Journal of Mohdar Catalysis, 60 (1990) 313-321 313

OLIGOMEBIZATION OF ALKYNES BY THE BhCl,-ALIQUAT 336 CATALYST SYSTEM PART 1. FOBMATION OF BENZENE DERIVATIVES

IBFUHIM AMJZR, TAMAR BERNSTEIN, MORIS EISEN, JOCHANAN BLUM*

Department of Organic Chemistry, The Hebrew University, Jerusalem 91904 (Israel)

and K. PETER C. VOLLHARDT

Department of Chemistry, University of California at Berkeley, and the Materials and the Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (U.SA. )

(Received August 22,1989; accepted January 4,199O)

The cycle-oligomerization of several terminal and internal alkynes under phase transfer conditions by the RhCl&liquat@ 336 catalyst is described. The kinetics of 1-heptyne cyclotrimerization at 90°C in 1,1,2,2- tetrachloroethane/water were found to follow the second-order rate law d[arenel/& = -k [alkynel [RhChJ when the molar ratio of substrate:rhodium chloride:quat was approximately 25:l:l. The activation energy of E,= 12.5 kcal mol-’ suggests that the catalysis is both chemically and diffusion controlled. F’roduct analysis is compatible with a mechanism that involves rhodacyclopentadiene rather than metal cyclobutadiene intermediates.

Introduction

The solvated ion pair [(C,H,,),[NCH,l+CRhCl,]-, formed from aqueous RhCls and Aliquat@ 336 [ 11, has been shown to be an efficient, long-lived catalyst for a variety of hydrogen transfer reactions. It promotes (i) double bond isomerization of allylic compounds 11 I, (ii) disproportionation and dehydrogenation of l,&cyclohexadienes [21, (iii) hydrogenation of olefmic and aromatic C-C double bonds by molecular hydrogen [ 3-81, and selective transfer hydrogenation of mono- and bis-unsaturated substrates by polymethylhydrosiloxane [ 9 1.

We now wish to report the application of the RhCl,-Aliquat 336 catalyst to the well known cyclotrimerization of alkynes [lo], and to present some kinetic studies of the catalytic process.

*Author to whom correspondence should be addressed.

0304-5102/90/$3.50 @ Eleevier Sequoia/Printed in The Netherlands

314

TABLE 1

Cyclotrimerisation of various alkynes in the presence of the R.hCl,-Aliquat 336 system”

Ekpt. Substrate Reaction Reaction Conversion Yield of Trisubstituted benzene

temperature time (%) trimera

(“0 (h) (%Jb

(relative yield, %I

1,2,4- 1,3,5-

1 CH,wL&C=CH 60 2 69 17 94 6 2 (CH,),CC=CH 60 2.5 100 32 90 10 3 CHJCH,),WH 90 2 89 89 87.5 12.5 4 CH,(CH,),C=CH 90 2 87 77 83 17 6 CH,(CH,),C=CH 90 2 70 31 66 14 6 CH,WH,),C=CH 90 2 66 32 82 18 7 C,H,CkCH 90 2 98 50= 84.5 16.6 8 CH,COCsCH 90 1.5 100 32 42 58 9 CH,OCOC=CH 90 2 97 31 66 34

10 H=WH&C=CH 90 26 89 2gd 11 CH,CkCCH, 90” 29 70 70 12 CH,OCOC=CCOOCH, 90 20 80 35

p;c&n w2itJona as given in the Experimental section (except those speciikd in the Table). 80 P u .

‘A mqjor side product in this reaction (11%) was acetophenone [91. ?he product mixture was separated into 23% 6-(5-indanylj-1-pentyne [ill and 6% 1,3-di-(5-indanyl)propaue

[121. Vhe reaction wa8 performed in a sealed pressure tube.

Experimental

General procedure for the cyclotrimerization of alkynes In a typical experiment, a mixture of 40 mg (1.52 X lo-* mol) of

RhCl,.3HzO, 61 mg (1.52 x lo-* mol) of crystalline Ahquat 336, 2 ml of triply distilled water, 1.45 ml of 1,1,2,2-tetrachloroethane and 0.545 ml of l- chloronaphthalene (internal standard) were heated under reflux with vigo- rous stirring for 10 min. A quantity of 376 mg (4 x 10e3 mol) 1-heptyne was added and the heating was continued for 2 h. The mixture was cooled, the organic layer dried, and its contents analyzed and separated on a preparative GC column packed with 10% OV-101 on Chromosorb W. There was obtained 41 mg (11%) of unreacted starting alkyne and 334 mg (89%) of a mixture 1,2,4- and 1,3,5&-ipentylbenzene (ratio 7:1), which was then separated either by HPLC on RP-18 (MeOH as eluent) or by GC on 10% OV-17.

