Aluminum Complexes with Sulfide-Linked Bis(phenolato) Ligands: Unusual Structure and Reactivity of the Methyl Bis(phenolato) Complex “[Al(tbmp)Me]” (tbmp ) 2,2′-Thiobis(6-tert-butyl-4-methylphenolato)) Wigand Braune, Haiyan Ma, Thomas P. Spaniol, and Jun Okuda* Institute of Inorganic Chemistry, RWTH Aachen University of Technology, Landoltweg 1, D-52056 Aachen, Germany Received November 29, 2004 Trialkylaluminum complexes, AlR 3 (R ) Me, Et), reacted with the sulfide-bridged bis- (phenol) tbmpH 2 (tbmpH 2 ) 2,2′-thiobis(6-tert-butyl-4-methylphenol)) in a 1:1 ratio to give monoalkyl compounds of the composition “[Al(tbmp)R]” with an unsymmetrical dinuclear structure with both six- and four-coordinate aluminum centers in the solid state. The reaction of 2 equiv of tbmpH 2 gave [Al(tbmp)(tbmpH)], which could be deprotonated with triethylamine to give [NEt 3 H][Al(tbmp) 2 ]. Upon reaction of [Al(tbmp)R] 2 with Lewis bases L (L ) Et 2 O, THF, propylene oxide), monomeric, five-coordinate adducts [Al(tbmp)R(L)] were formed, while 2-propanol gave the dinuclear complex [Al(tbmp)(µ-O i Pr)] 2 . Introduction Aluminum complexes of chelating O-donor ligands such as functionalized phenolato ligands exhibit a rich structural variety in both the crystalline and solution states. Currently there is considerable interest in employing structurally well-characterized aluminum complexes as efficient initiators for the ring-opening polymerization of heterocyclic monomers which include lactones, 1 lactides, 2 and, more recently, epoxides. 3 In particular, aluminum complexes with easily available bis(phenolato) ligands such as the methylene-linked ligand mbmp (mbmp ) 2,2′-methylenebis(6-tert-butyl- 4-methylphenolato); Chart 1) have attracted some at- tention. The introduction of a sulfide instead of a methylene bridge has led to an enhanced polymerization activity for the titanium-based alkene polymerization catalysts with linked bis(phenolato) ligands. 4,5 It has been shown for sulfide-linked bis(phenolato) ligands such as tbmp (tbmp ) 2,2′-thiobis(6-tert-butyl-4-meth- ylphenolato)) 6 that the heteroatom donor interacts with the Lewis acidic metal center, leading to higher coor- dination numbers, but in a hemilabile fashion. As (1) For reviews, see: (a) O’Keefe, B. J.; Hillmyer, M. A.; Tolman, W. B. J. Chem. Soc., Dalton Trans. 2001, 2215. (b) Nakano, K., Kosaka, N.; Hiyama, T.; Nozaki, K. J. Chem. Soc., Dalton Trans. 2003, 4039. (c) Che, C.-M.; Huang, J.-S. Coord. Chem. Rev. 2003, 242, 97. For bis- (phenolato) aluminum initiators, see: (d) Lin, C.-H.; Yan, L.-F.; Wang, F.-C.; Sun, Y.-L.; Lin, C.-C. J. Organomet. Chem. 1999, 587, 151. (e) Taden, I.; Kang, H.-C.; Massa, W.; Spaniol, T. P.; Okuda, J. Eur. J. Inorg. Chem. 2000, 3, 441. (f) Chen, H.-L.; Ko, B.-T.; Huang, B.-H.; Lin, C.-C. Organometallics 2001, 20, 5076. (g) Ko, B.-T.; Lin, C.-C. Macromolecules 1999, 32, 8296. (h) Ko, B.-T.; Wu, C.-C.; Lin, C.-C. Organometallics 2000, 19, 1864. (i) Ko, B.-T.; Chao, Y.-C.; Lin, C.-C. Inorg. Chem. 2000, 39, 1463. (j) Ko, B.