Journal of Molecular Catalysis, 60 ( 1990) 323-330 323

OLIGOMERIZATION OF ALKYNES BY THE RhCls-ALIQUAT 336 CATALYST SYSTEM PART 2. FORMATION OF 2,3-DISUBSTITUTED 1.PHENYLNAPIITHALENES BY CYCLODIMERIZATION OF PHENYLALWNES

IBRAHIM AMER, 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 Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (USA. )

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

The RhCl,-Aliquat @ 336 ion pair in 1,1,2,2-tetrachloroethane was shown to catalyze both cyclodimerization and trimerization of internal phenyl-alkynes in a highly regioselective manner. Thus, 1-phenyl-1-propyne, 1-phenyl-1-butyne and 4-phenyl-3-butyn-2-one result in the corresponding 2,&disubstituted 1-phenylnaphthalenes, in addition to the respective 3,5,6- trisubstituted 1,2,4&phenylbenzenes as the only cyclotrimerization prod- ucts. Diphenylacetylene yields 1,2,3_triphenylnaphthalene and hexaphenyl- benzene. Formation of small amounts of 1-chloro-2,&dimethyl4- phenylnaphthalene and l-(2_chlorophenyl)-2,3_dimethylnaphthalene, in the cycle-oligomerization of 1-phenyl-1-propyne, supports a mechanism in which initial oxidative coupling of the alkyne functions produces a 2,5- diphenylrhodacyclopentadiene capable of subsequent o&o-metallation of the phenyl substituents, followed by metal hydride transfer and reductive elimination of the resultant benzometallacycloheptatriene intermediate.

Introduction

In the preceding paper [ll we have revealed that various alkynes undergo catalytic cycZotrimmization in the presence of the rhodiumtri- chloride-Aliquat@ 336 ion pair to give mixtures of two substituted benzenes. We now find that internal alkynes bearing at least one phenyl substituent are converted not only into the expected benzene derivatives under these conditions, but also to a substantial degree into 2,&disubstituted l-

*For part 1 see [ll. **Author to whom correspondence should be addressed.

0304-5102/90/$3.50 0 Elaevier Sequoia/Printed in The Netherlands

phenylnaphthalenes (eqn. (1) 1.

C6H5C=CR

(1)

1 2 3

Such cycloaromatizations in which an aromatic hydrogen transfer takes place have been observed occasionally during the interaction of phe- nylalkynes with equimolar quantities of some transition metal complexes (e.g. [2-111). Catalytic cyclodimerizations of this type have, however, hardly been reported. An example is the transformation of phenylacetylene into 2-phenylnaphthalene mediated by (dicarbonyl)cyclopentadienyliron- (isobutylene) tetrafluoroborate [121.

Experimental

General procedure for the cycle-oligomerization of alkyl- and arylphenyl- alkynes

A 25 ml flask was charged with a solution of 40 mg (0.15 mmol) of RhC&3H20 in 2.Oml of triply distilled water and a solution of 1OOmg (0.26 mmol) of Aliquat 336, 3 mm01 of dodecane (or another suitable internal standard) and 4mmol of the alkyne in 1.5 ml of 1,1,2,2-tetrachloroethane. The mixture was stirred vigorously at room temperature for 10 min and then heated under refhnc with the aid of an oil bath thermostatted at 120 “C until the desired conversion was achieved. After cooling, the organic layer was separated, dried, concentrated, and its contents purified by either chroma- tography or by fractional crystallization.

Cycle-oligomerization of 1 phenyl-1 propyne (1, R = CH3) The progress of the reaction was monitored with the aid of a 1.5 m long

CC column packed with 12% OV-17 on Chromosorb W and terminated after 21 h at a conversion of 83%. The solvent-free residue was treated with a 1:l mixture of ether and hexane to give initial crops of 1,2,4-trimethyl-3,5,6- triphenylbenzene (2, R = CHs). Upon concentration of the filtrate and retreatment of the residue with ether and hexane, another crop of the trimer was obtained. The solvent was removed and the resulting mixture was separated either by column chromatography (on neutral alumina with hexane as eluent) or by PLC (on silica gel with the same eluent). The yield provided 213.5 mg (46%) of 2, R= CHB, 55.7mg (12%) of 2,3-dimethyl-l- phenylnaphthalene (3, R = CH3), 15.7mg (3%) of a 7:13 mixture of 1-chloro-2,3-dimethyl-4-phenylnaphthalene (4) and 1-(2-chlorophenyl)-2,3- dimethylnaphthalene (5), and 52 mg of uncharacterized material.

