Kenneth W. BorneH University of Missouri- St. Louis st. Louis, Missouri 63121
I
Nickel Complexes with Organic and Phosphorus Ligands An integrated set of inorganic experiments
T h e group of experiments presented here should fit well into the basic structure of upper division inorganic laboratory courses. T h e individual experiments are in themselves useful laboratory exercises and are not found in texts designed for such courses ( I , 2). However, lengthening the list of possible experiments for the inorganic laboratory is not the object of this article, nor is it considered a worthwhile goal in and of itself. I t is the author's contention t h a t the selection of two or more related syntheses (and the variety of characterization techniques involved) sums to a greater learning experience t h a n a n equal number of individual, unrelated experiments. The "package" presented here is illustrative of a n integrated approach to t h e laboratory course under discussion and will hopefully stimulate the generation of similar "modules" using other facets of inorganic chemistry. I t should be noted t h a t the starting materials for the syntheses described are readily available a t reasonable cost and t h a t each synthesis has been successfully reproduced by two or more undergraduates a t U.M.S.L. T h e experiments to he discussed are shown below.
2MC,H,
2PR,
+
+
Ni(I1)
Ni(H,O)&
-
0 I
Ni
(PRJ,NiX,
(I)
(2)
(R = alkyl or a r y l X =C1, Br, I, CN, etc.)
gaseous ammonia is bubbled through the solution. This reaction is conveniently carried out in a 250-ml three-neck flask fitted with a reflux condenser. Use of a n effkient hood is mandatory! The reaction mixture is cooled to 0°C and the deep blue Ni(NH&C12 filtered, washed twice with 20 ml portions of ice water, ethanol, and ether, respectively, and sucked dry. Yield is usually on the order of 40-45 g, approximately 90%. This step may be conveniently scaled down without noticeable sacrifice in yield. Note: Ni(NH&Clz is blue in natural light hut may appear purple under fluorescent lighting. Sodium eyelopentadienide, NaCsHs, is prepared by the reaction of sodium with cyclopentadiene (6) in tetrahydrofuran under a nitrogen or argon atmosphere. Alternatively, commercial NaCsH. solutions (THF) or mineral oil dispersions may be utilized if available. Tetrahydrofuran solutions of NaCJHJ react directly with Ni(NH&C12 according to the equation
The reaction is conducted in THF solution under an inert atmosphere, with the solid nickel salt heing added directly. The mixture is heated at -50°C for 2 hr; during this time the charaeteristic green color of nickelocene develops and NH. is evolved (cessation of the latter indicates complete reaction). The solvent is removed at reduced pressure and the nickelocene extracted into benzene which is in turn removed at reduced pressure. The solid product is sublimed at 0.1 mm Hg and 60'C to afford bright green crystals of the pure complex in approximately 80% yield, based on Ni(NH&CI.; e.g., 4.1 g of nickelocene from 8.5 g Ni(NH&Cls. The product is moderately air sensitive and should he handled accordingly. Synthesis of Nickelocene by Route B (7) A 5W-ml flask fitted with a dropping funnel and nitrogen inlet is purged with dry nitrogen for 30 min, at which time 120 ml 1,2dimethoxyethane (glyme), 8.5 ml cyclopentadiene, and 50 g powdered potassium hydroxide are added. The mixture is stirred for 20 min and 12 g Ni(HzO)aC11in 75 ml of dimethylsulfoxide added dropwise through the dropping funnel over a 45 min period. After an additional 30 min stirring, the mixture' is dumped into a mixture of 180 ml 6 M HCI and 200 g of ice (previously deaerated by bubbling nitrogen through the solution) and stirred for 15 min. The product is suction filtered, washed, first with ethanol then with ether (25 ml each), and vacuum dried. The latter operations Com~lexesand Technicrues Utilized
