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

Abstract

The Cp-containing carbene complexes [ Fe(C 5 H 5 )(CO){κ 2(C,O)&0xF700; C(OMe)C 6 H 4-o -O Me}][OTf] ( 2) and [Fe(C 5H 5)(CO)(CH 3CN){C(OMe)C 6H 4- 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 PPh 3 allows the isolation of the chelate complex [ Fe(C 5 H 5 )(PPh 3){ κ 2(C,Cl)&0xF700; C(OMe)C 6 H 4-o -C l}][OTf] ( 4). The reaction of [ Fe(C 5 Me 5 )(CO){κ 2(C,Cl)&0xF700; C(OMe)C 6 H 4-o -C l}][OTf] ( 5) with alkoxides RONa (R=Me, Et) affords the chelate complexes [ Fe(C 5 Me 5 )(CO){κ 2(C,O)&0xF700; C 6 H 4-o -C(OMe)(O R)(OR)}] 7 (R=Me) and 8 (R=Et), respectively. Similarly, the reaction of 3 with EtONa affords [ Fe(C 5H 5)(CO){κ 2( C, O)−C 6H 4-o-C(O 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(C 5Me 5)(CO) 2{C(OMe)C 6H 4- o-Cl}][OTf]. In contrast, treatment of the anisyl derivative [ Fe(C 5 Me 5 )(CO){κ 2(C,O)&0xF700; C(OMe)C 6 H 4-o -O Me}][OTf] ( 6) with EtONa gives selectively the carbene complex [Fe(C 5Me 5)(CO)(C 6H 4- 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 [MeOC 6H 4- o-(CO)OEt]. Clean formation of the methyl ester derivative [MeOC 6H 4- o-(CO)OMe] is observed upon oxidation of 2 with C 6H 5I +O −.