ORGANOMETALLIC ELECTRON-RESERVOIRS .37. ELECTRON-TRANSFER CHEMISTRY OF THE 20-ELECTRON COMPLEX [FE(0)(C6ME6)2] AND OF THE 19-ELECTRON COMPLEX [FE(I)(C6ME6)(ETA-5-C6ME6H)] - MILD C-H ACTIVATION BY O2 VIA SUPEROXIDE ION AND FUNCTIONALIZATION OF THE EXOCYCLIC METHYLENES IN THE RESULTING COMPLEXES [FE(0)(C6ME6)(ETA-4-POLYENE)]

Activation of methyl substituents by mild reactions with O2 has been achieved in paramagnetic bis-(arene)iron complexes and followed by functionalization of the nucleophilic exocyclic methylene groups. The 20e complex [Fe0(C6Me6)2] (2), best synthesized from [FeII(C6Me6)2]2+(PF6-)2 (1) and Na/Hg in THF at 20 °C, shows a Mössbauer doublet with isomer shift IS = 1.02 mm s-1 vs Fe and quadrupole splitting QS = -1.35 mm s-1 (293 K). It reacts at -40 °C with1/2 mol of O2 in toluene to give the thermally unstable o-xylylene complex [Fe0(C6Me6){η4-C6Me4(═CH2)2}] (4), characterized by NMR spectroscopy in C6D5CD3 at -50 °C (δCH2:1H, 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 HPF6 in THF to give only 1 and with PhCOCl in THF to give [FeII(C6Me6){η6-C6Me5CH(COPh)2}]2+, isolated as its PF6 salt 5, in which the enolic tautomer predominates. The reaction of 2 with O2 at 20 °C in toluene or at -40 °C in THF in the presence of 1 equiv of NaPF6 gives the 19e complex [FeI(C6Me6)2]+(O22-)1/2 (3a). The 19e complex [FeI(C6Me6)(η5-C6Me6H)] (7), obtained by one-electron reduction of its monocationic 18e precursor 6 with 1 equiv of the 19e complex [FeICp(C6Me6)], reacts with1/2 mol of O2 to give [Fe0(C6Me6){η4-C6Me5H(═CH2))] (8), a model reaction for the second H atom abstraction from 2 by O2. The 18e complex 6 reacts with t-BuOK to give 8 as well, consistent with the electron transfer O2 → O2- followed by deprotonation in the reaction of 7 with O2. Complex 8 reacts with the electrophiles CH3CO2H, PhCOCl, Ph3C+PF6-, I2, and [FeII-(C6H6)(η5-C6H7)]+PF6- (11) to give the respective complexes [FeII(C6Me6)(η5-C6Me5HCH2X)]+PF6- (X = H (6), COPh (9), CPh3 (10), I (13), [FeII(C6H6)(η4-C6H7)] (12)). Complex 8 deprotonates 9 to give 6 and [Fe(C6Me6){η4-C6Me5H(═CHCOPh)}] (14). The 18e complex [FeII(C6H3Me3)(η5-2,4,6-C6H4Me3)]+PF6- (15), obtained by hydride reduction of [FeII(C6H3Me3)]2+(PF6-)2, reacts similarly with t-BuOK in THF at -60 °C to give the thermally unstable complex [Fe0(C6H3Me3){η4-3,5-C6H4(═CH2)}] (16). The latter reacts with PhCOCl to give 15 and the dibenzoylated complex [FeIIC6H3Me3){C6H2Me2CH(COPh)2}]+PF6- (17). © 1990, American Chemical Society. All rights reserved.