-T.; Chao, Y.-C.; Lin, C.-C. J. Organomet. Chem. 2000, 598, 13. (k) Liu, Y.-C.; Ko, B.-T.; Lin, C.-C. Macromolecules 2001, 34, 6196. (l) Ziemkowska, W.; Kucharski, S.; Kolodziej, A.; Anulewicz-Ostrowska, R. J. Organomet. Chem. 2004, 689, 2930. (2) For initiators for lactide polymerization based on Schiff base ligands, see: (a) Spassky, N.; Winiewsky, M.; Pluta, C.; Le Borgne, A. Macromol. Chem. Phys. 1996, 197, 2627. (b) Radano, C. P.; Baker, G. L.; Smith, M. R., III. J. Am. Chem. Soc. 2000, 122, 1552. (c) Nomura, N.; Ishi, R.; Akakura, M.; Aoi, K. J. Am. Chem. Soc. 2002, 124, 5938. (d) Ovitt, T. M.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 1316. (e) Zhong, Z.; Dijkstra, P. J.; Feijen, J. J. Am. Chem. Soc. 2003, 125, 11291. For initiators for lactide polymerization based on other ligands, see: (f) Doherty, S.; Errington, R. J.; Housley, N.; Clegg, W. Organometallics 2004, 23, 2382. (3) (a) Atwood, D. A.; Jegier, J. A.; Rutherford, D. J. Am. Chem. Soc. 1995, 117, 6779. (b) Emig, N.; Nguyen, H.; Krautscheid, H.; Re ´au, R.; Cazaux, J.-B.; Bertrand, G. Organometallics 1998, 17, 3599. (c) Braune, W.; Okuda, J. Angew. Chem. 2003, 115, 67; Angew. Chem., Int. Ed. 2003, 43, 65. (d) Chisholm, M. H.; Navarro-Llobet, D.; Simonsick, W. J., Jr. Macromolecules 2001, 34, 8851. (e) Antelmann, B.; Chisholm, M. H.; Iyer, S. S.; Huffman, J. C.; Navarro-Llobet, D.; Pagel, M.; Simonsick, W. J.; Zhong, W. Macromolecules 2001, 34, 3159. For review on coordinate PO polymerization, see: Sugimoto, S.; Inoue, S. Adv. Polym. Sci. 1999, 146, 39. Kuran, W. Prog. Polym. Sci. 1998, 23, 919. (4) (a) Fokken, S.; Spaniol, T. P.; Kang, H.-C.; Massa, W.; Okuda, J. Organometallics 1996, 15, 5069. (b) Sernetz, F. G.; Mu ¨ lhaupt, R.; Fokken, S.; Okuda, J. Macromolecules 1997, 30, 1562. (c) Okuda, J.; Fokken, S.; Kleinhenn, T.; Spaniol, T. P. Eur. J. Inorg. Chem. 2000, 1321. (d) Nakayama, Y.; Watanabe, K.; Ueyama, N.; Nakamura, A.; Harada, A.; Okuda, J. Organometallics 2000, 19, 2498. (e) Amor, F.; Fokken, S.; Kleinhenn, T.; Spaniol, T. P.; Okuda, J. J. Organomet. Chem. 2001, 621, 3. (f) Fokken, S.; Reichwald, F.; Spaniol, T. P.; Okuda, J. J. Organomet. Chem. 2002, 663, 158. (g) Natrajan, L. S., Wilson, C.; Okuda, J.; Arnold, P. L. Eur. J. Inorg. Chem. 2004, 3724. (5) (a) Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Macromol. Chem., Rapid Commun. 1989, 10, 349. Miyatake, T.; Mizunuma, K.; Kakugo, M. Macromol. Chem., Macromol. Symp. 1993, 66, 203. (b) van der Linden, A.; Schavarien, C. J.; N. Meijboom, N.; Ganter, C.; Orpen, A. G. J. Am. Chem. Soc. 1995, 117, 3008. (c) Porri, L.; Ripa, A.; Colombo, P.; Miano, E.; Capelli, S.; Meille, S. V. J. Organomet. Chem. 1996, 514, 213. (d) Froese, R. D. J.; Musaev, D. G.; Matsubara, T.; Morokuma, K. J. Am. Chem. Soc. 1997, 119, 7190. Froese, R. D. J.; Musaev, D. G.; Morokuma, K. Organometallics 1999, 18, 373. Chart 1 1953 Organometallics 2005, 24, 1953-1958 10.1021/om049067b CCC: $30.25 © 2005 American Chemical Society Publication on Web 03/15/2005