R Carbon Synthesis and Reactions of Ferrocene R Carbon Carbon Contents Objectives 1 Introduction 1 Preparation of ferrocene 2 Acetylation of ferrocene 7 Preparation of [Fe(η-C5H5)(η-C6H6)]PF6 10 Reaction of [Fe(η-C5H5)(η-C6H6)] PF6 with nucleophiles 12 Manuscript prepared by Dr. Almas I. Zayya, Dr. A. Jonathan Singh and Prof. John L. Spencer. School of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand. R Carbon Objectives Introduction The principal aims of these experiments are to The archetypal organometallic compound provide experience in the synthesis, isolation, ferrocene, [Fe(η-C5H5)2], is of historical importance purification and characterisation of organometallic since its discovery and structural characterisation compounds. Purification techniques include in the early 1950s sparked extensive research into distillation, sublimation, chromatography and the chemistry of metal sandwich compounds.1 crystallisation. The main characterisation Two of the chemists who first proposed the correct technique used in these experiments is 1H NMR structure of ferrocene (Figure 1), Geoffrey Wilkinson spectroscopy using the benchtop Spinsolve and Ernst Otto Fischer, were awarded the Nobel spectrometer. Furthermore, students will Prize in Chemistry in 1973 for their pioneering work also develop their synthetic skills using inert on the chemistry of sandwich complexes. atmosphere techniques. Ferrocene is an example of a π-complex in which interactions between the d-orbitals of the Fe2+ metal centre with the π-orbitals of the two planar - cyclopentadienyl ligands (C5H5 ) form the metal-ligand bonds. Thus, all the carbon atoms in the cyclopentadienyl rings are bonded equally to the central Fe2+ ion. Ferrocene exhibits aromatic properties and is thermally very stable. It is also resistant to acidic and basic reagents. In this series of experiments, you will synthesise ferrocene and then perform several reactions with it. The various products prepared will be characterised by 1H NMR spectroscopy. Figure 1. Ferrocene [Fe(η-C5H5)2] R Carbon 1 Preparation of ferrocene There are two parts to this experiment: first, b) Ferrocene synthesis3 prepare freshly distilled cyclopentadiene (C5H6), and second, use it immediately to synthesise Charge a 250 mL 3-neck round bottom flask ferrocene. Both parts should be done in the equipped with a dropping funnel, magnetic stirrer fumehood. and nitrogen inlet, with DME (50 mL) and 4.25 mL of freshly distilled cyclopentadiene (Figure 2). Safety Stir the solution and flush with nitrogen.4,5 Take There are two parts to anthis aliquot experiment: (1 mL) for 1H NMR.first ,Add pre finelypare ground freshly distilled Dicyclopentadiene, cyclopentadiene and KOH (20 g) and stir the mixture vigorously for 15 1,2-dimethoxyethanecyclopentadiene (DME) are toxic. Avoid(C5H 6), and second, use it immediately to synthesise ferrocene. min to form a coloured mixture, which includes breathing vapour andBoth contact parts with should skin. Dimethylbe done in the fumehood. the cyclopentadienyl anion. Take an aliquot (1 mL) sulfoxide (DMSO) is dangerous because it for 1H NMR. Prepare a solution of finely powdered increases the permeability of the skin to other Safety FeCl2.4H2O (5 g) in 20 mL of DMSO under nitrogen substances. Avoid all contact with skin and and transfer the solution into the dropping funnel. clothing. HCl and KOH are very corrosive, handle Add the iron(II) chloride solution slowly over a with extreme caution.Dicy Iron(II)clopentadiene chloride tetrahydrate, cyclopentadiene and 1,2-dimethoxyethane (DME) are toxic. period of 30 min with efficient stirring. Take an (FeCl2.4H2O) and ferroceneAvoid breathingcan be harmful, vapour handle and contact with skin. Dimethyl sulfoxide (DMSO) is aliquot (1 mL) for 1H NMR after 2/3 of the FeCl2/ with care. Deuterochloroform (CDCl ) is toxic, dangerous because3 it increasesDMSO the solution permeability has been added,of the then skin another to other substances. handle with caution and do not ingest or inhale. Avoid all contact with skin andaliquot clothing. (1 mL) at HCl the end and of KOHaddition. are Continue very corrosive, handle a) Cracking of dicyclopentadienewith extreme caution. Iron(II)stirring chloride the reaction tetrahydra mixturete for(FeCl a further2.4H 215O) min and ferrocene can be harmful, handle with care.then Dpoureuterochloroform the dark slurry into (CDCla beaker3) containingis toxic, handle with Monomeric cyclopentadiene (C5H6) dimerises caution and do not ingest or inhalecrushed. ice (80 g) and hydrochloric acid (75 mL, rapidly at room temperature to dicyclopentadiene 6 M). Stir the mixture thoroughly to dissolve and by a Diels-Alder reaction. Thus, commercial neutralise any remaining KOH. Filter the precipitate dicyclopentadiene a)is thermallyCracking decomposed of dicyclopentadiene and wash with water. Collect the crude orange (cracking process) to obtain cyclopentadiene by ferrocene and dry in the air. Purify by sublimation fractional distillation (Scheme 1).2 The apparatus Monomeric cyclopentadiene to(C obtain5H6) orangedimerises crystalline rapidly material at and room record temperature to is set up using a Vigreuxdicyclopentadiene column and a 100 by a Diels-Alderyour yield reaction. (see Figure Thus, 3).2 commercial dicyclopentadiene is mL round bottom flask charged with 30 mL of dicyclopentadiene.thermally+ Monomeric decomposed cyclopentadiene (cracking process) to obtain cyclopentadiene by fractional 2 is collected in the 40-42distillation °C range. andThe is appkept aratuscool is set up using a Vigreux column and a 100 mL round using an ice bath untilbottom required. flaskTake an aliquotcharged (1 mL) with 30 mL of dicyclopentadiene.