹⁸O or H₂¹⁷O. This hypothesis states that even a difference in the number of neutrons in the hydrogen or oxygen atoms of water molecules makes water molecules behave as different entities with respect to the colligative properties of solutions. This concept can be extended to mixtures of ordinary benzene with either of its isotopes, C₆D₆ or ¹³C₆H₆, and those of ordinary acetic acid CH₃COOH with either of its isotopes, CH₃COOD or CD₃COOD.     

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.     

Substitution effect of or (R = CH3, C2H5) groups on the 119Sn and 1H NMR spectra of (CH3)4-nSn(OR)n compounds;m evidence for a polymeric structure

We investigated the ¹H and ¹¹⁹Sn NMR spectra of (CH₃)_4-nSn(OR)_n (n = 1, 2, 3; R = CH₃, C₂H₅) compounds. The different NMR parameters could not be interpreted with the aid of normal substitution effects based upon electronegativity considerations of the substituents. However, structural changes caused by polymerization could provide a rational explanation of the special NMR behaviour of these compounds.     

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⁺.     

Metalloidalmethyl substituent effects by 13C and 19F NMR : electron release in the neutral ground state.

¹³C and ¹⁹F chemical shift studies of a series of CH₂M(CH₃)₃ and CH₂M(C₆H₅)₃ (M  Si, Ge, Sn, Pb) - substituted aryl derivatives (phenyl; 1-naphthyl; 2-naphthyl) have established unambiguously that the order of hyperconjugative electron release in the neutral ground state is Pb>Sn>Ge>Si. This order is clearly at variance with the commonly accepted order(Pb>Sn>Ge>Si) based on studies of electron deficient substrates. The phenomenon is discussed in terms of current theories on σ-π interactions. In addition, substituent parameters (σ_I and σ_R^o) for the PB(CH₃)₃ group have been derived utilizing new data from the fluorophenyl tag. These new constants are compared with those previously reported.     

Preparation and Ir, 31P,and 93Nb NMR spectroscopic investigation of phosphine derivatives of η5-C5H5Nb(CO)4

UV irradiation of η⁵-C₅H₅Nb(CO)₄ in the presence of the phosphine ligands L (L = 2 PEt₃, Ph₂P(CH₂)₂PPh₂ (p₂(n), n = 1–5), cis-Ph₂PCH=CHPPh₂ (c-dpe)), and the mixed arsine-phosphine ligands Ph₂AsCH₂CH₂PPh₂ (arphos) and o-C₆H₄(AsPh₂)(PPh₂) (pab) yields the well defined complexes cis-[η⁵-C₅H₅Nb(CO)₂L]. The monosubstituted species η⁵-C₅H₅Nb(CO)₃L have been characterized spectroscopically. P₂Ph₄ forms mono- and dinuclear, mono- and biligate carbonylniobium complexes.Shielding of the ⁹³Nb nucleus increases in the sequences (i) Ph₂As- < Ph₂P-, (ii) chelate 4-ring < chelate 5-ring and (iii) η⁵-C₅H₅Nb(CO)₂L < η⁵-C₅H₅Nb(CO)₃L < η⁵-C₅H₅Nb(CO)₄, and ³¹P coordination shifts decrease in the order c-dpe > pab > arphos > p₂(2) > p₂(5) > p₂(4) ～ PEt₃ > p₂(3) > p₂(1). The trends generally parallel those for the corresponding NMR parameters of the vanadium complexes. Paramagnetic contributions to the overall shielding are smaller for the ⁹³Nb than for the ⁵¹V nucleus, and this is explained in terms of increased covalency and decreased π-interaction in the niobium complexes.