ORGANOMETALLIC COMPOUNDS OF TITANIUM, ZIRCONIUM, AND

The Organic Chemistry of Titanium. Isao Shiihara , Willis T. ... Formation of Alkyl and Aryl Titanium-Carbon Bond Compounds. DANIEL F. HERMAN. 1959,26...
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[CONTRIBUTION FROM THE CHEMICAL LABORATORY OF IOWASTATEC u m :

ORGANOMETALLIC COMPOUNDS OF TITANIUM, ZIRCONIUM, AND LANTHANUM’ HENRY GILMAN

AND

R . G. JONES*

Received June $, 19&

This report is concerned with an examination of some general and specific procedures carried out for the preparation of organometallic compounds of titanium, zirconium, and lanthanum, as well as a discussion of some reaction mechanisms on the intermediate formation of these types. HISTORICAL

Titanium. The first reported attempt a t the preparation of organotitanium compounds was that of Cahours (1) who obtained only a black reaction product of unknown composition from titanium tetrachloride and diethylzinc, and who observed no reaction of the metal with methyl or ethyl iodide. Kohler (2) recovered the components of an attempted reaction between phenylphosphorus dichloride and titanium tetrachloride. No ethyltitanium compounds were obtained by Schumann (3) in reactions of diethylzinc and titanium tetrachloride. Later, Peterno and Peratoner (4)examined the same reaction and obtained the molecular compound TiC14-2(C2H&Zn. This complex was vigorously decomposed by water, and in addition to gas and free zinc, a small quantity of oil was produced. Distillation of the oil gave n-octane and another liquid fraction which boiled between 220” and 270” and which was reported to contain titanium. The analysis of the substance gave values for “titanium” differing by 400% from the theoretical for (C2H&Ti; and the value found for carbon was in error by 40%. The authors admitted that their titanium tetrachloride may not have been pure, and it appears that the contaminant may have been germanium whose chloride is known to react with diethylzinc to give an organometallic compound. The attempts of Levy ( 5 ) to prepare organotitanium compounds met with no success. The metal, either alone or with sodium or potassium showed no reaction with alkyl iodides, and the metal did not react with diethylmercury, diethylzinc, or triethylaluminum. At 1lo”, diethylmercury and titanium tetrachloride gave ethylmercuric chloride, titanium trichloride, and an unidentified gas which contained neither titanium nor chlorine. At temperatures of 180” or above, the products were mercury, mercuric chloride, and titanium. These products do not necessarily imply the formation of ethyltitanium derivatives, for a t these temperatures diethylmercury is decomposed to metallic mercury which can reduce titanium tetrachloride to give free titanium and mercuric chloride. In the absence of a solvent, titanium tetrachloride and diphenylmercury did not react even at loo”, but in the presence of benzene a 1 Paper LXII in the series: “Relative Reactivities of Organometallic Compounds.” The preceding paper with Haubein is in the J. A m . Chem. Soc., 67, 1420 (1945). * Present address: Eli Lilly and Co., Indianapolis, Indiana.

505

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HENRY GILMAN AND R . G. JONES

