Metal-Metal Bonding in Sterically Frustrated Dipalladium Species Stefan Deeken, ² Gu 1 nter Motz, ‡ Viktor Bezugly, § Horst Borrmann, § Frank R. Wagner,* ,§ and Rhett Kempe* ,² Lehrstuhl Anorganische Chemie II, UniVersita ¨t Bayreuth, 95440 Bayreuth, Germany, Lehrstuhl Keramische Werkstoffe, UniVersita ¨t Bayreuth, 95440 Bayreuth, Germany, and Max-Planck-Institut fu ¨r Chemische Physik fester Stoffe, 01187 Dresden, Germany Received June 19, 2006 Stoichiometric-deficient lithiation of (2,6-diisopropylphenyl)(4-me- thylpyridin-2-yl)amine and reaction with [(cod)PdCl 2 ] (cod ) 1,5- cyclooctadiene) yield a dimeric Pd complex. X-ray structural analysis of this complex reveals a very short Pd-Pd distance (2.429 Å). Topological analysis of the electron density and the electron localization function from scalar relativistic density functional theory calculations clearly indicate a Pd(I)-Pd(I) σ-bonding interaction, for which the corresponding occupied localized orbital can be identified. Group 10 metal complexes stabilized by deprotonated 2-aminopyridines have become an intensively investigated class of compounds since 1998. 1 Because of the flexibility of the binding mode ranging from a strained η 2 coordinations predominantly observed in early-transition-metal and lan- thanide complexessto a bridging binding mode common in late-transition-metal chemistry, 2 two general types of com- pounds are observed. There are limited reports for the two heavier elements of group 10. 1,3 Amidopalladium complexes are intermediates of the Pd-catalyzed aryl amination 4 and rapidly reductively eliminate amido ligands as deprotonated 2-aminopyridines. 5 Recently, we initiated a research program exploring the reactivity of metal complexes stabilized by sterically demanding aminopyridinato ligands, 6 where we expected to form Pd-Pd-bonded species via steric frustration (Chart 1). Because of the steric bulk of the ligand, only two deprotonated aminopyridines should bind a dinuclear unit (Chart 1, right) and not four as in the thermodynamically stable paddlewheel arrangement (Chart 1, left), which could lead to a Pd-Pd bond. Metal-metal bonding is well documented for Pd complexes. 7 To the best of our knowl- edge, the shortest ligand-bridged Pd-Pd bond [2.391(2) Å] was described by Cotton and co-workers 8 for a Pd(III) dimeric unit and the shortest nonsupported one [2.4878(7) Å] by Kurasuwa et al. 9 for a Pd(I) dimeric unit of the corner- sharing L 3 -Pd(I)-Pd(I)-L 3 type. In this report, we present an unsymmetrical corner-sharing L 2 -Pd(I)-Pd(I)-L 3 com- plex in which the metal-metal bond is supported by deprotonated aminopyridines. Compound 1 [(2,6-diisopropylphenyl)(4-methylpyridin-2- yl)amine] can be synthesized via Pd-catalyzed aryl amination as previously reported. 6c The reaction of lithiated 1 with * To whom correspondence should be addressed. E-mail: wagner@ cpfs.mpg.de (F.R.W.), kempe@uni-bayreuth.de (R.K.). ² Lehrstuhl Anorganische Chemie II, Universita ¨t Bayreuth. ‡ Lehrstuhl Keramische Werkstoffe, Universita ¨t Bayreuth. § Max-Planck-Institut fu ¨r Chemische Physik fester Stoffe. (1) Spannenberg, A.; Arndt, P.; Kempe, R. Angew. Chem. 1998, 110, 824- 827; Angew. Chem., Int. Ed. 1998, 37, 832-835. (2) For review, please see: Kempe, R. Eur. J. Inorg. Chem. 2003, 791- 803. (3) (a) Oskui, B.; Mintert, M.; Sheldrick, W. S. Inorg. Chim. Acta 1999, 287, 72-81. (b) Schneider, A.; Freisinger, E.; Beck, B.; Lippert, B. J. Chem. Soc., Dalton Trans. 2000, 837-838. (c) Kempe, R.; Noss, H.; Fuhrmann, H. Chem.sEur. J. 2001, 7, 1630-1636. (d) Su, C.- W.; Chen, J.-D.; Keng, T.-C.; Wang, J.-C. Inorg. Chem. Commun. 2001, 4, 201-204. (e) Kamar, K. K.; Das, S.; Hung, C.-H.; Castineiras, A.; Kuz’min, M. D.; Rillo, C.; Bartolome, J.; Goswami, S. Inorg. Chem. 2003, 42, 5367-5375. (f) Mizota, M.; Sakai, K. Acta Crystallogr., Sect. 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(9) Murahashi, T.; Otani, T.; Mochizuki, E.; Kai, Y.; Kurosawa, H.; Sakaki, S. J. Am. Chem. Soc. 1998, 120, 4536-4537. Inorg. Chem. 2006, 45, 9160-9162 9160 Inorganic Chemistry, Vol. 45, No. 23, 2006 10.1021/ic0610987 CCC: $33.50 © 2006 American Chemical Society Published on Web 10/11/2006