Iron Catalyzed Hydroformylation of Alkenes under Mild Conditions: Evidence of an Fe(II) Catalyzed Process

Abstract

Earth abundant, first row transition metals offer a cheap and sustainable alternative to the rare and precious metals. However, utilization of first row metals in catalysis requires harsh reaction conditions, suffers from limited activity, and fails to tolerate functional groups. Reported here is a highly efficient iron catalyzed hydroformylation of alkenes under mild conditions. This protocol operates at 10-30 bar syngas pressure below 100 °C, utilizes readily available ligands, and applies to an array of olefins. Thus, the iron precursor [HFe(CO)][PhPNPPh] (1) in the presence of triphenyl phosphine catalyzes the hydroformylation of 1-hexene (S2), 1-octene (S1), 1-decene (S3), 1-dodecene (S4), 1-octadecene (S5), trimethoxy(vinyl)silane (S6), trimethyl(vinyl)silane (S7), cardanol (S8), 2,3-dihydrofuran (S9), allyl malonic acid (S10), styrene (S11), 4-methylstyrene (S12), 4- iBu-styrene (S13), 4- tBu-styrene (S14), 4-methoxy styrene (S15), 4-acetoxy styrene (S16), 4-bromo styrene (S17), 4-chloro styrene (S18), 4-vinylbenzonitrile (S19), 4-vinylbenzoic acid (S20), and allyl benzene (S21) to corresponding aldehydes in good to excellent yields. Both electron donating and electron withdrawing substituents could be tolerated and excellent conversions were obtained for S11-S20. Remarkably, the addition of 1 mol % acetic acid promotes the reaction to completion within 16-24 h. Detailed mechanistic investigations revealed in situ formation of an iron-dihydride complex [HFe(CO)(PPh)] (A) as an active catalytic species. This finding was further supported by cyclic voltammetry investigations and intermediacy of an Fe(0)-Fe(II) species was established. Combined experimental and computational investigations support the existence of an iron-dihydride as the catalyst resting state, which then follows a Fe(II) based catalytic cycle to produce aldehyde.

Multitasking FeOCN Composite as an Economic, Heterogeneous Catalyst for 1‐Octene Hydroformylation and Hydration Reactions

“…On the other hand it is also reported by Chikkali et al . that acidic nature of catalyst or catalyst support can increase the catalytic activity for hydroformylation . Therefore, it can be assumed that all the phases present in the composite collectively contribute to increasing the catalytic efficiency.…”

“…All the characterization data strongly indicate Scheme 2. A recent report of a carbonyl iron phosphine complex for hydroformylation, by Chikkali et al [19] Scheme 3. General scheme for Fe catalysed alkyne hydrations available in the literature.…”

“…[63,64] On the other hand it is also reported by Chikkali et al that acidic nature of catalyst or catalyst support can increase the catalytic activity for hydroformylation. [19] Therefore, it can be assumed that all the phases present in the composite collectively contribute to increasing the catalytic efficiency. It is worth noting that no catalytic activity was observed in our study when using the catalyst precusor (Fe(NO 3 ) 3 ) in the hydroformylation of 1-octene, conducted at 95°C/50 bar/6 h. This suggests that the impurities that may be present in the catalyst precursor do not in any way catalyse the hydroformylation reaction.…”

“…More recently, Chikkali et al reported the [HFe(CO) 4 (PPh 3 )] complex, which is active at 100°C and 10-30 bar pressure for various alkyl and aryl alkenes with a L : B regioselectivity of up to 76 : 24 (Scheme 2). [19] Apart from behaving as the active catalysts, iron complexes have also been used to promote the catalytic efficiency of various catalysts. Damiano et al reported a polymer supported H 3 Fe(CO) 11 and H 3 Os(CO) 11 mixture for hydroformylation of 1-Hexene.…”

“…More recently, Chikkali et al . reported the [HFe(CO) 4 (PPh 3 )] complex, which is active at 100 °C and 10–30 bar pressure for various alkyl and aryl alkenes with a L : B regioselectivity of up to 76 : 24 (Scheme ) …”