reaction took place, and phenylmercuric chloride, biphenyl, and titanium trichloride were formed. A study by Challenger and Pritchard ( 6 ) on the reactions of titanium tetrachloride with various organometallic compounds did not lead to the formation of any organotitanium compounds. With phenylmagnesium bromide and a-naphthylmagnesium bromide, the chief products were R - R compounds and a black solid containing trivalent titanium. Likewise, chlorobenzene, sodium, and titanium chloride gave diphenyl but no organotitanium compound. They also examined the reactions of titanium tetrachloride with triphenyl-arsenic, -antimony, and -bismuth. Browne.and Reid (7) observed that titanium tetrachloride and tetraethyllead gave a brown tarry substance tinted purple by titanium trichloride. Razuvaev and Bogdanov (8) found that no organotitanium compounds were produced when phenylmagnesium bromide and titanium trichloride were heated a t 180"for three hours. Pletz (9) claimed t o have made organotitanium compounds by the action of n-butyllithium on triethoxytitanium chloride and diethoxytitanium dichloride in benzene solution. The chief evidence presented for the formation of a butyl-titanium linkage was the reaction of the products with iodine monochloride to give a small quantity of n-butyl iodide. The possibility that the n-butyl iodide may have come from n-butyllithium, still present in the reaction mixture, was apparently overlooked. Our studies indicate that n-butyllithium, as well as other organolithium compounds and Grignard reagents, form complexes or molecular compounds with the various titanium compounds, and these complexes may remain unchanged for long periods of time but still give characteristic reactions of organolithium and organomagnesium compounds such as the color test I (10). Attempts were made by J. F. Nelson (11) t o prepare organotitanium compounds. The metal underwent no change on long refluxing with a solution of di-p-tolylmercury in xylene, nor with iodobenzene in tetralin (with or without various catalysts). No volatile ethyltitanium compounds were obtained by interaction of ethylmagnesium bromide and titanium tetrachloride. Zirconium. Hinsberg (12) heated diethylzinc with zirconium tetrachloride in a sealed tube. At 100" no reaction occurred; and at 180" the zirconium tetrachloride still remained unchanged, but the diethylzinc decomposed to give metallic zinc and a gas thought to be butane. Peters (13) found that metallic zirconium reacted neither with ethyl iodide nor with diethylmercury when heated in sealed tubes a t 200". Likewise, mixtures of zirconium tetrachloride with diethylmercury and with diphenylmercury Kere heated a t 200" with no reaction reported. Venable and Deitz (14) observed a reaction between zirconium tetrachloride and acetylene upon gentle heating; and a t 400°, methane and zirconium tetrachloride reacted in the gaseous phase. In both cases, small yields of water-insoluble, unidentified products were obtained. Lanth". The only mention of the possible formation of methyllanthanum compounds is by Rice and Rice (15) to some unpublished studies. Using the Paneth technique they found that free radicals reacted with a variety of metals including lanthanum. No mention was made of the isolation or identification of any alkyllanthanum types.

ORGANOMETALLIC COMPOUNDS

507

EXPERIMENTAL PART

Titanium Reaction with metallic titanium. A mixture of 5 g. (0.0141 mole) of diphenylmercury and 0.5 g. (0.0104 g. atom) of titanium powder was heated, in a sealed tube under nitrogen, at 130" for 12 days. On working up the mixture there was recovered 4.9 g. (98%) of the diphenylmercury. Reactions with titanium tetrachloride. (a) n-Butyllithium. A solution of 6.55 g. (0.0345 mole) of titanium tetrachloride (redistilled, b.p. 136") in 50 cc. of dry petroleum ether (b.p. 28-38') was added dropwise t o a solution of 0.138 mole of n-butyllithium in 100 cc. of petroleum ether cooled t o -10'. A black resinous precipitate formed instantly. The clear supernatant petroleum ether, after addition of all of the titanium tetrachloride, gave a negative color test 1. The black solid gave a positive color test I, and it was also shown t o contain lithium. When allowed to dry in the air, the precipitate burned spontaneously. The solid reacted vigorously with dilute acid t o give a clear, dark greenish-blue solution. The color of the solution slowly faded on contact with the air, and was instantly discharged with permanganate or bromine water. The blue water solution gave a black gelatinous precipitate of titanous hydroxide when ammonia was added. A portion of the black solid was hydrolyzed and then extracted with ether, but no ether-soluble titanium compound was obtained. The observations were checked in another parallel experiment. (1)) Phenyllithium. A suspension of bright yellow, crystalline titanium tetrachloride etherate (N),TiCI4-2(CtH&0, was prepared by adding 5.7 g. (0.03 mole) of titanium tetrachloride slowly to 35 cc. of ice-cold ether. To this suspension was added, during one-half hour, 100 cc. of ether solution containing 0.1 mole of phenyllithium. The reaction mixture first became red; then it darkened rapidly, and was finally deep black in color. On the addition of water, gas continued to be evolved slowly after the first vigorous reaction. The gas collected during 5 hours was analyzed and found to contain 0.004 mole of hydrogen From the ether layer there was obtained 4.12 g. (53.6%) of biphenyl. The black inorganic. residue dissolved in dilute acid t o give a blue-violet solution which was immediately decolorized by bromine water or permanganate. The violet solution also gave a black gelatinous precipitate when treated with ammonia. These properties are characteristic of trivalent titanium. Beactions with titanium tetraethoxide. (a) n-Butyllithium. Titanium tetraethoxide (17) was prepared in 56% yield from 0.5 mole of titanium tetrachloride as a clear, rather viscous liquid which boiled at 149"/15 mm. A solution of 6.8 g. (0.03 mole) of titanium tetraethoxide in 40 cc. of petroleum ether (b.p. 28-38') was cooled t o -5' and stirred while 0.085 mole of n-butyllithium in 75 cc. of petroleum ether (b.p. 28-38') was added. The solution quickly became green and then changed through dark blue to black. At one stage the reaction mixture was very viscous, and at the end of the reaction i t consisted of a blueblack, finely divided precipitate suspended in petroleum ether. The solid gave a positive color test i, but the petroleum ether gave a negative color test. The solvent was distilled off under an atmosphere of nitrogen, 75 cc. of dry ether was added, and the mixture was refluxed for 12 hours. After standing for 18 days the supernatant brown ether solution gave a positive color test I and contained both lithium and titanium. The black solid also gave a strong color test and contained lithium and titanium. Possibly organotitanium compounds were present in the black solid; however, no suitable solvent was found for the material. (b) Phenyllithium. A solution of 0.1 mole of phenyllithium in 75 cc. of ether was added dropwise during one-half hour t o 5.7 g. (0.025 mole) of titanium tetraethoxide in 25 cc. of ether at 0". The reaction solution remained clear until about two-thirds of the phenyllithium had been added, and then a bright orange, crystalline precipitate appeared suddenly. When stirring was discontinued, the precipitate settled leaving a yellow supernatant ether solution which gave a strong positive color test and contained lithium and tetravalent titanium. The orange solid gave a color test, burned spontaneously in t h e air,

