Diisopropoxy- and di-tert-butoxyethyne : Stable acetylene diethers

The rather stable acetylene diethers diisopropoxy- and di-t-butoxyethyne are prepared either from glyoxal or dioxane. Catalytic hydrogenation, acid-catalyzed hydration and formation of the corresponding hexacarbonyl dicobalt complexes are reported     

A reaction cell with sample laser heating for in situ soft X‐ray absorption spectroscopy studies under environmental conditions

A miniature (1 ml volume) reaction cell with transparent X‐ray windows and laser heating of the sample has been designed to conduct X‐ray absorption spectroscopy studies of materials in the presence of gases at atmospheric pressures. Heating by laser solves the problems associated with the presence of reactive gases interacting with hot filaments used in resistive heating methods. It also facilitates collection of a small total electron yield signal by eliminating interference with heating current leakage and ground loops. The excellent operation of the cell is demonstrated with examples of CO and H₂ Fischer–Tropsch reactions on Co nanoparticles.     

Production of excited electrons ine + e − interactions

We present a complete lowest order calculation of the processe ⁺ e ^?→(e ^*)→e ⁺ e ^? ρ based on a phenomenological Lagrangian where interference with “standard” amplitudes and spin correlation effects are considered. The calculation has been implemented in a Monte Carlo generator of unweighted events and can be used to study interactions with polarized beams as well as the effects of other excited fermions.     

Dinuclear complexes with a μ-cyano ligand. Part VIII(1). Synthesis and characterization of several derivatives ofcis-[CrX(H2O)(en)2]2+ (X=Cl or Br)

Summary The new complex double saltscis-[CrX(H₂O)(en)₂][M(CN)₄] (X=Cl or Br; M=Ni, Pd or Pt) have been synthesised and by anation either in the solid-state or in non-aqueous solvents the corresponding new dinuclear complexes with cyano bridgecis-[(en)₂XCr-NC-M(CN)₃] have been prepared. The complexes have been characterized by chemical analysis and by i.r. and electronic spectroscopy. Powder diffraction patterns indicate that the double salts are isostructural within each series. On the other hand, the dinuclear complexes show low crystallinity. The two dinuclear complexes derived from [Pt(CN)₄]^2– show strong Pt-Pt interactions both in the solid state and in solution.     

A theoretical study of the ground and first excited singlet state proton transfer reaction in isolated 7-azaindole–water complexes

A systematic study of the proton transfer in the 7-azaindole–water clusters (7-AI(H₂O)_n; n=1–4) in both the ground and first excited singlet electronic states is undertaken. DFT(B3LYP) calculations for the ground electronic state shows that the more stable geometry of the initial normal tautomer presents a cyclic set of hydrogen bonds that links the two nitrogen atoms of the base across the waters. For the n=4 cluster the water molecules adopt a double ring structure so that two cycles of hydrogen bonds are found there. From this structure full tautomerization implies only one transition state so that a concerted but non-synchronous process is predicted by our theoretical calculations. This behavior is found both in the ground and the excited states where CIS geometry optimizations and TD(B3LYP) energy calculations are performed. The difference between both states is the height of the energy barrier that is much lower in the excited state. Another clear difference between both electronic states is that full tautomerization is an endergonic process in the ground state whereas it is clearly exergonic (then favorable) in the excited state. This is so because electronic excitation implies a charge transfer from the five-member cycle to the six-member one of 7-azaindole so that the proton transfer from the pyrrolic side to the pyridinic one is favored. These results clearly indicate that full tautomerization will not likely occur in the ground state but it will be quite easy (and fast) in the excited state. Reaction is already feasible in the S₁ 1:1 complex but it is faster in the 1:2 complex. However the reaction slows again for the 1:3 complex and, finally, reaches a new maximum for the largest cluster studied here, the n=4 case. These results, which are in agreement with experimental data, are explained in terms of the number of hydrogen bonds that are involved in the transfer. The proton transfer through a ring formed by the substrate and two water molecules is found to be the more efficient one, at least in this system.     

