Methane cations, rate

The production of 1-alkenes from ethylene oligomerization was carried out with high selectivity in ionic liquids in the presence of a cationic nickel complex catalyst (ri -methallyl)-[bis(diphenylphosphino)methane-monoxide-K -P,0]nickel(II) hexafluoroantimonate, [(mall)-Ni(dppmo)]Sbp6 (240). The overall reaction rate of... 

The side reaction of hydrogenolysis of the methyl-ruthenium intermediate to methane also may become predominant when the carbonyl insertion-methyl migration step of the process (Scheme 1) proceeds at a low rate. To reduce this drawback some Lewis acid promoters (i.e. metal alkali cations, classical Lewis acids such as AII3, SbCl etc.)... 

HRu(CO) and/or other strong acids favour the activation of the substrate and increase the reaction rate but do not favour the carbonylation steps of the process. Thus the prevailing reactions are the hydrogenation of the acetyl groups to ethyl derivatives and of methyl groups to methane. In the presence of M [Ru(CO)3l3j salts and particularly when the cation is less solvated or selectively complexed by a specific crown-ether, the carbonylation steps of the process are favoured. 

In this context, note that the cycloaddition rate of a crown ether-annulated diazo(diphenyl)methane such as 1 with maleic anhydride is ion-selectively retarded in the presence of alkali perchlorates (21). This observation was attributed to a lowering of the HOMO (dipole) level, due to the electron-withdrawing electrostatic effect of the complexed cation. A parallel to the negative Hammett p values for cycloadditions of ring-substituted diazo(diphenyl)methanes with TONE (22) (p = —2.67) and chloranil (23) (p = —1.67) was drawn. 

It has been shown that cations of Cu(TT) within the coinpositicTn of the aiu-roncopperebromium catalyst contribute greatly tn the rate of oxidation of methane and butane, and these centres also play a significant role in a final oxidation of some intermediate products. Severe treatment of catalysts by stoichiometric air/fuel mixtures and high temperatures during the process of fuel combustion leads to a change in volume and surface phase composition of catalysts. Solid solutions of the composition MeCr (where Me u, Kg) and -... 

In addition to the cationic, radical, and non-synchronous concerted mechanisms outlined above, many other proposals have been offered [9, 56], In a recent provocative paper, an organometallic mechanism was postulated for the activation of alkanes by a ferryl porphyrin model species [79]. Less reactive substrates such as H2, D2 and CH4 were observed to inhibit the reaction between the synthetic catalyst and cyclohexane. In the proposed mechanism, a 2 -t- 2 C-H addition across the Fe-O bond is preceded by coordination of the alkane to the metal center to form an intermolecular <7-adduct. Inhibition arises from preferential binding of the smaller substrates to the congested metal site. Attempts to identify a similar effect with sMMO have been unsuccessful the presence of H2 had no effect on the rate of reaction between methane and Q (A. M. Valentine, S. S. Stahl, S. J. Lippard, unpublished results). 

A cationic hydrido-methyl complex, HPtCHs ", is formed upon the almost barrierless insertion of a Pt ion into a C-H bond of methane and then 1,2-migration of a hydrogen atom and subsequent elimination of H2 from the transition-metal center gives the platinum carbene cation PtCHi"" with an apparent rate constant of k - 8.2 x 10" cm molecule" s. The reaction of ground-state platinum atoms produced by the photodissociation of [PtMe3-(CsHiMe)] follows a termolecular mechanism [4c] ... 

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