325

Compound 2, R =CH, M.p. 225-227 “C (from ether-hexane) (lit. 1131 225-227 “C); 200 MHz

IHNMR (CDCI,): 1.846 (s, 3, CH,), 2.032 (s, 3, CH,), 2.046 (8, 3, CH,), 6.921-7.004 (m, 9, ArH), 7.033-7.303 (m, 6, ArH); 5OMHz 13C{lH} NMR (CCL-D20): 17.38, 18.08, 19.15, 125.44, 125.51, 126.18, 127.07, 128.16, 128.21, 129.03, 129.98, 131.25, 131.94, 133.50, 138.88, 139.51, 140.29, 141.50, 141.62, 142.00, 142.55 [141; GC-MS (70eV): m/z (rel. intensity) 348 (M+‘, loo), 330 [(M-CH3)+, 201, 317 (C&HI,+, 12), 303 (C,,H,,+, 6), 289 (G3H13+, 6) 225 (C&H,,+, 16), 241 (C&I13+, 15), 215 (C&L+, 8), 202 (CdL,‘+, 5), 178 (LH10’+, 8).

Compound 3, R =CH, M.p. 83-85 “C (from MeOH) (lit. 1151 85-86°C); 3OOMHz ‘H NMR

(CDCL, based on H-H decoupling studies): 2.109 (8, 3, CH,), 2.470 (8, 3, CH,), 7.168-7.424 (m, 8, ArH), 7.546 (8, 1, H4), 7.632 [d, 1, J7.8 = 7.9 Hz, H8]; 50MHz 13C{lH} NMR (CDCl,): 17.55, 21.15, 124.80, 124.83, 126.27, 126.93, 127.16, 128.32, 130.25, 131.74, 131.96, 133.11, 135.35, 138.34, 140.47; GC-MS (70eV): m/z (rel. intensity) 232 (100, M’), 217 [(M-CH3)+, 56)1, 216 (C1,H12’+, 25), 202 (C16H1,,‘+, 301, 189 (C1bHg+, 8).

Mixture of 4 and 5 Pale yellow oil; 200 MHz lH NMR (CDCL): 2.174 [s, CH3(2) of 41, 2.245

[s, CH3(3) of 53, 2.345 [s, CH3(2) of 51, 2.616 Is, CH3(3) of 41, 7.300 (m, H5’ of 5), 7.447 (dd, J4,6 = 2 Hz, J5,6 = 7.5 Hz, H6’ of 5), 7.520 (m, H7 of 4 and H4’ of 5), 7.573 (s, H4 of 5), 7.606 (dist. dt, J6,s = 2 Hz, Js,e,, = 7 Hz, H6 of 4), 7.070-7.650 (m, the other ArH), 8.045 (dd, J6,8= 2Hz, J7,8= 7Hz, H8 of 4), 8.327 (dd, J3,5= 1 Hz, J3,,=9Hz, H3’ of 5), 8.377 (dd, 55.7 = 2Hz, Js,e= 7Hz, H5 of 4); GC-MS (70 eV): m/z (rel. intensity) 268, 266 (M’, 33, loo), 253, 251 [(M-CH3)+, 1, 31, 231 (C$eH15+, 29), 216 (C&I&‘+, 87), 215 (W-L+, 78), 202 (C&L,‘+, 9), 189 (C&H,+, 9); found: C, 80.98, H, 5.95%. C&H&l requires: C, 81.04, H, 5.67%.

Cycle-oligonerization of lphnyl-l-butyne (1, R =Cfl& The reaction was conducted for 23 h during which 58% of the starting

material was consumed. Column chromatography afforded 31% of 1,2,4- triethyl-3,5,6kiphenylbenxene (2, R = C&H,) and 14% of l-phenyl-2,3- diethylnaphthalene (3, R = C&H,) but no chlorine-containing material.

