Methane reactions with cyclopentadienyl

Whereas alkylation of activated methylene systems by classical methods produces a mixture of mono- and dialkylated products, with the latter frequently predominating, phase-transfer catalytic procedures permit better control and it is possible to obtain only the monoalkylated derivatives. Extended reaction times or more vigorous conditions with an excess of the alkylating agent lead to dialkylated products or, with dihaloalkanes, carbocyclic compounds as the technique mimics dilute concentration conditions, e.g. the resonance stabilized cyclopentadienyl anion, generated under solidiliquid two-phase conditions, or under liquiddiquid conditions, reacts with 1,2-dihaloethanes to form spiro[2,4]hepta-4,6-diene (70-85%) [1-3]. Reaction with dichloromethane produces bis(cyclopenta-2,4-dien-l-yl)methane (60%) [4],... 

From the previous sections, the following points can be made. Nickelocene and the cyclopentadienyl ligands are hydrogenated with atomic hydrogen produced from the dissociative adsorption of on the surface. Carrier gas, and precursor compete for the adsorption sites. Nickelocene can almost completely cover the surface and thus prevent the adsorption of H. Even with low hydrogenation rate, the methanation reaction can be very efficient for the cleaning of the surface. Hence, a decrease in hydrogenation... 

A one-step chemical procedure (i, in the scheme) has proved valuable. Thus cholesterol and its oxidation product, dehydroisoandrosterone have been selectively aromatised by reaction with the electrophilic ruthenium complex (Cp Ru ), t -cyclopentadienyl Ru. obtained by protonation in THF of [Cp Ru(OMe)j2 (1 mol) with triflic acid, CF3SO3H (2 mol). The addition of cholesterol (2 mol) in THF during 40 hours at 120°C (or in dichloromethane at 90 C) afforded estrone in 48% yield with evolution of methane (ref. 114). 

The mechanism of formation of benzvalene from cyclopentadienyl-lithium and dichloromethane has been studied in detail. On employing dideuteriodichloro-methane, the deuterium label is found to be stereospecifically located at the C-1 position of the product, in contrast to earlier reports. These data are compatible with two routes (i) chlorocyclopropanation of the cyclopentadienyl-lithium and subsequent nucleophilic displacement of the chloro-substituent and (ii) attack of the cyclopenta-dienyl anion on the dichloromethane to produce a cyclopentadienyl carbenoid A distinction between these two routes comes from a study of the reaction with indenyl-lithium. The exclusive formation of 1- and 2-deuterionapthalene (0.6 1) as byproducts is compatible only with the carbenoid path (Scheme 6) in which 1,2-cheletropic addition affords benzobenzvalene uniquely labelled at C-1, as is observed. 

Cyclopentadienyl dicarbonyl ruthenium dimer 132 reacts with silver tetrafluoroborate and diphenylacetylene to afford the cyclobutadiene ruthenium complex 133 (Scheme 12). Irradiation of 133 in dichloro-methane in the presence of several alkynes leads to the arene cyclopentadienyl ruthenium complexes 125 in high yield. This reaction appears to be a general route to sterically crowded ruthenium arene cations (55). 

The electrochemistry of the complexes [(RCsH4)-Mo(X)( i-X)2]2. X = multiply bonding ligand, has been studied. The bis[(tricarbonyl metal)(q -cycl(q)entadienyl)]methane derivatives, metal = Mo, W have been synthesised ftom the reaction of bis-(cyclopentadienyl)-methane with (CH3CN)3M(CO)3, followed by oxidation of the intermediate anions. The preparations of [(Cp )(q -allyl)(q -allyl)W], Cp = Cp, Cp, q-C5H4t-Bu, obtained from [(q -C3H5>3WCl]2 and alkali metal cyclopentadienyls have been described. ... 

The unsubstituted cyclopentadienyl analogue of 1 Cp(CO)2lr similarly gave Cp(CO)Ir(CH3)H. The hydridomethyl compound 9 was not prepared directly from the dihydride 4 due to experimental difficulties. However, Bergman observed that primary alkyl complexes are thermodynamically more stable than secondary complexes [26]. For example, the reaction of 4 with n-propane (reaction 9) or n-pentane gave mixtures of primary and secondary insertion products (with preferential formation of primary compounds). Treating these mixtures at 110 °C converts the secondary complexes into the more stable primary derivatives this conversion takes place via reversible reductive elimination from the secondary hydrido alkyl isomers. This very interesting result allowed the preparation of selectively pure primary insertion products of linear alkanes and the achievement of methane activation (reaction 12). Thus, heating the secondary hydrido cyclohexyl compound 6 in cyclooctane under CH4 pressure caused the formation of the methyl product 9 which is the thermodynamic sink for the system. 

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