Versatile behaviour of iron–arylcarbene complexes towards alkoxides: CCl and CC bond activation reactions

The Cp-containing carbene complexes (2) and [Fe(C5H5)(CO)(CH3CN){C(OMe)C6H4-o-Cl}[OTf] (3) have been synthesised and characterised. Complex 2 has been characterised by a single-crystal X-ray diffraction analysis; the Fe–O distance of 2.045(5) Å suggests a rather strong bonding of the methoxy group. Substitution of one carbonyl ligand by PPh3 allows the isolation of the chelate complex (4). The reaction of (5) with alkoxides RONa (R=Me, Et) affords the chelate complexes 7 (R=Me) and 8 (R=Et), respectively. Similarly, the reaction of 3 with EtONa affords [Et)(OEt)2}] (9), for which the ArCl bond has been cleaved. No activation of the ArCl bond is observed for the unchelated complex [Fe(C5Me5)(CO)2{C(OMe)C6H4-o-Cl}][OTf]. In contrast, treatment of the anisyl derivative (6) with EtONa gives selectively the carbene complex [Fe(C5Me5)(CO)(C6H4-o-OMe){C(OEt)2}] (12). The ArOMe bond remains intact, but cleavage of the CαCAr bond occurs. This rearrangement process, i.e. α-elimination of the anisyl substituent, is favoured by the lability of the ortho-OMe group. Treatment of 2 with NaOEt gives as the only identified compound the ethyl ester [MeOC6H4-o-(CO)OEt]. Clean formation of the methyl ester derivative [MeOC6H4-o-(CO)OMe] is observed upon oxidation of 2 with C6H5I+O−.