Compound 2, R =C&ls M.p. 181-182 “C (from ether) (cf [IS]); 200~MHz ‘H NMR (CDCb):

0.629 (t, 3, J= 7.4Hz, CH,), 0.984 (m, 6, CH,), 2.101 (q, 2, J= 7.4Hz, CH,), 2.468 (m, 4, CH,), 7.063 (m, 9, ArH), 7.356 (m, 6, ArH); 50-MHz 13C{lH} NMR (CDCb): 15.28, 15.66, 23.39, 23.57, 24.57, 24.58, 125.53, 125.59, 126.43, 126.91, 126.94, 127.72, 130.04, 130.46, 130.57, 132.75, 137.28, 137.68, 138.80, 139.39, 141.12, 141.20, 141.32, 141.56; GC-MS (70eV): m/z (rel. intensity) 390 @I’+, loo), 375 [(M-CH,)‘, 81, 361 [(M-CsH5)+, 151, 347

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(G,H,,+, 33), 333 (C&L+, 13), 317 (Cz5H1,+, 50), 265 (Cz1H13+, 8), 253 (C2oH13+, 21), 241 (CmHm+, 19), 215 (C1,Hll+, 12), 202 (&Hi,,‘+, 9), 191

(&Hu+, 7), 178 (CldHl&+, 5); found: C, 92.13; H, 7.70% C3&13,, requires: C, 92.26; H, 7.74%.

Compound 3, R =C,H, M.p. 66-67 “C (from MeOH); 2OOMHz ‘H NMR (CDCl,); 1.010 (t, 3,

J=7.4Hz, CH3), 1.387 (t, 3, J=7.5Hz, CH3), 2.591 (q, 2, J=7.5Hz, CH,), 2.890 (q, 2, J= 7.4Hz, CH,), 7.024-7.508 (m, 8, ArH), 7.695 (s, 1, H4), 7.770 (d, 1, J = 8.1 Hz, H8); 5OMHz =C{lH} NMR (CDCL): 15.35, 15.51, 23.27, 25.84, 124.87, 126.17, 126.37, 126.87, 127.11, 128.13, 128.20, 130.33, 132.05, 138.60, 140.32, 140.43; GC-MS (7OeV): m/z (rel. intensity) 260 (M+, loo), 245 [(M-CH3)+, 321, 231 [(M-C2HS)+, 181, 216 (C,,H,,‘+, 71),

215 U&IL+, 88), 202 (Cu&,+, 23), 189 (C,,H,+, 7), 178 (CuHu,‘+, 2) <cf. [17]); found: C, 92,Ol; H, 7.66%. C!&-IZO requires: C, 92.26; H, 7.74%.

Oligomerization of 4phenyl-3butyn-2+me (1, R = COCH,) Deviating from the general procedure, the oil bath was kept at 90 “C.

Full conversion was already achieved after 3.5 h. Most of the trimer was obtained by treatment of the reaction mixture (after removal of the solvent) with a 1:l mixture of ether and hexane. The more soluble material was separated by column chromatography on silica gel, eluting with a 1:4 mixture of ether-hexane to furnish 68% of 1,2,4-triacetyl-3,5,6_triphenylbenzene (2, R = COCH3), and 20% of 2,3-diacetyl-1-phenylnaphthalene (3, R = COCH&

Compound 2, R =COCH, M.p. 221-224°C (from ether-hexane); IR (Nujol): 1680 cm-’ (C=G);

200MHz ‘HNMR (CDCls): 1.788 (s, 3, CH,), 1.839 (s, 3, CHs), 1.888 ts, 3, CH,), 6.949-6.998 (m, 4, ArH), 7.127-7.171 (m, 6, ArH), 7.250-7.413 (m, 5, ArH); 50MHz 13C{lH} NMR (CDCI,): 31.63, 31.79, 32.62, 127.47, 127.63, 127.88, 127.99, 128.40, 128.68, 128.80, 130.05, 130.46, 133.97, 136.75, 136.89, 137.05, 137.52, 138.45, 140.69, 141.72, 143.92, 204.57, 205.98, 206.22; MS (7OeV, 110°C): m/z (rel. intensity) 432 CM”, 62), 417 [(M-CH3)+, 1001,

399 (CmHd&+, 14), 358 tC2,Hls0’+, ll), 357 (C&H170+, 8), 356

(CLHmO~‘+, 13), 301 (G&L+, 10); found: C, 82.99; H, 5.76%. C3,,H24O3 requires: C, 83.31; H, 5.59%.

