Kinetics and Catalysis, Vol. 41, No. 5, 2000, pp. 604--611. Translated from Kinetika i Kataliz, Vol. 41, No. 5, 2000, pp. 666-673. Original Russian Text Copyright 9 2000 by Flid, Kuznetsov, Grigor 'ev, Belor:

Catalytic Syntheses of Polycyclic Compounds Based on Norbornadiene-2,5 in the Presence of Nickel Complexes: III. Cyclic Dimerization of Norbornadiene-2,5 in the Presence of Organophosphorus Additives V. R. Flid, V. B. Kuznetsov, A. A. Grigor'ev, and A. P. Belov Lomonosov State Academy of Fine Chemical Technology, Moscow, 117571 Russia ReceivedDecember17, 1999 Abstract--The cyclodimerization of norbornadiene-2,5 (NBD) catalyzed by the systems formed on the basis of bis(rl3-allyl)nickel and organophosphorus compounds and the process kinetics are studied. The formation rate of all products follows the overall second-order rate law: first order with respect to the catalyst and NBD. The addition of phosphines and phosphites substantially decreases the reaction rate compared to that in nickel systems containing no organophosphorus additives. The influence of the phosphine ligand structure and temperature on the ratio of the reaction products is studied. The blocking of one coordination site on the nickel atom changes the process kinetics. The loss of two vacancies results in the loss of the catalytic activity of the system. A mechanism explaining the stoichiometry and composition of the reaction products is proposed. INTRODUCTION In our previous papers [ 1, 2], we described the catalytic cyclodimerization of norbornadiene-2,5 (NBD) catalyzed by Ni(0) complexes. The NBD-nickel systems formed by different methods from the starting nickel complexes are the true catalysts of this reaction. The modifying additives used in NBD cyclodimerization, along with transition metal compounds, are known to stabilize the catalytically active state of the metal and, in some cases, affect the process rate and ratio of the products [3-5]. Organophosphorus compounds are the most efficient. A detailed study of their role in NBD cyclodimerization would make it possible to deliberately affect this reaction. In addition, the use of phosphine ligands that form a strong bond with the metallic center is an important step toward heterogenized catalytic systems. EXPERIMENTAL The synthesis of bis(rl3-allyl)nickel and all procedures concerning its storage and transfer into a reactor were carded out according to the procedures described in [1, 2]. Kinetic experiments were carded out at constant temperature in 25-mi static vacuum reactors with sampler. The reaction mixture was analyzed and the process course was monitored by gas chromatography on a CarloErba model 4200 chromatograph using an SPB-I capillary column (30 m long).

The concentrations of reactants and reaction conditions were varied within the following limits: Concentration of NBD Concentration of Ni(CaHs)2 Temperature Molar ratio organophosphorus ligand : nickel

0.5-5.0 mol/l 0.01--0.10 mol/l 10--100~ 1--4

The following organophosphorus compounds (Fluka) were used: (a) Phosphines: trimethylphosphine, triethylphosphine, triisopropylphosphine, tri-tert-butylphosphine, tricyclohexylphosphine, triphenylphosphine and triortho-tolylphosphine, and bis(1,2-diphenylphosphino)ethane (Diphos); (b) Phosphites: triethylphosphite and triphenylphosphite. An organophosphorus ligand was introduced into a reaction solution either at the stage of formation of the nickel NBD complexes or during the reaction; metaxylene was used as a solvent. The following physicochemical methods were used for the identification of the products: (1) Liquid chromatography coupled with mass spectrometry on an MS-80 Kratos mass spectrometer attached to a Carlo-Erba model 4200 chromatograph (spectra were recorded in an electron impact regime at an ionization energy of 50 eV, an ionization current of 100 mA, and a temperature of the source of 150~

0023-1584/00/4105-0604525.00 9 2000 MAIK"Naukallnterperiodica"