2-Piperidino-1,1,2-triphenylethanol: a highly effective catalyst for the enantioselective arylation of aldehydes

Here we report the use of 2-piperidino-1,2,2-triphenylethanol (5) as an outstanding catalyst for the ligand-catalyzed arylation of aldehydes. The use of 5 and a 2/1 mixture of Et(2)Zn/Ph(2)Zn provided the corresponding chiral diarylcarbinols with enantiomeric excess of up to 99% ee. The effect of temperature on the reaction enantioselectivity was studied and the inversion temperature (T(inv)) was determined to be 10 degrees C for reaction with p-tolylaldehyde. Most remarkably, lowering the amount of catalyst (5) to 0.5 mol % still afforded excellent levels of enantiocontrol (93.7% ee). Kinetics of the catalyzed and uncatalyzed arylation of aldehydes was studied by means of in situ FT-IR. The background uncatalyzed addition rates to p-tolylaldehyde when using pure Ph(2)Zn and Et(2)Zn/Ph(2)Zn (2/1) suggest that in the latter case a mixed zinc species forms (EtPhZn) minimizing the undesired nonselective addition. Formation of EtPhZn was modeled at the DFT calculation level. A four-center TS (TS-V) corresponding to the Et/Ph scrambling was localized along with two dimers (D-IV and D-VI). The model supports the hypothesis that Et/Ph exchange is a kinetically facile process. Gas evolution experiments during the formation of the active catalyst showed that the formation of an active site with a ONZn-Et (10) moiety is kinetically favored over ONZn-Ph (11). Finally, the phenyl transfer to benzaldehyde was modeled at the PM3(tm) level through anti and syn 5/4/4 tricyclic TS structures for both 10 and 11. The model could correctly predict the sense and selectivity of the overall process and predicted that 11 should be more selective than 10.     

A DFT study of the electronic spectrum of the alpha-keggin anion [Co(II)W(12)O(40)](6-)

Multiplet splittings for several excited configurations of [Co(II)W(12)O(40)](6-) were calculated using DFT methods. In agreement with the experimental interpretation of the spectrum the calculations found that the first strong band corresponds to Co d-d transitions, but it is worth noting that superposed to these transitions there are charge transfer transitions from cobalt to tungsten. The calculations also showed the importance of Jahn-Teller distortions in the excited states. With the exception of the consequences derived from a smaller splitting of d cobalt orbitals the d-d spectrum of [CoCl(4)](2-) is similar to that of the more complex Keggin anion. Finally, the energy of the bielectronic transition (4)A(2) --> (4)T(1)(P) was estimated via an approximate procedure based on ligand field theory.     

Gradient optimization of polarization exponents inab initio MO calculations on H2SO → HSOH and CH3SH → CH2SH2

Summary Analytical gradients were used to optimize the polarization function exponents in the 6-31G(d) and 6-31G(d, p) basis sets for the reactants, transition structures and products in the reactions H₂SO HSOH and CH₃SH CH₂SH₂. The optimizedd exponents on the heavy atoms change by ±10% in the course of the reactions and depend on the bonding of the heavy atoms. Thep exponents on the hydrogens change by as much as a factor of 5 and depend on the element to which the hydrogen is bonded and its valency. The effect of exponent optimization on the relative energies is small (±3 kcal/mol). With the 6-31G(d, p) basis set, optimization of the polarization exponents can make some of the bonds significantly more polar, as judged by the Mulliken charges.     

Higher order corrections to the processe^ + e^ - \to v\bar vy

A calculation of the neutrino counting reaction \(e^ + e^ - \to v\bar vy\) is presented and implemented in a Monte Carlo generator of unweighted events. The non-photonic corrections are included following the star-scheme. The photonic corrections have been exponentiated following the “inductive” and the “structure functions” approach. For a realistic experimental set-up, the total corrections around theZ ⁰ pole amount to ～5% with respect to the one-loop result. The final precision achieved is better than 1%.