the microtcole loborotory
edited by ARDEN P. ZlPP SUNY-Canland Cortland. NY 13045
Microscale Synthesis of transChlorocarbonylbis(triphenylphosphine)rhodium(l) and Its Reactions-A Versatile Metal Carbonyl Complex An Intermediate- or Advanced-Level Inorganic Chemistry Experiment Mom, M. Singh, Zvi Szafran, and Ronald M. Pike Merrimack College. North Andover, MA 01845 Metal carhonyls are most often prepared by the direct reaction of the metal with carbon monoxide. This reaction is fairly dangerous, as carbon monoxide is a highly toxic gas. In this experiment, an alternate route to the synthesis of earhonyl compounds is presented. employing the safer N , N - d i m e t h y l f o r m a m i d e ((CH?),ZI ICH4,NICOIH. DMFl a* the source of the . .,. . . . carbonyl g r o u p . ~ h ec£s are characterized using infrared spectroscopy.
Experlmental Section Safety Note: Rhodium(II1) chloride hydrate and all rhodium products are toxic heavy metal compounds. They may be fatal if swallowed. ORL-RAT LD50: 1302 mgkg. Contact with the skin should be avoided. DMF and triphenylphosphine (PPhd are harmful if swallowed, inhaled, or absorbed through the skin. The vapor is irritating to the eves. skin. and mucous membranes: ORL-RAT ~ ~ 5 2800 0 : m g k g (DMF), 700 mgkg (PPhd.
which is highly toxic. By the end of the addition, shiny yellow crystals of product usually precipitate from the solution. To complete the precipitation, add a few drops of absolute ethanol, and cool the solution in an i c e salt bath for 20 min. Collect the product by vacuum filtration using a Hirsch funnel. Wash the crystals with one 0.5-mL portion of absolute ethanol, followed by two 0.5-mL portions of ether. Dry the crystals on a clay tile or on filter paper. Obtain the IR spectrum of the compound either as a Nujol mull or as a KBr pellet (vco = 1965 cm-'). Determine the melting point of the compound (d. 170 'C).
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Synthesis of trans-ChimcarbonylbIJ(triphenyC phosPhbe)rhodlvm(n(1)
Place a solution of 25 mg (0.12 mmol based on RhCM of hydrated rhadium(II1) chloride in 1-1.5 mL of DMF in a 10-mL round-hottom flask equipped with a water candenaer and a magnetic stir bar. With stirring, heat the red solution to reflux until the color changes to lemon yellow (approximately 20 m i d . After cooling,filter the solution using a Pasteur filter pipet ( I ) . Collect the filtrate in a 10-mL beaker. Transfer the beaker to a hood. With stirring, add about 100 mg of triphenylphosphine in small portions, waiting until no futher evolution of gas is evident between additions. Caution: The gas being released is carbon monoxide,
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solution will immediately turn red-brown in color. (The ehlorine-CC4 solution can he easily prepared by bubbling chlorine gas [hood] through CCL for 30 s. The chlorine may be delivered from a cylinder or generated directly from the reaction of solid potassium pemanganate and concentrated HCI). Allow the mixture to stand for 10 min, whereupon precipitation of the product should begin. Attach the conical vial to a rotary evaporator, and strip off all solvent. (Alternatively, in the hood, gently heat the solution under a stream of nitrogen until all solvent has evaporated.) The CC1, chloroform mixture stripped off should be collected for proper disposal. Add 1mL of absolute ethanol to the product residue. and triturate the mixture witha rnicrnsoatula. Collect the vellow micracrvstals by \,acuum filtrntion using a Hirseh fun. "el. Wash the pwduct with m e 0.5-mL portion each of ethanol and ether. Dry the solid on a clay plate or on a filter paper. Obtain the IR spectrum of the compound (vco = 2110 em-') as a KBr pellet or a Nujol mull. Note the intensity of the CO band. Qualitatively, compare the spectrum with that of the starting material, (1).
Addition of chlorine to compound (1) as prepared above results in s six-coordinate rhodium(II1) species (2). Safety Note: Chloroform is an anaesthetic agent and is classified as a carcinogen. Avoid breathing t h e fumes. ORL-RAT LD50: 908 mgkg. IHL-HMN LCLo: 25,000 ~~m/5M Carbon . tetrachloride isalso classified as a carcinogen. Avoid contact with the skin. Avoid breathing the fumes. ORL-RAT LD50: 2350 meke. INL-HMN LCLo: 5 ppm/SM ~ h e s e s o h ma h d d be used in the hood. Chlorme gas isextremely desrrurtlve to the respratmy tract. Useonly in the hood. Add approximately 1mL of chlorine-saturated CC14 to a solution of 25 mg (0.036 mmol) of tram-Rh(CO)Cl(PPhs)ain 1.5mL chloroform contained in a 5-mL conical vial equipped with a magnetic spin vane. The
Journal of Chemical Education
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S a f e t y Note: T h e entire procedure should he carried out in the hood. SO2 is a toxic gas that attacks the mucous membranes. IHL-HMN LCLo: 1000 ppmIl0 M. In a 5-mL beaker, dissolve 10 mg (0.014 mmol) of (I) in 1 mL of chloroform. Place this in the liquid SO2 generator shown in the figure. The generator consists of a widemouthed bottle (100 mL) fitted with a three-hole ruhher stopper. A centrifuge tube and vent tube are fitted into the stopper as shown. The bottom of the bottle is covered with solid NaHS03. The centrifuge tube is filled with an acetonefdry ice slush. Place the beaker in the center of the container, so that the centrifuge tube is =entered directly above it. The Pasteur pipet is filled with dilute HC1 and inserted loosely (Continued on page A1.92)
the micromde laboratory
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Dry Ico/Acetona Slush CandcnrcdS02
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into the third hole in the stopper. The HCI is slowly dripped onto the NaHS03 powder, generating SOz gas, which condenses onto the centrifuge tube. The condensed liquid SOz,in turn, drips directly into the reaction beaker. The solution tums green upon addition nf the SO,. ..............
