Reactive Polymers, 12 (1990) 45-50 45 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

THE STUDY OF H Y D R O G E N A T I O N S OF OLEFINS CATALYZED BY P O L Y M E R - S U P P O R T E D

P A L L A D I U M - L A N T H A N O I D BIMETALLIC CATALYSTS

WANG LI and HE BINGLIN

Institute of Polymer Chemistry, Nankai University, Tianjin (P.R. China)

(Received January 9, 1989; accepted in revised form June 12, 1989)

Palladium-lanthanoid bimetallic complex catalysts supported on chloromethylated poly- styrene beads derivatized with anthranilic acid have been synthesized. Their characteriza- tion and catalytic activity have been studied. Under mild conditions, the polymer-bound Pd-La complex catalyzed the hydrogenation of olefins. The hydrogenation rate was correlated with the solubility parameter, 8, of the solvents and substrates. The rates of hydrogenation of octene were studied and the dependence of factors such as catalyst concentration, octene concentration, hydrogen pressure and temperature has been de- termined. The rate equation for the hydrogenation of octene in ethyl acetate solvent was found to be R = kPHCca t. The activation energy of this reaction was 3.0 kcal /mol . It was also found that the promotion effect by anchored Ln ions varied with the atomic number of the Ln series. When the f electron number was O, 7 or 14, the polymer-bound Pd-Ln catalyst possessed the highest activity in hydrogenation.

I N T R O D U C T I O N

To date polymer-bound catalysts contain- ing one kind of metal have been widely studied and applied [1]. Recently there have appeared some papers devoted to the study of bi- metallic complex hydrogenation catalysts pro- moted with rare earth metal ions [2]. The catalytic activities were found to be greatly increased by the co-catalyst.

It has been reported that rare earth com- pounds could be applied to homogeneous catalysts for the hydrogenation of olefins. However, the activity was very low and severe conditions were required. Hidai et al. [3] have

made some homogeneous bimetallic catalysts containing cobalt and ruthenium, and dis- covered that they showed enhanced catalytic activity for the hydroformylat ion of cyclohe- xene. Unfor tunate ly this catalyst was not sta- ble and was readily decomposed in air. It has been found that polymeric catalysts contain- ing only one kind of rare earth metal have no obvious catalytic activity for hydrogenation. However, the rare earth metal ion could be used as a promoter of a polymer-bound metal complex catalyst, and greatly increased the catalytic activity. So far research concerning bimetallic catalysts containing rare earths has not been widely reported in the literature.

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46

Pd (OA=b_

Pd*+

LaC13.3H20

@-_-pd~+ ____ La3+ CH30H- Hz0 (l:l)

pH = 12

Scheme 1.

The present authors now report the synthe- sis of Pd-Ln bimetallic complex catalysts supported on chloromethylated polystyrene beads containing the bidentate ligand, anthranilic acid. The catalyst was prepared as shown in Scheme 1 (where the encircled P denotes polystyrene). The hydrogenation of octene with the catalyst has been investigated.

EXPERIMENTAL

I. Synthesis of catalysts

a. Synthesis of polymer support A styrene-divinylbenzene (57%) copolymer

was obtained by suspension polymerization. Chloromethylation was carried out according to the procedure of Pepper et al. [4], and the chlorine content was 10.23%. Excess anthra- nilic acid in 95% alcohol was then anchored onto the beads as follows [5]. To 1.0 g of the chloromethylated beads suspended in 50 ml of alcohol was added 0.5 g of anthranilic acid. The reaction mixture was stirred for 20 h, then filtered, and the beads were washed with 200 ml of absolute ethanol.

b. Synthesis of polymer-supported Pd-Ln com- plex

Two grams of the above polymeric ligand and a certain amount of Pd(OAc), were sus- pended in 20 ml of acetone under nitrogen and stirred for 24 h at reflux temperature.

After cooling, the reaction mixture was washed with acetone and filtered, and the polymer was reacted with a certain amount of LnCl, .3H,O under reflux in 25 ml of ab- solute alcohol for 10 h.

of @ ____Pd2 +____Ln3 + to

&_!:EY:Ln3+

The resulting complex was maintained un- der reflux in methanol-water (1 : 1) at pH 12 for 6 h as described previously [6]. A chelate resin-supported colloidal metallic palladium catalyst associated with a rare earth metal ion was obtained. The catalyst was stored under nitrogen.

