Articles Lithium Complexes of N-Donor-Functionalized CyclopentadienylsA Pyrazolate-Based Bimetallic Version Jens C. Ro ¨der, Franc Meyer,* and Hans Pritzkow Anorganisch-Chemisches Institut der Universita ¨ t Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany Received October 16, 2000 The two new pyrazole-based dinucleating ligands 3,5-bis(fluoren-9-ylmethyl)-1H-pyrazole (H 3 L a ) and 3,5-bis(inden-3-ylmethyl)-1H-pyrazole (H 3 L b ) have been prepared and structurally characterized in the case of H 3 L a , and their lithium complexes Li 3 L a and Li 3 L b are reported. These systems can be viewed as coupled dinucleating versions of two widely used Cp fragments bearing pendant amino or amido side chains, which is confirmed by the crystal structure of the solvent-separated ion pair [Li 2 L a (thf) 4 ][Li(thf) 4 ]. In solution, 7 Li NMR spectroscopy indicates the predominant presence of contact ion pairs. The crystal structure of the partially lithiated compound [Li 2 HL a (thf) 5 ] is also presented. Introduction Complexes of side-chain-functionalized cyclopenta- dienyl (Cp) ligands (or derivatives thereof such as indenyl and fluorenyl) have received enormous attention in the past decade, which is particularly true for Cp ligands bearing pendant amino or amido side chains. 1-4 The donor substituent tethered to the Cp ligand might serve an intramolecular function, e.g. acting as a (possibly hemilabile) chelate donor in generic type A complexes (Scheme 1). It might also serve an intermo- lecular function, e.g. by coordinating to a second metal ion, anchoring to a solid support, or providing solubility. 3 Many of the complexes reported in the literature that feature linked amino-Cp or amido-Cp ligands are mononuclear type A compounds, and such systems are being explored with great success in both main-group (s- and p-block) 4 and transition-metal chemistry. 1-3 Synthetic applications of type A complexes, such as their use as catalysts for olefin polymerization, 5 are often based on the presence of (at least) two active coordina- tion sites at the single metal center, thus suggesting an alternative bimetallic approach in which two proxi- mate metal ions can work in concert. It is well-known from natural metalloenzymes con- taining di- or oligonuclear active sites that cooperativity of two adjacent metal ions might enable very particular and efficient transformations of small substrate mol- ecules. 6 To study such cooperative reactivity in small biomimetic coordination compounds, we have been * To whom correspondence should be addressed. Fax: (0049)-6221- 545707. E-mail: franc.meyer@urz.uni-heidelberg.de. (1) (a) Okuda, J. Comments Inorg. Chem. 1994, 16, 185. (b) Mu ¨ ller, C.; Vos, D.; Jutzi, P. J. Organomet. Chem. 2000, 600, 127. (2) See for example: (a) Fedushkin, I. L.; Dechert, S.; Schumann, H. Organometallics 2000, 19, 4066. (b) Groux, L. F.; Be ´langer-Garie ´py, F.; Zargarian, D.; Vollmerhaus, R. Organometallics 2000, 19, 1507. (c) Segnitz, O.; Winter, M.; Merz, K.; Fischer, R. Eur. J. Inorg. Chem. 2000, 2077. (d) Philippopoulos, A. I.; Donnadieu, B.; Poilblanc, R.; Hadjiliadis, N. J. Organomet. Chem. 1999, 582, 286. (e) Schumann, H.; Rosenthal, E. C.; Demtschuk, J.; Molander, G. A. Organometallics 1998, 17, 5324. (f) Gomes, P. T.; Green, M. L. H.; Martins, A. M. J. Organomet. Chem. 1998, 551, 133. (g) Foster, P.; Chien, J. C. W.; Rausch, M. D. J. Organomet. Chem. 1998, 545-546, 35. (h) Ziniuk, Z.; Goldberg, I.; Kol, M. J. Organomet. Chem. 1997, 545-546, 441. (i) Sinnema, P.-J.; van der Veen, L.; Spek, A. L.; Veldman, N.; Teuben, J. H. Organometallics 1997, 16, 4245. (j) Hughes, A. K.; Kingsley, A. J. J. Chem. Soc., Dalton Trans. 1997, 4139. (k) Enders, M.; Rudolph, R.; Pritzkow, H. Chem. Ber. 1996, 129, 459. (l) Herrmann, W. A.; Morawietz, M. J. A.; Priermeier, T.; Mashima, K. J. Organomet. Chem. 1995, 486, 291. (3) (a) Siemeling, U.; Jutzi, P. J. Organomet. Chem. 1995, 500, 175. (b) Jutzi, P.; Redeker, T. Eur. J. Inorg. Chem. 1998, 663. (4) Jutzi, P.; Dahlhaus, J. Coord. Chem. Rev. 1994, 137, 179. (5) See for example: (a) Shapiro, P. J.; Bunel, E.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1990, 9, 867. (b) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587 and references therein. (c) Emrich, R.; Heinemann, O.; Jolly, P. W.; Kru ¨ ger, C.; Verhovnik, G. P. J. Organometallics 1997, 16, 1511. (d) Blais, M. S.; Chien, J. C. W.; Rausch, M. D. Organometallics 1998, 17, 3775. (d) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. Angew. Chem. 1999, 111, 163. (e) Witte, P. T.; Meetsma, A.; Hessen, B. Organometallics 1999, 18, 2944. Scheme 1 811 Organometallics 2001, 20, 811-817 10.1021/om0008878 CCC: $20.00 © 2001 American Chemical Society Publication on Web 02/03/2001