Perfluoroalkyl-metal compounds

Scheme 2.109 Principal methods for generation of fluorinated carbanions and perfluoroalkyl metal compounds (Rp = (per)fluoroalkyl, Arp = (per)fluoroaryl, M = metal, X = halogen, B = base, S = solvent). The particularly unstable trifluoromethyl anion can be stabilized by formation of an adduct with a suitable solvent, for example DMF, which itself acts as a CFj"" source in a haloform-like reaction (bottom).

If the metal is a soft Lewis acid, for example zinc, cadmium, or copper, the corresponding perfluoroalkyl metal compounds are stabilized by the more covalent character ofthe metal-carbon bond (Scheme 2.118). The copper(I) compounds, in particular, can be readily isolated, handled, and reacted even at elevated temperatures. 

However, a recent study of highly fluorinated organic compounds indicates that the perfluorocarbanion is stabilized simply by inductive effects (106). These effects may possibly be adequate to account for the stability of the perfluoroalkyl metal compounds. 

The chemistry of the metal carbonyls has been the subject of hundreds of research papers, most of them appearing in the last decade of renaissance of inorganic chemistry. Reviews have appeared on the metal carbonyls themselves (/, 2) and on such related topics as the anionic carbonyl-metallates (S), metal-olefin complexes (4,5), tricarbonyl(diene)iron species (6), perfluoroalkyl metal compounds (7), andTr-cyclopentadienyl andir-arene (S, 9) metal derivatives. ... 

H. C. Clark Advan. Fluorine Perfluoroalkyl derivatives of the 44 Transition metal compounds, p. 54... 

Perfluoroalkyl cadmium compounds are also known. Bis(trifluoromethyl)cadmium has been prepared at —78°C by cocondensing Cd atoms with CF3 radicals generated in a hexafluoroethane plasma (see Metal Vapor Synthesis of Transition Metal Compound and also by the unusual reaction of activated cadmium powder with difluorodihalomethanes, for example, CF2CI2, CF2Br2, or CF2BrCl, in DMF (equation 7). ... 

Several perfluoroalkyl and polyfluoroalkyl, and a number of perfluoro-vinyl and pentafluorophenyl compounds of tin have been prepared (Table II). Their study has added much to our knowledge of the chemical and spectroscopic properties of fluorocarbon-metal compounds. 

Perfluoroalkyl, polyfluoroalkyl, fluoroalkenyl, and pentafluorophenyl transition metal compounds have been obtained by at least seven different kinds of reaction so far. 

Perfluoroalkyl iodides also react with 7r-cyclopentadienylcobalt dicarbonyl 105), TT-cyclopentadienylnickel carbonyl 102a, 106), l,2-bis(diphenyl-phosphino)ethanenickel dicarbonyl 107), and di[l,2-bis(diphenylphos-phino)ethane]molybdenum dicarbonyl 106) to afford perfluoroalkyl transition metal compounds. 

Perfluoroalkyl or -aryl halides undergo oxidative addition with metal vapors to form nonsolvated fluonnated organometallic halides and this topic has been die subject of a review [289] Pentafluorophenyl halides react with Rieke nickel, cobalt, and iron to give bispentafluorophenylmetal compounds, which can be isolated in good yields as liquid complexes [290] Rieke nickel can also be used to promote the reaction of pentafluorophenyl halides with acid halides [297] (equation 193)... 

Because the forces of attraction prevail when molecules are brought into sufficiently dose proximity under normal conditions, release is best effected if both the strength of the interaction and the degree of contact are minimized. Aliphatic hydrocarbons and fluorocarbons achieve the former effect, finely divided solids the latter. Materials such as microcrystalline wax [64742 42-3] and hydrophobic silica [7631-86-9] combine both effects. Some authors refer to this combined effect as the ball bearing mechanism. A perfluoroalkylated fullerene nanosphere would perhaps be the ultimate example of this combined effect (17). These very general mechanistic remarks can be supplemented by publications on the mechanism of specific classes of release agents such as metallic stearates (18), fatty acids and fluorinated compounds (19), and silicone-coated rdease papers (20,21). The mechanism of release of certain problem adherents, eg, polyurethanes, has also been addressed (22,23). 

Calibrants are required to calibrate the mass scale of any mass spectrometer, and it is important to find reference compounds that are compatible with a particular ion source. Calibrants commonly used in electron ionization (El) and chemical ionization (Cl), such as perfluorocarbons, are not applicable in the ESI mode. The right calibrants for LC-ESI-MS should (1) not give memory effects (2) not cause source contamination through the introduction of nonvolatile material (3) be applicable in both positive- and negative-ion mode. The main calibrants used or still in use to calibrate ESI-MS can be divided into the following categories polymers, perfluoroalkyl triazines, proteins, alkali metal salt clusters, polyethers, water clusters, and acetate salts. 

Perfluoroalkyl transition metal carbonyl complexes146 are prone to a-fluorinc elimination pathways as it is well-known that C-F bonds a to the metal center are weaker than in aliphatic compounds. Thus, a-elimination of fluorine from perfluoroalkyliron(II) tetracarbonyl complexes, e.g. 10,147 has been observed. 

---