Rieke’s method

Highly activated magnesium, prepared using Rieke s method (see 10.2.3.2.1 and 10.2.3.2.3), reacts with 1,3-dienes, including 1,3-butadiene, isoprene, myrcene and ( ),( )-1,4-diphenyl-1,3-butadiene . 

Rieke s method quantitatively reacts dibromothiophene 8 with Rieke zinc (Zn ) to generate a ca 9 1 or higher ratio of isomers 9 and 10 (Scheme 2.2) [33], The ratio varies with the reaction conditions, temperature and, in some cases, substituent bulk. Despite this, polymerization affords exclusively HT polythiophene. Chen and co-workers demonstrated that steric congestion on the catalyst determines selectivity in the coupling reaction [33]. 

Little is known of alkyl and arylcadmium halides. They cannot be obtained by reacting cadmium metal with organic halides, unless active cadmium is prepared by Rieke s method (p. 18). The dialkyls are usually prepared by the Grignard method. Their main use is to convert acyl halides into ketones. Pure Et Cd does not react with benzoyl chloride, but it does so in the presence of the magnesium salts which are by-products in the Grignard synthesis. 

Solutions of HT PATs in CHCI3 have shown fluorescence with a maximum emission wavelength of 570 nm [94]. This wavelength corresponds to the onset of the TT-TT transition in the electronic absorption spectra. Solutions of the regiorandom poly(3-alkylthiophenes) that have been prepared by Rieke s method fluoresce at A = 550 nm [94]. 

The zinc-mediated Reformatsky reaction is one of the classical methods for carbon-carbon bond formation. To date, various main group metals and transition metals have been used for this reaction. Rieke s activated indium powder mediates readily the coupling of ethyl a-bromoacetate and a variety of carbonyl compounds yielding /3-hydroxy esters in good yields (Scheme 87).3 Later, commercially available indium powder has been found to be equally effective for the indium-based Reformatsky reaction in THF.28 This indium Reformatsky reaction is accelerated by ultrasound irradiation (Scheme 88).322,323 Indium(i) iodide also mediates the Reformatsky reaction of aldehydes and ketones to give /3-hydroxy esters, presumably via organoindium(m) diiodide (Scheme 89).27... 

Lithium halides (bromide or Iodide) may well modify the Lewis character of the zinc atom, probably via a zincate species [53], and prevent the efficient coordination of the zinc atom to the double bond, coordination which is required for the carbocyclization. Thus, in the Rieke method, it is essential to wash the active zinc thoroughly since the lithium naphthalenide reduction of zinc bromide also generates lithium bromide, which is detrimental to the success of the reaction. Indeed, the insertion of Rieke s zinc in the presence of LiBr leads to the linear organozinc iodide but not to the cyclic product [52]. 

In this context, it is worth questioning Rieke s active metal preparation method, which should also produce such energy-rich, disorganized structures. Since the conventional metal salt reductions require prolonged heating, some deactivation can result from annealing, minimized in reactions performed under sonication in shorter times at lower temperature. ... 

A useful technique for the preparation of n and Cu powders) is by electrolysis with puls< efficiency in allylation achieved by using s involves reduction of ZnCl with Na in liquid 1 Ketones. Rieke zinc produced by the r reacts with alkyl halides, and the organozin treatment with CuCN and acid chlorides. S readily prepared in this direct manner. a-Chkj method using chloroacetyl chloride in the couf 3-Thienylzinc halides. These reagenii Rieke zinc. They undergo Ni-catalyzed coupln... 

Rieke zinc is prepared by placing lithium metal (10 mmol), a catalytic amount of naphthalene (1 mmol), and 12-15 ml of THF in one flask placed in an ice bath. Once this mixture has stirred for about 30-60 s, it will turn dark green, indicating the formation of lithium naphthalenide. Zinc chloride dissolved previously in 12-15 ml of THF is then cannulated dropwise (ca. 3 s per drop) into the lithium naphthalenide, and stirring is continued for 30 min after the transfer is complete. This method is not only safer due to the use of lithium... 

Finally, the most reactive Rieke zinc yet prepared is generated by the reduction of Zn(CN)2 with lithium using an electron carrier such as naphthalene. Some of this zinc s chemistry will be described later in the text. The reaction details are the same as Method 2. 

Fig. 17. Rieke method for regiospecific synthesis of poly(3-alkylthio-phene)s with 100% head-to-tail couplings.

Upon exposure to F vapor, thin films (7-12 tm thick) of HT PATs exhibit maximum electrical conductivities of 1000 S/cm for PDDT, 200 S/cm for POT, and 150 S/ cm for PHT (as measured in air) [74]. Thin films of PATs prepared from the FeCIi method show maximum conductivities between 20 and 0.1 S/cm. McCullough et al. have routinely measured conductivities of 100-200 S/cm in these samples in HT PDDT. In contrast, PDDT from FeCl3 gave conductivities of 0.1-1 S/cm (58-70% HT). Rieke and coworkers have reported that the electrical conductivity for their HT PATs is 1000 S/cm [91]. Rieke... 

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