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HENRY GILMAN AND R. G. JONES

reacted violently with water, and contained lithium, halogen, tetravalent titanium, but no reduced titanium. Upon standing or warming up to room temperature, the solid darkened and became sticky, and could not be purified for analysis. After i t had turned black, the material still gave a positive color test, but i t contained reduced titanium as was evidenced by the strongly reducing, blue-violet aqueous solution obtained when i t was decomposed with dilute acid. The orange precipitate obtained in another experiment using 0.03mole of titanium tetraethoxide and 0.12 mole of phenyllithium in 125 cc. of ether turned completely black within 5 hours. The black solid was extracted with ether, in a Soxhlet apparatus, under nitrogen for 20 hours. Only biphenyl, 2.95 g. (32y0),was obtained from the ether which also gave a negative color test. The black solid remaining in the thimble gave a strong positive color test, and contained lithium and trivalent titanium. TABLE I REACTIONS OF TITANIUM AND ZIRCONIUMCOMPOUNDS WITH METHYLLITHIUM AND ETHYLMAGNESIUM BROMIDE PEP CENI

TKCor Zrxl

Tic14 Ti(OCdW4 ( 4 ZrC1, ZrC14 Tic14 Ti(OC*H& Ti(OCrHd4 (e) ZrCL ZrCL (f)

MOLE

RM

0.025

CH,Li CHaLi CHsLi CHILi C2HsMgBr CzHlMgBr CzHiMgBr CnHiMgBr CtHsMgBr

-02

.03 .02 .03 .03 .03 .025

.03

MOLE

RH HYDPOOEN (b)

mole (a) % (c) (b) - -- -

64.3 10.5 0.0025 7 .0053 18 58 38 56 .0048 16 25 50 .OOo& 2.7 21 52 13.8 .Om3 45 58 13.3 .0153 34 .0158 35 9 51 .0112 45 .os 36 37 .12 48 18.7 .0179 60

0.1 .08 .12 .04 .12 .12 .12

--

-

(a) Saturated hydrocarbon evolved prior t o hydrolysis. (b) Gases evolved upon hydrolysis of the reaction mixture. (c) The per cent yields of hydrogen are arbitrarily based on the reactions: 2 Ti 6 Ha0 -+ 2 Ti(OH)* 3 Hn, and ZrXt HzO -t ZrOX, Hn. (d) A black precipitate of titanous hydroxide remained in the flask subsequent t o hydrolysis. (e) The gas evolved prior to hydrolysis also contained 2% of ethylene but no hydrogen. (f) Prior t o hydrolysis, 2% of unsaturated hydrocarbons was evolved; and the same quantity of unsaturated hydrocarbons was evolved subsequent to hydrolysis.

+

+

+

+

(c) Phenylmagnesium bromide. To a well-stirred solution of 6.84 g. (0.03 mole) of titanium tetraethoxide in 50 cc. of ether cooled to -15", was added 0.113 mole of phenylmagnesium bromide in 50 cc. of ether over a one-hour period. The mixture gradually darkened during the addition of the Grignard solution, and a brown, finely divided precipitate separated. When the mixture was allowed t o warm up to room temperature, the brown precipitate changed to a black, tar-like substance. The supernatant liquid gave a negative color test, but the black tar gave a strong positive color test I. From the ether solution was obtained 1.9 g. (22%) of biphenyl. The black residue reacted vigorously with water or dilute acids to give an aqueous solution containing titanous ions. It was unchanged after heating for 5 hours in boiling xylene; the color test was still positive and magnesium, titanium, and halogen were still present. See, also, Table I for five other reactions of titanium compounds with organometallic compounds.

