POLYMERIZATION AND POLYCONDENSATION PROCESSES

10 Reactions of New Pi-Complex Catalysts GÜNTHER WILKE, BORISLAV BOGDANOVIČ, PAUL HEIMBACH, MICHAEL KRÖNER, and ERNST WILLI MÜLLER

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on October 31, 2017 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0034.ch010

Max-Planck-Institut für Kohlenforschung, Mülheim-Ruhr, Germany

Three molecules of butadiene can be combined into 1,5,9-cyclododecatriene, using typical Ziegler-type catalysts.

New

π-complex

catalysts

have

been developed by which it is possible to direct the synthesis at will in direction off a trimerization or dimerization.

1,5-Cyclo-octadiene

or 1,5,9-

cyclododecatriene can be obtained in 9 5 % yields. The

catalysts can be isolated and are

crystalline—for instance,

Ni-(O)-[P(C H ) ] . 6

5

3

4

mostly It has

been possible to isolate a definite intermediate of the trimerization, the structure of which has been determined.

Some reactions of this intermediate

elucidate the mechanism of the trimerization. The cyclic olefins obtained from butadiene are valu able starting materials for the production of α-ω difunctional compounds.

i s reported i n 1959 at the Symposium on Stereoregulated Polymers i n Boston ( I ) , ^ it is possible to combine three molecules of butadiene into trans,transmis-1,5,9cyclododecatriene, using a typical Ziegler-type catalyst w h i c h can be prepared b y reaction of T i C l w i t h A l ( C H ) C 1 . 4

2

5

2

One can polymerize ethylene, using the same catalysts, into h i g h molecular weight polyethylene ( 9 ) . W i t h special catalyst combinations, yields of over 9 0 % can be obtained at normal pressure and at about 40° C . B y using a catalyst prepared on the basis of 137 PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

ADVANCES IN CHEMISTRY SERIES

138


chromium compounds, thesized ( J ) :

frans, r T a n s , r T a n s - l , 5 , 9 - c y c l o d o d e c a t r i e n e

has

been

syn

This article presents investigations on the elucidation of the reaction mecha nism of this remarkable cyclo-oligomerization, as w e l l as improvements i n the cyclotrimerization and cyclodimerization of butadiene. In this latter connection two well-known processes should be mentioned: About 10 years ago Ziegler and coworkers (10, 11) investigated the thermal dimerization of butadiene. T h e y obtained, under extreme conditions, vinylcyclohexene as a main product and 1 5 % of 1,5-cyclo-octadiene. In 1954, Reed (5) reported that it is possible to synthesize 1,5-cyclo-octadiene from butadiene w i t h Reppe catalysts obtained from nickel carbonyl. T h e yields were i n the range of 30 to 4 0 % . Recently, some patents granted to the Cities Service C o . (1,6) show that great improvements have been made i n this process also. Soon after discovery of cyclotrimerization, w e tried to find a way to change this reaction into a cyclodimerization w h i c h w o u l d lead to 1,5-cyclo-octadiene. However, a l l our efforts to alter the typical Ziegler-type catalysts to effect cyclo dimerization were fruitless as long as catalysts based on titanium compounds were used. Later on we tried to prepare a catalyst based on nickel compounds, be cause the Reppe-Reed catalysts have shown that nickel is effective in some way i n such a reaction; but on treating nickel compounds w i t h organometallic compounds, a precipitate of metallic nickel which had very little activity as a catalyst was always obtained. T h e n a simple way was found to stabilize the reduced nickel by 7r-complex formation. This method finally originated from investigations on the dimerization of ethylene by A 1 ( C H ) in the presence of a nickel cocatalyst (8). 2

