Precursors cation

The 20e complex Fe(C6Me6)2, easily synthesized in high yield by Na/Hg reduction of the dry di-cationic precursor in THF at 20 °C [28], is also very useful for functionalization. Its reaction with electrophiles RX directly gives functional cyclohexadienyl iron cations, which saves one step with respect to the route using hydride protection/deprotection [47] Scheme V ... 

Robinson, T., L. D. Kispert et al. (1985). EPR study of acceptor dopedp-terphenyl crystals The oriented radical cation precursor for a conducting polymer. J. Chem. Phys. 82 1539-1542. 

Rh(diene)(P )2+ cation precursors are formed (133, 134 also /, p. 270), and indeed such complexes may be used in place of the in situ catalysts in either media (11, 244, 269-271). 

CulnS2, CulnSe2. CuInS2 (CIS),films have been grown from mixed copper(II) chloride, indium(III) chloride cation precursor, and sodium sulfide anion precursor solutions.121122 XPS and XRD analyses revealed that, when the copper/indium concentration ratio in the solution was 1.25, a stoichiometric CIS film could be grown. The electrical parameters obtained with different copper/indium concentration ratios have been investigated.121... 

Lindroos, S. Charreire, Y. Bonnin, D. Leskela, M. 1998. Growth and characterization of zinc sulfide thin films deposited by the successive ionic layer adsorption and reaction (SILAR) method using complexed zinc ions as the cation precursor. Mater. Res. Bull. 33 453—459. 

Several substituted l-oxaspiro[4.5]dec-6-enes have been prepared by employing a mild amberlyst-15-catalyzed Sn2 oxaspirocyclization. As can be seen below, the tertiary <00TL3411> and secondary <00TL3415> allyl alcohols 89 serve as the n-allyl cation precursors and the other hydroxy groups function as nucleophiles. 

The cation pool method is based on the irreversible oxidative generation of organic cations. In the first step, the cation precursor is oxidized via an electrochemical method. An organic cation thus generated is accumulated in the solution in the absence of a nucleophile that we want to introduce onto the cationic carbon. Counter anions which are normally considered to be very weak nucleophiles are used to avoid the nucleophilic attack on the cationic center. In order to avoid thermal decomposition of the cation, electrolysis should be carried out at low temperatures such as -78 °C. After electrolysis is complete, the nucleophile is then added to obtain the desired product. The use of a carbon nucleophile results the direct carbon-carbon bond formation. 

In a recent study, some mechanistic aspects of this templated process have been determined quantitatively [28]. Using UV-Vis spectroscopy to monitor the kinetics of the macrocyclization reaction, it has been established that the rate of ring closure of the cationic precursor to the [ljimidazoliophane (4) is increased up to ten times in the presence of 0.04 mol/1 solution of a chloride source. The chloride stabilizes the transition state (i.e. a kinetic template) favouring the macrocyclization through hydrogen bonding. 

Xie R, Rutherford M, Peng X (2009) Formation of high-quality I—III—VI semiconductor nanocrystals by tuning relative reactivity of cationic precursors. J Am Chem Soc 131 5691-5697... 

In a subsequent study, it was found that a hydride source like H2O, an acid (TsOH) or molecular hydrogen have an enhancing effect on the catalytic activity of the cationic precursor [Pd(TsO)2(PPh3)2]. Water, in combination with CO, generates the hydride [91] and reforms it if Pd - H+ consuming side... 

Although cyclic azoalkanes are well known as biradical precursors [159] they have been used as 1,2- and 1,3-radical cation precursors only recently [160-164]. Apart from the rearrangement products bicyclopentane 161 and cyclopentene 163, the PET-oxidation of bicyclic azoalkane 158 yields mostly unsaturated spirocyclic products [165]. Common sensitizers are triphenyl-pyrylium tetrafluoroborate and 9,10-dicyanoanthracene with biphenyl as a cosensitizer. The ethers 164 and 165 represent trapping products of the proposed 1,2-radical cation 162. Comparison of the PET chemistry of the azoalkane 158 and the corresponding bicyclopentane 161 additionally supports the notion that the non-rearranged diazenyl radical cation 159 is involved (Scheme 31). 

Rates and product distributions obtained during the solvolysis of secondary 2md tertiary cationic precursors provide the data for the norbomyl controversy. One of the reasons the debate has not been ended is the complexity of the solvolysis mechanism. Rate measurements should provide information on the energy difference between the ground and transition states of the reaction. Their analysis, however, is often clouded by a series of questions. 

