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Notes Synthesis and Characterization of a Dimagnesiated Aromatic Compound: Oligomeric Derivatives of 1,4-Bis(chloromagnesio)-2,5-di-tert-butylbenzene Cathrine E. Reck and Charles H. Winter* Department of Chemistry, Wayne State University, Detroit, Michigan 48202 Received May 27, 1997X Summary: The synthesis of 1,4-bis(chloromagnesio)-2,5di-tert-butylbenzene was conducted by treating 1,4-bis(chloromercurio)-2,5-di-tert-butylbenzene with methylmagnesium chloride. The dimagnesiated compound was characterized by hydrolysis, halogenation, and treatment with allyl bromide. NMR spectra suggest that 1,4bis(chloromagnesio)-2,5-di-tert-butylbenzene exists as a mixture of oligomers. Introduction Grignard reagents have been intensively studied over the last century.1 Despite the abundance of aromatic compounds bearing one magnesium substituent, there are very few examples of aromatic compounds containing two or more magnesium groups attached to the same ring.2-5 Evidence for aromatic “poly-Grignard” derivatives has come from analysis of products obtained upon electrophile addition.2,4 The crystal structure of tetrameric o-phenylenemagnesium has been reported, which exists with one terminal magnesium-carbon bond and one ortho carbon bridging between two magnesiums of the tetrameric unit.3 Furthermore, several dimeric arylmagnesium compounds with bridging aryl groups have been structurally characterized.6 However, structural information on aromatic “poly-Grignard” reagents of the type that might be generated and used in typical synthetic procedures has not been reported. X Abstract published in Advance ACS Abstracts, September 1, 1997. (1) For leading references, see: Handbook of Grignard Reagents; Silverman, G. S., Rakita, P. E., Eds.; Dekker: New York, 1996. Bickelhaupt, F. J. Organomet. Chem. 1994, 475, 1. Walborsky, H. M.; Topolski, M. J. Am. Chem. Soc. 1992, 114, 3455. Noyori, R.; Kitamura, M. Angew. Chem., Int. Ed. Engl. 1991, 30, 49. Garst, J. F. Acc. Chem. Res. 1991, 24, 95. Walling, C. Acc. Chem. Res. 1991, 24, 255. Walborsky, H. M. Acc. Chem. Res. 1990, 23, 286. Erdik, E. Tetrahedron 1984, 40, 641. Lai, Y.-H. Synthesis 1981, 585. Felkin, H.; Swierczewski, G. Tetrahedron 1975, 31, 2735. (2) For leading references, see: Wittig, G.; Bickelhaupt, F. Chem. Ber. 1958, 91, 883. Hart, F. A.; Mann, F. G. J. Chem. Soc. 1957, 3939. Smith, C. F.; Moore, G. J.; Tamborski, C. J. Organomet. Chem. 1971, 33, C21. Tamborski, C.; Moore, G. J. J. Organomet. Chem. 1971, 26, 153. Haper, R. J., Jr.; Soloski, E. J.; Tamborski, C. J. Org. Chem. 1964, 29, 2385. Ghosh, T.; Hart, H. J. Org. Chem. 1988, 53, 3555. Harada, H.; Hart, H.; Du, C.-J. F. J. Org. Chem. 1985, 50, 5524. (3) Tinga, M. A. G. M.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.; Horn, E.; Kooijman, H.; Smeets, W. J. J.; Spek, A. L. J. Am. Chem. Soc. 1993, 115, 2808. (4) Eaton, P. E.; Lee, C.-H.; Xiong, Y. J. Am. Chem. Soc. 1989, 111, 8016. (5) For a structural discussion of di-Grignard compounds, see: Bickelhaupt, F. Angew. Chem., Int. Ed. Engl. 1987, 26, 990. (6) (a) Thoennes, D.; Weiss, E. Chem. Ber. 1978, 111, 3726. (b) Markies, P. R.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.; Smeets, W. J. J.; van der Sluis, P.; Spek, A. L. J. Organomet. Chem. 1990, 393, 315.