The syntheses are listed in the table along with the most suitable methods of characterizing the complexes. Since the emphasis placed on characterization may vary considerably from department t o department this subject is not discussed in detail here. Rather, the interested reader is referred t o several texts which describe characterization of inorganic compounds by various physical and wet chemical methods (1-4). Experimental Synthesis of Nickeiocene by Route A (5) A solution of 48 g of NiC12.6H20 in approximately 100 ml of water is heated at 60°C for 4-5 hr, while approximately 4W g of 422
/ Journal ot Chemical Education
Compound (CsHi ,Ni
LsNiXl CsHsNi(L)X
Experimental techniques Distillation a t atmospheric pressure Inert Atmosphere Sublimation Nanaqueous solvent recrystallization
Characterization techniques ir, mp, m.s., vis-uv
ir, vis-uv, mp, magnetic moment nmr, ir vis-uv, m p
Inert Atmosphere Nonaqueous Solvent Recrystallization CsHsNiCnH,,O6 Inert Atmosphere nmr, ir, vis-uv Column Chromatography m.s. m p
should be conducted in a glove bag or Schlenk apparatus. The product should be further purified by sublimation as described above unless it is to he used immediately in another synthesis. Yields of onlv 30-505 are eenerallv obtained. but this is oartiallv eompensatedfor by [he ease and Geed of t h e ~ynrheaiar&ve tb route A . The product obtarned may be characterized by rts melt. ing point and infrared and mas* spectra. Synthesis of [(C6H5)3P]2NiC12(8) To s solution of 2.5 g Ni(H2O)eCb in 30 ml of ethanol, a slurry of 5.0 g triphenylphosphine in an additional 50 ml of ethanol is added. The mixture is heated at reflu for 1 hr under a nitrogen or argon atmosphere. The purple product (3-5 g, 45-1570) precipitates from solution and is filtered hot, washed with 50 ml ethanol, and vacuum dried. Analogous complexes containing other tertiary phosphines or anionic ligands are similarly prepared by use of appropriate starting materials and alcohol or acetic acid solvents. The geometries, magnetic properties and colors of the complexes LzNiXz are dramatically affected by the nature of L and X (912).
Synthesis of rr-C5H,Ni(PR,)X Complexes Nickelocene (1.9 g, 10 mmol) and 6.5 g (10 mmol) of [(C6H&P]sNiCL2 are refluxed in 150 ml of tetrahydrofuran under a nitrogen or argon atmosphere for 4-6 hr; The reaction mixture rapidly acquires the deep red-purple color of the product (nCsHs)Ni[P(CaHs)dCI.The solvent is removed at reduced pressure and the residue dissolved in hot benzene and filtered. Addition of hexane to the benzene filtrate and cooling to OC ' affords red-purple crystals of the product in 80-90% yield (13). This reaction is an example of a large general class of reactions of nickelacene with (PR&NiXz compounds, the products n-CaHrNi(PRs)sX being readily characterized by melting points, proton nmr, and visible-ultraviolet spectroscopy (14-16). The complexes may be utilized to synthesize compounds containing metal-carbon sigma bonds by reactions with Grignard or organolithium reagents (14, are, however, mcder16, 17). The derivatives (T-CJHI)N~(PRJ)R' ately air sensitive and require much more careful handling than the other complexes described here. Reaction of Nickeiocene with CH3O2CC=CC02CH3 According to the method of Dubeek (17) nickelocene (2.2 g) and dimethylacetylene dicarboxylate (1.5 g) in -30 ml of THF are stirred under nitrogen or argon at roam temperature. The mcderate temperature and slight excess of nickelacene are dictated partially by the fact that the organic compound is a severe lachrymator. The time required for essentially complete reaction is (conveniently) about one week. The solvent is removed at reduced pressure and unreaeted niekelocene sublimed off at 60"C/0.1 mm Hg. The red-orange product may be purified by chromatography on alumina (CHCI~/hexane)and is readily crystallized from methanol/hexane. It melts at 83-85°C and has distinctive ir, nrnr, and mass spectra (17). Its solid state structure has been determined (18). Discussion Experiments 1 and 4. The synthesis of nickelocene introduces the student to the technique of operation of an inert atmosphere and to the broad area of pi-bonded, "sandwich" compounds. Unlike its diamagnetic and very stable cousin ferrocene, (n-C5H~)zNiis paramagnetic, having two electrons more than the number required to achieve the inert gas configuration (19). This is reflected in the high reactivity of nickelocene evidenced in experiments 3 and 4. In experiment 4 the