Compound 3, R =COCH, M.p. 176-178 “C (from ether); IR (Nujol): 1690, 1664cm-’ (C--_-o);

2OOMHz ‘HNMR (CDC13): 2.106 (s, 3, CHs), 2.756 (6, 3, CH,), 7.280-7.331 (m, 3, ArH), 7.460-7.601 (m, 5, ArH), 8.024 (dd, 1, J1 = 2.0 Hz, Jz = 6.9Hz, H8), 8.403 (s, 1, H4); 5OMHz 13C{lH} NMR (CDCl,): 27.05, 31.72, 126.79, 127.32, 128.12, 128.31, 129.25, 130.08, 130.80, 131.10, 131.95, 133.26, 134.25, 136.15, 136.40, 139.01,206.01,206.77; MS (70 eV, 90°C): m/z (rel. intensity) 288 (M+, 14), 287 [(M-H)+, 661, 273 [(M-CH3)+, 731, 272 (C19H1202’+, loo), 230 (C,,H,,‘+, ll), 214 (C14H1402’+, 30), 201 tC13H1302f, 73), 200

327

(&H1202’+, 16), 199 (GH1&+, 20); found: C, 83.42; H, 5.27%. C20H1602 requires: C, 83.31; H, 5.59%.

Cycle-oligomerization of diphenylacetylene (1, R = C&&I The reaction was carried out at reflex for 27 h, during which 49% of the

starting material was consumed. Most of the hexaphenylbenzene (2, R = C6H5) was obtained by removal of the solvent and addition of a 1:l mixture of ether and hexane. The soluble material was purified by column chromat- ography on neutral alumina (hexane as eluent). Apart from the recovered starting material (510/o), there was obtained 32% of 2, R = C,H,, that was identical with an authentic sample, and 16% of 1,2,3-triphenylnaphthalene (3, R= C,H,); m.p. 150°C (from ethanol) (lit. 1181 151 “C); 2OOMHz ‘HNMR (CDC13): 6.846-6.972 ( m, 5, ArEI), 7.143-7.295 (m, 9, ArEI), 7.402-7.620 (m, 4, ArH), 7.950 (d, 1, J = 6Hz, H8), 7.964 (s, 1, H4); MS (7OeV, 70°C): n/z (rel. intensity) 356 (IN+, loo), 279 (C22H15+, ll), 278 (CmH14’+, lo), 178 (C&L,‘+, 6).

Results and discussion

While the trimerization of te rminal alkynes catalyzed by the RhCL- Aliquat 336 system furnishes mixtures of 1,2,4- and 1,3,5-trisubstituted benzenes 111, this work shows that under the same conditions internal phenylalkynes, C.&H&=CR, convert to the unsymmetrical trimers 2 exclusively. The dimerization products formed in these catalyses are solely l-phenyl-2,3-disubstituted naphthalenes free of the corresponding 2-phenyl- 1,3-disubstituted analogs. In light of these results and those presented in the preceding paper, we assume that both the cyclotrimerization and the cyclodimerization processes proceed through a common metallacyclopenta- diene intermediate, namely complex a. Complexes b and c are not likely to take part in the dimerization unless they reversibly isomerized to a. The rhodacyclopentadiene derivative c may, of course, be involved in the catalytic cyclotrimerization reactions.

R ‘6”5 w5

‘6”5 R R L = unspecified

Ln Ln Ln ligands

a b C

A plausible mechanism for the cycle-oligomerization of internal phe- nylalkynes is given in Scheme 1. The phenyl moieties in a may undergo ortho-metallation and lead to the formation of a highly strained rhodium hydride d (for similar strained metallacyclic species see e.g. 1191) that in turn, might rearrange to e. Upon reductive elimination this intermediate gives a 2,3-disubstituted 1-phenylnaphthalene (3) and the starting rhodium complex (see Scheme 1). When the latter process takes place in the presence of excess alkyne, regeneration of a completes a catalytic cycle.

323

i Scheme 1.

