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Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 178-181
Improved Nickel Complex Catalyzed Oligomerization of Isoprene in Aprotic Polar Solvents Isao Mochlda, Hldenorl Okamoto, Karunorl Kitagawa, Hlroshl Fujitsu, and KenJlroTakeshlta Research Institute of Industrial Science, Kyushu Universb, Fukuoka, Japan 8 12
The catalytic activity of NiCI,jPPh& reduced by NaBH, for the ollgomerization of isoprene was studied in aprotic polar solvents such as HMPA. The catalytic turnover number and the reaction rate were found to be enhanced in such solvents. The catalytic turnover number in HMPA could be over I000 at 80 O C by the prolonged reaction time. The principal products were cyclic dimers and trimers,Selectivity among which depended on the concentration of isoprene charged. The rate of dimerlzatbn was further accelerated by the addition of suitable amine In a suitable amount. The schematic aspect of this reaction in HMPA Is dlscussed.
Introduction Dimerization reactions of conjugated dienes have been intensively studied using various catalyst systems that contain transition metal ions of various coordination structures (Bird, 1967; Heimbach et al., 1970; Jolly and Wilke, 1974; Wade et al., 1976). The present authors have reported the enhanced activity of NiClz[PPh&-NaBH4 by the addition of amines in the presence of a suitable amount of water using benzene as the solvent (Mochida et al., 1976,1977,1978). By choosing a proper amine, linear or cyclic dimers could be synthesized at high selectivity. However, the turnover number of the catalyst was rather small, so that the complete conversion of isoprene could never be achieved when the mole ratio of the substrate charged to the catalyst was over 100. Low turnover numbers of the catalyst have been reported for isaprene (Pittman and Smith, 1975a), being different from butadiene (Kiji et al., 1973; Pittmann and Smith, 1975b; Pittmann et al., 1975), although some palladium or iron catalysts were reported to show an excellent catalytic turnover for this reaction (reportedly over 1500) (Wu and Swift, 1972; Takahashi et al., 1973; Neilan et al., 1976). In the present paper, the authors report the improved turnover number as well as the enhanced activity of the catalyst system for the oligomerization of isoprene by using some aprotic polar solvents. Experimental Section NiC12[PPh,], was prepared by the method described in the literature (Itatani and Bailar, 1967). All organic reagents were purified by distillation under nitrogen. The oligomerization reaction was carried out in a sealed glass tube which was kept in an oil bath at constant temperature. The reaction components consisted of 0.5 mmol of NiCl2[PPh3I2,1.5 mmol of NaBH4, 1mL of n-hexane (internal standard), 4.5 mL of hexamethylphosphoric amide (HMPA), and 1mL of isoprene (the mole ratio of isoprene/Ni was 20 in the case). After the content was frozen in liquid nitrogen, the tube was degassed in vacuo to be sealed. After the reaction was over, the reaction mixture was washed with 1 N HC1 (to remove HMPA) and then a mixture of isoprene oligomers and the internal standard were analyzed by a gas chromatograph using a column packed with Apiezon grease L. The oligomeric products in the present study were dimethyloctadienes (2,6- and 2,7-dimethyl-2,6-octadiene and 2,6-dimethyl-1,6-octadiene) (DMOD), 2,6-dimethyl-1,3,6octatriene (DMOT), dipentene (1.8(9)-p-menthadiene) (DP), 1,5-and 2,5-dimethyl-1,5-cyclooctadiene (DMCOD), 0196-4321/81/1220-0 178$01.OO/O