A similar procedure was applied for the cyclotrimerization reactions listed in Table 1, except that most products were separated by column chromatography on alumina and their identity determined either by com- parison with authentic samples or by their characteristic MS and NIvfR spectra. The ‘HNMR spectral data of the various 1,2,4- and 1,3,5- trisubstituted benzenes are given in Table 2.

Results and Discussion

Table 1 shows that both terminal and internal alkynes oligomerize in the presence of the RhCl,-Ahquat 336 catalyst. The efficiency and selectivity

TA

BL

E

2

‘H N

MR

sp

ectr

a of

var

iou

s 1,

2,4-

an

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nes

Com

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nd

Spe

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l da

ta

1,2,

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1,2,

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lben

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eth

yl

trim

elli

tate

trim

eth

yl

trim

esat

e

300~

~~

(C

cl,)

: 0.

960

(t,

9, J

= 7

.3 H

z),

1.20

0 (m

, 6)

, 1.

560

(m, 6

),

2.52

1 (m

, 6)

, 6.

744

(d,

l, J

= 7

.4H

z),

6.80

0 (8

~ l)

,

6.91

4 (d

, 1,

J =

7.4

Hz)

L

l31

300~

~~

(C

cl,)

: 0.

928

(t,

9, J

= 7

Hz)

, 1.

361

(m,

6),

1.56

0 C

m, 6

),

2.49

5 (t

, 6,

J =

8I-

M

6.67

2 (4

3)

11%

141

300

mz

(CD

CI,

):

1.20

2 (s

, 9)

, 1.

322

(5,

9),

1.34

9 (5

, 9)

, 7.

146

(dd,

l,

Ja,e

= 2

.3 H

z, 55

.6 = 8.

5 H

z),

7.52

1 (d

, l,

J5,6

=

8.5H

z),

7.63

6 (d

, 1,

J3

,5=

2.3

Hd

[l

51

3ooM

Hz

(Ccl

,):

1.33

0 (a

, 27

),

7.13

1 (8

, 3)

tl

5, 16

1 30

0~~

~

(Ccl

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0.91

7 (t

, 9,

J =

7 H

Z),

1.

348

(m,

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1.

547

(m,

6),

2.50

8 (m

, 6)

, 6.

771

(d,

l, J=

7.4

Hzh

6.

880

(d,

1, J

= 7

.4H

z),

6.89

1 (s

, 1)

300~

~~

(C

C],

):

0.89

8 (t

, 9,

J =

~H

z),

1.34

8 (m

, 12

),

1.56

1 (m

, 6)

, 2.

482

(t,

6, J

= 7

Hz)

, 6.6

62 (8

, 3)

2oon

g.13

~

(ccl

,):

0.89

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, 9,

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6 H

z),

1.24

6 (m

, 18

),

1.53

3 (m

, 6)

, 2.

541

(m,

6),

6.76

6 (d

, 1,

J =

7 H

z), 6

.792

(S, 1

)~

6.87

1 (d

, 1,

J =

7 H

z)

200~

~

(Ccl

,):

0.88

7 (t

, 9,

J =

6 H

Z),

1.

308

(m,

18),

1.

560

(m,

6),

2.51

0 (t

, 6,

J=

6.5

Hz)

, 6.

655

(s,

3)

[l71

200

wz

(Ccl

,):

0.88

8 (t

, 9,

J =

5 H

Z),

1.

289

(m,

24),

1.

530

(m,

6),

2.54

3 (m

, 6)

, 6.

777

(d,

l, J

= 7

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z),

6.79

6 (8

, l)

, 6.

893

(d,

1, J

=7.5

Hz)

29

0~~

~ (C

cl,)

: 0.

887

(t,

9, J

= 6

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),

1.29

0 (m

, 24

),

1.53

4 (m

, 6)

, 2.

480

(t,

6, J

= 6.

5 H

z),

6.66

2 (8

, 3)

[l

71

200~

~~

(C

cl,)

: 0.

887

(t,

9, J

= 7

Hz)

, 1.

276

(m,

30),

1.

532

(m,

6),

2.54

1 C

m, 6

), 6

.780

(4

1, J

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Hz)

, 6.7

93 (8

, I),

6.8

92

(d,

1,

J =

7 H

z)

[l71

200

MH

Z

(Ccl

,):

0.88

0 (t

, 9,

J =

7 H

Z),

1.

276

(m,

30),

1.

