Cation-cyclohexane complex

Fig. 18 Structures of cation-benzene and cation-cyclohexane complexes...

Two recent studies cast more light on this problem and they are particularly interesting because they relate directly to the context of cationic polymerisation. In the first Bogomolova et al. examined the electronic spectra of mixtures of stannic chloride and styrene or a-methylstyrene in ethyl chloride and cyclohexane. Complexation with the first moncaner gave a band at 295 nm with an extinctimi coefficient of about 1,000 cm in ethyl chloride and about 2,000 in cyclohexane. The in-... 

The intramolecular hydroacylation of aldehydic olefins is catalyzed by cationic Rh complexes of chelating phosphines in polar nonprotic solvents. The rate decreases with increasing substrate Rh ratio since the substrate complex with the catalyst inhibits the reaction. However, since this complexation also prevents the decarbonylation of the aldehyde, catalyst deactivation decreases, leading to a higher turnover. The only effective catalytic C—H activations are carried out with [RhCl(CO)(PMe3)2] under photolysis which removes CO. Alkanes are converted to alkenes in the order cyclooctane > cyclohexane > n-decane n-hexane. Up to 200 turnovers cyclooctane per hour are observed. In order to generate terminal... 

Both methylcyclopentane and cyclohexane were found to give the methylcyclopentyl ion which is stable at low temperature, in excess superacid. When alkanes with seven or more carbon atoms were used, cleavage was observed with formation of the stable t-butyl cation. Even paraffin wax and polyethylene ultimately gave the t-butyl cation after complex fragmentation and ionization processes. 

This is consistent with the observed products of oxidation, i.e. benzyl alcohol, benzaldehyde and benzoic acid and with the observed oxidation of cyclohexane. Radical-cations are, however, probably formed in oxidation of napthalene and anthracene. The increase of oxidation rate with acetonitrile concentration was intepreted in terms of a more reactive complex between Co(III) and CH3CN. The production of substituted benzophenones at high CH3CN concentration indicates the participation of a second route of oxidation. 

The cyclohexane-containing system (203) was also prepared in an attempt to obtain metal complexes with clam type geometries (Owen, 1983). As for the previous system, it was considered that such complexes might show enhanced shielding of the cation, from both the solvent and the counter ion present, but still allow the bound metal to be readily released on demand. As is evident from our earlier discussion, both these are desirable properties for metal-ion transport systems. 

Recently, detailed kinetic studies of the hybrid[type II , 02 - type RH] photo-oxidations of cyclohexane and cyclohexane-dn in both NaY and BaY have been reported. A kinetic isotope effect kulko of 5.7 was determined for X > 400 nm in BaY. This substantial isotope effect, which is nearly identical to the isotope effect on the kinetic acidity of cyclohexane, requires that the proton abstraction step, k, in the alkane radical cation superoxide ion pair be smaller than the back-electron transfer, k, to regenerate the charge-transfer complex (Fig. 18). If kpT were larger than k, the rate expression, Eq. (A) in Fig. 18, would be reduced to Eq. (B) and only a small isotope effect on et would be anticipated. 

Class (3) reactions include proton-transfer reactions of solvent holes in cyclohexane and methylcyclohexane [71,74,75]. The corresponding rate constants are 10-30% of the fastest class (1) reactions. Class (4) reactions include proton-transfer reactions in trans-decalin and cis-trans decalin mixtures [77]. Proton transfer from the decalin hole to aliphatic alcohol results in the formation of a C-centered decalyl radical. The proton affinity of this radical is comparable to that of a single alcohol molecule. However, it is less than the proton affinity of an alcohol dimer. Consequently, a complex of the radical cation and alcohol monomer is relatively stable toward proton transfer when such a complex encounters a second alcohol molecule, the radical cation rapidly deprotonates. Metastable complexes with natural lifetimes between 24 nsec (2-propanol) and 90 nsec (tert-butanol) were observed in liquid cis- and tra 5-decalins at 25°C [77]. The rate of the complexation is one-half of that for class (1) reactions the overall decay rate is limited by slow proton transfer in the 1 1 complex. The rate constant of unimolecular decay is (5-10) x 10 sec for primary alcohols, bimolecular decay via proton transfer to the alcohol dimer prevails. Only for secondary and ternary alcohols is the equilibrium reached sufficiently slowly that it can be observed at 25 °C on a time scale of > 10 nsec. There is a striking similarity between the formation of alcohol complexes with the solvent holes (in decalins) and solvent anions (in sc CO2). 

In HC1 solution, in the presence of SnCl2, Mov forms complexes [MoO(Hd)2]+ with the dioximes (H2d) of cyclohexane-1,2-dione and cyclopentane-1,2-dione. Several compounds of tetradentate Schiff bases255,274 with oxomolybdenum(V) have been prepared and the crystal structure of frans-[MoO(salen)(MeOH)]Br has been determined.274 The Mo—O, distance is 1.666(10) A, and there is close interaction in the crystal between each cation and an attendant bromide anion. 

The photo-induced electron transfer of l,4-bis(methylene)cyclohexane in acetonitrile-methanol solution with 1,4-dicyanobenzene (DCB) affords two products, both consistent with nucleophilic attack on the radical cation followed by reduction and protonation or by combination with DCB ).63 In the absence of a nucleophile, the product mixture is highly complex, as is the case under electro-oxidative conditions. Under UV irradiation, /nmv-stilbene undergoes dimerization and oxygenation (to benzaldehyde) by a single-electron mechanism in the presence of a sensitizer such as 2,4,6-triphenylpyrilium tetrafluoroborate (TPT).64 This reaction was found to yield a similar product mixture with the sulfur analogue of TPT and their relative merits as well as electrochemical and photophysical properties are discussed. 

Busson and van Beylen [205] studied the role of the cation and of the carbanionic part of the active centre during anionic polymerization in non polar media. They were interested in the problem of complex formation between the cation and the monomer double bond [206] and they therefore measured the reaction of various 1,1-diphenylethylenes with Li+, K+ and Cs+ salts of living polystyrene in benzene and cyclohexane at 297 K. Diphenylethy-lene derivatives were selected for two reasons. 

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