The palladium and Ln contents were de- termined by inductively coupled argon plasma atomic emission spectrometry (Atmoscan 2000).

2. Instruments and hydrogenation procedure

The reaction vessel was a 50 ml flask with a side arm consisting of a three-way stopcock. It was attached to a reaction system with a manometer, a gas burette and a vent, used as a gas vent during deaeration. The reaction vessel, provided with a magnetic stirrer, was immersed in a water bath and maintained at 40 o C. The catalyst (45 mg) was suspended in 10 ml of solvent and the system was evacuated and flushed three times with hydrogen. The mixture was stirred for 30 min, then 10 ml of a solution of substrate was introduced through

the silicone rubber stopper. Hydrogenation was started with resumption of stirring• Stir- ring was carried out so fast that the rate of reaction did not depend on the stirring speed. The rate of the hydrogenation was de- termined by the initial rates of the uptake of hydrogen•

For the discussion of kinetics, the initial rates with fresh catalyst were used. The rate of uptake of hydrogen was measured using the partial pressure of the mixed gases.

R E S U L T S A N D D I S C U S S I O N

1. Kinetics for hydrogenation of octene in ethyl acetate

The overall rate of hydrogenation of octene has been measured and the dependence on catalyst concentration, hydrogen pressure, concentration of substrate and temperature have been investigated. Ethyl acetate was used as a solvent. The hydrogenation product was octane.

A plot of the rate of hydrogen uptake against catalyst concentration is shown in Fig. 1. The rate increases linearly with increasing

u

to

v

% ×

e~

8

6

4

2

0 i I [ I I

0 2 4 6 8 I0

(Cpd+CLa) X 104(mol'l -I)

Fig. I. Dependence of rate of hydrogenation of octene on catalyst concentration, with 1 M octene in ethyl acetate under 1 atm of hydrogen at 4 0 ° C . (©, N : Pd : La = 1 : 0 . 5 8 : 0 . 0 6 5 ; e , N : Pd : La = 1 : 0.31 : 0.057).

47

c>

o g-

×

7.0

6 .0

5 .0

4 .0

3 .0

2 .0

0 - 0 0

"-(3

0 0

0.0

I I I I 0.5 1.0 1.5 2.0

Octene concentration (mol/l)

Fig. 2. Dependence of rate of hydrogenat ion of octene on octene concentrat ion, with 0.4779 m M catalyst (based on Pd) in ethyl acetate and under 1 arm of hydrogen at 40 o C.

catalyst concentration. Here the catalyst con- centration includes the sum of concentration of the main catalyst Pd ° and co-catalyst La I".

The quantitative dependence of the rate on substrate concentration (M) is shown in Fig. 2. The rates are constant in the range of concentration of octene from 0.1 to 2.0 M.

A plot of the rate of hydrogen uptake against hydrogen pressure is shown in Fig. 3. The rate increases linearly with increasing hydrogen pressure.

According to regression analysis, the kinetic experiments indicate that the rate of hydro- genation of octene, R can be represented by the following eqns. (1)-(3):

In R = - 14.2 + 1.02 In PH2 (1)

In R = 0.0463 + 0.988 In Cc, t (2)

In R = - 7.43 + 0.004 In Coctene (3)

Here R is the rate of hydrogen consumption, mol/1 s. Their correlation coefficients (r and standard deviations (S) are shown in Table 1. The overall equation is:

In R = -6 .94 + 1.04 In PH2 + 0.98 In Cca t

-7 .3

0t / 5.0

°~ 4. 0

3,0 -%

,--4

× 2 . 0

i .

O. 0 152 304 456 608 760

Hydrogen pressure (mmHg)

Fig. 3. Dependence of rate of hydrogenation of octene

on hydrogen pressure, with 0.4779 mM catalyst and 1

M oc tene in e thy l a c e t a t e a t 40 o C.

o r

R = 9.683 X 1 0 - 4 p H f c a t

The rate constant at 4 0 ° C is k40oc = 9.683 x 10 -4 mmHg -1 s -1.

