Metal carbonyl anion generation using potassium fluoride or tetrabutylammonium fluoride

Mechanistic Study of the Phase-Transfer-Catalyzed Reduction of Nitrobenzene to Aniline by Iron Carbonyl Complexes. Role of the Radical Anion [Fe3(CO)11]•-

“…On the other hand, a parallel reaction run employing 1 and a 1:1 molar amount of [Et 4 N] [Cl], in place of [Et 4 N]2, gave an approximately 80% conversion in 3 h, with the rest of the nitrobenzene then being more slowly converted upon stirring overnight. The reason for the remarkable slowing down of the reaction after some time is to be ascribed to the fact that, after 3 h, no more 1 was present in solution or as a solid and the only observable organometallic species in the organic phase was Fe(CO) 5 (3), formed by decomposition of 1 (vide infra). Fe(CO) 5 has also been reported to promote the reduction of nitroarenes to anilines under biphasic conditions, but at least under our conditions, this process was slower than the reaction of 1.…”

“…The reason for the remarkable slowing down of the reaction after some time is to be ascribed to the fact that, after 3 h, no more 1 was present in solution or as a solid and the only observable organometallic species in the organic phase was Fe(CO) 5 (3), formed by decomposition of 1 (vide infra). Fe(CO) 5 has also been reported to promote the reduction of nitroarenes to anilines under biphasic conditions, but at least under our conditions, this process was slower than the reaction of 1. 21 These results clearly show that, contrary to what is commonly accepted, 2 plays no role in the phase-transfer-catalyzed reduction of nitroarenes by 1.…”

“…4,7 Although we cannot exclude that this explanation plays a role, 32 we recall that CO induces an immediate disproportionation of 7 to 4 and 5. 19 Since, in the presence of excess 1, 5 transfers an electron to Fe 3 (CO) 12 to generate 2 equiv of 7 (eq 3) that can further disproportionate, the generation of a small amount of 7 in the presence of 1 and under a CO atmosphere initiates an autocatalytic conversion of Fe 3 (CO) 12 to Fe(CO) 5 . This process has already been observed in the case of the reaction between 1 and chloride under a CO atmosphere.…”

“…(3), [12][13][14][15] or Fe(CO) 5 (4). 2,14,16,17 Whenever 1 is used as the iron compound, it needs to be activated by a base, which may be hydroxide ion under biphasic [2][3][4]7 or even triphasic 8 conditions, fluoride ion in the presence of water, 5 or basic alumina 6 (otherwise very high temperatures or hydrogen pressure are required 16 ).…”

“…2,14,16,17 Whenever 1 is used as the iron compound, it needs to be activated by a base, which may be hydroxide ion under biphasic [2][3][4]7 or even triphasic 8 conditions, fluoride ion in the presence of water, 5 or basic alumina 6 (otherwise very high temperatures or hydrogen pressure are required 16 ). In all of these cases, 2 was proposed to be formed by interaction of the base with 1, eventually via [Fe 3 (CO) 11 ] 2- (5), and to be the species responsible for the reduction of the nitro compound. Several aspects of the reaction mechanism, including the finding that the hydrido-imido cluster [HFe 3 (µ 3 -NPh)(CO) 9 ] -(6) 18 plays no role in the reaction, have been already analyzed by us in a work in collaboration with Geoffroy and his group.…”