1,5,9-trimethyl-1,5,9-cyclododecatriene (TMCDT) and linear trimers. Oligomers other than linear trimers were identified in a previous paper (Mochida et al., 1976). The mixture of linear trimers formed in this reaction was fractionated by gas chromatograph and the isolated samples were analyzed with NMR, mass and IR spectroscopy. 2,6,1l-Trimethyl-1,6,9,1l-dodecatetraene (TMDT) ('H NMR (CDC13)6,1.50 (m, 2H), 1.59 (S, 3H), 1.70 (S, 3H), 1.83 (S, 3H), 2.00 (m, 4H), 2.74 (d, 2H, J = 7 Hz), 4.65 (S, 2H), 4.85 (S, 2H), 5.17 (t, lH, J = 7 Hz), 5.58 (d, t, lH, J = 16.7 Hz), 6.12 (d, lH, J = 16 Hz)) was a major identified product. Results and Discussion Catalytic Activity of NiClz[PPh3]2-NaBH4in HMPA for the Oligomerization of Isoprene. NiClz[PPh3l2-NaBH4catalyst system in HMPA showed excellent activity for the oligomerization of isoprene as shown in Table I, where its catalytic activities at various temperaturea are described, using the isoprene/nickel mole ratio of 20. The catalyst system in HMPA required no addition of water nor amine as the cocatalyst. The dimerization hardly proceeded at 80 "C in the nonpolar solvents such as benzene as shown in Table I. The conversion reached up to 91% by the reaction in HMPA even at 50 "C for 24 h, where the conversion was less than 20% in benzene even if promoted by @-picoline,the best cocatalyst (Mochida et al., 1978). The catalytic activities in HMPA at the different isoprene/nickel ratios are summarized in Table 11, where the ratio was varied from 20 to 1000 and the reaction temperature was fixed at 80 "C. At the ratio of 20, the conversion reached 90% by 1 h. When the mole ratios were 180 and 240, the conversion reached 100% by the reaction for 24 and 48 h, respectively. By extending the reaction time to 11 days, the conversion also achieved 100% even at the ratio of 1000, although the carbon balance for the identified oligomers was a rather low 80% in this case. Such a high catalytic turnover number was never observed in benzene by using the same catalyst, where it was 60 at the highest (Mochida et al., 1978). The conversions achieved by several fmed reaction times at 80 "C were plotted against the ratios of isoprene/nickel in Figure 1. The conversion decreased sharply with the increasing ratio at the fixed reaction time, indicating that the reaction was negative order in isoprene. The influences of HMPA concentration of the conversion are shown in Figure 2. The addition of HMPA in more than 20 mole ratio to the complex was sufficient for 0 1981 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 1, 1981
179
Table I. Catalytic Activity at Several Reaction Temperaturesa yield, %
react ion temp,"C 30 50 65 80 100 50
DMOD 18.3 18.1 12.4 13.1 7.8 12.8
conv, % 24.4 36.0 83.8 87.5 84.6 91.4 5.3
8OC
DMOT 0.8 2.4 22.0 16.3 12.6 31.3
DP 1.5 6.0 25.9 20.0 22.3 31.2 4.2
DMCOD 1.5 4.8 15.4 22.7 32.4 17.5 0.2
TMCDT 1.5 1.5 2.9 5.6 1.4
TMDT other trimers 0.3 0.1 2.0 0.1 3.0 3.7 7.4 4.2 2.8 0.6 3.5 0.5
NiCl,(PPh,),, 0.5 mmol; NaBH,, 1.5 mmol; n-hexane, 1mL; isoprene, 1 mL; HMPA, 4.5 mL; reaction time, 1h. tion time, 1 2 h. In benzene, reaction time 24 h.
Reac-
Table 11. Catalytic Turnover Number of Nickel Catalyst in HMPAa ~~
isoprene / Ni molar ratio 206
~
~
yield, % conv, % 87.5 29.1 7.2 94.8 96.2 97.6 97.5 97.7 81.0 27.6 98.2 50.5 99.1
DMOD 13.1 2.1 0.9 13.0 5.6 3.3 2.0 0.4 0.9 0.3 1.2 0.4
DMOT 16.3 7.0 1.2 15.0 26.7 16.9 13.6 8.4 6.3 1.3 8.5 2.5 0.7
DP 20.0 8.8 2.0 26.3 35.4 20.3 17.4 9.8 8.3 2.6 14.0 8.5 19.3
DMCOD
TMCDT
TMDT other trimers
22.7 2.9 5.6 2.8 1.2 5.1 1.5 3.3 180 0.2 1.1 1.2 0.6 20c 4.8 27.1 1.4 0.4 40 2.5 21.7 3.5 0.3 8OC 10.0 2.2 41.8 2.5 120c 13.5 46.1 3.9 1.5 18OC 18.4 1.6 49.9 9.1 24OC 22.0 9.9 3.3 30.3 5OOc 4.6 6.9 3.2 8.8 240d 17.7 18.2 35.6 2.9 500d 16.3 10.2 8.9 3.7 1000e 2.2 11.2 29.3 30.9 NiCl,(PPh,),, 0.2-0.5 mmol; NaBH,:Ni complex = 3; n-hexane, 1mL; isoprene, 1-30 mL; HMPA:Ni complex = 50; Reaction time. 1 h. Reaction time, 24 h. Reaction time, 48 h. e Reaction time, 11 reaction temperature, 80 "C. days. 80:
b
I
If
\
0, ,
0 0
250
0
500
50
IsopreneINi molar ratio
Figure 1. Effect of the molar ratio of isoprene to NiClz(PPh3)2:0, reaction time 1 h; 0 , reaction time 24 h; e, reaction time 48 h.