ORGANOMETALLIC COMPOUNDS

509

Zirconium Reactions with zirconium tetrachloride. The zirconium tetrachloride, obtained from the Titanium Alloy Manufacturing Co., was used directly. Anal. Calc'd for ZrC14: Zr, 39.2;C1, 60.8. Found: Zr, 39.3, 39.6;C1, 59.8. (a) Bromomagnesium derivative of acetomesitylene. A solution of 2.8 g. (0.012mole) of zirconium tetrachloride in 75 cc. of benzene containing a little ether was added to the bromomagnesium derivative (18)prepared from 0.06 mole of ethylmagnesium bromide and 0.055 mole of acetomesitylene in 75 cc. of ether. No reaction appeared to take place after refluxing the mixture for 4 hours, and hydrolysis yielded 75% of the acetomesitylene. (b) Benzenediazonium chloride. Zirconium tetrachloride in water was treated with one equivalent of an ice-cold hydrochloric acid solution of benzenediazonium chloride. An insoluble double salt did not form, and no solid separated on dilution with methanol. (c) Aluminum carbide. An aqueous hydrochloric acid solution containing 0.064 mole of the chloride was rapidly stirred while powdered aluminum carbide was gradually added. Much gas was evolved during the exothermic reaction, but no organozirconium compounds could be detected. A reaction under corresponding conditions with mercuric chloride and aluminum carbide gave a 19.3% yield of methylmercuric chloride. This unique procedure for preparing some methylmetallic compounds was first reported by Hilpert and Ditmar (19). (d) Ethynylsodium. Zirconium tetrachloride ammoniate (u)),prepared by passing gaseous ammonia over 11.6 g. (0.05 mole) of zirconium tetrachloride, was powdered and added to 200 cc. of liquid ammonia containing 0.22 mole of ethynylsodium (21). The zirconium tetrachloride ammoniate remained in suspension and no reaction appeared to take place. The solid remaining after evaporation of the ammonia was a very fine, soft powder, totally insoluble in benzene and in ether, and only slightly soluble in pyridine. Water reacted vigorously with the powder leaving the hydroxide as the only compound of zirconium. A better zirconium compound for reactions in liquid ammonia would probably be zirconium tetrabromide which is reported t o be freely soluble without the formation of ammoniates (22). (e) Phenylethynyllithium. A saturated benzene solution of zirconium tetrachloride etherate (containing 0.01 mole of the chloride) was added dropwise to a filtered ether solution of phenylethynyllithium (23) (prepared from 0.059 mole of phenylacetylene). The reaction mixture gradually turned brown and finally black. When the mixture was hydrolyzed, zirconium hydroxide was obtained. On evaporation of the ether-benzene layer, a dark resin was left which did not contain zirconium. (f) n-Butyllithium. To 100 cc. of a 1.0 molar solution of n-butyllithium (0.1 mole) in petroleum ether (b.p. 28-38") was added 4.66 g. (0.02 mole) of the chloride. The powder remained in suspension and no reaction appeared to take place. After 7 days the petroleum ether solution no longer gave color test I, but the brown precipitate gave a strong color test. When taken into the air on a spatula, the precipitate ignited spontaneously and burned vigorously; it contained lithium and reacted violently with water leaving a precipitate of zirconium hydroxide. (g) Phenyllithium. A suspension of the etherate from 4.8 g. (0.02 mole) of zirconium tetrachloride in 25 cc. of ether was stirred a t -15" while 0.08 mole of phenyllithium in 80 cc. of ether was added during 15 minutes. There was no darkening of the reaction mixture until after the cold-bath was removed, and then the mixture gradually became black. On adding water, after 11 hours, the black color was immediately discharged leaving a white precipitate of zirconium hydroxide. The evolved gas was shown to consist mainly of hydrogen with traces of carbon dioxide, oxygen, and unsaturated hydrocarbons. The yield of hydrogen was 0.0033 mole or 16% based on the reaction: ZrXz HzO -+ ZrOXl+ H1. From the ether layer was obtained 2.72 g. or 46% of biphenyl. It was found incidentally in these experiments that the etherate of zirconium tetrachloride is much more soluble in benzene than in ether. Whereas, an ether solution

