110118-62-2Relevant articles and documents
Arene exchange by P donors in the 19-electron complexes FeICp(arene): Kinetics, mechanism, and salt effects. Interconversion, radical-type reactions, and electron-transfer chemistry of the new 17-electron and 19-electron radicals FeICpLn (L = phosphine, phosphite; n = 2, 3)
Ruiz, Jaime,Lacoste, Marc,Astruc, Didier
, p. 5471 - 5483 (2007/10/02)
The 19e complexes FeICp(C6H6-nMen), 1 (0 ≤ n ≤ 6), react with P donors (PMe3, PPh3, PPh2H, PPh2D, dppm, dppe, P(OMe)3, P(OPh)3) to give products resulting from arene exchange and radical reactions of the 17e radicals FeCpL2, 2 (H or Cl abstraction, Arbuzov-type reaction, P-O cleavage, and coupling with Hg). These reactions are potentially side reactions in the electrocatalytic exchange starting from the 18e complexes 1+, but reduction of 1+ by the 19e species FeICpL3, 3, proceeds faster except for L = P(OPh)3. Complex 1 was used as an electrocatalyst (1%) for the quantitative synthesis of [FeCp(PMe3)3]+, 3a+, [FeCp{P(OMe)3}3]+, 3b+, [FeCp(dppe)(NCMe)]+, 13+, and [FeCp(dppm)(NCMe)]+, 10, in a THF suspension at 20°C. The 19e complex 3a (L = PMe3) is also formed in stoichiometric reactions of 1 with PMe3 in the presence of reducible substrates (CO2, perylene, p-dicyanobenzene, and methyl p-cyanobenzoate) as well as in disproportionation reactions of 1 induced by sodium salts. Double ion exchange in the latter reactions gives reactive ion pairs containing the organoiron anion and the Na+ counter cation. This disproportionation can also be catalyzed by NaPF6. The kinetics of the ligand exchange of 1 with P donor is shown to follow a second-order process according to the following rate law: -d[FeCp(toluene)]/dt = k[FeCp(toluene)] [P donor]. The reaction rate depends on the nature of the P donor and on the arene. The associative mechanism is confirmed by the large, negative entropy of activation (ΔS? = -22 ± 3 cal mol-1 K-1 for P(OMe)3). A fast preequilibrium, FeCp(η6-arene) ? FeCp(η4-arene), is proposed, which avoids a high-energy 21e intermediate or transition state. In the course of the reaction of 1 with L = PPh3, the 17e species FeICpL2 was characterized by its ESR spectrum at 10 K showing three g values around 2 and a characteristic triplet indicating the coupling with two P ligands. Another entry into the 19e species 3a is the one-electron reduction of the cathodic precursor. For example, Na/Hg reduction of [FeCp(PMe3)3]+PF6-, 3a+, gives Hg[FeCp(PMe3)2]2, p while its reduction on sodium mirror gives [FeCp(PMe3)2H], 4a, as the reactions of 1 with PMe3. This confirms the fast equilibrium FeICpL2 + L ? FeICpL3 (L = PMe3).