† Monomeric for 1H NMR. You willcyclopentadiene need 4.25 mL for partis collected b. in the 40-42 °C range and is kept cool using an ice bath 1 + In a laboratory session, it mightuntil be convenient required. to set up one Take fractional distillationan aliquot (1 mL) for H NMR. You will need 4.25 mL for part apparatus to carry out the crackingb. process of dicyclopentadiene. Scheme 1. Cracking of dicyclopentadiene b) Ferrocene synthesis3 Charge a 250 mL 3-neck round bottom flask equipped with a dropping funnel, R Carbonmagnetic stirrer and nitrogen2 inlet, with DME (50 mL) and 4.25 mL of freshly distilled cyclopentadiene. Stir the solution and flush with nitrogen.4,5 Take an aliquot (1 mL) for 1H NMR. Add finely ground KOH (20 g) and stir the mixture vigorously for 15 min to form a coloured mixture, which includes the cyclopentadienyl anion. Take an aliquot (1 mL) for 1H NMR. Prepare a solution of finely powdered FeCl2.4H2O (5 g) in 20 mL of DMSO under nitrogen and transfer the solution into the dropping funnel. Add the iron(II) chloride solution slowly over a period of 30 min with efficient stirring. Take an aliquot (1 mL) for 1H NMR after 2/3 † In a laboratory session, it might be convenient to set up one fractional distillation apparatus to carry out the cracking process of dicyclopentadiene. 2 of the FeCl2/DMSO solution has been added, then another aliquot (1 mL) at the end of the FeCl2/DMSO solution has been added, then another aliquot (1 mL) at the end of addition.of addition. Continue Continue stirring stirring the the reaction reaction mixture mixture for a further for 15 a min furt thenher pour 15 the min then pour the dark slurrydark slurry into into a beaker a beaker containing crushed crushed ice (80 gice) and (80 hydrochloric g) and hydrochloricacid (75 mL, acid (75 mL, 6 M). Stir the mixture thoroughly to dissolve and neutralise any remaining KOH. 6 M). StirFilter the precipitate mixture and thoroughly wash with water. to dissolve Collect the andcrude neutraliseorange ferrocene any and remaining KOH. Filter thedry precipitatein the air. Purify and by sublimation wash with to obtain water. orange Collect crystalline the material crude and orangerecord ferrocene and dry in theyour air. yield. Purify2 by sublimation to obtain orange crystalline material and record your yield.2 Scheme 2. Formation of ferrocene. 3 Figure 2. Experimental setup for ferrocene synthesis. R Carbon 3 3 Crude ferrocene Sublimation apparatus Sublimation Crude ferrocene of ferrocene Sublimed Sublimation ferrocene apparatus (a) Crude ferrocene (b) Sublimed ferrocene Tasks:Figure 3(a)-(b). Purification of crude ferrocene via sublimation. - Determine the theoretical and percentage yields of ferrocene. Tasks 1 - Record• Determine the H theNMR theoretical spectra and ofpercentage all aliquots yields taken• Record during the 1 theH NMR synthetic spectrum procedureof purified using theof ferrocene. Spinsolve NMR spectrometer. ferrocene using the Spinsolve NMR spectrometer. Prepare the NMR sample using 50 mg of • Record the 1H NMR spectra of all aliquots taken ferrocene in 1 mL of CDCl3. - Record during the the1H synthetic NMR spectrumprocedure using of purifiedthe ferrocene using the Spinsolve NMR Spinsolve NMR spectrometer. • Record an IR spectrum of ferrocene. spectrometer. Prepare the NMR sample using 50 mg of ferrocene in 1 mL of CDCl3. - Record an IR spectrum of ferrocene. Questions Sublimation• Why is it crucial of to ferrocene use freshly distilled • AssignSublimed the IR andferrocene NMR spectra of ferrocene. cyclopentadiene for the synthesis of • Explain how the spectra support the sandwich ferrocene? structure of ferrocene. Tasks: • If all the reagent are stable to air before the • Generally, aromatic protons resonate between reaction begins and the product ferrocene is also 6.5-8.5 ppm in the 1H NMR spectrum. Explain stable to air, why must the experiment be done - - Determine the theoretical and percentage whyyield thes C of5H 5ferrocene. protons in ferrocene resonate under a nitrogen (inert) atmosphere? 4 upfield at 4.16 ppm. - Record• What makes the ferrocene1H NMR sublime spectra easily? of all aliquots taken during the synthetic procedure using the Spinsolve NMR spectrometer. - Record the 1H NMR spectrum of purified ferrocene using the Spinsolve NMR spectrometer. Prepare the NMR sample using 50 mg of ferrocene in 1 mL of CDCl3. - Record anR IR spectrum of ferrocene. Carbon 4 4 1H NMR Spectra Figure 4.