Rates of hydrogenation were measured in the temperature range 20 o C-70 o C. The rela- tionship between R and temperature is indi- cated in the Arrhenius plot shown in Fig. 4. Under constant reaction conditions, In R = b --Ea/,.~Z. The activation energy, E a , i s

calculated to be 3.0 kca l /mo l for the hydro- genat ion of octene. Accord ing to the Arrhenius equation,

In k = In k o - E / ~ T

TABLE 1

Statistical coefficients

E q u a t i o n r S

(1) 0.9996 0.0265

(2) 0.9928 0.1200

(3) 0 .6600 0.0470

I 3.1

- 7 . 4 -

, " 4 I

-7.5 -- ¢o

I

. - 7 . 6 - -

v -7 .7 --

-7 .8 --

-7 .£ 3.0

I I I I 3.2 3.3 3.4 3.5

T-1 X '103(K-1)

48

3.6

Fig. 4. Arrhenius plot for the rate of hydrogenation of octene, with 0.4779 mM Pd and 1 M olefin in ethyl acetate under 1 atm of hydrogen.

the value of k0 tion is

R = 0.131 e x p ( - - -

= 0.131. The total rate equa-

l537 ) T P H f c a t

2. Catalytic hydrogenation of octene in various solvents

Hydrogenat ion of octene in the presence of resin-supported P d - L a catalyst (45 mg) was carried out in various solvents at 40 °C under an atmospheric pressure of hydrogen. The hydrogenation rates are plotted against the solubility parameter, 8, as shown in Fig. 5. A considerable correlation between the value of

and the hydrogenat ion rate is observed. From this, it is suggested that the rate of hydrogenat ion depends on the polarity of the solvent used. The solvent effect on the rate is assumed to be based on three factors: (1) the degree of swelling of the resin, (2) the polar gradient between the bulk solvent and the localized environment of the catalytic center, and (3) the solvation of the active center on the catalyst. The active center consists of Pd ° and Lam in the catalyst, in which the La 3+

8 . 0

~ 6 . 0

,--. 5 . 0

~ 4.0 ~ 5

× 3 . 0

2 . 0

1 .0 I I I I I I l " I 8 9 I0 i i 12 13 14 15 16

6 ( 2 5 )

Fig. 5. Relationship between hydrogenation rate and 8 value of the solvent, with 0.4779 m M Pd catalyst and 1 M octene under 1 atm of hydrogen at 40 ° C. (Curve 1, ethyl acetate; 2, ethane; 3, methanol; 4, benzene; 5, toluene; 6, chlorobenzene; 7, acetone; 8, ethanol; 9, N,N-dimethylformamide; 10, tetrahydrofuran; 11, acetic acid).

possesses positive charge and results in ex- istence of polarity on the catalyst surface. (Further details will appear in subsequent papers to be published). Such polarity should decrease the rate of diffusion of the non-polar olefin to the catalytic center. When the polar- ity of the solvent begins to increase, there are many small solvent molecules around La 3÷. The solvation of La 3 + is then stronger, mak- ing it less favourable for adsorption, activa- tion and even the "spilling" of hydrogen onto the Pd surface. The result is a decrease in the hydrogenation rate. However, as the polarity of the solvent is increased, a new polar gradi- ent is formed. As a result, the solvent around the surface of the polymer support is more polar than the catalytic center and this aids the diffusion of non-polar substrates to the catalyst surface because of the swelling of the catalyst. As a result, the hydrogenation rate is increased. Figure 5 shows the relationship between the hydrogenation rate and the solu- bility parameter. When the value of increases from 9 to 11.8, the hydrogenation

49

rate decreases. When 8 is over 11.8, the rate again increases.

3. Catalytic hydrogenation of various olefins

All reactions were started after pretreat- ment with hydrogen in the presence of solvent for 30 min. Table 2 summarizes the initial rates of hydrogen uptake for the hydrogena- tion of various olefins with the polymer-sup- ported P d - L a bimetallic catalyst.