5

3

T h e first active catalyst system found was prepared b y reaction of nickel acetylacetonate w i t h organoaluminum compounds i n the presence of phenylacetylene. A dark red solution was obtained w h i c h reacted at 80° C . under pressure w i t h butadiene to about 2 4 % cyclo-octadiene, 8% vinylcyclohexene, and 6 3 % a\\-transcyclododecatriene. The component w h i c h stabilizes the reduced nickel was then changed systematically to discover the possibility of directing the synthesis at w i l l in the direction of a trimerization or dimerization. Today we can synthesize cyclooctadiene i n yields of 9 5 % or cyclododecatriene i n similarly good yields only b y altering the electron-donor molecules used in preparing the catalyst. W h a t compounds are the active catalysts in this process? B y this method of catalyst preparation we do not obtain a mixture of indefinite composition, but τΓ-complexes w h i c h can be isolated and are mostly crystalline. If, for instance, nickel acetylacetonate is reduced in the presence of P ( C H ) we obtain a new compound, N i - ( 0 ) - [ P ( C H ) ] . This compound is itself an active catalyst for the cyclo-oligomerization of butadiene, producing about 65 to 7 0 % cyclo-octa diene, 2 0 % vinylcyclohexene, and 10% cyclododecatriene. Instead of P ( C H ) we can introduce A s ( C H ) a n d isolate N i - ( 0 ) - [ A s ( C H ) l as an active catae

6

r >

3

5

3

4

e

e

5

3

6

5

3

4

PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

5

3

WILKi

ET AL.

139

Reactions of New Pi-Complex Catalysts


lyst, b y w h i c h we obtain yields of 1 1 % cyclo-octadiene, 5% vinylcyclohexene, a n d 8 1 % cyclododecatriene. These examples explain the general principle. B y this method w e have synthesized a great number of different compounds, a selection of w h i c h is shown below.

\

/

F o r studying the cyclotrimerization reaction mechanism these n e w catalyst systems seemed to be much more convenient than the above-mentioned Zieglertype catalysts. T h e authors assumed the following reaction sequence: 7r-Complex formation between butadiene molecules and the transition metal of the catalysts, preformation of the ring a n d activation of the butadiene molecules in this complex. C - C linking w i t h formation of, for instance, cyclododecatriene w h i c h still remains o n the transition metal in the form of a new π-complex. Displacement of cyclododecatriene b y further butadiene molecules w h i c h again form an intermediate complex, starting a new cycle. T o prove this idea we tried to isolate a reaction intermediate. Below is de scribed the synthesis of a compound w h i c h seems to be very important i n this connection. B y reaction of nickel acetylacetonate with organometallic compounds i n ether i n the presence of all-£rans-cyclodecatriene, we obtained an intensely red solution from w h i c h dark r e d crystals could be isolated. These are volatile under high vacuum a n d have the composition N i C H . T h e mass spectrum shows the molecule to have peaks at 220 a n d 222. This is i n agreement w i t h N i C H , i f we consider that nickel consists of the isotopes N i a n d N i . T h e infrared spec trum shows that a l l double bonds are shared w i t h nickel, because there is no absorption corresponding to normal trans double bonds. 1 2

1 8

1 2

5 8

1 8

6 0

If a solution of this compound is shaken w i t h hydrogen, three equivalents of gas are absorbed immediately. W e obtain as reaction products cyclododecane and metallic nickel. B y heating to 140° C , the compound can be decomposed into cyclododecatriene a n d nickel. Reaction of the compound w i t h carbon monoxide at normal pressure a n d 2 0 ° C . yields cyclododecatriene a n d nickel carbonyl.




140

T h e authors assumed that this compound might have a planar structure w i t h a trigonal nickel atom i n the center of the ring. If we take into consideration that aU 7r-electrons of the three double bonds are shared w i t h the nickel atom, we find that nickel can only reach a 16-electron shell. This electron configuration is very unusual for zero-valent nickel. T o date w e cannot exactly decide whether the compound has a planar structure or not. A n x-ray investigation w h i c h might clear u p this problem is under way. Nevertheless, the authors feel that they also have some chemical indication for a possible structure. T h e centro-nickel com pound was treated w i t h carbon monoxide at — 80° C . In a short reaction period, the red color disappeared and precisely one equivalent of C O was absorbed, form ing white crystals. Apparently the C O now occupies the fourth coordination posi tion of the nickel atom w h i c h thereby can fill its electron shell to a closed noble gas shell. B u t this compound is stable only below 0° C . Above that temperature, it decomposes, forming one-fourth N i ( C O ) , three-fourths N i , and cyclododeca triene. A t first, w e interpreted this reaction by assuming that starting from a trigonal planar structure the addition of one C O led to a strongly distorted tetrahedral structure, stable at l o w temperature. A t higher temperatures, however, this structure was converted into a perfect tetrahedron, a transformation apparently impossible for the ring, so that the compound decomposed. Latest results, how ever, indicate that this explanation cannot be correct, because the authors were able to synthesize a comparable compound, w h i c h is completely stable at room temperature, b y addition of P ( C H ) instead of C O : 4