560

(m,

6),

2.51

3 (t

, 6,

J =

6 H

Z), 6

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(% 3)

[17

]

200~13~

(ccl

,):

7.11

0 (m

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, 7.

260-

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648

(m,

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Ll8

1

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cl,)

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332

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2Hz)

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z),

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J =

7.2

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7.

732

(8,

3)

[l91

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~~

(C

DC

l,):

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547

(8,

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2.61

7 (8

, 3)

, 2.

665

(8,

3),

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1 (d

, 1,

J =

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Hz)

, 8.

110

(dd,

l,

53.5

= 1

.6%

Js

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z),

8.21

0 (d

, 1,

J3

,6=

1.6

Hd

[2

01

200M

Hz

(CD

Cl,

):

2.71

8 (s

, 9)

, 8.

706

(s,

3)

[2l1

300

~~

(D

MS

C&

,):

3.82

0 (8

, 3)

, 3.

845

(s,

3),

3.90

0 (a

, 3)

, 7.

820

(d,

l, J,

,, =

7.5

Hz)

, 8.

162

(dd,

l,

53.5

=

1.5H

z,

J6,6

= 7.

5Hz)

, 8.

243

(d,

1, J

3,5=

l.

5Hz)

[2

21

3ooM

Hz

(DM

SO

d,):

3.

945

(s,

9),

8.62

1 (s

, 3)

12

21

316

vary in accord with the structures of the substrates. Terminal alkynes react faster than internal ones, and give mixtures of 1,2,4- and 1,3,5-trisubsti- tuted benzenes. Except for expt. 8, in which 3-butyn-a-one is reacted, the unsymmetrically substituted arene is formed preferentially. While the oligomerization of 1-heptyne yields exclusively the cyclic trimers, both the lower and higher homologs give linear oligomers (mainly dimers to hexamers) as side products. Cyclic tetramers could not be detected in any of our reactions. NMB and mass spectral analyses revealed also the formation of small amounts of mono- and dichlorinated linear products (up to 6% of the overall yield), as the result of halogen transfer from the catalyst [231. (For an analogous chlorine transfer, see the succeeding paper 1241.) Thus, e.g., 7-chloro-7,9-hexadecadiene, CHS(CH&CCl=CHCH=CH(CH2)&!H3 was detected among the reaction products of 1-octyne (expt. 4) and 5,6-dichloro- 2,2,7,7-tetramethyl-3-octyne among those of t-butylacetylene (expt. 2).

The terminal diyne, 1,8heptadiyne, was found to react slowly in the absence of a dienophile to give both the dimer 6-(5-indanyll-1-pentyne [ll] and the trimer 1,3-di(5-indanyl)propane [121 (expt. 10). In the presence of an active alkyne, catalytic cocyclo-oligomerization takes place. This process will be reported in a separate paper.

2-Butyne was reacted as a representative internal alkyne. It yields hexamethylbenzene as the only reaction product. Dimethylacetylene dicar- boxylate gives, however, only 44% of hexamethyl mellitate (expt. 121, owing to partial hydrolysis of the starting material under the reaction conditions.

Since 1-heptyne undergoes exclusively cyclotrimerization, this substrate has been chosen for kinetic studies.

Experiments which were carried out at different alkyne concentrations (between 0.5 and 3.0 M) in the presence of 1.52 x 10M4M of I&Cl3 and the same amount of Aliquat 336 revealed that the cycle-oligomerization is first order in substrate, at least during the first 75% of the reaction. The rate dependence on the concentration of the rhodium catalyst was found to be

2.5

“f 2.0 si

z 1.5

r‘

-i

g I.0

.g .c- 0.5

4 8 12

IRhl,M x IO-’

Fig. 1. Dependence of the initial rate of 1-heptyne cyclotrimerization on the concentration of the rhodium catalyst; conditions az given in the Experimental section.

317

[Aliquot 3363, Mx10e2

Fig. 2. Dependence of the initial rate of 1-heptyne cyclotrimerization on the concentration of Aliquat 336.

linear up to 0.07 M, which suggests a pseudo first-order behavior in this range. At 0.08 M the rate approaches a constant value (Fig. 1).

A similar linear dependence on the concentration of the phase transfer catalyst was observed between 0.01 and 0.005 M. At 0.06 M, when the ratio Aliquat 336:rhodium is 1, the catalysis becomes independent of the quat. Above this concentration, however, the quaternary ammonium salt starts to act as an inhibitor and the rate dependence becomes negative (Fig. 2).