+

510

HENRY GILMAN A N D R. G . JONES

saturated with zirconium tetrachloride contained only 0.064 mole per liter, the solid crystalline etherate dissolved in benzene to the extent of 0.167 mole per liter. (h) n-Butylmagnesiumbromide. A solution of 0.24 mole of n-butylmagncsium bromide in 112 cc. of ether was added dropwise to a rapidly stirred suspension of 14 g. (0.06 mole) of the chloride in 75 cc. of ether cooled to - 10". The reaction mixture became black during the addition of the Grignard reagent, and after the cold-bath was removed a veryslow evolution of gas took place. The ether of the reaction mixture was distilled off on a waterbath, and the gases were collected and analyzed. Besides 0.0261 mole (10.9% yield) of butane; 0.0094 mole of unsaturated hydrocarbons, 0.0081 mole of carbon dioxide, and 0.0133 mole of oxygen were present. The gas contained no trace of hydrogen. The gas evolved when the mixture was hydrolyzed contained 0.059 mole (98% yield) of hydrogen (based on the equation: ZrX2 H20 -+ ZrOXz H2) and 0.0144 mole (14%) of butane. The hydrolyzed mixture was extracted with ether, and, after drying, the ether extract was fractionally distilled. A fraction boiling between 29' and 34' was shown to contain unsaturated compounds, and a higher fraction appeared t o contain some octane but the quantity was too small for unequivocal identification. (i) Phenylmagnesiumbromide. A suspension of 0.05 mole of zirconium tetrachloride in 75 cc. of ether was treated with 0.1 mole of phenylmagnesium bromide in 50 cc. of ether. The dark brown supernatant ether solution gave a positive color test I, and contained magnesium but no zirconium. The mixture was distilled to dryness on the water-bath and heated for 3 hours at 90'; and then the black solid was treated with water. The gas evolved was shown t o be hydrogen (0.0098 mole). Ether was also liberated, and 4.33 g. or a 56% yield of crude biphenyl (m.p. 65-66") was obtained. I n a duplicate experiment the black solid was shown to contain zirconium and magnesium as well as halogen, and i t gave a strong color test I. Zirconium tetraphenozide and methyllithium. A suspension of 9.26 g. (0.02 mole) of zirconium tetraphenoxide (24) in 25 cc. of ether was cooled t o -15' and stirred while 0.08 mole of methyllithium in 60 cc. of ether was added dropwise. Gas was evolved during the addition, but the reaction mixture did not darken. After removal of the cold-bath, a great deal more gas was evolved as the mixture gradually turned black. The gas obtained prior to hydrolysis contained 0.0555 mole (69% yield) of methane. Subsequent to hydrolysis, 0.0164 mole (20.5%) of methane and 0.00065 mole (3.3% yield) of hydrogen were obtained. See, also, Table I for four other reactions of zirconium compounds with organometallic compounds. Reactions of titanium and zirconium compounds with methyllithium and ethylmagnesium bromide. The general results of these several experiments are given in Table I, and the following is a description of a typical experiment. I n a 250-cc. Claisen flask provided with a stirrer, dropping-funnel in the bent neck, and a connection of the side-arm through a condenser t o a gas collector, was placed 7 g. (0.03 mole) of zirconium tetrachforide and 50 cc. of ether. The apparatus was swept out with nitrogen. To this suspension, rapidly stirred and cooled t o -lo", was added from the dropping-funnel 110 cc. of a n ether solution containing 0.12 mole of methyllithium. The addition of the methyllithium required about one-half hour during which time the solid in the reaction vessel became lemon yellow in color but did not darken. The cold-bath was removed, and upon warming u p t o about 15' the reaction mixture began to turn black. At the same time a rather vigorous evolution of gas set in (accompanied by no noticeable heat effects). After the gas evolution was complete, which required about one-half hour, the apparatus was swept out with nitrogen and the gases were collected over water. Methane was found to be the only saturated hydrocarbon present. Traces of carbon dioxide, unsaturated hydrocarbons, and oxygen were indicated. The yield of methane was 56'% on the basis of the methyllithium used. The black reaction mixture was allowed to stand at room temperature, but no apparent further change took place. After 16 days, the mixture was hydrolyzed by adding distilled water. A vigorous reaction occurred, and another quantity of gas was evolved which was collected over water and analyzed. This second gas contained hydrogen, 0.0048 mole

+

+

ORGANOMETALLIC COMPOUNDS

511

(16% yield), and methane, 0.03 mole (25% yield). As was the case in the reaction involving n-butylmagnesium bromide, for example, the hydrogen probably came from the reaction of finely divided zirconium metal or a di- or tri-valent zirconium compound with water. Traces of carbon dioxide, oxygen, and unsaturated hydrocarbons were also present. The white precipitate remaining in the reaction flask was filtered off, washed with water and shown to be zirconium hydroxide.