CATALYTIC SYNTHESES OF POLYCYCLIC COMPOUNDS. III. (2) FTIR spectroscopy on an IFS-113 Bruker spectrometer; (3) NMR spectroscopy on a Bruker MSL-200 spectrometer; ~H NMR spectra were recorded at a working frequency of 200 MHz using CDCI 3 and C6D6 as solvents; 13C NMR spectra were recorded at a working frequency of 62.9 MHz using CDC13 as a solvent; (4) X-ray electron spectroscopy (XES) on Riber LAS-4000 and ES-2401 spectrometers using MgKa as a source (1253.6 eV) (power, 300 W; pressure, 10-5 Pa). The Cls line (285.0 eV) was used as a standard. The resolution ability was of the order of 0.1 eV, and the accuracy in the determination of the position of the levels was 0.2 eV. The samples were prepared and transported into the vacuum chamber of the spectrometers in an atmosphere of argon. NBD dimers were identified using the published data [6, 7]. RESULTS AND DISCUSSION The cyclodimerization of NBD catalyzed by the nickel systems affords a set of isomeric products with the penta- and hexacyclic structures [2].

I

NiLn

NBD

-(L-L) or (NBD-L)

9

Ni(NBD)2

and subsequent equilibrium transformations NBD

Ni(NBD)2 ~

NBD

Ni(NBD)3 ~

Ni(NBD)4.

A similar process was studied in the presence of organophosphorus additives. The analysis of the composition of the reaction products indicates two substantial differences from the systems without a modifying ligand. First, along with the exo-trans-exo (I) and exo-trans-endo (If) isomers, we succeeded in obtaining (up to 15%) the endo-trans-endo (III) isomer of pentacyclo[8.2.1.14,7.02,9.03,8]tetradeca-5,11diene. Second, the endo-endo (IV) and exo-endo (V) isomers of hexacyclo[7.2.1.13,715,13.02,8.04.6]tetradeca_ 10-ene (which are absent from the reaction products and appear only after the thermal decomposition of intermediates in stoichiometric amounts with respect to nickel):

IIl

V

Figure 1 shows that the induction period during which the true catalysts (Ni(0) complexes containing one phosphine ligand and norbornadiene ligands) of the process are formed preceds the cyclodimerization process. The study of the influence of phosphine and phosphite additives on the process showed that its rate decreases with an increase in the P/Ni molar ratio from 1 to 4, and the reaction completely ceases when the ratio becomes -2.3. The kinetic regularities of the process change in the interval from 0 to 2.3, along with the general decrease in the rate. Therefore, nickel comNo. 5

The true catalysts of the process are the complexes of Ni(0) formed during the induction period from the starting nickel compounds by ligand substitution

II

IV

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plexes with at least two blocked coordination sites are inactive in NBD cyclodimerization. Since complexes with different compositions may exist in a solution under the indicated conditions, this idea required addition confirmation. For this purpose, we carried out a series of experiments using the bidentate phosphine ligand Diphos. The cyclodimerization rate substantially decreases with an increase in the Diphos concentration, although the kinetic regularities and the ratio of the products remain unchanged. As can be seen from the data presented below, the process completely stops when Diphos is 30% in excess of Ni.

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FLID et al.

C, mol/I

w x 106moll -t s-l

w x 105moll-I s-1 2.0 II

24

24

i

11.6

4 ~

........

~

1,2 16

2

I

" 0.8

0.4

1 0

16

~

) 1

2

i 3

) 4

) 5

i 6

8

"1 7

t, h

Fig. 1. Changein the concentrationsof NBD and products of its cyclic dimerizationI-III during the kinetic experiment. 10~ meta-xylene, catalyst Ni(C3Hs)2-P(CH3) 3, Cca t = 0.030 tool/l, ratio P/Ni = 1. Curvenumberingcorresponds to the numberingof products.

1

2

3

4

5

CNBD, mol/!

