122 Ligands and reagents

6. (a) M. Momenteau, B. Loock, C. Huel, and J. L'hoste, J . Chem. Soc., Perkin Trans. I , 283 (1988) and references therein; (b) E. Tsuchida, E. Hasegawa, T. Komatsu, T. Nakata, K. Nagao, and H. Nishida, Bull. Chem. SOC. Jpn., 64,888 (1991) and references therein; (c) Y. Naruta, F. Tani, N. Ishihara, and K. Maruyama, J . Am. Chem. Soc., 113, 6865 (1991) and references therein.

7. Available from Aldrich Chemical Company, Inc. 8. (a) G. Wittig, in Newer Methods of Preparative Organic Chemistry, Vol. 1, Interscience, New

York, 1948, p. 579; (b) R. G. F. Giles and M. V. Sargant, J . Chem. SOC. Perkin Trans. 1,2447 (1974) and (c) M. E. Snook, P. F. Mason, and R. F. Arrendale, J. Chromatogr., 324, 141 (1985) and references therein.

9. J. S. Lindsey and R. W. Wagner, J. Org. Chem., 54, 828 (1989). 10. Tsuchida et al. have prepared 3 from 1 in 9.3% overall yield by a different procedure. See

E. Tsuchida, T. Komatsu, E. Hasegawa, and H. Nishide, J. Chem. Soc., Dalton Trans., 2713 (1990).

11. M. Momenteau, J. Mispelter, B. Loock, and E. Bisagni, J. Chem. Soc., Perkin Trans. I , 189 (1983).

19. TRIBENZOCYCLYNE* (TBC) AND TETRABENZOCYCLYNEt (QBC)

SUBMITTED BY DON SOLOOKI,' JOSEPH D. FERRARA: DENNIS MALABA,' JOHN D. BRADSHAW,' CLAIRE A. TESSIER,'

and WILEY J. YOUNGS' CHECKED BY JENS A. JOHN and JAMES M. TOUR"

Cyclyne ligands are macrocyclic polyalkynes' which have available car- bon-carbon triple bonds for coordination to transition metal atoms or ions. Cyclynes with three alkynes in a 12-membered ring (cyclotriynes) such as tribenzocyclyne (TBC) are conjugated, antiaromatic, planar molecules and have cavities which are large enough to fit low-oxidation-state, first-row transition metals. The distance from the center of the cavity to the center of the alkynes is about 2.1 A.' Tribenzocyclyne has been shown to be a versatile ligand for coordinating transition metals. Several modes of metal coordina- tion to TBC have been firmly established: a metal can coordinate to the three alkynes in the cavity of TBC to give a planar metallo~yclotriyne;~ two molecules of TBC can coordinate to a metal through the alkynes to yield

* 5,6,11,12,17,18-Hexadehydrotribenzo[a,e,i]cyclododecene.

* Department of Chemistry, The University of Akron, Akron, O H 44325-3601. 5,6,11,12,17,18,23,24-Octadehydrotetrabenzo[a,e,i,m]cyclohexadecene.

Present address: Molecular Structure Corp., 3200 Research Forest Drive, The Woodlands, TX 77381-4238. I# Department of Chemistry, The University of South Carolina, Columbia, SC 29208.

Inorganic Syntheses, Volume 31 Edited by Alan H . Cowley

Copyright © 1997 by Inorganic Syntheses, Inc.

19. Tribenzocyclyne (TBC) and tetrabenzocyclyne (QBC) 123

1 n-BuLi. 2 MgBr? KOt-Bu, EtzO THF , UM@‘] 2 aqueous workup I I I , KH MgBr

L

cCU pyridine renux ’ q+ 0

TBC QBC

+ other cyclync

a sandwich ~ o m p l e x ; ~ and three metals can coordinate to the three alkynes so that the metals are above the plane of the TBC molec~ le .~ Tribenzocyclyne can be prepared by Stephens-Castro coupling,6 a bromination/dehydro- bromination route,’ or through palladium-catalyzed coupling.* Here we report a detailed procedure used in our laboratory for the synthesis of TBC by Stephens-Castro coupling of copper(1) (2-iodopheny1)acetylide. In addi- tion to TBC, tetrabenzocyclyne (QBC),6ag a nonplanar cyclyne with four alkyne units, is also formed in low yield. The synthesis of the precursor (2-iodopheny1)acetylene is as described by Brandsma et al.’ with some modifications. In addition to the benzocyclynes reported here, thiophene’ and methoxy-substituted benzene” derivatives have also been prepared by this method. This procedure requires approximately 7 days.