molecule has formally undergone a l,4-Diels-Alder addition to afford the stable 18-electron product. If this option is elected the student might wish to give some thought to
formed and the mechanistic imthe nature of the plications of the observed stereospecificity. Experiment 4 stands alone if (r-CsHs)zNi is availahle. The relation to organic chemistry is obvious and should be beneficial to the student.. Experiments 2 and 3. (Nickelocene available or synthesized by the student) The synthesis of the four-coordinate complexes LzNiX2 is straightforward in all instances. Depending on the nature of L and X the compounds may exhibit either tetrahedral or square planar geometry. This information for a particular complex may be ohtained by visible spectroscopy or magnetic susceptibility measurements by the nmr method of Evans (20, 21) and verified by consulting the chemical literature (8-12). Synthesis of several of these complexes and investigation of their visihle-uv spectra should allow the student to establish a "mini" spectrochemical series. Synthesis 3 is a rather remarkable transformation considering the number of bonds broken and formed, the "cleanness" of the reaction, and the high yields ohtained. The student electing this combination should give thought to the "electron count" for the reactants and products (effective atomic number rule). To the author's knowledge the kinetics and mechanisms of these reactions have not been studied. This could provide a further exercise for advanced students. Summary We have presented a group of experiments involving the coordination chemistry of nickel which provide considerable latitude in terms of experimental and characterization techniques. Although the experiments may he carried out individually, we feel that the strongest feature of the program is the opportunity to perform two or more experiments sequentially. This requires planning on the part of the student as to quantities utilized, provides greater depth than a similar number of isolated experiments, and gives a "research flavor" to the inorganic laboratory course. Student response to this approach has been favorable and it is hoped that this discourse will serve to stimulate the development of similar sequences based upon other areas of inorganic chemistry. Acknowledgment The author is indebted to Dr. J. Y. Corey, Dr. E. R. Corey, and Dr. L. Barton for valuable discussious. Literature Cited ( I ) Jolly, W. L., '"TheSynthesis and Characterization of Inorganic Compounds."Prentie*-Hail, Enalewood Cliffs, N.J.. 1910. (2) Angeliei, R. J., '%nthesis and Technique in Inorganic Chemistry," W. B. S a m dem, Philadel~his1969. (3) Drsgo, R. S.. .'Physics! Methods in Inorganic Chemistry." Van Nostrand Reinhold. New York 1965. (4) King. R.B., "Organometalli~Synth~s,"Vol. I, Acsdemie h. NewYork. 1965. 151 Corder J. F.. Chem Be,. 96. 3084 11962). 16) Reference (4). pp. 65-66. (71 Jolly, W. L. (Editor), "Inorganic Synfherwr," McGraw-Hill, New York. 1968. Val. XI. p. 122. (8) Itatani. H.. and Baiiar, J. C. Jr.. J. A m m Chrm. Sac., 89.1SW 11967). (9) Vensn%i,L.M..J.Chrm. Soe.. 71911958). (10) Rigo,R..Pceile. C.. andTureo,A.,lnorg. Chom., 6.163611967). (11) Haytor, R. G.,snd Hurniec,F.S.,lnorg. C k m . , 4.1101 119651. Chrm. Soc.. 92. 2691 I19701 and ref(12) LaMar, G. N., and sheman, E. 0.. J erenesa therein. (13) Schmll. G.E..U.S.Patenf3054815. Sept.. 196% Chem.Abafr, 58.149411963). (14) Yamaznki, H.. Niahido. T.. Matsumoto, Y.. Sumida. S.. and Hagihara. N., J 01gonometal. C k m . . L 86(19661 (151 v a n d m Akker, M,,and Jeliinek. F.. Re. Trav. Chim.. 86,891 119671. (16) Rausch, M.D.,Chang. Y. F., sndGordon. H.B.,lnorg. C k m . . 8.1355l1969). (17) D u b c k , M . , J A m s r Chsm. Sor., 82,6193I19M)l. (IS) Dahi. L.F..snd Wei. C. H.,lnorg. Chem.. 2.713119631. (19) Cotton. F. A,. and Wilkinson, G., "Advanced lnoxgsnie Chemistry." 3rd Ed.. Wiley-lnteneience, Nou York. 1972. pp. 136-43. I201 Evsna.D.F., J. Chem. Soc.. 2W311959). (21) Crauford.T.H.andSwansn. J.J. J.CHEM.U)UC.,48,362I19711.
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