The relative rate of NBD cyclodimerization as a function of the ratio Diphos/Ni(C3Hs)2 is as follows:

Fig. 2. Reactionrates of the formationof dlmers I, II, and III as functionsof the concentrationof NBD.80~ catalyst Ni(C3H5)2-P(CH3)3, Ccat= 0.030 tool/l,rneta-xylene.

Diphos/Niratio, 0 0.20 0.40 0.60 0.80 1.00 1.20 1.30 mol/mol Relative rate, 1 0.81 0.64 0.48 0.31 0.15 0.04 0

ith product; and Ccatand CNBDare the concentrations of Ni(C3Hs)3-PR3 and NBD, respectively.

wlwo

An increase in the electron density at the nickel atom usually favors a more efficient occurrence of the reaction [4]. Hence, we could expect an increase in the process rate in the presence of phosphine ligands. However, in fact, the overall reaction rate decreases by a factor of 1.5 to 4, which can be related to a decrease in the lability of phosphine-NBD nickel complexes relatively to that of the homotigand norbornadiene complexes. The favorable electronic influence of the phosphine ligand is probably compensated by the negative sterie effect, which hinders the coordination and intramolecular rearrangement of NBD molecules in the complex.

Comparison of the process rates w at different Diphos/Ni ratios with the standard w0 (in the absence of Diphos) allows us to conclude that nickel complexes incorporating Diphos lose their catalytic activity in the reaction. Therefore, at least three free coordination vacancies at the metal atom are needed for catalytic cyclodimerization of NBD. Hence, the reaction was studied in the presence of monodentate phosphines (PR3) and phosphites taken in an equimolar ratio to nickel. The formation rates of dimers I-III as functions of the concentrations of Ni(C3Hs)2-P(CH3) 3 and NBD presented in Figs. 2 and 3 indicate that the reactions have first orders with respect to the catalyst and reactant; that is, all products with the pentacyclic structure are formed according to the general kinetic Eq. (1), which is valid for monodentate phosphine mad phosphite ligands with different structures:

app

wi = ki Cc~tCNBD,

(1)

where wl is the rate of the formation of the ith product; k app is the apparent rate constant of the formation of the

In the presence of phosphites, the process rate decreases to a greater extent (by 20--40 times), which can be due to the enhancement of the electron-withdrawing properties of phosphites compared to those of phosphines. The ratio of the NBD cyclodimerization products depends on the nature of the phosphine ligand. The values of Eb of Ni2p3a in the X-ray electron spectra of the samples are close and indicate approximately the same electronic influence of various phosphine ligands on the central atom (Table I). The rate of the reaction and its activation parameters also change insignificantly (Tables 2, 3). KINETICSAND CATALYSIS VoL 41

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Table 1. Influence of the nature of the organophosphorus ligand and temperature on the ratio of NBD cyclodimerization products Conic angle for PR3, 0

