Cations trityl

The resulting macrocyclic ligand was then metallated with nickel(II) acetate. Hydride abstraction by the strongly electrophilic trityl cation and proton elimination resulted in the formation of carbon-carbon double bonds (T.J. Truex, 1972). 

Ph3C BF4, CH2CI2, 5-30 min, 80-95% yield. " The mechanism of this cleavage has been determined to involve complex formation by the trityl cation with the sulfur, followed by hydrolysis, rather than by hydride abstraction. ... 

This ester is formed from the anhydride in pyridine and is quantitatively cleaved with H2NNH2-H2O, Pyr-AcOH. The sensitivity of detection of this ester is high with its absorbance maximum of 513 nm and extinction coefficient of 78,600 in 5% CI2CHCO2H/CH2CI2 where it forms the trityl cation. ... 

Draw stick structures to represent each of the following species (a) 2,2.3,3-tetramethylhexane, CH C(CH3),C(CH )2CH,CH2CH3 (b) the trityl cation, (C6Hj)3Ci (c) butadiene, CH2CHCHCH2. 

B. Triphenylmethyl (Trityl) Cation The highly stable triphenylmethyl cation (85) is found to undergo a wide variety of photoreactions depending on such variables as the nature of the solvent, the pH of the medium, and the presence or absence of... 

Dependence of Product Formation on Solvent Composition in the Irradiation of the Trityl Cation (Inert Atmosphere)... 

When the trityl cation was photolyzed in 3-3% H2SO4 — 96 5% HOAc — 0-2% H2O in the presence of oxygen, three products were formed ... 

An interesting X-ray structure of the highly strained, sp hybridized vinyl cation 8 was recently reported by Muller et al. The synthesis of 8 was accomplished by the reaction of alkynylsilane 7 and triphenylmethyl (trityl) cation. 

Furthermore, several functionalities remained unaffected, namely the acid-labile TBDMS or PMB groups.118 Deprotection yields were in the range of 85-95% when methanol was used at room temperature as the solvent, whereas acetonitrile or dichloromethane led to very sluggish or nonexistent reactions, respectively. Cleavage of primary trityl ethers was also accomplished using the same conditions in a very rapid and effective fashion. The trityl pyranosides and furanosides assayed were selectively deprotected in 2-3 h and yields higher than 85% were achieved. This reaction was also more efficient when conducted in methanol, which acts as a nucleophile to trap the generated trityl cation. 

For protonation-dehydration processes, such as trityl cation formation from triphenylcarbinols, equation (24), the water activity has to be included if the formulation of the activity coefficient ratio term is to be the same as that in equation (7), which it should be if linearity in X is to be expected see equation (25). The excess acidity expression in this case becomes equation (26) this is a slightly different formulation from that used previously for these processes,36 the one given here being more rigorous. Molarity-based water activities must be used, or else the standard states for all the species in equation (26) will not be the same, see above. For consistency this means that all values of p/fR listed in the literature will have to have 1.743 added to them, since at present the custom... 

A diaryldihydrosilane with a hexacoordinated silicon center, produced through intramolecular coordination, is reported not to react with benzaldehyde, although the silane is capable of reducing silver ion to silver metal.113 There is also a report of a heptacoordinate silicon hydride species with the ability to transfer hydride to trityl cation while remaining inactive toward methanol.108114... 

On the basis of these results we embarked on a systematic study on the synthesis of vinyl cations by intramolecular addition of transient silylium ions to C=C-triple bonds using alkynyl substituted disila alkanes 6 as precursors.(35-37) In a hydride transfer reaction with trityl cation the alkynes 6 are transformed into the reactive silylium ions 7. Under essentially nonHnucleophilic reaction conditions, i.e. in the presence of only weakly coordinating anions and using aromatic hydrocarbons as solvents, the preferred reaction channel for cations 7 is the intramolecular addition of the positively charged silicon atom to the C=C triple bond which results in the formation of vinyl cations 8-10 (Scheme 1). 

