Metal alkyls Friedel-Crafts reaction

To optimize the alkylation conditions, ferrocene was reacted with allyldimethyl-chlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group lO metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. 

We have recently shown that metal-exchanged zeolites give rise to carbocationic reactions, through the interactions with alkylhalides (metal cation acts as Lewis acid sites, coordinating with the alkylhalide to form a metal-halide species and an alkyl-aluminumsilyl oxonium ion bonded to the zeolite structure, which acts as an adsorbed carbocation (scheme 2). We were able to show that they can catalyze Friedel-Crafts reactions (9) and isobutane/2-butene alkylation (70), with a superior performance than a protic zeolite catalyst. 

Alkylation of benzene is old technology. The French chemist, Charles Friedel, with his American partner, James Crafts, in 1877, stumbled (almost literally) across the technique for alkylating benzene with amyl chloride (C5H11CI). The use of a metallic catalyst, in this case aluminum, was the key. The Friedel-Crafts reaction is classical and remains a principal route for alkylating benzene with ethylene to make EB. 

Benzylation of toluene with benzyl chloride, which is a typical example of Friedel-Crafts alkylation, is known to be catalyzed by Lewis-type superacids such as A1C13 and BF3. This type of catalyst has been mostly used for the Friedel-Crafts reaction, which is one of the most studied of organic reactions. This reaction was performed over several metal oxides and sulfates, and iron sulfates showed an unexpected effectiveness for the reaction (102-104). The catalytic activities of FeS04 and Fe2(S04)3 for the reaction were examined in detail the activities were remarkably dependent on calcination temperature, the maximum activity being observed with calcination at 700°C (105-107). Catalytic actions analogous to the above case were also observed with other Friedel-Crafts reactions, the benzoyl-ation of toluene with benzoyl chloride (108), the isopropylation of toluene with isopropyl halides (109), and the polycondensation of benzyl chloride UIO). 

In retrospect, it is ironic to it that when I met Ernst Schumacher in 1969 (he was then Professor at the University of Bern in Switzerland) we did not talk about the experiments he did at Zurich in the same building where I was at that time. Instead, his interest focussed on our work on borazine transition metal compounds and we discussed in some detail whether it would be possible to incorporate metal atoms like chromium or molybdenum between the layers of hexagonal boron nitride (BN) in a similar way as it can be done with graphite. In the course of these discussions I did not mention that, after I had moved to Zurich, we had begun to investigate the reactivity of nickelocene towards both nucleophilic and electrophilic substrates. The reason was that we were still at the beginning, and while we had been able to prepare a series of monocyclopentadienyl nickel complexes from Ni(C5H5)2 and Lewis bases, our attempts to obtain alkyl- or acyl-substituted nickelocenes by the Friedel-Crafts reaction failed. 

The application of the ideas of Lewis on acids, which correlate a wide range of phenomena in qualitative fashion, has as yet led to very few quantitative studies of reaction velocity but has led to detailed speculations as to mechanisms (Luder and Zuffanti, 118). Friedel-Crafts reactions are considered to be acid-catalyzed, the formation of a car-bonium ion being the first step. The carbonium ion then acts as an acid relative to the base benzene which, upon loss of a proton, yields the alkylated product. Isomerizations of isoparaffins can be explained in similar fashion (Schneider and Kennedy, 119). An alkyl halide yields a carbonium ion on reaction with acids such as boron trifluoride, aluminum chloride, and other metal halides. 

Si-H is believed to be equivalent to H-H and hence Si-H can add a C-C multiple bond to produce SiC-CH. The reaction is usually mediated by precious metal complexes such as chloroplatinic acid in a homogeneous liquid phase. This reaction may correspond to the alkylation of Si compounds with olefins and unsaturated compounds. A typical alkylation reaction is an acid catalyzed Friedel-Crafts reaction, e.g. an alkylation of benzene with propene to yield... 

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