Eb (Ni2p3/2), eV*

P(CH3)3

118

853.8

P(C2Hs)3

132

854.0

P(C6Hs)3

145

854.0

P(i-C3H7)3

160

853.9

P(C6H 11)3

170

854.2

P(t-C4H9)3

182

853.9

P(o-CH3C6H4)3

194

854.0

Organophosphorus ligand

Ratio of dimers, % II

T, ~ 10 25 60 90 10 25 60 90 10 25 60 9O 25 6O 90 25 6O 9O 25 6O 90 25 60 90

18 20 24 29 20 26 33 38 25 29 47 64 36 54 67 38 53 69 39 57 72 44 59 76

66 64 61 57 65 60 55 51 63 51 45 30 64 46 33 62 47 31 61 43 28 56 41 24

III 16 16 15 14 15 14 12 11 12 10 8 6

* XES data. In contrast, the steric features of phosphine characterized by the conic angle 1 substantially affect the mutual orientation of coordinated NBD molecules in the complex and, hence, the ratio of dimers with different structures. We can follow the tendency of the increasing fraction of dimer I over those of II and III with an increase in the phosphine volume. Isomer III is not formed in the presence of the bulkiest phosphines P(iso-C3H7) 3, P(C6Hli) 3, P(tert-C4H9) 3, P(orthoCH3C6H4)3. When the temperature increases in the 10-90~ interval, the yield of dimer I increases while the amount of dimers II and l l I (Table 1) decreases. The larger the size of the phosphine ligand, the more pronounced this tendency. For example, in the presence of trimethylphosphine, when the temperature increases from 10 to 90~ the yield of isomer I increases 1.6 times and the yields of II and IH decrease 1.2 and 1.1 times. When triphenylphosphine is used, the yield o f l increases 2.6 times and those of H and 11I decrease 2.1 and 2.0 times, respectively. Based on the obtained kinetic data and the results of the previous studies [2], we propose the mechanism that describes the behavior of the phosphine-containing system. 1The concept of a conic angle was introduced by Tolman and defined as an angle of a cylindricalcone with the vertex at a distance of 2.28 A from the reaction center [8]. KINETICS AND CATALYSIS

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According to the published data [9], the phosphine ligand is much more strongly bound to the nickel atom than NBD. Therefore, a Ni-PR 3 fragment can be considered a w x 10s mol I-'l s-1

12

w x 106 mol[ -1 S- 1

o

I

12

8

8

4

4

0

I 0.02

I 0.04

I i 0.06 0.08 Ccat, mold

I 0.10

0

Fig. 3. Reactionrates of the formationof dimers I, II, and HI as functionsof the concentrationof the catalyst.80~ catalystNi(C3Hs)2-P(CH3)3, CNBD= 1.0 tool/l,meta-xylene.

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FLID et al.

Table 2. Apparent second-order rate constants (kapp) in the formation of isomers I, II, and III as functions of the temperature and nature of the organophosphorus lil and Organophosphorus ligand

T, ~

k app x 10 4, I mo1-1 s-1

II

E a, kJ/mol III

10 0.014 0.051 0.012 25 0.070 0.224 0.056 60 1.680 4.240 1.050 90 15.80 31.06 7.630 10 P(C2Hs)3 0.013 0.042 0.0098 25 0.059 0.014 0.0320 60 1.160 1.930 0.4200 90 9.520 12.80 2.7600 10 0.012 P(C6Hs)3 0.030 0.0058 25 0.051 0.090 0.0180 60 0.930 0.890 0.1600 90 7.190 3.370 0.6700 25 0.047 P(i-C3H7) 3 0.084 60 0.990 0.840 90 8.470 4.170 25 0.040 P(C6HII)3 0.O65 60 0.720 0.640 90 5.540 2.490 25 0.035 P(t-C4H9) 3 0.056 60 0.710 0.530 90 5.880 2.290 25 0.022 P(o-CH3C6H4) 3 0.028 60 0.420 0.290 90 3.370 1.060 Note: Solvent meta-xylene. Relative error m the determination of constants is 10%.

P(CH3)3

II

III

75.0

68.1

69.1

70.4

61.1

60.2

68.5

50.4

50.7

71.9

54.0

68.2

50.4

70.8

51.3

69.7

50.3

Table 3. Activation parameters of NBD cyclic dimerization in the presence of organophosphorus ligands Organophosphorus ligand P(CH3)3

Reaction product I

II III P(C2Hs)3

I

II IlI P(C6Hs)3

I

II III P(i-C3HT)3

I

II III P(C6HI 1)3

I

II III P(t-C4H9)3

I

II III P(o-CH3C6H4) 3

I

II III

Preexponential factor, 1 mo1-1 s-1

Activation enthalpy AH#, kJ/mol

Activation entropy AS"#,J mol-I K-!