General Procedure

Unless otherwise stated, all manipulations are carried out under an atmo- sphere of argon using standard Schlenk technique^.'^ The glassware used in the preparation of (24odophenyl)acetylene and the Stephens-Castro coup- ling of copper acetylide is dried in an oven at 140°C overnight. Potassium tert-butoxide (Aldrich)”* is sublimed at 150°C on a diffusion-pump vacuum

* Superscript letters refer to “notes added by checkers” at the end of this section.

124 Ligands and reagents

line torr) and stored in the dry box (lower yields of (2-iodo- pheny1)acetylene are obtained when commercially available potassium t- butoxide is used without purification). n-Butyllithium (2.5 M in hexanes, Aldrich)b is standardized with diphenylacetic acid before use.'4 Phenylacety- lene (Aldrich) is vacuum distilled from anhydrous sodium sulfate prior to use. Iodine, copper(I1) sulfate pentahydrate (Fisher), hydroxylamine hydrochlo- ride, and magnesium bromide diethyl ether (Aldrich)' are used as received. Tetrahydrofuran (Aldrich) is freshly distilled under argon from sodium ben- zophenone. Pyridine (Fisher) is distilled under argon from barium oxide. Flash chromat~graphy'~ is carried out using 40 ,um silica gel (Baker).

A. (2-iodophenyl)acetylened

Procedure

The reaction vessel consists of a four-necked, 2-L flask fitted with a powder addition tube (300 mL), gas inlet, septum, and mechanical stirrer. In a dry box, the reaction flask is charged with KO-t-Bu (21.72 g, 0.1935 mol) and n-BuLi (155 mL, 2.5 M in hexanes, 0.388 rnol); the powder addition tube is charged with MgBr2.0Et2 (100 g, 0.44 mol) and attached to the reaction flask. The flask is equipped with a mechanical stirrer and a septum before it is removed from the dry box. A mineral-oil bubbler is attached to the gas inlet of the flask. The flask is then cooled to - 78°C as is 450mL of THF in a separate flask. Throughout the remainder of the procedure, the reaction mixture is stirred and maintained at - 78°C. Tetrahydrofuran is transferred slowly over the course of - 10 min to the reaction mixture via cannula (an exothermic reaction ensues). The mixture is then allowed to stir until a homogeneous red-brown solution results ( - 1 h). Phenylacetylene (19.4 mL, 0.176 mol) is added via syringe, producing a deep green solution. After 3 h, MgBrz.OEtz is added slowly to the reaction mixture. The reaction turns cream colored after 15 min and is allowed to stir for another 45 min. In a separate flask, iodine (49.14 g, 0.1936 mol) is dissolved in 250 mL of THF, cooled to - 40°C, and transferred via cannula to the reaction mixture. A more pale, cream color persists. At this point, the reaction mixture is allowed to warm to room temperature over 16 h while stirring.

Workup, in air, is begun by adding 250 mL of water and acidification to pH 5 with 1 M HCl. The reaction mixture is transferred to a 2-L separatory funnel with the assistance of 250 mL of diethyl ether. The aqueous phase is drawn off and set aside. The organic layer is washed twice with 300-mL portions of saturated aqueous Na2SzO3 and saturated aqueous NaCl. This is followed by a wash with two 200-mL portions of water. The extract is dried over MgS04, and concentrated in vacuo. Analysis by gas chromato-

19. Tribenzocyclyne (TBC) and tetrabenzocyclyne (QBC) 125

gram indicates that 60% of the phenylacetylene is converted to (2-iodo- pheny1)acetylene. Considerable decomposition of the product may result from heating the product; therefore, unreacted phenylacetylene is removed from the crude product by trap-to-trap fractionation13 at 21°C on a diffu- sion-pump vacuum line torr) through traps at - 20 and - 196°C. The small fraction collected at - 20°C generally contains (24odophenyl)acety- lene. The fractionation is carried out for approximately 12 h, whereupon the residues of the distillation pot and contents of the - 20°C trap are combined and collectively run through a plug of silica gel (10 cm diameter by 10 cm tall column, elution with hexanes). (2-1odophenyl)acetylene (20.5 g) is isolated in 51% yield based upon phenylacetylene and is deemed to be pure by GC and NMR.

