100681-72-9Relevant academic research and scientific papers
Nucleophilic attack on the cyclohexadienyl ligand: From mono- to heterobifunctional (cyclohexadiene)iron complexes and the role of the electron-transfer pathway in hydride abstraction
Mandon, Dominique,Astruc, Didier
, p. 2372 - 2377 (2008/10/08)
With the aim of synthesizing heterobifunctional cis-1,2-cyclohexadienes from benzene, we have investigated hydride abstraction from exo-substituted complexes [Fe(C6H6)(η4-C6H7R)] (3) and the second addition of a functional nucleophile to the functional complexes [Fe(C6H6)(η5-C6H 6R)]+ (2). Although hydride abstraction by [Ph3C]+ from [Fe(η5-C6H6R)(CO)3] (R ≠ H) was known to be sterically inhibited, we first attempted to remove a hydride from the known complexes 3 (R = CH2Ph (3b), CHS(CH2)3S (3c), CH-(CO2Et)2 (3d), CN (3e)) according to an electron-transfer (ET) pathway. The ET between 3b and [Ph3C]+ is exergonic (ΔG° = -5.5 kcal/mol-1) and proceeds at -50°C, giving Ph3C° and the 17e FeI complexes 3b+, both characterized by ESR spectroscopy. The species 3+ are stable at -50°C for R = CH2Ph or CHS(CH2)3S, and slow H atom transfer to Ph3C° occurs between -50 and -40°C to give the desired cations [Fe-(C6H6)(η5-C6H 6R)]+ (2) in high yields. However, the 17e FeI complex is not stable at -50°C with R = CH(CO2Et)2 and decomposes to R° and [Fe(C6H6)(η5-C6H 7)]+ (2a) in 70% yield. Above -40°C, 3b+ and 3c+ also decompose to R° and 2a faster than H atom transfer occurs. Addition of KCN to 2b and 2c in acetone at 20°C gives the heterobifunctional (cis-1,2-cyclohexadiene)iron(0) complexes 4b and 4c. The X-ray crystal structure of 4b has been reported and its decomplexation using FeCl3 gives cis-1,2-PhCH2CNC6H4 (5) free of any rearomatized product (the latter is easily formed thermally).
