Halophilic reactions of pentafluorohalobenzenes with transition-metal carbonyl anions

Metal carbonyl anions as model metal-centered nucleophiles in aromatic and vinylic substitution reactions

“…23 As it is already evident only the heavy halogen (Cl, Br, I), but not fluorine is substituted by carbonylates. This is noteworthy, since common "electronegative" nucleophiles, 30 and even "soft" carbanions 22,23 , substitute fluorine in such substrates as 1-Br, 1-Cl or 2, as is only to be expected for Ad N E mechanism (shown on Scheme 3 for an alkenyl halide).…”

“…Dehalogenation of bromo-and iodopentafluorobenzenes with soft enolate 24 or sulphur 25 nucleophiles is believed to proceed via halophilic mechanism. Metal carbonylates react via HME pathway with all the three halopentafluorobenzenes (Hal =Cl, Br, I) 22 . The same is true of bromo and certain chloropolyfluoroalkenes:…”

“…Bromides showed higher reactivity than the corresponding chlorides, however only lower limits of the intermolecular element effect k Br /k Cl could be evaluated (>100 for the 1-I/1-Cl pair with [Mn(CO) 5 ]K, 22 and >20 for 3-Br/3-Cl pair with [Re(CO) 5 ]Na 23 ). All the reactions with bromides take place instantaneously upon the reactant mixing.…”

“…Experiments with polyfluorinated aryl and vinyl halides have been described previously. [21][22][23]26 [CpFe(CO) 2 ]K was obtained quantitatively (95-98%) by reductive cleavage of the dimer [CpFe(CO) 2 ] 2 with excess of NaK 2.8 alloy (0.10-0.15 ml per 1 mmol of dimer). 33 [Re(CO) 5 ]Na was prepared by the reduction of Re 2 (CO) 10 with 0.5% NaHg (30-50% excess) and purified by the low temperature crystallisation from THF.…”

“…Our own studies have revealed that metal carbonyl anions are another large group of nucleophiles which can react via HME pathway with polyfluorinated aryl 21,22 and alkenyl 23 halides. Here we will give a brief account of these studies including new data on the reactions of metal carbonyl anions (carbonylates) with non-fluorinated aryl and vinyl halides.…”