9.8 x 107 1.9 x 107 1.6 x 106 1.3 x 107 7.2 x 105 1.1 x 105 5.2 x 106 6.1 • 103 1.4 x 103 1.9x 107 2.4x 104

72.3 65.4 66.4 67.7 58.4 57.5 65.8 47.7 48.0 69.2 51.3

-92.5 -106.2 -127.0 -109.4 -133.5 -148.7 -117.1 -173.1 -185.4 -106.2 -161.6

3.6 x 106 6.1 x 103

65.5 47.7

-120.1 -173.1

9.0 x 106 5.5 x 103

68.1 48.6

-112.4 -173.9

3.6x 106 1.8 x 103

67.0 47.6

-120.1 -183.1

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CATALYTIC SYNTHESES OF POLYCYCLIC COMPOUNDS. III. matrix that is unchanged during the overall catalytic process. If the step of NBD dimer formation is intramolecular and the products are formed in the intermediate n-complex, their structure should be determined by the structure of the NBD--phosphinenickel intermediates.When modeling this step, one shouldtake into account that Ni(0) in ole-

609

fin complexes has the electron configuration 3dl~ sp 3hybridization,and the corresponding tetrahedral structure of the coordination polyhedron, and NBD can act as a monodentate or a chelate ligand. Therefore, we propose the process mechanism in the following form: 111

IV

VII.1 PR3 I

PR3 VI ~

~

~

_

~/~I

NBD ~. ,It

=

VII.2

!R~-- '~IIII.3 ~

~R 3

Scheme

~

1. Mechanismof catalyticNBD cyclodimerizationin the presenceof nickelphosphinecomplexes.

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FLID et al.

Complex VII, which is in equilibrium with complex VIII, dominates in the solution. GLC analysis of the reaction solutions confirms the existence of complex VII in large amounts. The possibility of both the endoand exo-orientation of the monodentate NBD molecule in complex VII is confirmed by the formation (due to its thermal decomposition at 200~ of two hexacyclic stereomers with the endo-endo (IV) and endo-exo (V) structures, whose total amount corresponds to the starting bis(rl3-allyl)nickel. The introduction of excess organophosphorus ligand into the system destroys complex VII. This is indicated by the absence of products IV and V and discoloration of the reaction solution. Let us consider in more detail the stoichiometry of the formation of pentacyclic dimers I-Ill. In the framework of the model of the tetrahedral coordination Ni(0) polyhedron, four variants of complex VIII containing three monodentate NBD molecules (VIILI-VIIL4) can be formed. These complexes differ in the exo/endo-orientation of the NBD molecules relative to Ni: VIII.1 contains only exo-oriented NBD molecules, VIII.2 contains two exo- and one endo-, VIII.3 contains one exo- and two endo-, and V i l l a contains three endo-coordinated NBD molecules (see Scheme 1). A comparison of the structures of the products with NBD ligand orientation in complexes VIII.I-VIII.4 indicates that dimer I can be formed from complexes VIII.1 and VIII.2, dimer II can be formed from VIII.3 and VIII,2, and dimer III can be formed from VIII.3 and VIII.4. Complexes VIII.1-VIIL4 are formed from intermediates VIL1 and VII,2 that differ in the orientation of the monodentate NBD ligand. The second (chelate) NBD molecule can exist only in the endo-position due to steric reasons. Since the NBD that attacks complex VII from the solution is characterized by exo-addition [9], mixed variants of NBD coordination occur in the first step of VIII formation (complexes VIIL2 and VIIL3). Then, compounds VIII.1 and VIII.4 are formed due to a change in the orientation of the NBD ligands at the equilibrium steps. Some aspects of the proposed mechanism can conveniently be considered using the results of simple statistical analysis. If all possible NBD orientations relative to the nickel atom in the intermediate complexes were equiprobable and complexes VIII.2 and VIIL3 were formed mostly at low temperatures, dimers I, If, and III would be formed at a ratio of 1 : 4 : 1. The data in Table 1 show that, at 10~ the ratio of the products differ insignificantly from the predicted value. However, already at this temperature, we observe an "excess" of isomer I over III, which suggests that the exo-orientation of the NBD ligands is preferable. For example, for P(CH3)3, the ratio of products I-III is 1.1 : 4.3 : 1.0, and