Interestingly, reaction of alkynyl disilane 14 with trityl cation did not result in the formation of stable vinyl cations. Obviously, the formation of the four-membered disilacyclobutane ring is unfavorable. Similarly, treatment of alkyne 15 with the pre-formed triethylsilylarenium ion 1 derived from toluene did not give the expected intramolecular transfer of the silylium ion to the triple bond. Instead, only a complex product mixture was obtained. 

Scheme 3. Reaction of alkyne 16 with trityl cation...

The heuristic value of equation (3) is that we can see what is required for a good initiator D and I(R ) must be as large a possible, and AHS(R+) should be small compared to AHS(RI>1+) in other words, as an efficient initiator we need a large cation whose parent radical has a high ionisation potential, and which forms a strong bond to monomer. On the last two counts the trityl cation must be one of the least suitable. These considerations indicate that the first four ions listed in Table 1 should merit detailed study as initiators for vinyl polymerisations. 

In view of the useful interpretations which can be given to the differences in E1/2 values, an obvious step is to select the E1/2 of one convenient ion as a zero or reference point. We follow Taft [14] and Breslow [15] in selecting E1/2 for the triphenylmethylium (trityl) cation, as this ion is easy to procure and is stable under acidic conditions. It seems useful to define a quantity Ef/2 which is 1/2 of the species in question minus EV2 of the triphenylmethylium ion measured under the same conditions of concentration, temperature, solvent, and nature and concentration of base electrolyte, and against the same reference electrode ... 

The advantage of this procedure is that one can make useful comparisons between sets of measurements obtained under a variety of conditions. An informative example of the method is presented in the next section. In practice, it is often convenient to add trityl cations to a solution of an unknown as a marker one must, however, beware of offering to the trityl cation a substrate from which it can abstract a hydride or other ion, with formation of a more stable cation [8]. 

We consider first the problem arising from the nature and shape of the cations. Many workers have attempted to estimate the KD of the ion-pair P+nA" for various growing cations with various A", basing their estimates on the KD of the corresponding trityl salts in the same solvent. These attempts were misguided because of the geometrical and electrostatic differences between the propeller-shaped trityl cation and the most common... 

A more serious and pervasive criticism of this work, and indeed of all studies with trityl cations as initiators, is that the rate of initiation is set equal to the rate of consumption of... 

The earlier paper (Subira et al., 1976) contains results on isobutyl vinyl ether (IBVE) which are republished together with new measurements on methyl (MVE)-, ethyl (EVE)-, and isopropyl (IPVE)-vinyl ethers in CH2C12 over the temperature range 0 °C to -40 °C with m = (2-15) x 10"2, [Ph3CSbCl6] = (5.5-8) x 10"5 mold 1 (Subira et al., 1988). The rate of disappearance of the Ph3C+ ion in the presence of the monomer is considerably smaller than the rate of consumption of the monomer under all conditions, and as mentioned above, the authors identify the rate of disappearance of the trityl cation with the rate of initiation, in our notation... 

In their view the A is the trityl cation, which is regenerated at the end of the polymerisation. As we have shown, it is unlikely that the Ph3C+ itself is the initiator, so the chemistry of the real initiation remains unknown. 

Cathodic Reduction of the Trityl Cation in Methylene Dichloride, P.H. Plesch, A. Stasko and D. Robson, Journal of the Chemical Society, (B), 1971, 1634-37. 

Cyclic (diene)Mo(CO)2Cp (or In) cations have been prepared by trityl cation mediated alkoxide abstraction from cyclic ( 73-allyl)Mo(CO)2Cp (or In) complexes bearing a syn alkoxy in the a position (e.g. 55, Scheme 14)81b 86. Additionally, protonation of (r/3-allyl)Mo(CO)2In (or Cp ) complexes bearing a vinyl group (e.g. 56, Scheme 14) affords the corresponding (diene)Mo+ cations8115 87. 

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