Lanthanum Reaction with metallic lanthanum. A mixture of 3 g. (0.0084 mole) of diphenylmercury and 0.73 g. (0.0053 g. atom) of lanthanum "as sealed in a tube under nitrogen and heated at 135". After about 60 days the contents of the tube started to darken; and a t the end of 100 days the tube was opened under nitrogen and carbon dioxide was passed through the black liquid product. Extraction with benzene removed all of the organic material, and from this extract which gave no lanthanum test there was isolated a 15% yield of biphenyl bur no benzoic acid. The metallic residue from the benzene extraction was apparently a lanthanum amalgam; i t dissolved in dilute hydrochloric acid with the evolution of gas (probably hydrogen), and left droplets of mercury. T o a Schlenk tube containing 0.5 g. (0.0036 g. atom) of small pieces of lanthanum and 1 p. (0.0049 mole) of iodobenzene was added 5 cc. of ether; and t o another tube containing the same quantities of lanthanum and iodobenzene was added 2 cc. of benzene. The tubes were sealed and set aside a t room temperature, and a t the end of 4 months there was no evidence of any change. Reactions with lanthanum chloride. Anhydrous lanthanum chloride was prepared by heating the hydrated salt LaC18.7 HzO, in a current of hydrogen chloride. The anhydrous chlaride was then powdered and heated in a stream of dry nitrogen until free of hydrogen chloride. .i?ial. e'ilc'd for LaCI?: La, 55.64; C1,43.36. Found: La, 56.99; C1, 42.94. '1 suspension of 9.4 g. (0.038 mole) of lanthanum chloride in 50 cc. of ether was stirred while 90 cc. of 1.42 molar phenyllithium (0.128 mole) was added. There was no apparent reaction, and after 3 hours the ether was removed and replaced by 50 cc. of dry benzene. Whttn this mixture was refluxed it gradually blackened, and after standing overnight the mixture comisied of a dark solid with a supernatant dark brown liquid. Dilution of 10 cc. of the iiquid, which gave a strong color test I, with 20 cc. of petroleum ether induced no pre:ipitation. The liquid reacted vigorously with water, and the brown color disappeared. Analysis of 10 cc. aliquots of the liquid gave the following values: C1, 0.000 equiv.; Br, 0.0029 equiv.; bzise, 0.0156 equiv., or a total of 0.0185 equiv.; and Li, 0.0166 equiv.; La, O.OG29 equiv., or a total of 0.0195 equiv. The dark color of the liquid and the excess of lanl hanum over the negative ions, indicated in the analyses, suggest that some reduced form of lanthanum was present. Possibly the dark color was due to metallic lanthanum or a lower-valent lanthanum bromide in colloidal suspension. Analyses of the 10 cc. aliquots alsc showed 0.0012 mole of biphenyl (mixed m.p.). i, solution of 0.1 mole of methyllithium in 65 cc. of ether was added t o a suspension of 8.2 4:. (0.033 mole) of lanthanum chloride in 25 cc. of ether a t -5'. S o reaction took place; honever, when the mixture was allowed to warm up t o room temperature, i t gradually colored yellow, and a slow evolution of gas set in. During the course of two days, the white lant hanuin chloride gave place t o a brownish-yeilow precipitate which softened and turned to a thick brown syrup and then solidified again. After the fourth day, no more gas was evolved. The gas was collected, and analysis showed it t o contain 0.0135 mole of methane as the only constituent. This is a 13.5% yield on the basis of methyllithium. After 10 day3 no further change had taken place in the reaction mixture. The brown solid was filtered under nitrogen and washed with ether until the washings gave only a slight halogen test, but a negative color test I. The solid, dried under nitrogen, gave a strong color test

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HENRY GILMAN AND R. G . JONES

I, and also a color test 11 (25)with p-iododimethylanilines which showed the presence of methyllithium. The brown material burned spontaneously in the air and reacted violently with water to give a solution which contained halogen, lanthanum, and lithium ions. Another reaction was carried out between 11.5 g. (0.047 mole) of lanthanum chloride and 0.15 mole of methyllithium in 175 cc. of ether. After removal of the ether, the brown solid residue was heated at 150"/30 mm. for one-half hour, but nothing distilled. A suspension of 11.2 g. (0.041 mole) of lanthanum chloride in 10 cc. of ether and 0.152 mole of ethylmagnesium bromide in 50 cc. of ether appeared not t o react. After removal of most of the ether, the mixture was heated at 90" for 5 hours without any apparent change. No distillate was obtained after heating at 270"/20 mm. for one-half hour. DISCUSSION