5 6

According to this m~h~ism, the men-Lund hydrogen (in d) becomes H4 in the final product. Indeed, when the oligomerization of l-phenyl-l- propyne (1, R= CHS) was conducted in the presence of D& (conditions under which metal hydrides undergo H-D exchange 1201) both the NMR and the MS spectra indicate 95% incorporation of deuterium - mostly at the 64 position of the resulting naphthalene derivative. The H4 singlet at 7.546 ppm in the ‘H NMR spectrum of 3, R = CHs, diminished to an extent of 95%, the C4 signal at 127.16 ppm in the non-decoupled 13C NMR spectrum lost its multiplicity, and the molecular peak in the mass spectrum was shifted to m/z 233. The use of DZO caused, however, no induration of deuterium in the trimerization product, since the formation of 2 does not involve the intermediacy of a metal hydride. The isolation of deuterium-free 2 indicates that the transformation of a to b is not reversible.

Although we have not defined the exact nature of the non-organic ligands of the intermediates a, d and e, it is obvious that at least one of them is chlorine. Thus, if instead of the hydrogen transfer d-, e the halogen ligand rearranges, complex f is generated, and upon reductive elimination a 2,3-disubstituted 1-chloro-4-phenylnaphthalene is formed. (For similar rhodium~atalyzed Cl-H exchange process, see e.g. 1211. ) In fact, during the cyclooligomerization of 1-phenyl-1-propyne (1, R = CH3), we obtained 3% of a mixture of two chlorinated 2,3-dimethyl-1-phenylnaphthalenes. By detailed

329

‘H NMR analysis, the structures of the chlorinated compounds were shown to be 1-chloro-2,3-dimethyl-4-phenylnaphthalene (4) and 1-(2-chlorophenyl)- 2,3-dimethylnaphthalene (5). The formation of 5 can be explained by the

4 5 6 7

reversibility of the ortho-metallation and Cl ligand transfer in d to give the metallacyclic complex g. This intermediate then undergoes further ortho- metallation, hydrogen transfer and reductive elimination (g+ h-, i-, 5).

Theoretically, g could undergo also o&o-metallation at the chlorinated phenyl ring. However, the sequence of transformations g+ j-+ 6 is quite improbable since the chlorine deactivates the 6’ position of the ring. Thus, it is not surprising that 5-chloro-2,3-dimethyl-l-phenylnaphthalene (6) was not detected among the oligomerization products of 1, R = CH+

IHNMR analyses indicated the absence of chlorine-containing naph- thalenes in the oligomerizations of 1-phenyl-l-butyne (1, R = CzHs) and diphenylacetylene (1, R = C&H,). When, however, 4-phenyl-3-butyn-2sne (1, R = COCH,) was reacted under conditions more severe than those described in the Experimental section (i.e. under vigorous reflex), < 1% of 2,&diacetyl- l-chloro-&phenylnaphthalene (7) was isolated. CC-MS (7OeV): m/z (rel. intensity) 324, 322 CM”, 27, 82), 309, 307 [(M-CH3)+, 13, 381, 291 (C,&,3’C10+, 5), 289 U&,H,,36C10+, 141, 267 K1,Hlo3’C10+, 331, 265 (C1,H1095C10+, NO), 201 (C.&H,+, 23) 1. The NMR spectrum reveals that 7 is not accompanied by a second isomer. (lHNMR (CDCl& 2.021 [s, 3, COC&(P)], 2.111 [s, 3, COC&,(3)1, 7.306-7.431 (m, 5, ArH), 7.633-7.722 (m, 2, A&), 7.790 (dd, 1, &,s = 1.5Hz, J7,8= 7.5 Hz, H8), 8.404 (dd, 1, Js,s= 7.5Hz, J5,, = 1 Hz, H5)). The absence of a second chlorinated di- actylphenyhraphthalene may result from the pronounced activation of the benzylic carbon in d, R = COCH3, by the electron-attracting acetyl groups. Consequently, all the transferable chlorine becomes attached at this position.

Since the ratio of dimer to trimer in the various oligomerizations is not a&cted significantly by the electronic and steric structures of the alkyne (it proved to vary only between 1:2 and 1:3), we assume that the relative rate of both processes is determined at one of the initial common steps. Thus, the three alkynes that trimerize slowly also undergo slow cyclodimerization, while 4-phenyl-3-butyn-2-one forms both benzene and naphthalene deriva- tives at a much higher rate.

Acknowledgements

This research was supported by grant No. 6640013 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-O& 76SFOOO98.

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