B. COPPER (I) (2-10DOPHENYL)ACETYLIDE'

Procedure

Following the procedure of Castro et a1.I6 CuSO,. 5 H 2 0 (22.6 g, 0.0903 mol) and ammonium hydroxide (28%, 150 mL) are placed in a 2-L Erlenmeyer flask under an argon purge. The deep blue solution is stirred for 15min before adding 400 mL of water and NHzOH.HCI (12.55 g, 0.18 mol). Addi- tion of (2-iodopheny1)acetylene (20.6 g in 500 mL of ethanol) gives a canary yellow copper(1) (2-iodopheny1)acetylide precipitate. Water is added as needed to allow stirring. The reaction mixture is filtered. The filter cake is washed three times with 200 mL each of water, ethanol, and ether so that it will not dry completely. The copper(1) (2-iodopheny1)acetylide is allowed to air-dry for 24 h c25.5 g, 97% based upon (2-iodopheny1)acetylenel.

Caution. When dry, copper acetylides are known to be shock and thermally sensitive. Copper ( I ) (2-iodopheny1)acetylide should therefore be handled with care.

C. ~,~,~~,~~,~~,~~-HEXADEHYDROTRIBENZO[T~,~,~] CYCLODODECENE (TBC)' AND 5,6,11,12,17,18,23,24-

OCTADEHYDROTETRABENZO[u, e, i, mlCYCLOHEXADECENE (QW

Procedure

A 1-L flask is charged with the copper(1) (24odophenyl)acetylide (17.9 g, 0.0616 mol) and placed under an active vacuum to remove remaining vol- atiles and effect constant weight (ca. 18 h at lo-, torr). About 500 mL of

126 Ligands and reagents

pyridine is added to give an approximate 0.1 M suspension of the copper acetylide. The mixture is refluxed for 6.5 h and pyridine is removed in vacuo. The crude product is extracted with about 100OmL of either acetone or diethyl ether, and the insolubles are removed by filtration before the solvent is removed on a rotavapor. Tribenzocyclyne is sublimed at 160°C on a diffu- sion-pump vacuum line torr) for approximately 48 h [yield 2.9 g, 47.7% based upon copper(1) (2-iodopheny1)acetylidel. Recrystallization from boiling toluene (ca. 5 mL), followed by washing with cold hexanes, provides spectroscopically pure TBC. Tetrabenzocyclyne' is isolated by extraction of the residue left in the sublimator with acetone followed by column chromatography (elution with a 1 : 4 mixture of dichloromethanefhexanes, 0.50 g isolated, 8% yield). A trace amount of the hexabenzocyclyne (HBC) is also isolated.'

Pro pert ies

(2-1odophenyl)acetylene should be protected from light and stored over copper metal. The 'H NMR spectrum (CDC13) exhibits doublets at 7.81 (1H) and 7.48 (lH), triplets at 7.27 (1H) and 6.99 (lH), and a singlet at 3.3 6 (1H). The 13C NMR spectrum (CDC13) exhibits peaks at 138.7, 133.4, 129.9, 128.6, 127.7, 100.4, 85.1, and 81.0 6. A very weak C=C stretch is observed at 2130 cm-' in the IR spectrum.

Copper(1) (2-iodopheny1)acetylide exhibits a stronger C=C stretch at 1935 cm- ' in the IR spectrum.