the catalytic activity. The same activity was observable a t its mole ratio of 200, whereas an excess of amine retarded the reaction as reported in a previous paper (Mochida et d.,1976). The product distribution wm essentially unchanged regardless of the HMPA concentration. The major products in HMPA were cyclic dimers and trimers, although considerable amounts of DMOD and DMOT were detectable at low isoprene/nickel ratios. The selectivity of DMCOD increased with increasing isoprene/nickel mole ratio, reaching the maximum of 50% at the ratio of 180. The selectivity of DP achieved the maximum value (35%) at the ratio of 40 and decreased above this ratio. TMCDT and linear trimers were minor products at lower ratios; however, their yields increased considerably at larger ratios, their total yield reaching 40% of the products at the ratio of 1000. The reaction profiles at isoprene/nickel ratios of 20 and 240 are shown in Figures 3 and 4, respectively. These figures indicate that the rate of the oligomerization reaction in HMPA is much faster than that enhanced by @-picoline in benzene. At a low ratio of isoprene/nickel, the major
100 150 HMPA /Ni m l a r ratio
200
Figure 2. Effect of the concentration of HMPA on the reaction NiClZ(PPh&,0.2 mmol; NaBH,, 0.6 mmol; n-hexane, 1mL, isoprene, 4.8 mL; at 80 O C for 24 h: 0 , conversion; 0,DMOD; A, DMOT; 0 , DP; a), DMCOD; e, TMCDT; 0 , TMDT.
-
7
yo-
Y
P
F
@yo:!8E=Or :6: 6
0
0 . 5Reaction1 Time 1.5 (hr.)
2
2L
Figure 3. Catalytic activity of NiClz(PPh8)z-NaBH4in HMPA; NiCl,(PPh&, 0.5 mmol; NaBH,, 1.5 m o l ; isoprene, n-hexane, 1mL; HMPA, 4.5 mL; at 80 O C : 0 , conversion; 0,DMOD; A, DMOT; 0 , DP; a, DMCOD; @, TMCDT, 0 , TMDT, 0 , conversion in benzene + @-picoline.
products were initially DP and DMOT; however DMCOD became dominant by longer reaction time. A t a large ratio
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 1, 1981
Table 111. Effect of the Solvents on the Catalytic Activity yield, % solvent HMPA" DMF" DMA" DMS?" TMU DMF~ DMA~ HMPA~ DMAC HMPAC
conv,%
DMOD
DMOT
DP
DMCOD
TMCDT
94.8 95.2 96.6 14.7 19.9 18.4 36.5 27.6 53.0 50.5
13.0 13.0 13.5 2.6 0.2 0.1 0.3 0.3 0.3 0.4
15.0 15.3 14.8 2.1 1.2 1.4 2.1 1.3 3.0 2.5
26.3 31.0 21.8 4.0 2.6 2.2 5.2 2.6 5.4 8.5
27.1 27.8 35.9 3.2 3.2 3.4 5.8 4.6 11.3 10.2
4.8 3.1 5.2 1.5 2.9 2.8 5.8 6.9 9.6 8.9
TMDT other trimers 1.4 3.0 3.1 0.6 8.3 1.2 14.6 8.8 18.1 16.3
0.4 1.9 1.4 0.2 1.6 1.3 1.9 3.2 5.4 3.7
a NiClb(PPh,),, 0.5 mmol; NaBH,, 1.5 mmol; n-hexane, 1mL; isoprene, 1mL; so1vent:Ni = 50; reaction temperature and time 80 C and 24 h. NiC1,(PPha),, 0.2 mmol; NaBH,, 0.6 mmol; n-hexane, 1mL; isoprene, 10 mL; so1vent:Ni = 50; Same conditions same as in b except for reaction time 48 h. reaction temperature and time, 80 C and 24 h.
V
50
Time dependenceof the reaction; NiC12(PPhJ2,0.2 mmol; NaBH,, 0.6 mmol; n-hexane, 1 mL; isoprene, 4.8mL; HMPA, 1.7 mL; at 80 OC: 0 , conversion; 0,DMOD; A, DMOT; 0 , DP; a, DMCOD @, TMCDT; 0 ,TMDT.
