Fluoroalkyl, transition metals

So far as possible, the same order has been used for the fluoroalkyl derivatives in each group of transition metals a-bonded alkyl, alkenyl, and alkynyl derivatives, 7r-bonded derivatives, and then derivatives bonded via N, P, O, or S in that order. In some cases, notably olefin complexes, there is ambiguity about the bonding and this should be borne in mind when searching for particular compounds. Fluoroaryl and heteroaryl derivatives form a more homogeneous group of compounds, and their parameters are considered together across the transition series. 

Volume 7 contains two reviews which update previous chapters by the same authors in Volume 5B. Dr. Fields has devoted his 19F NMR review to fluoroalkyl and fluoroaryl derivatives of transition metals, while Dr. Witanowski and his co-authors have covered all of the literature, pertaining to nitrogen NMR, which appeared between 1972 and 1976. A valuable contribution of spin-spin coupling interactions between carbon and first row nuclei has been provided by Dr. Wasylishen. 

Functionalization of highly fluorinated molecules at transition metal centers is limited not only by the difficulty of G-F bond activation, but also by the well-established observations that metal-fluoroalkyl and metal-fluoroaryl bonds are stronger and much more kinetically inert than the corresponding metal-alkyl and metal-aryl bonds. Thus, migration, alkene metathesis, GO insertion, alkene insertion, a- and / -elimination of fluorinated substrates are all very challenging to achieve. The reactions described in this chapter form the reaction repertoire for the transition metal complexes interacting with fluorocarbons, a very different set from those for hydrocarbons. 

The interpretation of the experimental a constants for the fluoroalkyl and nitroxide radicals is complicated because the stereochemistry at the radical center is not well defined. This complication does not exist for radicals derived from aromatic compounds. Consequently, several research groups have investigated aromatic radicals to characterize the factors governing spin delocalization to /3-fluorine atoms. One aspect of this work concerns the epr spectra of nitrobenzene anion radicals. Another concerns the contact chemical shifts of paramagnetic transition metal complexes. The latter approach was initiated by Eaton, Josey, and Sheppard who examined stable bis(phenylaminotroponiminato)-nickel(II) complexes (55a). More recently, we have examined the contact chemical shifts in the nmr spectra of nickel acetylacetonate complexes of aniline derivatives (556). 

Electron-withdrawing substituents, especially fluoroalkyl groups, stabilize transition metal derivatives. Compounds such as octafiuorotetramethyl-eneiron tetracarbonyl display remarkable thermal and oxidative stability. There has been speculation that these compounds are stabilized by negative hyperconjugation or no bond resonance. Spectroscopic evidence (105, 105a) has been cited in favor of resonance structures such as... 

Fluoroalkylation reaction can also be performed using transition-metals catalysis. In the presence of a catalytic amount of tetrakis(triphenylphosphme)nickel, polyfluoroaUcyl iodide reacted with thiophene to produce the 2-substituted isomer 93 as the sole product. To complete the reaction, addition of sodium hydride was required to absorb hydroiodic acid by-product [52]. 

Fluoroalfyl Derivatives Table IV). The F magnetic resonance spectra available for fluoroalkyl metal compounds thus far are mainly for derivatives of transition metals, only a few spectra having yet been reported for the many known derivatives of the main group elements. 

Fluoroalkyl groups are easily removed from tin by aqueous base (46, 73-75). Fluoroform is liberated quantitatively when trimethylperfluoromethyltin is treated with aqueous alkali in the cold (77). Even hot water will produce monohydro-perfluoroalkanes from the perfluoroalkyltin compounds. A similar easy hydrolysis to afford monohydro-perfluoroalkanes occurs with perfluoroalkyllead, -germanium, and -antimony compounds. Moreover, fluoroalkyl derivatives of transition metals are also very easily decomposed by aqueous alkali, but fluoroalkanes are not a principal decomposition product (Section VI). 

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