Thus, under our standard working conditions given in the Experimental section, the kinetics obeyed the second-order rate law (eqn. (1))

-Sd[alkynel/dt = d[arenel/dt = 4 [alkynel [RhCl,]

with k = 0.99 f 0.05 M-l min-‘.

(1)

Since most of the metal ion was shown to be transferred to the organic phase prior to the addition of substrate to the reaction mixture, the observed rate dependence on the quaternary ammonium salt suggests that the latter at&&s also the intrinsic properties of the rhodium catalyst. This suggestion is actually supported by the data given in Table 3, which indicate a rate dependence also on the nature of the phase transfer catalyst. The rate was found to be affected by the structure of both the cation and the counter-ion. As expected, highly accessible onium ions were found to be more efficient than those of low accessibility 1251. As to the effect of the anion, it is noteworthy that iodide ion has no significant poisoning effect on the catalysis [26] and tetrabutylammonium iodide is, in fact, more efficient than the corresponding chloride and hydrogen sulfate. (A few analogous cases have been reported in the literature [27, 281.1

In analogy to some other processes catalyzed by the RhCl,-Aliquat 336 system [ 1, 2, 5, 71, it was found that there is no reaction in the absence of water and that the organic solvent has a mild influence on the catalysis. Polar solvents were found to lead to higher rates than non-polar ones. Representative initial rates of cyclotrimerization of 1-heptyne in 1,1,2,2- tetrachloroethane, o-xylene, and dodecane under the conditions given in the Experimental section are 2.16 X lo-‘; 1.81 X lo-‘, and 1.17 X 10-2Mmin-‘,

318

TABLE 3

Cyclotrimerization of 1-heptyne at 90°C by RhCle and various quatemary onium salm in a two-liquid-phase system”

Expt. Quatomary onium salt initial reaction rate (M mm-” x 10m2)

hexadecyltrimethymmmonium bromide rne~ylt~~yl~o~~ bromide tetraoctylammonium bromide tetrabutylammonium bromide ~trabutyl~o~~ iodide tetrabutylammonium chloride ~~bu~l~o~~ hydrogen sulfate tetrabutylphosphonium bromide

3.02 f 0.15 2.36 f 0.15 1.03 f 0.06 1.64 f 0.09 0.83 f 0.03 0.46 f 0.03 0.52 f 0.06 0.94 f 0.07

“Reaction conditions as given in the Experimental section, except that different phase transfer catdyata were used.

respectively. Since it has already been shown that the nature of the organic medium has hardly any influence on the metal extraction from the aqueous phase [ll, it may be postulated that the solvent effect is associated with the solvation of the ion pair [(C,H,,>,NCH,]‘[RhCl*]- and of other rhodium species. It should be pointed out, however, that neither the organic nor the aqueous medium takes part in the catalytic cycle, and deuterium labeling of the solvents does not lead to the formation of deuterated arenes.

For 1-heptyne the catalysis was found to be equally selective between 60 and 90 “C. Initial rates that have been measured at 60, 70, 80 and 90 “C for several substrate concentrations can be expressed in terms of Arrhenius plots of log[ratel us. l/T x low3 (e.g. Fig. 3) from which the thermodynamic constants of the reaction are deduced, The observed values of E,= 12.5 kcalmol-l and AH* = 11.8 kcalmolWX, which are lower than those of typical chemically-controlled reactions but higher than those of diffusion- controlled reactions 1291, suggest that both processes contribute to the progress of the catalysis. The mass transfer in the catalysis is assumed to be

2.7 2.8 2.4 3.0 k/f xio-‘K

Fig. 3. Arrhenius plot of cyclotrimerization of l-heptyne by the l%hCl&liquat 336 catalyst system at 60-90 *C!.

319

L n+2 Rh

1

RCsCR’ ( 1 RCECR’

Scheme 1.

associated with the formation of vesicles. Such particles have lately been found in catalyst systems of RhCls and various quaternary ammonium salts 1301.

From among the various pathways that have been suggested for metal-catalyzed cyclotrimerization of alkynes [313, we can exclude in our case the ‘cyclobutadiene pathway’ due to the absence of 1,2,&trisubstituted benzenes in the product mixtures. Likewise, we can eliminate those mechan- isms that involve hydrogen transfer, since neither the application of deuterated organic solvents nor the use of DzO (which leads to the formation of rhodium deuterides [2,73) causes deuterium labeling of the arenes. Actually, the evidence in hand is best compatible with the ‘common metallacyclopentadiene mechanism’ [lo] shown in Scheme 1.