Figure 4.
(240) where the reaction was very slow, DMCOD was the major product from the early stage of the reaction. A significant production of TMCDT should be noted at this ratio. Accelerated Rate by the Addition of &Picoline. In previous papers (Mochida et al., 1977,1978),0-picoline was reported to enhance significantly the catalytic activity for the dimerization of isoprene in benzene, where the principal products were cyclic dimers. Accordingly, 0-picoline can be expected to increase the catalytic activity in HMPA, because the large turnover number was achieved; however, the rate was not high enough at large isoprene/nickel ratios. The results were shown in Figure 5. In the case of isoprene/nickel ratio of 240, the conversion after 24 h increased considerably by the addition of &picoline, but it decreased sharply when its mole ratio against the catalyst was over 50. A suitable amount of the amine can accelerate the elimination of coordinated products; however, the excess may block the coordination of isoprene in HMPA due to its strong coordination ability. A selective formation of DP (45%) can be noted at the amine/nickel ratio of 10. Without the amine, the selectivity was only 14% a t this isoprene/nickel ratio and the same conversion level. Catalytic Activity in Other Aprotic Polar Solvents. The activity of the nickel catalyst for the oligomerization was further examined in some other aprotic polar solvents: NJV-dimethylformamide (DMF'), NJV-dimethylacetamide (DMA), tetramethylurea (TMU), and dimethyl sulfoxide (DMSO). Conversions and product distributions in them are summarized in Table 111. DMF, DMA, and TMU also enhanced the activity. In contrast, DMSO showed no enhancement in spite of its similar polarity. The amide group common to the effective solvents may play an essential role for the activation of the catalyst. Among am-
#-Picoline/ Ni molar ratio
100
Figure 5. Effect of &picoline on the reaction; NiC12(PPh&, 0.2 mmol; N a b , 0.6 m o l ; n-hexane, 1mL; isoprene, 4.8 mL; HMPA, 1.7 mL; at 80 "C for 24 h: 0 , conversion;0, DMOD; A, DMOT; 0 , DP; a), DMCOD; @, TMCDT; 0 , TMDT. Scheme I D P
DMCOD
A I
1
TMCDT
TMDT
'
ides, DMA was the best solvent, showing the highest conversion under any conditions, although the conversions in these solvents were over 90% by 1h at low isoprene/ nickel ratios. Product distributions in these amide solvents were identical. Mechanistic Consideration Heimbach and his co-workers (Heimbach et al., 1970) studied extensively the cyclic dimerization of butadiene by the nickel complex and proposed the mechanism. The
Zd. Eng. Chem. Prod. Res. Dev. 1881, 20,
major steps of the oligomerizationare described in Scheme I, where additional schemes for the formation of trimers are included, although the essential ideas follow the scheme proposed by Heimbach et al. (1970). The steps leading to the fifteen carbon (C-15) chain have been less mechanistically explained, although TMCDT-nickel complex was isolated (Jolly and Wilke, 1974). At the initial stage, two molecules of isoprene may form the a-allyl nickel complexes (I) and (II). Successive insertion of another isoprene molecule may produce (IV) and (V) intermediates. Elimination of intermediate C-15 molecules with and without the ring closure from the complex catalyst leads to cyclic trimers (TMCDT) and linear trimers (TMDT), respectively. Along with the scheme, the explanation of the present results and some ideas for future work can be derived. Figure 1 may indicate the removal of the oligomeric products from the coordination sphere is rate determining, isoprene coordinating the catalyst as soon as the sites are open. Such a situation can be assumed as product-poisoning if the oligomeric products easily coordinate again. Since the amine and the amide can share the coordination sites of the nickel ion with isoprene and its oligomers, their reversible coordination can accelerate the elimination of the products when coordinating ability of the additive is suitable. The excess addition of the amine may occupy all the coordination sites of the catalyst to prohibit the coordination of the substrate. Coordination ability of the amide is much weaker than that of amine so that any retardation of the catalytic reaction may not take place. A considerable amount of trimer was found in the product at high isoprene/nickel ratios, using HMPA without any addition of amine, whereas strong coordination ability of amine may not allow the coordination of three molecules of isoprene. The weak but distinct coordination ability of the amide group may stabilize the nickel complex of zero valence not to coagulate into the metal. This ability may be favorable for the high catalytic turnover. In addition, HMPA would be effective for the reduction of NiC12(PPhJ2by NaBH4 without water because its high polarity may be sufficient for the dissolution of the reductant.