for the more bulky PPh 3, it is 2.1 : 5.3 : 1.0; that is, the exo.coordination of the NBD ligands becomes still more preferable with an increase in the conic angle 0 of phosphine. An analysis of the product composition suggests that complexes VIII.I and VIII,4 are formed with an increase in temperature. Taking into account the above assumptions, the statistical ratio of complexes VHL1VIII.4 is 1 : 3 : 3 : 1., resulting in the formation of dimers I-III in a ratio of 1 9 2 : 1. However, for P(CH3)3, the ratio of the dimers with a temperature increase approaches 2 : 4 : 1, As at low temperatures, with an increase in 0, the content of dimer I increases, while those of II and HI. For PPh3 decrease, the ratio of the products at 90~ is 10.7 : 5.0 : 1.0. This can be related to the fact that the formation of complex VIII.4 containing only endo-NBD fragments is spatially hindered. Dimer lII is not formed at all when phosphines with 0 higher 160~ are used. It is most likely that, in the presence of such bulky ligands as P(iso-C3HT)3, P(CtHt 1)3, P(tert-Bu)3, and P(ortho-CH3CtH4)3, the formation of complex VIII.3 (and hence VIII.4) is suppressed, since the simultaneous endo-orientation of two, and the more so three, NBD molecules becomes very unfavorable. An increase in the concentration of dimer I with an increase in the sizes of the phosphine ligands can be explained by the fact that the NBD molecules, under these conditions, are forced to take a more compact exo-coordination. CONCLUSION Based on the results obtained, we conclude that, although the use of various phosphine ligands enables one to control the ratio of products I-III over a broad range, we failed to obtain a quantitative yield of individual isomers in the considered system, because neither the variations in the concentrations of the catalyst or NBD nor a change in the reaction temperature can substantially affect the ratio of the products due to the similarity of the kinetic behavior and closeness of the activation parameters. However, the use of phosphines completely excludes the formation of heterocyclic dimers and enables one to obtain compound III, which is not formed in the traditional systems. ACKNOWLEDGMENTS This work was supported by the Russian Foundation for Basic Research (project no. 99-03-32151) and the Haldor TopsideA/S. The authors thank Supelco for providing us with chromatographic columns. KINETICS AND CATALYSIS Voi. 41

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1. 2. 3. 4. 5. 6.

REFERENCES Flid, V.R., Manulik, O.S., Grigor'ev, A.A., and Belov, A.P., Kinet. Katal., 1998, vol. 39, no. 1, p. 56. Flid, V.R., Manulik, O.S., Grigor'ev, A.A., and Belov, A.P., Kinet. Katal., 2000, vol. 41, no. 5, p. 597. Yoshikawa, S., Aoki, K., Kiji, J., and Furukawa, J., Bull. Chem. Soc. Jpn., 1975, vol. 48, no. 11, p. 3239. Yoshikawa, S., Aoki, K., and Furukawa, J., Bull. Chem. Soc. Jpn., 1976, vol. 49, no. 4, p. 1093. Tolman, C.A., Chem. Rev., 1977, vol. 77, no. 3, p. 313. Arnold, D.A., Trecker, D.J., and Whipple, E.B., J. Am. Chem. Soc., 1965, vol. 87, no. 12, p. 2596.

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7. Dzhemilev, U.M., Podpod'ko, N.R., and Kozlova, E.V., Metallokompleksnyi kataliz v organicheskom sinteze (Catalysis by Metal Complexes in Organic Synthesis), Moscow: Khimiya, 1999. 8. Masters, Ch., Homogeneous Transition-Metal Catalysis, London: Chapman and Hall, 1981.

9. Collman, J.E, Higedus, L.S., Norton, J.R., and Finke, R.G., Principles and Applications of Organotransition Metal Chemistry, Mill Valley: University Science Books, 1989. 10. Lautens, M., Tam, W., and Edwards, L.G., J. Org. Chem., 1992, vol. 57, no. 1, p. 8.