The most generally useful reactions for the preparation of all types of organometallic compounds are the reactions of salts with RM compounds of other metals:

MX

+ RM'+RM + M'X

In the reaction of the halides or alkoxides of titanium and zirconium with organolithium compounds or the Grignard reagents, the first stage is the formation of a complex. The stability of this complex is markedly influenced by the temperature; and to some extent by the medium which can, as mentioned earlier (26), significantly affect stability and reactivity by the formation of coijrdination compounds. For example, in the relatively low coiirdinating petroleum ether there is probably formed a moderately stable complex of the type ZrClr-xGHaLi from zirconium tetrachloride and n-butyllithium. In the second stage of the reaction, which generally takes place with some rapidity a t room temperatures, the initial complex is converted t o other complexes having the metal in a lower valence state. Typical examples would be TiX-xRLi or TiX2.xRLi. Actually, the reduction in some cases appears t o go down t o the free metal. Accompanying this second stage is the liberation of R groups. The fate of the R groups is determined largely by the nature of the group and somewhat by the medium. When the R group is aryl, coupling is the chief reaction and this leads to biaryls. For example, when the RM compound is phenyllithium or phenylmagnesium bromide the yields of diphenyl range up to 56%. However, when the R group is alkyl (like methyl or ethyl) there is no appreciable coupling and almost pure RH compound is formed in yields ranging up to 70%. It is probable that these simple alkanes are formed by the action of the corresponding free radical on the solvent (27): CH3

+ (CzHs)zO+CH4

Coincidental with the second stage of the reaction, it appears that there may be the formation of double organometallic compounds, or a complex of the

* Color test I1 is specific for many organolithium compounds. However, p-bromodimethylaniline, which has been the reagent used heretofore, gives a negative test with methyllithium. Mr. R. V. Christian has shown that p-iododimethylaailine gives a positive and highly sensitive test with methyllithium.

ORGANOMETALLIC COMPOUNDS

513

(R-Ti) or (R-Zr) with the RLi or RMgX compounds (Reactions I1 and IV). Such complexes could decompose with the reduction of the metal and the expulsion of a free radical. Related evidence in support of such a mechanism is the work of Hein (28) on the spontaneous decomposition of (CaHs)sCrOH in the presence of an alkali metal halide or a hydrohalogen acid whereby a phenyl group is liberated as a free phenyl radical. (CsHs)&rOH 4- HI-+(Cd&)4CrI

+ CaH6. +HzO

The following series of reactions probably best accounts for the reactions of zirconium tetrachloride (or titanium tetrachloride or tetraethorcide) with RLi of RMgX compounds :

+ RM + ZrCl4-xRM..................... 111 ZrClr-xRM [RZrC&.(x - 1)RM] + MC1 . . . . . . . . . . . .[I11 [RZrCG.(x - l ) R M ] + ZrCla.(x - l)RM + R . . ........ [111] ZrCL.(x - 1)RM + [RZrCh.(x - 2)RM] + MC1 . . . . . . . . [IV] [RZrClz. (x - 2)RMl + ZrClz. (x - 2)RM + R . .......... [VI ZrCll

4

2R

--+

R

-R

[where R is aryl]. . . . . . . . . . . . . . . . .

1 [where R is alkyl 1.. . . . . . . . . . . . . . [VI11

+ (H) + RH ZrClz.(x - 2)RM + H20 + Zr(OH)* + RH + MC1 + Hz.. . [VIII] R

The more moderate reactions with lanthanum chloride appear t o have some features in common with the reactions of the chlorides of titanium and zirconium: there is a reduction to a lower valence state; the phenyl group couples to give diphenyl; and the methyl group gives methane. However, it is interesting to note that ethylmagnesium bromide appears not to undergo any appreciable reaction with lanthanum chloride under conditions where there is a marked reaction with titanium and zirconium tetrachlorides. In general, it may be stated that there is a t this time only indirect evidence for the formation of organometallic compounds of titanium, zirconium, and lanthanum. On the basis of present information on organometallic compounds, it appears that the more stable organometallic types of these metals will have an aryl group, as is the case with organomanganese compounds (29); that stability will be increased by complexes with compounds like diethylzinc, as is the case with organostrontium and organobarium compounds (30); and that the order of relative reactivities of these RM compounds will be low (31). There are currently available about thirty general procedures for the preparation of organometallic compounds. The state of knowledge in the preparation of organometallic compounds of the so-called transitional metals is SO largely empirical that only studies by several workers using the many procedures available will provide answers to the properties of these types.

