A Bimetallic Ruthenium Ethylene Complex as a Catalyst Precursor for the Kharasch Reaction Laurent Quebatte, Euro Solari, Rosario Scopelliti, and Kay Severin* Institut des Sciences et Inge ´ nierie Chimiques, E Ä cole Polytechnique Fe ´ de ´ rale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland Received January 13, 2005 Summary: A bimetallic complex, in which a RuCl 2 (η 2 - C 2 H 4 )(PCy 3 ) fragment is connected via three chloro bridges to a (η 6 -p-cymene)RuCl 2 fragment, has been synthesized and characterized by single-crystal X-ray crystallography. This complex was used to catalyze the atom transfer radical addition of CCl 4 and CHCl 3 to olefins at temperatures between 0 and 40 °C. Turnover frequencies of up to 1550 h -1 were observed, making the new complex one of the most active catalysts for this type of reaction described so far. In 1973, Matsumoto and co-workers reported that the complex [RuCl 2 (PPh 3 ) 3 ](1) can be used as a catalyst for the addition of polychloromethanes to 1-olefins. 1 This type of reaction proceeds via a radical mechanism and is commonly referred to as the “Kharasch reaction”. 2 For a long time, complex 1 was one of the most active cata- lysts for the Kharasch reaction and several applications in organic synthesis were reported. 3 Over the last 6 years, a number of ruthenium-based catalysts with su- perior performance have been described. 4,5 Our group has recently shown that a mixture of the dimeric com- plex [(1,3,5-C 6 H 3 i Pr 3 )RuCl 2 ] 2 (2) and PCy 3 can be used to catalyze the addition of CHCl 3 to aromatic olefins under exceptionally mild conditions. 6 As a product of the reaction between 2 and PCy 3 , the tetranuclear complex 3 has been identified, which itself proved to be a very efficient catalyst (Scheme 1). The general utility of complex 3 in atom transfer radical reactions, however, is limited by its very low solubility. Therefore, we have investigated whether it is possible to replace the bridg- ing nitrogen ligand with other labile two-electron-donor ligands. Furthermore, we wanted to substitute the (1,3,5-C 6 H 3 i Pr 3 )Ru fragment by a (cymene)Ru fragment, which would allow us to use the commercially available complex [(cymene)RuCl 2 ] 2 (4) as the starting material. As a potential substitute for the µ-N 2 ligand of the catalyst precursor 3, olefins appeared to be of special interest, since olefin π-complexes have been discussed as intermediates in the catalytic cycle of ruthenium- catalyzed Kharasch reactions. 4a We therefore investi- gated the reaction of complex 4 with 1 equiv of PCy 3 in the presence of various olefins. When the reaction was performed under an atmosphere of ethylene, complex 5 could be obtained in the form of red crystals in 80% yield (Scheme 2). 7 Complex 5 is quite soluble in methylene chloride and moderately soluble in aromatic solvents such as benzene (1) Matsumoto, H.; Nakano, T.; Nagai, Y. Tetrahedron Lett. 1973, 14, 5147. (2) Kharasch, M. S.; Jensen, E. V.; Urry, W. H. Science 1945, 102, 128. (3) (a) Minisci, F. Acc. Chem. Res. 1975, 8, 165. (b) Iqbal, J.; Bhatia, B.; Nayyar, N. K. Chem. Rev. 1994, 94, 519. (4) For reviews see: (a) Delaude, L.; Demonceau, A.; Noels, A. F. Top. Organomet. Chem. 2004, 11, 155. (b) Severin, K. Curr. Org. Chem., in press. (5) For some selected examples see: (a) Quebatte, L.; Scopelliti, R.; Severin, K. Angew. Chem., Int. Ed. 2004, 43, 1520. (b) Lee, B. T.; Schrader, T. O.; Martı ´n-Matute, B.; Kauffman, C. R.; Zhang, P.; Snapper, M. L. Tetrahedron 2004, 60, 7391. (c) Tutusaus, O.; Delfosse, S.; Demonceau, A.; Noels, A. F.; Vin ˜ as, C.; Teixidor, F. Tetrahedron Lett. 2003, 44, 8421. (d) Tutusaus, O.; Vin ˜ as, C.; Nu ´n ˜ ez, R.; Teixidor, F.; Demonceau, A.; Delfosse, S.; Noels, A. F.; Mata, I.; Molins, E. J. Am. Chem. Soc. 2003, 125, 11830. (e) Opstal, T.; Verpoort, F. New J. Chem. 2003, 27, 257. (f) De Clercq, B.; Verpoort, F. J. Organomet. Chem. 2003, 672, 11. (g) Simal, F.; Wlodarczak, L.; Demonceau, A.; Noels, A. F. Eur. J. Org. Chem. 2001, 2689. (h) Tallarico, J. A.; Malnick, L. M.; Snapper, M. L. J. Org. Chem. 1999, 64, 344. (6) Quebatte, L.; Haas, M.; Solari, E.; Scopelliti, R.; Nguyen, Q. T.; Severin K. Angew. Chem., Int. Ed. 2005 44, 1084. (7) A solution of complex 4 (100 mg, 163 µmol) and PCy3 (45.6 mg, 163 µmol) in toluene (10 mL) under an atmosphere of ethylene was heated to 60 °C for 9 h. Upon cooling to room temperature, crystals of complex 5 formed, which were isolated after 24 h and washed with pentane (yield 80%). 1 H NMR (400 MHz, toluene-d8 + C2H4): δ (ppm) 1.28 (d, 3 J ) 7 Hz, 6 H, p-CH3C6H4CH(CH3)2), 1.27-1.31 (m, 6 H, PCy3), 1.74-1.95 (m, 18 H, PCy3), 2.11 (s, 3 H, p-CH3C6H4CH(CH3)2), 2.16-2.22 (m, 6 H, PCy3), 2.51 (m, 3 H, PCy3), 2.88 (sept, 3 J ) 7 Hz, 3 H, p-CH3C6H4CH(CH3)2), 4.17 (m, 2 H, C2H4), 4.66 (m, 2 H, C2H4), 5.04 (d, 3 J ) 6 Hz, 1 H, p-CH3C6H4CH(CH3)2), 5.25 (d, 3 J ) 6 Hz, 1 H, p-CH3C6H4CH(CH3)2), 5.33 (d, 3 J ) 6 Hz, 1 H, p-CH3C6H4CH(CH3)2), 5.51 (d, 3 J ) 6 Hz, 1 H, p-CH3C6H4CH(CH3)2). 13 C NMR (101 MHz, toluene-d8 + C2H4): δ (ppm) 18.74, 22.13, 22.49 (s, CH3, cymene), 27.00 (s, PCy3), 28.24-28.37 (m, PCy3), 29.76 (m, PCy3), 31.36 (s, CH(CH3)2), 61.03 (d, 2 JPC ) 2 Hz, C2H4), 78.19, 78.65, 79.33, 80.05 (s, CH, cymene), 96.40, 99.79 (s, C, cymene). 31 P NMR (162 MHz, toluene-d8 + C2H4): δ (ppm) 44.37 (s). Anal. Calcd for 5‚(toluene): C, 50.57; H, 6.77. Found: C, 50.25; H, 6.72. Scheme 1 Scheme 2 1404 Organometallics 2005, 24, 1404-1406 10.1021/om050027x CCC: $30.25 © 2005 American Chemical Society Publication on Web 02/23/2005