2

5

3

Therefore, the instability of the former and the stability of the latter compound must have another reason than a geometrical one. Today, it is assumed that the type of bonding between the nickel and the ligand is different i n both cases. If it is now assumed that cyclododecatriene-nickel could be an intermediate i n the cyclododecatriene synthesis, this compound should undergo displacement re actions w i t h other electron donors and especially w i t h butadiene. T o test this hypothesis the centro-nickel compound was treated w i t h cyclooctadiene and a new, nicely crystalline, yellow compound was obtained w h i c h was found to be bis( 1,5-cyclo-octadiene) n i c k e l :


WILKE ET AL

Réactions of New Pi-Complex Catalysts

141


B y this reaction, the nickel atom can reach an 18-electron shell, and this might be the reason w h y the cyclododecatriene molecule can be displaced so easily by cyclo-octadiene. In the same way, cyclo-octatetraene displaces a cyclododecatriene molecule, but there are two different possibilities. If this reaction is conducted at —40° C , an orange-colored crystalline compound is obtained, w h i c h has a similar structure. T w o cyclo-octatetraene molecules are bound to one nickel atom to yield bis (cyclooctatetraene ) nickel :

T h e same reaction when carried out at 20° C , leads to black crystals with a metallic luster, of composition ( N i C g H g ) ^ , w h i c h may be polymeric because the solubility is very low. O n each side of the folded cyclo-octatetraene ring, one nickel atom shares the π-electrons of two double bonds.

X

T h e two compounds, bis (cyclo-octadiene) nickel and (cyclo-octatetraene) nickel, can also be synthesized directly by reduction of nickel acetylacetonate i n the presence of olefins. But bis (cyclo-octatetraene) nickel is obtained only by a displacement reaction on the centro-nickel compound. T h e next step was to investigate the reaction of the centro-nickel compound w i t h butadiene. W h e n a solution of this compound is saturated with butadiene at room temperature, we observe that after a certain period the excess of butadiene has reacted w i t h formation of cyclododecatriene and a new complex w h i c h can be isolated by removing the cyclododecatriene under high vacuum. T h e same catalytic reaction can be carried out by using bis (1,5-cyclo-octadiene) nickel as a catalyst. Cyclododecatriene synthesized i n this way consists of three isomers. T h e main product is trans,trans,trans-cyc\ododecatnene and the isolated by-products are trans,trans,cis- and cfs,cts,£rans-cyelododecatriene. The latter compound is a new isomer, previously unknown ( b . p . 110° C , n ^ 1.5129). T h e synthesis of this isomer furnished very good proof of the correctness of the configuration assumed for *rans-£rans,cis-cyclododecatriene, w h i c h , however, had been con tested by Greenwood ( 3 ) . T h e intermediate complex mentioned above can be prepared in a very pure state if the centro-nickel compound is treated at —40° C . w i t h an excess of buta diene. Also in this case the cyclododecatriene w i l l be displaced, but no catalytic reaction takes place, and if the excess butadiene is removed at low temperature, 14

2


142



the residue contains cyclododecatriene, nickel, and butadiene i n a mole ratio of 1:1:3. The cyclododecatriene again can be removed under h i g h vacuum, and the complex can be recrystallized from l i q u i d butadiene. W i t h this complex, different reactions were carried out:

Reaction w i t h C O yielded cyclododecatriene and nickel carbonyl. Shaking w i t h hydrogen gave metallic nickel and n-dodecane. Heating the complex to 100° C . and then shaking w i t h hydrogen formed metallic nickel and cyciododecane. Reaction w i t h C O at —60° C . yielded nickel carbonyl and a C ketone. A d d i t i o n of one mole of P ( C H ) formed a crystalline complex w h i c h was identical w i t h the compound obtained from cyclododecatriene-centro-niekel and P(C H ) . 1 3