181
181-185
In previous papers (Mochida et al., 1976, 1977, 1978), the formation of DMCOD was reported to be selective when sterically bulky amines were used, because the intermediate for DP is more sensitive to the sterical interaction with the coordinated amine. HMPA may be compatible with the intermediate for DP as indicated by its rather selective formation at low isoprene/nickel ratio; however, another isoprene molecule can react with this intermediate to form the intermediate for trimers (IV),(V), when its concentration is high, because nickel ion of the intermediates (I, 11,111)can provide another coordination site for another molecule of isoprene. In a previous paper (Mochida et al., 1978),the consecutive transformation of DP into DMCOD was postulated;however, it was very slow in HMPA. The catalytic turnover number was fairly improved by using HMPA; however, the rate was still rather low when the large amount of the reactant was charged. Addition of a proper amine in a suitable amount and proper selection of phosphine ligand look promising to hasten the reaction, maintaining the large turnover number expected in HMPA. Further survey for the best additive is now in progress. Literature Cited Bird, C. W. "Transltlon Metal Intermedlates in Organic Synthesis", Lcgos Press; London, 1987. Heknbach, P.; Jolly. P. W.; Wllke, G. A&. Orgenomet. Chem. 1970, 8, 81. Itatanl, H., Bailar, J. C., jr. J. Am. Chem. Soc. 1987, 89, 1800. Jolly, P. W.; Wlke, 0. "The Organlc Chemlstty of Nlckel", Amdemlc Press: New Yolk, 1974. Klji, J.; Yamamoto, K.; Mltani, S.; Yoshlkawa, S.; Furukawa, J. Bull. Chem. Soc. Jpn. 1973, 46, 1971. Mochlda, I.; Kltagawa, K.; Fujitsu, H.; Takeshlta, K. Chem. Lett. 1977. 4 1 6 J . Catel. 1978, 54, 175. Mochlda, I.; Yuasa, S.; Selyama, T. J. Catel., 1978, 47, 101. NeUan, J. P.; Laine, R. M.; Cortese, N.; Heck, R. F. J. Org. Chem. 1978, 47, 3455. P M n , C. U. Jr.; Smith, L. R. J. Am. Chem. Soc. 1975a, 97, 34. Plttman, C. U., Jr.; Smlth. L. R. J. Am. Chem. Soc. 1975b, 97, 1749. Pittmen, C. U., Jr.; Smith, L. R.; Hanes. R. M. J . Am. Chem. Soc. 1975, 97, 1742. Takahashi, K.; Hata, G.; Mlyake, A. Bull. Chem. Soc. Jpn. 1973, 46, 800. Wade. R. C.; Hdeh, D. 0.;Hughes, A. N.; Hul, B. C. Catel. Rev. 1976, 74, 211. Wu, ChingYong; Swift, H. E. J . Catal. 1972, 24, 510
Received for review June 4, 1980 Accepted August 13, 1980
Studies of the Chloramination of Dimethylamine and 1,l-Dimethylhydrazine Harry H. Sisler,' Mllap A. Mathur, Sampat R. Jaln, and Rlchard Greengard Department of Chemistry, University of Fbr&t, Gainesvilk, F&&t
326 7 1
The choloramination of dimethylamine in a solution of KOH in l-butanol was carried out in the presence of NH3 at room temperature. The major products were 1,ldimethylhydrazine, the dimethylhydrazone of formaldehyde, and 1,1,4,4-tetramethyC2-tetrazene. The yield of the hydrazlne approximated 30% based on the chloramlne used. 1,l-Dimethylhydrazine was reacted with ammonia-free chloramine in ether solution. The products included CH,, Npr the dimethylhydrazone of formaldehyde, and 1,1,4,4-tetramethyl-2-tetrazene. The reactions of 1,ldimethyihydrazine with HgO and with A g p In ether and aqueous and alkallne solutions were carrled out. Mechanisms for the formation of the various oxidation products are proposed.
Introduction The reaction of chloramine with dimethylamine to form 1,l-dimethylhydrazine was reported more than two decades ago (Omietanski et al., 1956; Sisler and Kelmen, 1957, 0196-4321/81/1220-0181$01.25/0
1958). In the intervening years, several byproducts of the chloramination of dimethylamine have been reported including 2,2-dimethyltriazanium chloride (Utvary and Sisler, 1966,1968; Utvary et al., 1969; Sisler et al., 1969; 0 1981 American Chemical Society