514

HENRY GILMAN AND R. G. JONES SUMMARY

A series of reactions has been described concerned with the preparation of organometallic compounds of titanium, zirconium, and lanthanum. The first stage in the reaction of halides of these three metals with RLi or RMgX compounds is the formation of a complex like TiC14-xRLi. Then, this complex, which is generally unstable thermally, undergoes a change in which the metal is reduced t o a lower valence stage. In the case of titanium and zirconium the metals are reduced to the trivalent and divalent stages, and, in some experiments, t o the free metal. Accompanying the reduction is a liberation of organic radicals. Where the radical is aryl, there is a coupling reaction to give a diary1 like diphenyl. When the radical is methyl or ethyl, there is abstraction of hydrogen from the medium t o give methane or ethane. Mechanisms have been proposed for the intermediate formation of organometallic compounds of these transitional metals. AMES,IOWA REFEREPU’CES (1) (2) (3) (4) (5) (6) (7) (8)

CAHOURS, Ann., 122, 48 (1862). KBHLER,Ber., 13, 1626 (1880). SCHUMANN, Ber., 21, 1079 (1888). PETERNO AND PERATONER, Rer., 22, 467 (1889). LEVY,Ann. Chim. Phys., [VI] 26, 433 (1892). CHALLENGER AND PRITCHARD, J . Chem. SOC.,126, 864 (1924). BROWNE AKD REID,J . Am. Chem. SOC., 49, 830 (1927). R~ZUVAE AND V BOGDANOV, J . Gen. Chem., (U.S.X.R.), 3, 367 (1933); Chem. Abstr., 23, 2340 (1934). (9) PLETZ,J . Ge7~.Chem., (U.S.S.R.),8 , 1298 (193s) Chem. Abstr., 33,4193 (1939). (10) CILMAN AND SCHULZE, J . Am. Chem. SOC.,47, 2002 (1925). (11) Unpublished studies by J. F. Nelson. (12) HIXSBERG, Ann., 239, 253 (1587). (13) PETERS,Ber., 41, 3173 (1908). (14) VEXABLE AND DEITZ, J . ElishaMichell Sci. SOC.,38, Nos. 1 and 2,74 (1922). (15) RICEAND RICE,“The Aliphatic Free Radicals,” The Johns Hopkins Press, Baltimore (1935), p. 58. (16) D E M E T R OAXD I ~ L ~ D I K OPraktika S, (Akad. Athenon), 6 , 449 (1930); Chem. Abstr., 27, 3160 (1933). (17) BISCHOFF AND ADKINS,J.Am. Chem. Soc., 46, 256 (1924). (18) F u s o ~FUGATE, , AND FISHER, J . Am. Chem. soc., 61, 2362 (1939). GILMAN AND JONES, J . Am. Chem. Soc., 63, 1162 (1941). (19) HILPERTAND DITYAR,Ber., 46, 3738 (1913). J . Am. Chem. SOC.,20, 815 (1898). STAHLER AND DENK,Ber., 38, 2611 (20) MATHETVS, (1905). (21) Elms AND MUNDERLOH, Ber., 61, 377 (1918). (23) YOUNG, J. Am. Chem. Soc., 67, 1195 (1935). AND YOUNG, J. Org. Chem., 1,315 (1936). (23) GILMAN J .Hprakt. , Chem., 116, 7 (1926). (24) J ~ N T S C AND SWISS, J . Am. Chem. Soc., 62, 1847 (1940). (25) GILMAN (26) GILMAN AKD JONES, J . Am. Chem. S O C . , 62,1243 (1940).

ORGANOMETALLIC COMPOUNDS

515

(27) EVANSAND CO-WORKERS, J . Am. Chem. SOC.,68, 720, 2284 (1936); 61, 898 (1939); 62, 534 (1940). (28) HEIN,Ber., 64, 2708 (1921). J . Org. Chem., 2, 84 (1937). (29) GILMANAND BAILIE, (30) GILMAN, MEALS,O’DONNELL, AND WOODS,J. Am. Chem. SOC., 66,268 (1943); GILMAN AND WOODS,J . Am. Chem. SOC., 67, 520 (1945). GILMAN,HAUBEIN, O’DONNELL, AND WOODS,J . Am. Chem. SOC., 67,922 (1945). (31) See pp. 520-524 in Gilman, “Organic Chemistry,” John Wiley and Sons, New York (1943).