Perfluoroalkyl zinc

Relative intensities of ions (m/z (rel. int.) [ion]) observed in the El mass spectra of some bis(perfluoroalkyl)zinc compounds ... 

Solvated perfluoroalkyl zinc reagents have been prepared by reaction of perfluoroalkyl iodides with zinc in ethereal solvents such as dioxane [36,37]. Self-coupled and cross-coupled products can be formed when a mixture of acetic anhydride and methylene chloride was used [38-40] (Scheme 11). 

Scheme 2.119 Synthetic use of perfluoroalkyl zinc reagents - generated in situ by sonication - for various types of reaction [51].

The trifluoromethylation of aryl iodides has been achieved using the reaction with (trifluoromethyl)-trimethoxyborate and a copper(I)/phenanthroline catalyst." A copper chloride/phenanthroline catalyst has also been used together with (TMP2Zn), zinc bis-tetramethylpiperidide, in the reaction of aryl iodides with perfluoroalkyl derivatives to yield arylperfluoroalkanes. The mechanism is thought to involve initial formation of bis(perfluoroalkyl)zinc species followed by rate-limiting transmetalation with copper halide and reaction with the aryl iodide to give the coupled product." ... 

Organometallic reagents of lithium, magnesium, zinc, aluminum, copper, etc. add to alkenes and alkynes.226 Carbozincation was reported to be improved by sonication. Perfluoroalkyl zinc reagents generated in situ add to alkynes in the presence of a copper salt (Fig. 39).227... 

Schorn et al. [22] used the standard HMQC pulse sequence with delays optimized for to provide the needed two-bond C—F correlations used to assign the resonances in a bis(n-perfluoroalkyl)zinc complexes. To be able to distinguish correlations due to leakage from J p correlations in the / f experiment, no decoupling was applied during the acquisition period. Cross-peaks from 7cf correlations were easily identified from their large doublet splitting in the F chemical shift dimension. 

The importance of solvent effects in the preparation of perfluoroalkyzinc reagents is further illustrated in the reaction of perfluoroalkyl iodides with zinc-copper couple. In DMSO, DMF, and HMPA, the main products are the fluo-roolefins The formation of the fluoroolefin is facilitated when the reaction is carried out in the presence of potassium thiocyanate [30] (equation 21)... 

Under sonication conditions, the reaction of perfluoroalkyl bromides or iodides with zinc can be used to effect a variety of functionalization reactions [39, 40, 41, 42] (equation 30) Interestingly, the ultrasound promoted asymmetric induction with the perfluoroalkyl group on the asymmetric carbon was achieved by the reaction of perfluoroalkyl halides with optically active enamines in the presence of zinc powder and a catalytic amount of dichlorobisftc-cyclopenta-dienyl)titanium [42] (equation 31)... 

In related work, palladium, nickel, or methyl viologen (MV ) were used to catalyze the conversion of perfluoroalkyl iodides to a-perfluoroalkyl carbinols in the presence of zinc [43, 44] (equations 32 and 33) Only aldehydes react under these conditions... 

In the presence of zinc, bromotnfluoromethane and perfluoroalkyl iodides react with thiocyanates and isocyanates to give the corresponding perfluoroalkyl sulfides and substituted perfluoroalkylacetamides, respectively [48 (equation 39)... 

Tnfluoromethanesulfinate can be prepared from the reaction of trifluoromethyl bromide with sulfur dioxide and zinc [50] (equation 41) Similar insertion occurs when perfluoroalkyl iodides are used as precursors (equations 41 and 42)... 

Perfluoroalkyl iodides can be directly carboxylated with zinc and carbon dioxide under ultrasonic conditions [39] (equation 45) or by the reaction of perfluoroalkyl iodides with carbon dioxide with a zinc-copper couple in DMSO [57] (equation 46) Alkylation of the intermediate carboxylate gives the corresponding ester [52]... 

In dissociating solvents, perfluoroalkyl iodides react with a zinc-copper... 

This study relates to a continuous process for the preparation of perfluoroalkyl iodides over nanosized metal catalysts in gas phase. The water-alcohol method provided more dispersed catalysts than the impregnation method. The Cu particles of about 20 nm showed enhanced stability and higher activity than the particles larger than 40 nm. This was correlated with the distribution of copper particle sizes shown by XRD and TEM. Compared with silver and zinc, copper is better active and stable metal. 

The formation of relatively ill-defined catalysts for epoxide/C02 copolymerization catalysts, arising from the treatment of ZnO with acid anhydrides or monoesters of dicarboxylic acids, has been described in a patent disclosure.968 Employing the perfluoroalkyl ester acid (342) renders the catalyst soluble in supercritical C02.969 At 110°C and 2,000 psi this catalyst mixture performs similarly to the zinc bisphenolates, producing a 96 4 ratio of polycarbonate polyether linkages, with a turnover of 440 g polymer/g [Zn] and a broad polydispersity (Mw/Mn>4). Related aluminum complexes have also been studied and (343) was found to be particularly active. However, selectivity is poor, with a ratio of 1 3.6 polycarbonate polyether.970... 

Asymmetric induction of between 30 and 66% has been reported for the addition of perfluoroalkyl iodides to chiral arene/chromiumtricarbonyl complexes using ultraso-nically dispersed zinc at room temperature (Scheme 3.19) [101], Photochemical decomposition of the organometallic intermediate affords a chiral alcohol product. The reaction is carried out in DMF as solvent and high overall yields are reported e.g.80 % (R = Et). Only a small excess of the perfluoroalkyl iodide is required and the conversion is complete in under 1 h. 

Despite the lower reactivity of solvated perfluoroalkylzinc reagents, perfluoroalkyl iodides undergo synthetically useful zinc-mediated reactions under Barbier conditions which often employ ultrasound and co-catalysts. Under these conditions, the zinc reagents are not well characterized and radical intermediates and SET mechanisms are proposed in some cases. Representative examples are presented below and include the ultrasound-promoted, zinc-mediated perfluoroalkylation of various substrates as reported by Ishikawa and coworkers (Scheme 10)123 126. Yields of carbinols could be improved by use of Ti(II) co-catalyst. Ultrasound promoted the coupling of perfluoroalkyl iodides with vinyl and allyl halides in the presence of Pd co-catalysts. 

The exchange reaction of perfluoroalkyl iodides and iodopentafluorobenzene with dialkylzinc in the presence of Lewis base, such as diglyme or pyridine, afforded the corresponding bis(trifluoromethyl)zinc and bis(pentafluoro-phenyl)zinc in high yield [41] (Scheme 12). 

Under ultrasonic conditions, the reaction of perfluoroalkyl iodides with zinc has been utilized by Ishikawa to effect perfluoroalkylation of a variety of organic... 

Similarly,palladium, nickel complex [49] or methyl viologen (MV2+) [50] have also been used to catalyze the reaction of perfluoroalkyl iodides with aldehydes in the presence of zinc to give the corresponding a-perfluoroalkyl carbinols (Scheme 17). 

Perfluoroalkyl iodides reacted with trialkylsilyl chloride in DMF in the presence of zinc followed by hydrolysis with acid to give perfluoroaldehydes in good yields [55]. Recently, Hu reported a new preparation of perfluoroalkyl aldehydes via reaction of perfluoroalkyl halides and DMF, initiated by redox... 

Perfluoroalkyl iodides reacted with ethyl carbonate, carbon dioxide, sulfur dioxide, and alkyl phosphates in the presence of a more active zinc-copper couple to afford the corresponding perfluoroalkylated products [57-59] (Scheme 21). 

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