Organometallics 1990, 9, 2155-2164
2155
Electron-Transfer Chemistry of the 20-Electron Complex [Feo(C6Me6),] and of the 19-Electron Complex [Fe'(C,Me,)(775-C,Me,H)]: Mild C-H Activation by 0 2 via Superoxide Ion and Functionalization of the Exocyclic Methylenes in the Resulting Complexes [F~'(c,M~,)(q4-po~yene)]+J Didier Astruc, * J Dominique Mandon,§ Alex Madonik,§ Pascal Michaud,§ Nicole Ardoin,t and Franqois Varretll Laboratoire de Chimie Organique et Organom6tallique, URA CNRS No. 35, Universit6 de Bordeaux I, 35 1, cows de la Libgration, 33405 Talence C&ex, France, Laboratoire de Chimie des Organom6talliques, URA CNRS No. 415, Universit6 de Rennes I , 35042 Rennes C&ex, France, and Groupe de Physique et Chimie du Solide, URA CNRS No. 807, Universit6 du Maine, 720 17 Le Mans C a e x , France Received December 29, 1989
Activation of methyl substituents by mild reactions with 0, has been achieved in paramagnetic bis(arene)iron complexes and followed by functionalization of the nucleophilic exocyclic methylene groups. The 20e complex [Fe0(C6Me&](2), best synthesized from [Fer1(C6Me6)z]2+(PF~)2 (1)and Na/Hg in THF at 20 "C, shows a Mossbauer doublet with isomer shift IS = 1.02 mm s-l vs Fe and quadrupole splitting QS = -1.35 mm s-l (293 K). It reacts at -40 "C with '1, mol of O2 in toluene to give the thermally unstable (4), characterized by NMR spectroscopy in C6D5CD3 o-xylylenecomplex [Feo(C6Mes)~?4-C,Me,(=CHz)2)] at -50 "C (6CH2: 'H,4.42 and 5.04 ppm; 13C, 144.8 ppm; vs TMS). Complex 4,in which the o-xylylene ligand is unusually coordinated by the double bonds of the ring, reacts with HPF, in THF to give only 1 and with PhCOCl in THF to give [Fen(C6Me,)(?6-C6Me5CH(COPh)2)]2+, isolated as its PF6salt 5,in which the enolic tautomer predominates. The reaction of 2 with 0 at 20 "C in toluene or at -40 "C in THF in the presence of 1 equiv of NaPF, gives the 19e complex [FeT(C6Me6)2]+(0,z-)lj2 (3a). The 19e complex [Fe1(C6Me6)(?5-C6Me6H)] (7), obtained by one-electron reduction of its monocationic 18e precursor 6 with 1 equiv of the 19e complex [Fe'Cp(c@$], reacts with '1, mol of Ozto give [Feo(C,Me,)l?4-C,Me5H(=CH2)}] (€9,a model reaction for the second H atom abstraction from 2 by 02.The 1% complex 6 reacts with t-BuOK to give 8 as well, consistent with the electron transfer O2 02'-followed by deprotonation in the reaction of 7 with 02.Complex 8 reacts with the electrophiles CH3C0 H, PhCOCl, Ph3C+PFs, I,, and [Ferr(C,H,)(a5-C,H,)]+PF,- (11)to give the respective complexes [Fe"(C6Me6)(~5-C6Me5HcHzx)]+PF6(x = H (6),COPh (9), CPh3 (lo),I (13),[Ferr(C6Hs)(?4-C6H7)] (12)). Complex 8 deprotonates 9 to give 6 and [Fe(C6Me6)l?4-C6Me5H(=CHCoPh)}] (14). The 1% complex [Fe*r(C6H3Me3)(?5-2,4,6-C6H4Me3)]+PF6(151, obtained by hydride reduction of [Fer*(C6H3Me3)]2+(PF6-)42, reacts similarly with t-BuOK in THF at -60 "C to give the thermally unstable complex [Feo(C6H3Me3)p-3,5-C6H4(=CH2)}] (16). The latter reacts with (17). PhCOCl to give 15 and the dibenzoylated complex [Fer (C6H3Me3)(C6H2Me2CH(COPh)21]+PFs
-
Introduction Electron-transfer pathways provide powerful means of activating aromatic hydrocarbons by metals.2 They also bring about the structural transformation of aromatic ligands in organometallic complexes.24 The reactions of molecular oxygen appeared useful to us for the activation of aromatics in electron reservoir complexes because exergonic electron transfer (ET) obtained in these reactions5 gives ion pairs in which the superoxide ion, O