Tribenzocyclyne is a bright yellow solid which decomposes at 21 5-220°C. The 'H NMR spectrum (CDC13) exhibits multiplets centered at 7.32 (6H) and 7.17 6 (6H) typical of an AA'BB spin system. The "C NMR spectrum (CDCI3) exhibits peaks at 132.0, 128.6, 126.7, and 92.9 6. A very weak C-C stretch is observed at 2217cm-' in the IR spectrum. Mass spectroscopic evidence indicates a parent ion at mfe = 300.

Tetrabenzocyclyne is a colorless solid which decomposes at 220°C. An AA'BB' spin system is again observed in the 'H NMR spectrum (CDC13) where QBC exhibits multiplets centered at 7.53 (8H) and 7.26 6 (8H). The 13C NMR (CDCI3) exhibits peaks at 132.3, 128.0, 125.6, and 91.1 6 . A very weak C=C stretch is observed at 2214cm-' in the IR spectrum. Mass spectroscopic evidence for QBC includes an M + ion at mfz = 400, a peak corresponding to the loss of acetylene at m/z = 374, and a doubly charged M + + ion at m/z = 200.

Hexabenzocyclyne has been characterized by mass spectroscopy (EI) giving m/z = 600 (M'), 574 (loss of HC-CH), and 300 (M"). 'H NMR (CDC13) shows multiplets centered at 7.33 (12H) and 7.05 6 (12H).

19. Tribenzocyclyne (TBC) and tetrabenzocyclyne (QBC) 127

Acknowledgments

We would like to thank Dr. Michael J. Taschner for helpful discussions. C. A. T. and W. J. Y. would like to thank the Petroleum Research Fund, Office of Naval Research, State of Ohio through the Edison Center for Sensors and Technology at CWRU, and the National Science Foundation for supporting different aspects of this research.

Notes Added by Checkers

(a) Commercially available potassium t-butoxide (Aldrich) was not purified further. (b) n-Butyllithium (1.6 M in hexane, Lithco) was titrated with a standard solution of t-butanol in xylenes using 1,lO-phenanthroline as an indicator. (c) Magnesium bromide diethyl ether is freshly prepared as follows: Magne- sium (2.00 g, 0.0823 mol) and ether (80 mL) are combined. 1,2-Dibromo- ethane (5.50 mL, 0.0638 mol) is added dropwise so that the reaction is refluxing vigorously. After the addition is complete, the reaction mixture is stirred for 0.5 h. The product is then removed via cannula and used directly. (d) The procedure was modified as follows. A three-necked flask (250 mL) is equipped with a mechanical stirrer. The flask is charged with KO-t-Bu (3.10 g, 0.0275 mol) and n-BuLi (35.0 mL, 0.0560 mol) under nitrogen. After cooling to - 78"C, precooled THF (65 mL) is added slowly. The mixture is stirred under nitrogen at - 78°C for 0.5 h. Phenylacetylene (2.75 mL, 0.0250 mol) is added via syringe and the resulting green mixture is stirred for 2 h. Then freshly prepared MgBr2.0Et2 (0.0638 mol, see note c) is added slowly and the reaction mixture is stirred for 1 h at - 78°C. A solution of iodine (7.00 g, 0.0276 mol) in THF (36 mL) is added and the reaction is allowed to come to room temperature overnight. The mixture is worked up as described in the experiment and then purified by chromatography (silica gel, hexane) to yield 2.18 g (38%) of the title compound as a yellow oil. (e) The procedure was adhered to using the following amounts: CuS04.5H20 (2.38 g, 0.00952 mol), NH40H (28%, 16.0 mL), H 2 0 (40 mL), NH20H*HCI (1.32 g, 0.0190 mol) and (2-iodopheny1)acetylene (2.18 g, 0.00954 mol) in ethanol (50 mL). The described workup yielded 2.52 g (91%) of the title compound as a yellow solid. (f) The following modifications were used: Copper(1) (2-iodophenyl) acety- lene (2.52 g, 0.00868 mol) is placed under vacuum (1 mmHg, 12 h) to remove volatiles. Pyridine (87 mL) is added and the suspension is heated to reflux for 6 h. The solvent is removed in vacuo. The solid residue is dissolved in diethyl ether and the insolubles are removed by filtration. After removal of the

128 Ligands and reagents

solvent, the crude product is purified by chromatography (silica gel, hexane) to yield 0.28 g (22%) of TBC as a yellow solid.

