Combined ¹ H NMR and DFT study of the solvent effects on the iron pentacarbonyl-catalyzed photo-assisted isomerization of allyl alcohol

Abstract

The relative rates of iron pentacarbonyl‐catalyzed photo‐induced isomerization of allyl alcohol to propanal in various solvents have been measured using 1H NMR spectroscopy. The reactions were run in linear and cyclic alkanes, alcohols, and amines in order to investigate solvent effects on the isomerization mechanism upon ultraviolet irradiation. The isomerization was efficient in nonane, hexane, cyclohexane, and benzene. The isomerization was very slow or completely suppressed in ethanol, propanol, isopropanol, triethylamine, and pyridine. Density functional theory calculations predicted thermodynamically favorable (ΔGo < 0) formation of Fe(CO)4–solvent compounds in the suppressing alcohol/amine solvents and unfavorable (ΔGo > 0) formation in the hydrocarbon solvents. The strong solvent ligation likely prevents formation of Fe(CO)3●(η2‐alkene) necessary for isomerization. Copyright © 2013 John Wiley & Sons, Ltd.

Solvent Effects in the Homogeneous Catalytic Reduction of Propionaldehyde with Aluminium Isopropoxide Catalyst: New Insights from PFG NMR and NMR Relaxation Studies

“…This first observation suggests that solvents with a high hydrogen‐bond accepting ability are inhibiting catalyst activity, possibly by a coordination with the metal centre of the aluminium catalyst, hence blocking the access of the aldehyde reactant to the active metal centre. This explanation has been reported in other homogeneous catalytic processes using similar type of catalysts . Solvation effects could also occur by producing solvation shells of solvent molecules around the reactant species, hence preventing the reactant from accessing such active sites .…”

“…Using such parameters it has been possible to elucidate solvent effects in a variety of homogeneously catalysed reactions. For example, Chase et al . studied the isomerization of allyl alcohol to propionaldehyde using an iron pentacarbonyl catalyst.…”

“…It is worth noting that solvents may also affect reaction rate of homogeneously catalysed reactions by transition state stabilization . Such transition states are difficult to detect but their existence is often supported by density functional theory (DFT) calculations …”

FTIR investigation of the equilibrium structure of osmium pentacarbonyl in alcohol solvents

“…Instead, the polar hydroxyl group induces an electron density shift in IPC. Hydrocarbon solvents such as cyclohexane and other alkanes do not induce any deformation [21,22]. This specific solvent interaction may facilitate unique solvent-dependent reaction dynamics [21,40].…”

“…In solution, however, typically just one or two carbonyls are lost under comparable photoexcitation conditions [16][17][18][19][20]. It has been shown that in arene, alcohol and amine solvent media, 60-90% of iron pentacarbonyl (IPC) molecules may undergo structural and electronic deformations and weakly hexacoordinate with a single solvent molecule, forming an Fe(CO) 5 -solvent complex [21][22][23][24]. Similar studies have shown that Ru(CO) 5 interacts with a single solvent molecule via a nearly identical mechanism, albeit more strongly and to a greater extent than IPC [25,26].…”