320

In this mechanism, initially two ligands L (probably Hz0 or Cl) of the starting catalyst 1 are replaced in a stepwise manner by two acetylene moieties RC%CR’ (in terminal alkynes either R= H or R’ = H) to give complex 3. Oxidative coupling then furnishes the rhodacyclopentadienes of 4 and 5. Terminal alkynes form two complexes of type 4: one in which R = H (4a) and one in which R’ = H (4b). For bulky R’s 4a is sterically less hindered than 4b. Coordination of a third alkyne molecule to 4 and 5 results in the formation of the very reactive intermediates 6 and 7. Alternatively, 6 and 7 may be formed by direct addition of RWR’ to 3 [lob]. By analogy to some other transition metal-catalyzed alkyne cyclotrimerizations that appear kinetically similar to our system 1321, we assume that the generation of 6 and 7 is rate-limiting. The transformation of 6 and 7 into the substituted benzenes 12 and 13 may proceed either via the rhodacycloheptatrienes 6a, 8b and 9, via benzene-rhodium complexes 10 and 11, or via both types of intermediates. The catalytic cycle is completed when the eliminated rhodium species RhL, regenerates 3 by its reaction with two new alkyne molecules.

The preferential formation of 1,2,4-trisubstituted benzenes from most of the terminal alkynes is associated with the fact that complex 7 can be transformed into the precursors of both 12 and 13, while complexes 6 (terminal alkynes give two complexes: 6a where R = H and 6b where R’ = H) yield only the precursors of 12.

Acknowledgement

This research was supported by grant No. 86-00013/l from the U.S.-Israel Binational Science Foundation (BSF), Jerusalem, Israel, and by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Science Division of the U.S.D.E. under contract DE-AC-OS- 76SF00098.

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10 See, e.g. (a) N.E. Schore, Chem. Rev., 38 (1988) 1081 and references therein; (b) K. P. C. Vollhardt, Angew. Chem. Znt. Ed. Engl., 23 (1984) 639 and references therein.

11 R. Grigg, R. Scott and P. Stevenson, J. Chem. Sot., Per&in Trans. 1, (1988) 1357. 12 A. J. Hubert and J. Dale, J. Chem. Sot., (1965) 3160.

321

13 U. M. DzhemiIev, F. A. Selimov and V. R. Khaiizov, Bull. Acad. Sci. USSR, 35 (1986) 1478. 14 T. Masuda, Y.-X. Deng and T. Higashimura, Bull. Ckm. Sot. Jpn., 56 (1983) 2798. 15 A. K. Jhingan and W. F. Maier, J. Org. C&em., 52 (1987) 1161. 16 D. C. Neckers, J. Org. Chem., 44 (1979) 894. 17 K. C. Eapen, S. S. Dua and C. Tamborski, J. Org. Chem., 49 (1984) 478. 18 See, A. Mantovani, A. Marcomini and U. Belluco, J. Mol. Catal., 30 (1985) 73. 19 H. Noeth and J. Deberi, Kern. Kozlem., 40 (1973) 9. 20 R. Riemschneider and T. Wons, Monatsh. Chcm., 114 (1983) 1267. 21 C. J. Pouchert and J. R. Campbell (eds.), The AZ&i& Library of NMR Spectra, Vol. 6,

Aldrich Chemical Co., Milwaukee, WI, 1974, Spectrum 14C. 22. A. Borrini, P. Diverse, G. Ingrosso, A. Lucherini and G. Serra, J. Mol. Catal., 30 (1985) 181. 23 See, e.g. M.L. Deem, E. J. Iobst and M. D. Zink, Znorg. Chem. Acta, 157 (1989) 153. 24 I. Amer, J. Blum and K. P. C. Vollhardt, J. Mol. Cut& 60 (1990) 323. 25 M. HaIpern, Y. Sasson and M. Rabinovitz, Tetmhedron, 38 (1982) 3183 and references

therein. 26 J. E. Gordon and R. E. Kutina, J. Am. Chem. Sot., 99 (1977) 3903. 27 See A. Men, Angew. Chem. Znt. Ed. Engl., 12 (1973) 846. 28 J. McIntosh and H. KhaIiI, J. Org. Chem., 42 (1977) 2123. 29 See, e.g. J. M. Smith, Chemiccd Engineering Kinetics, McGraw-Hill, New York, 1975, pp.

297-298. 30 G. Barak and Y. Sasson, private communication. 31 L. P. Yur’eva, Russ. Chem. Rev., 43 (1974) and references therein. 32 See, e.g. D. R. McAhster, J. E. Bercaw and R. G. Bergman, J. Am. Chem. Sot., 99 (1977)

1666.