Cholin chloride, shown in Scheme 1, was recently shown to be a versatile cationic precursor for the preparation of a wide variety of ionic liquids (48). This precursor is particularly interesting, as cholin is a vitamin B4 additive to animal food. Therefore, it is not expected to be restricted in applications by health-related concerns, whereas a number of other ionic liquids remain to be fully evaluated for their environmental and health effects, including the ones based on imidazolium ions. 

In the method of competition kinetics, the intermediate cation is partitioned between two competing nucleophiles whose concentration is in excess over that of the cation precursor. For Scheme 1.4, where one of the nucleophiles is the solvent,... 

The carbene carbon of III-XI resonates at rather low held in NMR spectra (5 = 205-300 ppm) compared to the corresponding carbon atom of the cationic precursors (5 = 135-180 ppm). 

The cationic precursor complex [Mo(NO)2(MeCN)4]2+ is itself prepared from [Mo(CO)3(MeCN)3] and [NO]PF6 in MeCN.26 The exchange reactions of the MeCN in this dication have been studied by NMR, two MeCN ligands being relatively easily dissociated. It is assumed that these are irons to the cis NO groups. The cationic complexes [Mo(acac)(NO)2(MeCN)2]+ and [MoCl(NO)2(MeCN)3]+ have also been prepared, the former in which the MeCN groups are mutually trans does not dissociate MeCN, whereas the latter exchanges the one MeCN which is trans to NO.28... 

With the exception of 46 and 47 [Eqs. (12) and (13), the other neutral formyls in Table II have been prepared by hydride attack on metal carbonyl cation precursors. The most extensively studied of these have been (i7-C5H5)Re(NO)(CO)(CHO) (38) and (T7-C5H5)Re(NO)(PPh3)(CHO) (39). The former was reported approximately simultaneously by Casey (56), Gladysz (57), and Graham (5Conditions employed for its preparation are summarized in Eq. (10). Formyl 38 can be obtained as a solid, but the... 

Protonation of silicon monoxide can in principle give rise to two different isomers the O-protonated SiOH+ and the silicon-protonated form HSiO+. SiOH+ is formed upon reaction of water with silicon cations200 and is believed to play a key role in the depletion mechanism of atomic silicon in the earth s ionosphere50. Theory (MP4) predicts the two cationic isomers to be separated by a substantial barrier of 91.5 kcalmol-1 (with respect to the formation of HSiO+ from SiOH+)193. The neutral counterpart SiOH" has been generated in a NR experiment from the cationic precursor (equation 28)193,201 (accessible via electron impact ionization of tetramethoxysilane). Neutral HSiO —in line with theoretical predictions202,203 —was successfully generated via Charge-Reversal NRMS... 

Many cyclopropyl cation precursors indeed readily rearrange to allyl cations under stable ion conditions.159-162 However, a distinct cyclopropyl cation 46 showing a significant 2n aromatic nature has been prepared by the ionization of 11-methyl-ll-bromotricyclo[4.4.1.01,6]undecane in SbF5-S02ClF solution at — 120°C163 [Eq. (3.30)]. 

This side reaction, which complicates the condensation of allylsilanes anti-126, was suppressed by using a-acetoxy acetals such as anti-131 as the oxonium cation precursor. Under these conditions, the desired cis-2,6-disubstituted dihydropyran 132 was isolated in moderate yields but high diastereoselectivity (dr = 94 6 Scheme 13.46). 

The PbTi03 films were grown epitaxially on SrTiOs (001) substrates as described previously [2], Cation precursors were either titanium isopropoxide (tip) or titanium tertbutoxide (ttb), and tetraethyl lead (tel). The oxidant was O2, with N2 carrier gas. Films were typically deposited at 750°C at a total pressure of 10 Torr (P02 = 2.5 Torr). Under appropriate growth conditions, the PbTi03 films replicated the high crystalline quality of the substrates (0.01° typical mosaic). Films thinner than 40 nm remained lattice matched with the SrTiC>3, while the epitaxial strain was mostly relaxed in thicker films. 

That carbenoid insertion products can be formed from cationic precursors is underlined by investigations of the base-induced decomposition of 21. Bicyclobutane (22), which could be rationalized as a product of intramolecular carbene insertion (Frey and Stevens, 1964),... 

Phosphorus atoms in ylides largely retain the tetrahedral ligand geometry of the phosphonium cation precursor, but the bond to the ylene-ylide carbon atom is shortened, indicating an increase in bond order. 

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