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Abstract
The sandwich compound, [CpFe(tol)]PF6 is photoreactive, cyclic voltammetry is used to monitor the reactivity of the CpFe compound. We determined [CpFe(tol)]+ undergoes a irreversible reduction, unless it is at cold temperature. When the sandwich compound is exposed to light it results in a reaction with the solvent forming [CpFe(CH3CN)3]+. Addition of phenanthroline to the[CpFe(CH3CN)3]+, results in [CpFe(phen)3]2+, because phenanthroline is a stronger ligand than CH3CN.
Introduction
Photochemistry is the result of absorption of visible or ultraviolet light by compound. The light will cause electrons to enter excited state resulting in a reaction. The light source for photochemistry can be anything from the sun, to a laser, to a light bulb. The typical reaction isreplacement of the ligands on a compound with the solvent1.
This experiment looks specifically at photochemistry of iron(II) sandwich compound ([CpFe(tol)]PF6). Cp is η5-C5H5 and tol is η6-toluene. The reactions of this compound can be monitored by cyclic voltammetry because iron-containing compounds are electrochemically active. This experiment looks at the effects of light, temperature and ligandpresence play in reaction of CpFe2.
Procedure
Chemicals
Chemicals were obtained from BSC chemistry stockroom, no chemicals were purified or dried.
Synthesis
[CpFe(tol)]PF6 was prepared by combining 2.506g of ferrocene, 0.502g of aluminum powder, and 4.504g of aluminum chloride, 50mL toluene, and 0.25mL of water. The mixture was stirred and refluxed for 2 hours under nitrogen, producing adark-brown solution. The mixture was cooled and stored. The mixture was poured into a 100mL of ice-water, it was stirred and chunks were broken with a glass stirring rod. The mixture was moved to a seperatory funnel, 0.5g of ascorbic acid was added. The ascorbic acid reduced any remaining ferricinium ion. 25mL of hexane was added to perform an extraction, the aqueous layer was removed, this waspreformed three times. 10mL of water containing 2g of NH4PF6 was added slowly to the aqueous layer producing a yellow precipitate. The mixture was stirred for 10 minutes. The product was purified by running through a 10cm column of F-20 alumina, protected from the light. The product volume was reduced to 5mL by using the rotovap. Diethyl ether was added to precipitate the product, the solution wasfiltered and stored.
Characterization
H+ NMR was performed on JOEL NMR 300MHz, in acetonitrile-d6. The spectra was analyzed using Delta software.
Electrochemical Analysis
Electrochemical analysis was performed on BASi CV-50W Voltammetric Analyzer. The samples dissolved in 0.1M TBAH(tetra-n-butylammonium hexafluorophosphate) in CH3CN and flushed with nitrogen. The reference electrode was Ag/AgCl,the counter electrode was a platinum wire, the working electrode was a glassy carbon electrode. The scans had sample intervals of 1mV, with sensitivity of 100uA/V. The Ag/AgCl electrode was calibrated using a 5mM ferocene in 0.1M TBAH in CH3CN. 5 scans were taken a various scan rates; 25mV/sec, 50mV/sec, 100mV/sec, 150mV/sec, 200mV/sec. These scans were also used to calculate the area of theelectrode.
For the analysis of the photochemical reactivity of [CpFe(tol)]PF6 was performed over 5 CV scans. 5mM [CpFe(tol)]PF6 in 0.1M TBAH in CH3CN was made by dissolving 0.08977g in ??mL. Half of the solution was placed under 500 watt lamp for 20 minutes. Meanwhile, a CV scan was taken, at 100mV/sec scan rate, of the other half of solution without light exposure. The solution was then placed inan acetone/dry ice bath, resulting in a drop of temperature, a second scan was taken. After, the 20 minutes of light exposure the light exposed solution was scanned, then returned to the light for an additional 20 minutes of light. Following the additional exposure a forth scan was taken. 42mg of phenanthroline was added to the approximately 30mL solution, the solution was stirred, and a fifth...