From Table 2, it is observed that there is a maximum value for the hydrogenation rate of the olefins as the length of their carbon chain is increases. The activity of the substrates seems to be sensitive to steric hindrance, e.g., with methyl acrylate and methyl methacry- late, and to the molecular size (with the exception of 1-octadecene) of substrate, par- ticularly in the case of cyclic olefins. When an electrophilic group is attached to a car- bon-carbon double bond (as in allyl chloride), the hydrogenation rate decreases sharply.

4. Promotion effect of rare earth metal

To investigate the accelerating effect of co-catalysts, a similar polymer-supported Pd °

TABLE 2

Hydrogenation rates of olefins a

Substrate Initial rate Substrate Initial rate (ml/min) (ml/min)

1-Pentene 7.27 Cyclohexene 9.34 1-Hexene 12.46 Styrene 14.01 1-Heptene 13.23 Methyl 1-Octene 16.09 acrylate 10.38 1-Octade- Methyl meth-

cene 10.38 acrylate 8.30 a-Pinene 3.11 Allyl chloride 4.15 Cyclopen- Acrylic acid 11.94

tene 12.46

a Using 45 mg (0.4779 m M Pd, 0.053 mM La) of polymer-supported Pd-La catalyst and 1M of substrate under 1 atm of hydrogen, at a temperature of 40 o C, and in 20 ml of ethyl acetate.

50

7 . 5 ~

7.0--

.~ 6.5--

"~ 6.0-- v

tt~ i o

x 5.5--

5.0--

4.5 I I I 1 I I I I 1 I I I I I I I 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

Atomic No. La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tu Yb Lu

Fig. 6. Relationship between hydrogenation rate of octene and the atomic number of the lantharoid series, with 45 mg of catalyst (0.4779 m M Pd) and 1 M octene in ethyl acetate (total volume 20 ml) under 1 atm of hydrogen at 40 ° C.

catalyst without any Ln was synthesized. From a comparison of their activities in hy- drogenation, it is found that the rate of hy- drogen uptake of the Pd-La catalyst is 2.2 times that of a similar Pd catalyst without La [7].

With the contents of palladium and rare earth metal kept constant,, the authors synthe- sized a series of polymer-supported Pd-Ln bimetallic co-catalysts. Lanthanum which has the lowest atomic number of the lanthanum series possesses the highest accelerating effect on the catalyst. The results are shown in Fig. 6. It can be seen that the activity for the hydrogenation of octene corresponds to the stability of the f electron in the rare earth metal. When the f electron number is equiv- alent to 0, 7 or 14 (i.e. empty, half-filled or full), La 3+, G d 3+ and L u 3+ a r e accelerating co-catalysts and the corresponding polymer- supported Pd-Ln catalyst possesses the highest activity in hydrogenation.

Sherrington (Eds.), Polymer-Supported Reactions in Organic Synthesis, John Wiley & Sons, Chichester, 1980, p. 249.

2 J.S. Rieck and A.T. Bell, Studies of the interactions of H 2 and CO with Pd/S iO 2 promoted with La203, CeO 2, Pr6Oll, Nd203 and Sm203, J. Catal., 99 (1986) 278.

3 M. Hidai, A. Fukuoka, Y. Koyasu and Y. Uchida, Hydroformylation of cyclohexene catalysed by homo- geneous bimetallic systems, J. Chem. Soc., Chem. Commun., (1984) 516.

4 K.W. Pepper, H.M. Paisley and M.A. Young, Proper- ties of ion-exchange resins in relation to their struc- ture. Part VI. Anion-exchange resins derived from styrene-divinylbenzene copolymers, J. Chem. Soc., (1953) 4097.

5 N.L. Holy, Versatile polymer-bound hydrogenation catalyst. Anthranilic acid anchored palladium(II) catalysis, J. Org. Chem., 43 (1975) 4686.

6 P.L. Ho and L. Wang, Hydrogenation of alkenes and alkynes with palladium complexes and colloidal pal- ladium on chelate resin, XXV International Con- ference on Coordination Chemistry, Nanjing, China, 1987, El , p. 721.

7 L. Wang and P.L. Ho, The promotion of lanthanum in polymer supported palladium catalyst, to be pub- lished.

REFERENCES

1 C.U. Pittman, Jr., Catalysis by polymer-supported transition metal complexes, in: P. Hodge and D.C.