S0276-7333(97)00430-5 CCC: $14.00
We have recently described the syntheses of perlithiated,7 permagnesiated,8 and perzincated ruthenocenes,9 which were prepared by reaction of the appropriate methylmetal with a permercurated ruthenocene. Given the facile preparation and novelty of the permetalated ruthenocenes, we sought to extend this chemistry to polymetalated benzene derivatives.10 Herein we describe the synthesis and reactivity of 1,4-bis(chloromagnesio)-2,5-di-tert-butylbenzene. NMR spectra of this compound suggest that it exists as a mixture of oligomers obtained by shifting of the Schlenk equilibrium from the monomer. Results and Discussion The preparative chemistry is outlined in Scheme 1. The requisite dimercurated derivative 2 was prepared from 1,4-di-tert-butylbenzene (1) by fusion with mercuric trifluoroacetate (2.2 equiv) at 210 °C,11 followed by treatment with sodium chloride in water/methanol. 1,4Di-tert-butylbenzene could not be tri- or tetramercurated under the fusion conditions, even with excess mercuric trifluoroacetate and extended heating. Exclusive formation of the 1,4-dimercurated compound, as opposed to the 1,3-isomer, was evident from the NMR spectra. Treatment of 2 with methylmagnesium chloride (4.5 equiv) in refluxing 1,2-dimethoxyethane (DME) for 18 h led to a white suspension containing 1,4-bis(chloromagnesio)-2,5-di-tert-butylbenzene (3). Hydrolysis at room temperature afforded 1 (80%), while quenching with D2O resulted in 1-d2 (71%) with >95% deuterium incorporation in the 2- and 5-positions. Since the carbon-mercury bond is stable to hydrolysis under the reaction conditions, the hydrolysis experiments are consistent with the formulation of 3 as a dimagnesiated species. Treatment of 3 with bromine afforded 1,4dibromo-2,5-di-tert-butylbenzene (4, 90%),12 while addition of iodine gave 1,4-diiodo-2,5-di-tert-butylbenzene (7) Bretschneider-Hurley, A.; Winter, C. H. J. Am. Chem. Soc. 1994, 116, 6468. (8) Seneviratne, K.; Bretschneider-Hurley, A.; Winter, C. H. J. Am. Chem. Soc. 1996, 118, 5506. (9) Seneviratne, K.; Winter, C. H. Organometallics 1997, 16, 2498. (10) Synthesis and properties of hexalithiobenzene: Baran, J. C., Jr.; Hendrickson, C.; Laude, D. A., Jr.; Lagow, R. J. J. Org. Chem. 1992, 57, 3759. Xie, Y.; Schaefer, H. F., III. Chem. Phys. Lett. 1991, 179, 563. Smith, B. J. Chem. Phys. Lett. 1993, 207, 403. (11) These conditions are an adaptation of those used to prepare hexakis[(trifluoroacetoxy)mercurio]benzene: Deacon, G. B.; Farquharson, G. J. Aust. J. Chem. 1976, 29, 627; J. Organomet. Chem. 1974, 67, C1. (12) Kofod, H.; Kumar, L.; Sutton, L. E. J. Chem. Soc. 1958, 1790.
© 1997 American Chemical Society
4494 Organometallics, Vol. 16, No. 20, 1997
Notes
Scheme 1. Preparation and Reactions of 3
(5, 88%).13 Addition of allyl bromide afforded 1,4-ditert-butyl-2,5-diallylbenzene (6, 87%). Ketones and other carbonyl-containing compounds gave mixtures of many products upon reaction with 3. Use of DME in the formation of 3 is critical. Other solvents (THF, Et2O, HMPA, NEt3, TMEDA) led to mixtures of (methylmercurio)benzene species, with 310 °C; IR (Fluorolube, cm-1) 3032 (w), 3020 (w), 3002 (w), 2946 (s), 2873 (m), 2851 (m), 2835 (m), 1487 (w), 1464 (s), 1418 (w), 1386 (w), 1370 (m), 1361 (m), 1356 (m); IR (Nujol, cm-1) 1276 (w), 1252 (w), 1238 (w), 1115 (m), 1103 (m), 1057 (s), 1023 (m), 1017 (m), 880 (m), 868 (m), 836 (w); 13C CP/MAS NMR spectrum 174.04 (s, C-Mg), 165.43 (s, C-Mg), 160.18 (s, C-Mg), 154.67 (s, C-C(CH3)3), 152.95 (s, C-C(CH3)3), 135.75 (s, aromatic C-H), 127.14 (s, aromatic C-H), 124.50 (s, benzene C-H), 71.20 (s, free CH3OCH2CH2OCH3), 70.37 (s, coordinated CH3OCH2CH2OCH3), 61.66 (s, coordinated CH3OCH2CH2OCH3), 59.10 (s, free CH3OCH2CH2OCH3), 36.77 (s, C(CH3)3), 35.82 (s, C(CH3)3), 33.88 (broad s, C(CH3)3). Microanal. Found: C, 33.10, 33.46; H, 6.70, 6.75; Cl, 20.20, 20.09; Hg, 5.96, 5.91.
Notes NMR Data for 7: 1H NMR (DMSO-d6, 23 °C, δ) 7.46 (d, J ) 2.5 Hz, C2-H), 7.36 (d, J ) 8.5 Hz, C5-H), 7.06 (dd, J ) 2.5, 8.5 Hz, C4-H), 1.41 (s, C(CH3)3), 1.25 (s, C(CH3)3), 0.45 (s, MgCH3); 13C{1H} NMR (DMSO-d6, 23 °C, ppm) 174.72 (s, C1), 153.96 (s, C3 or C6), 146.09 (s, C3 or C6), 134.42 (s, C2), 125.02 (C4 or C5), 123.17 (C4 or C5), 35.50 (s, C(CH3)3), 34.15 (s, C(CH3)3), 33.25 (s, C(CH3)3), 31.31 (s, C(CH3)3), 13.14 (s, MgCH3). NMR Data for 8: 1H NMR (DMSO-d6, 23 °C, δ) 7.48 (s, J ) 2.5 Hz, C2-H), 7.44 (d, J ) 8.5 Hz, C5-H), 7.15 (dd, J ) 2.5, 8.5 Hz, C4-H), 1.49 (s, C(CH3)3), 1.27 (s, C(CH3)3); there was insufficient signal to noise to measure the 13C{1H} spectrum. The 1H NMR data are equally consistent with 8 being bis(2,5-di-tert-butylphenyl)magnesium.
Acknowledgment. We are grateful to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for the support of this research. Supporting Information Available: NMR spectra of the dimagnesiated white solid (8 pages). Ordering information is given on any current masthead page. OM9704307
