In the Laboratory JChemEd.chem.wisc.edu • Vol. 75 No. 6 June 1 9 9 8 • Jo urna l o f Chemic a l Educ a tio n 773 The Microscale Laboratory The Microscale Synthesis and Electrochemistry of Low - Valent Mononuclear Complexes ( 3 –C 3 H 5 )Fe(CO) 3 X ( X = I, Br, Cl ) Enrico Mocellin,* Richard Russell, and Mauro Ravera** AMC 2 – Australasian Microscale Chemistry Centre, School of Biological and Chemical Sciences De a kin Unive rsity, G e e lo ng , Vic to ria 3 2 1 7 , Austra lia We have previously outlined the value of unified micro- scale laboratory programs (1). Continuing with this theme, we now describe the microscale synthesis and electrochemical be- havior of the mononuclear complexes (η 3 –C 3 H 5 )Fe(CO) 3 X ( X = I, Br, Cl). T his experiment is especially well suited to students who have completed a basic lecture series on organo- metallic chemistry and associated electrochemical techniques and who have an understanding of linear sweep voltammetry at solid electrodes (2). The reaction of diiron nonacarbonyl with allyl halides (3) affords mixtures of the stereoisomer η 3 complexes 1 and 2 as shown in eq 1. Fe 2 (CO) 9 + CH 2 =CH–CH 2 X → (C 3 H 5 )Fe(CO) 3 X + Fe(CO) 5 +CO (1) CO Fe OC X CO CO Fe X CO CO 1 2 HC CH 2 CH 2 HC CH 2 CH 2 endo exo X = I, Br, Cl Experimental Procedure General Methods All materials were used as purchased without further puri- fication. Elaborate glassware-drying procedures are not required. For the electrochemistry a standard three- electrode cell is configured to allow the tip of the reference electrode (saturated standard calomel electrode [SSCE] or silver/silver chloride [Ag/AgCl]) to be proximate to the working electrode (hanging mercury drop electrode [HMDE] or mercury amalgam on gold electrode [Hg/Au]) and platinum solid electrode. T he cell is completed with an aux- iliary electrode (platinum wire) and a two- way gas bubbler. Experiments are performed in acetonitrile, dichloromethane, or tetrahydrofuran. All measurements are carried out under N 2 or Ar atmosphere in quiescent deoxygenated solvent solutions, which have been purified according to the standard literature procedures. Solutions (5 mL) are prepared 1 × 10 3 M with respect to the analyte and 1 × 10 1 M in [Bu 4 N][PF 6 ]. Preparation of (C 3 H 5 )Fe(CO ) 3 X (X = I, Br, Cl) Attach a nitrogen inlet to the side arm of a 25-mL two- necked round-bottom flask containing a magnetic stirring bar, and flush the apparatus for several minutes. Without discon- necting the inert gas tube, introduce into the flask Fe 2 (CO) 9 1 (250 mg, 0.68 mmol), 5 mL of hexane, and the relative quan- tity of halide (C 3 H 5 X: X = I 64 μL, 0.70 mmol; X = Br 60 μL, 0.70 mmol; X = Cl 61 μL, 0.75 mmol). Connect a water condenser to the flask and, using Tygon tubing, attach an oil bubbler, thus also providing an outlet for the gas purge. Place the flask in a sand bath on a magnetic-stirring hot-plate and heat. T he suspension is heated at 40 ° C for the indicated times depending on the allyl halide used (X = I or Br, 35 min, X = Cl, 40 min). CAUTION: allyl chloride boils 45 ° C. Maintain a very slow flow of nitrogen during the reaction to help remove the CO, but avoid stripping the solvent. Cool the solution to room temperature and filter through a short chromatog- raphy column (1 cm × 1 cm) of silica (80–230 mesh), to re- move FeX 2 . T he separation is accelerated by applying a slight vacuum to the filter flask at the bottom of the column. Wash the silica with small portions of hexane until the silica is white. T he solvent is removed from the relevant fraction un- der reduced pressure. 2 Recrystallize the target products from hexane. Yields: I (1:1) 67%, Br (7:1) 46%, Cl(25:1) 35%. *Corresponding author. * * O n leave from Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Università di To rino , via P. G iuria 7 , 1 0 1 2 5 To rino , Ita ly. x e l p m o C ) o x e : o d n e ( R M N a R I b H 1 ) d ( H 2 ) d ( H 3 ) m ( o d n e o x e o d n e o x e o d n e o x e I = X ) 1 : 1 ( 3 8 . 3 7 3 . 2 1 2 . 4 9 7 . 3 4 6 . 4 3 9 . 5 , s v 4 3 0 2 , s v 0 8 0 2 s v 9 0 0 2 , h s 4 1 0 2 r B = X ) 1 : 7 ( 0 5 . 3 9 5 . 2 3 4 . 4 2 1 . 4 8 9 . 4 1 5 . 5 , s v 5 4 0 2 , s v 0 9 0 2 s v 1 1 0 2 l C = X ) 1 : 5 2 ( 4 3 . 3 4 7 . 2 3 5 . 4 6 3 . 4 0 2 . 5 2 3 . 5 c , s v 1 5 0 2 , s v 6 9 0 2 s v 3 1 0 2 a C hemical shift (δ) ppm in CDCl 3 downfield from TMS observed at 270 MHz; d = d o ub le t, m = triplet o f triplets. b ν CO (cm 1 ) in hexane. c Partially obscured by the major isomer. Table 1. IR and 1 H NMR Spectral Data for Complexes under Study