References

1. M. Nakagawa, The Chemistry of the Carbon-Carbon Triple Bond, Part 2, S. Patai, (ed.) Wiley:

2. H. Irngartinger, L. Seiserowitz, and G. M. J. Schmidt. Chem. Ber., 103, 1119 (1979) 3. (a) J. D. Ferrara, C. A. Tessier, and W. J. Youngs, J. Am. Chem. SOC. 107,6719 (1985). (b) J.

D. Ferrara, A. A. Tanaka, C. Fierro, C. A. Tessier, and W. J. Youngs, Organometallics, 8, 2089 (1989). (c) J. D. Ferrara, C. A. Tessier, and W. J. Youngs, Organometallics, 6,676 (1987).

4. J. D. Ferrara, A. Djebli, C. A. Tessier, and W. J. Youngs, J. Am. Chem. Soc., 110,647 (1988). 5 . (a) A. Djebli, J. D. Ferrara, C. A. Tessier, and W. J. Youngs J . Chem. Soc., Chem. Commun.,

548 (1988). (b) J. D. Ferrara, C. A. Tessier, and W. J. Youngs, Inorg. Chem., 27(13), 2201 (1988).

6. (a) R. D. Stephens and C. E. Castro, J . Org. Chem., 28. 3313 (1963). (b) 1. D. Campbell, G. Eglinton, W. Henderson, and R. A. Raphael, J. Chem. SOC., Chem. Commun., 87 (1966). (c) H. H. Staab and K. Neunhoeffer, Synthesis, 424 (1979).

7. (a) H. A. Staab and F. Graf, Tetrahedron Lett., 7, 751 (1966). (b) H. A. Staab and F. Graf, Chem. Ber., 103, 1107 (1970). (c) H. A. Staab and R. Bader, Chem. Ber., 103, 1157 (1970).

8. C. Huynh and G. Linstrumelle, Tetrahedron, 44(20), 6337 (1988). 9. D. Solooki, J. D. Bradshaw, C. A. Tessier, W. J. Youngs, R. F. See, M. R. Churchill, and

Chichester, 1978, pp. 635-712.

D. Ferrara, J. Organomet. Chem., 470, 231 (1994). 10. H. Hommes, H. D. Verkruijsse, and L. Brandsma, Tetrahedron Lett., 2495 (1981). 11. D. Solooki, V. 0. Kennedy, C. A. Tessier, and W. J. Youngs, Synlett, 427 (1990). 12. W. J. Youngs, J. D. Kinder, J. D. Bradshaw, and C. A. Tessier, Organometallics, 12, 2406

13. D. F. Shriver, The Manipulation of Air-Sensitive Compounds, Krieger, Malabar, FL, 1982. 14. W. G. Kofron and L. M. Baclawski, J . Org. Chem., 41, 1879 (1976). 15. W. C. Still, M. Kahn, and A. Mitra, J. Org. Chem., 43, 2923 (1978). 16. C. E. Castro, E. J. Gaughan, and D. C. Owsley, J. Org. Chem., 31,4061 (1966).

(1993).

20. (CH LO R 0 ME THY LENE) BIS [ TRIMETH Y LS IL A N El CBIS(TRIMETHYLS1LY L)CHLOROMETHANE]

SUBMITTED BY RICHARD A. KEMP* and ALAN H. COWLEY’ CHECKED BY HARMUT SCHULZ’ and MALCOLM H. CHISHOLM’

2n-BuLi CH2C12 + 2(CH3)3SiCl - “[(CH3)3Si]2CC12” + 2LiCI + 2C4Hlo

“[(CH3)3Si]2CC12” + n-BuLi + “[(CH,),Si],C(Cl)Li” + n-BuCl

“C(CH3)3Si12C(C1)Li” + CH3CH20H + [(CH3),Sil2CHC1 + LiOCH2CH3

* Union Carbide Corporation, 3333 Highway 6 South, Houston TX 77082. ’ Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712. ? Department of Chemistry, Indian University, Bloomington, IN 47405.