2

2

5

5

3

3

H o w can these results be interpreted? T o clear u p this question, the follow i n g mechanism for the structure of this intermediate complex has been proposed:

I

Έ

M

Formula II shows one trans-double bond w h i c h is shared w i t h the nickel atom. Furthermore, there are six carbon atoms w h i c h are i n the state of an ^ - h y b r i d i zation. E a c h C atom shares one ττ-electron w i t h the nickel. ( T h e complex shows the correct molecular weight for N i C H , and there is no absorption i n the infra red spectrum characteristic of double bonds.) This formulation has some rela tionship to structures w h i c h have been recently proposed by different authors (2,4) for various allylic groups bonded to transition metal carbonyls. Formulas I and III represent two alternate structures w i t h σ bonds between the carbon and nickel, w h i c h allow the above-mentioned reactions to be ex plained i n a classical manner: 1 2

1 8

Reaction w i t h carbon monoxide at room temperature effects an electron m i gration resulting i n ring closure. T h e n cyclododecatriene is displaced b y more C O molecules: PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.


WILKE Et AL.

Reactions of New

Pi-Complex Catalysts

143

Hydrogénation prevents ring formation because hydrogen atoms become bonded to both ends of the chain; n-dodecane is obtained as the hydrogénation product. Heat-initiated electron migration leads to ring closure. This step is similar to the first step of the C O reaction. T h e following decomposition gives cyclo dodecatriene, w h i c h forms cyclododecane when hydrogenated. In the course of the C O reaction at —60° C , one C O molecule w i l l be intro duced between one of the N i - C bonds formulated i n the alternative structures, and electron migration results i n formation of the ketone:

y- Nifco)

¥

F i n a l l y , the addition of one molecule of P ( C H ) induces an electron migra tion w i t h formation of cyclododecatriene. N o displacement occurs and the product obtained is identical to that prepared from the cyclododecatriene-centro-nickel complex itself: 2

5

3

Summary A definite intermediate i n the trimerization reaction, w h i c h gives very detailed information about the reaction mechanism has been isolated. I n addition, a very simple method for the synthesis of 1,5-cyclo-octadiene i n yields of 9 5 % has been developed. This process seems to have some technical interest, because 1,5-cyclooctadiene is a very valuable starting material for producing suberic acid and caprolactam. Literature Cited (1) Burks, R. E . Sekul, A . A . (to Cities Service Research and Development Co. ), U . S. Patent 2,972,640 ( April 27, 1959 ). (2) Dehm, H. C., Chien, J . C . W., J. A m . Chem. Soc. 82, 4429-30 ( 1960 ). (3) Greenwood, Ν. N . , Morris, J. H . , J. Chem. Soc., 1960, 2922-7. (4) Heck, R. F., Breslow, D . S., J . A m . Chem. Soc. 83, 1097-102 ( 1961 ). (5) Reed, H . W . B., J. Chem. Soc. 1954, 1931-41. (6) Sekul, Α. Α., Sellers, H . G. ( to Cities Service Research and Development Co. ), U . S. Patent 2,964,575 ( April 2, 1959 ). (7) Wilke, G., J. PolymerSci.38, 45-50 ( 1959 ). (8) Ziegler, K., Gellert, H . G., Holzkamp, E . , Wilke, G., Brennstoff-Chem. 35, 321-5 ( 1954 ). (9) Ziegler, K., Martin, H . , Makromol. Chem. 18/19, 186-94 ( 1956 ). PLATZER; POLYMERIZATION AND POLYCONDENSATION PROCESSES Advances in Chemistry; American Chemical Society: Washington, DC, 1962.


144

(10) Ziegler, K., Sauer, H . , Bruns, L . , Froitzheim-Kühlhom, H . , Schneider, J., Liebigs Ann. Chem. 589, 122-56 ( 1954 ). (11) Ziegler, K., Wilms, H . , Ibid., 567, 1-43 ( 1950 ).


RECEIVED October 9, 1961.


POLYMERIZATION AND POLYCONDENSATION PROCESSES

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