Activation C-F bonds

The a-C—C bonds adjacent to carbonyls, alcohols, and nitriles are often the targets for activation [92]. This section focuses on recent developments of transition metal-catalyzed C—CN bond cleavage. 

The C—F bond is the strongest single bond to carbon, and seledive C—F transformation is still a great challenge under mild conditions [105]. Ozerov and co-workers 

For aromatic C— F bonds, the Suzuki-type cross-coupling of perfluorinated arenes, such as octafluorotoluene and perfluorobiphenyl, in the presence of nickel catalysts has been developed (Equation 11.47) [108]. In these reactions, triethylamine is used as a base, whereas stronger inorganic bases are typically used in Suzuki coupling reactions. 

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Abstract This chapter highlights the use of iV-heterocyclic carbenes as supporting ligands in arylation reactions different than the more common cross-coupling reactions, including C-F bond activation, catalytic arylation, homocoupling, direct arylation and oxidative Heck reactions. 

The bond dissociation energy of fluoromethane is 115 kcal mol , which is much higher than the other halides (C-Cl, C-Br and C-1, respectively 84, 72 and 58 kcal mol ) [6], Due to its strength, the carbon-fluorine (C-F) bond is one of the most challenging bonds to activate [7], A variety of C-F bond activation reactions have been carried out with different organometallic complexes [8], Among them, nickel [9] and ruthenium complexes have proven to proceed selectively under mild conditions [10],... 

The C-F bond activations in C6F6 and related compounds with ruthenium [200, 201] and rhodium [17, 78, 201] complexes, for which an SNAr mechanism is energetically unfavorable, have been explained by SET pathways. Both SN2 [128, 129, 131, 170-174, 199, 202] and SET [130, 132, 199] mechanisms have been proposed for the reaction of Co(I) complexes with alkyl and vinyl halides. 

Fluorous organometallic chemistry, examples, 1, 842 Fluorous solubles, in organometallic synthesis, 1, 81 Fluorous solvents, for hydroformylations, 11, 450 Fluorous tin hydrides, preparation and applications, 9, 346 Fluorovinyl groups, vinylic C-F bond activation, 1, 753 Fluoro vinyltitanocenes, synthesis, 4, 546 g tfZ-Fluorovinyltributylstannane, in carbonylative cross-coupling, 11,413... 

Lactones, via indium compounds, 9, 686 Lactonizations, via ruthenium catalysts, 10, 160 Ladder polysilanes, preparation and properties, 3, 639 Lanthanacarboranes, synthesis, 3, 249 Lanthanide complexes with alkenyls, 4, 17 with alkyls, 4, 7 with alkynyls, 4, 17 with allyls, 4, 19 with arenes, 4, 119, 4, 118 and aromatic C-F bond activation, 1, 738 bis(Cp ), 4, 73... 

Platinum complexes (continued) with aryls, thallium adducts, 3, 399 with bis(alkynyl), NLO properties, 12, 125 with bisalkynyl copper complexes, 2, 182-186 with bis(3,5-dichloro-2,4,6-trifluorophenyl), 8, 483 and C-F bond activation, 1, 743 in C-H bond alkenylations, 10, 225 in C-H bond electrophilic activation studies, 1, 707 with chromium, 5, 312 with copper, 2, 168 cyclometallated, for OLEDs, 12, 145 in diyne carbometallations, 10, 351-352 in ene-yne metathesis, 11, 273 in enyne skeletal reorganization, 11, 289 heteronuclear Pt isocyanides, 8, 431 inside metallodendrimers, 12, 400 kinetic studies, 1, 531 on metallodendrimer surfaces, 12, 391 mononuclear Pt(II) isocyanides, 8, 428 mononuclear Pt(0) isocyanides, 8, 424 overview, 8, 405-444 d -cP oxidative addition, PHIP, 1, 436 polynuclear Pt isocyanides, 8, 431 polynuclear Pt(0) isocyanides, 8, 425 Pt(I) isocyanides, 8, 425 Pt(IV) isocyanides, 8, 430... 

These oxidative—addition reactions have been treated extensively by Su et al. (29-31), using the VBSCD model. In all cases, a good correlation was obtained between the computed barriers of the reaction and the respective AEst quantities (which enter into the expression of G), including the relative reactivity of carbenoids, and of PtL2 versus PdL2 (29-31). Another treatment led to the same reactivity patterns for C—F bond activation reactions by Rh(PR3)2X and Ir(PR3)2X d8 complexes, which are isolobal to carbenoids (30). A similar extended correlation was found recently for C—Cl activation by d10-PdL2 (32), and is dealt with in Exercise 6.9. 

In view of the relative C—X bond energies, C—F bond activation can be expected to be strongly disfavored. Nevertheless, there is an increasing number of cases where C—F bond addition to electron-rich metal complexes is observed. For example, QF6 oxidatively adds to the Cp Rh(PMe3) fragment, whereas QF5H undergoes only C—H activation.65 Hexafluorobenzene slowly adds to... 

The remaining routes into metal-bound fluorides really owe more to serendipity than to any systematic approach. C—F bond activation has led to several metal fluorides which are detailed extensively in a review article by Kiplinger, Richmond and Osterberg [6], Decomposition of weakly coordinated anions can occur but frequently gives poor yields [7]. 

The only other route to scandium fluoride derivatives has been via C—F bond activation of fluoro-alkenes with [ScR(Cp )2] (R = H, Me) to give [ScF(Cp )2] [1], Very recent work has produced the first report of an organometallic yttrium fluoride. The reaction between [(CsH5)3Y] and Me3NHF results in the isolation of [ (C5H5)2YF(THF) 2] which has been fully characterised by elemental analysis, infra-red, mass and NMR spectroscopies and X-ray diffraction [8]. 

The design of transition metal complexes capable of C—F bond activation for the functionalization of fluorocarbons has attracted attention recently. It has been known for several years that oxidative addition of an aromatic C—F bond takes place at tungsten(O) to yield stable tungsten(II) metallacycles, the cleaved carbon and fluorine atoms both finishing up bound to the metal centre (Eqn. (2)) [34-36]. 

C F bond activation is atttacting increasing interest in coimection with green chemistry. Perfluoroarenes are more reactive than the corresponding perfluoroalkanes, possibly because of the easier access to the C-F bond in CeFg versus C6F12. Photochemical routes are common as in equation (22). ... 

K. Krogh-Jespersen and A. S. Goldman, Transition States for Oxidative Addition to Three-Coordinate Ir(I) H-H, C-H, C-C, and C-F Bond Activation Energies, In Transition State Modeling for Catalysis, D. G. Truhlar and K. Morokuma, Eds., ACS Symposium Series 721, American Chemical Society Washington, D. C., 1999, pp. 151-172. 

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