When the reaction is cmnplete (approx. 2 min), remove the heaker and allow the sol. vmr to evaporate under a gentle nitrogen purge, holding the beaker in an icesalt bath. The green residue is collected by scraping with a spatula, and the IR spectrum obtained immediately as a Nujol mull (uco = 2030 em-', other bands may appear due to incomplete conversion or decomposition). Compare the infrared spectrum to those of the previous two products, (1) and
tron rules in predicting the reactivity of same inorganic compounds. The compound (I), which is an unsaturated 16electron system, undergoes oxidative addition reactions relatively easily to form saturated 18-electron species, (2) ( 6 6 ) . 5. The nature of the reaction of metal ions in DMF rolvent (7.81. 6. The explanation for the shifts of ",-a values in these compounds ( 4 . 6 , 9 ) . To make this experiment more appropriate for an advanced-level laboratory or for undergraduate research, it can he extended in several ways such as synthesis of a series of trans-Rh(CO)XLd4. 10. 11) studies of their electronic (121and 1 3 c N M R apertra (13) and other oxidative addition reactions
(2).
The reversihility of the SO2 adduct formation reaction can be easily demonstrated by warming the the green adduct on a watch glass held over a water bath (hood),regenerating the original yellow trans-compound, (1). This can he monitored via infrared spectroscopy. Dlscucurlon tram-Carhonylcblorohis(triphenylphosphine)rhodium(I). (I), is a well-known homogeneous catalyst used for the hydroformylation of olefins and the decarbonylation of carbonyl compounds. In this experiment students are introduced to a number of practical and theoretical aspects of inorganirorganometallic chemistry with special reference to this compound. These are briefly outlined below: 1. The synthesis and reactions of the catalyst (!). 2. The importance of chemical safety (21, e.g., use of a solvent (DMF) as a mild carbonylating agent (3,40) instead of CO or itssubstitutes such as formaldehyde or formic acid, which are toxic and corrosive, respectively. 3. The characterization of reaction types: a redox reaction to generate C12 gas, an acid-base reaction tonroduce SO?and its adduct (401 with ( I ) , and finally, an oxidative addition reaction where CI? has beenoxidatively added to ( I ) to form (2) (4b, 5). 4. The application of the 16- and 18-elec-
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Journal of Chemlcal Education
Literature CRed 1. Msyo, D. W.: Pike, R. M.;Butcher. S. S. Microscola OrgonieLoborolory, 2ndcd.:Wiley: New York, 1989: p 28. 2. szsiran. 2.:Sineh. M. M.:. PikCR. . M . J . Chem. Educ.
19.66,k26f 3. Ruai na,A.: l0cek.A. A.Nofure 1965.M6.295.
4. (a) Grinberg,A. A,; Singh, M. M.;Varshav8kii. Yu. S. Russian J . Inorg. Chrm. 1965.13, 1399. (hi Sineh M. M.: Vamhamkii. Yu. S. Rusriian J . Inor;. chi;. 1969.14.278. 5. cotton, F. A,: Wiikinsm. G. Advanced 1nargonic Chemiatry, 5thcd.: Wiley: NowYork. 1 9 8 8 ; ~ 1189. 5. Mitche1l.P. R.;Palish, R. V. J.Chem. Educ. 1969,45, 811. 7. Vsrshsvskii,Yu.S.;Kiseleua,N.V.:Cherkasova,T.G.: Buzina. N. A. J.Or8momet. Chem. 1971.31.119. 6. Gaawsrni,K.;Singh,M. M. J.Inorg.Nuc1. Chsm. 1977, 39, 1718. 9. Gray. H. B.; Ballhausen, C. d. J Am. Cham. Soe. 1963, 85,260. 10. Vaska, L.; Peona, Jr. Suoman Kernistilethi 1971.814,
317. 11. Veska.L.:Miller.W. V.:Flvnn.B.R. Chem. Commun.
1977,16,1950. 13. Bresler,L.S.:Buzina,N.A.;Varshavskii,Yu.S.:Kiwleva. N. V.: Cherkasova. T. G. J . O~mnomel.Cham.
English translations of refs 4 and 10 are available from the authors.
Resamed at the 1 9 7 m Natlonal Meeting ot me American Chemical Sacletv. Dallas. T X . 1 9 8 9 . Full detslls can be found in lhe torthcarnlng text Micm scale lnwganlc Laboratory oy Szafrsn. 2 . Pike. R M Dngn. M M Wl ey hew Yor* 1990
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