Articles Diffuse Diffraction from Parallel/Antiparallel Metallocene Pillars Levi J. Irwin, Paul D. Zeits, Joseph H. Reibenspies, and Stephen A. Miller* Department of Chemistry, Texas A&M UniVersity, College Station, Texas 77843-3255 ReceiVed May 18, 2006 X-ray diffraction analyses of dimethyl ansa-metallocenes (CH 3 ) 2 C(C 5 H 4 )(C 29 H 36 )M(CH 3 ) 2 (M ) Zr or Hf) have revealed diffuse diffraction bands in the 0kl and h0l single-crystal reciprocal lattice images, but not in the hk0 plane. This is consistent with metallic disorder in two dimensions and constitutes a rare example of diffuse diffraction for an organometallic compound. The metal is apparently partitioned between two sites with a 60:40 occupancy ratio. Structural interpretation of the X-ray data is consistent with a 60:40 ratio of parallel/antiparallel (+z, -z) metallocene pillars dispersed in the x-y directions. Diffuse diffractionsalbeit weakersis also observed for the half-metallocene (C 29 H 37 )Mn(CO) 3 , which occupies parallel/antiparallel pillars in an 80:20 ratio. Introduction Diffuse X-ray diffraction is a somewhat common occurrence in the field of inorganic materials chemistry. 1 This phenomenon typically arises in ionic crystals or alloys because of disorder present in the crystal that can be characterized in real space as attributable to point defects, line defects, planar defects, and three-dimensional defects. 2 Likewise, diffuse diffraction is also somewhat common in organic molecular crystals, 3 with sub- stitutional and orientational disorder giving rise to defects in the molecular lattice. 1 However, diffuse diffraction is not as well documented in the realm of organometallic chemistry 4 possibly because a ubiquitous goal (and prevalent outcome) in this field is the synthesis of discrete molecular species that are homogeneous in solution and retain their structural uniformity in the solid state. In our ongoing research of dimensionally expansive (>1 nm) organometallic complexes, we have identified and investigated an ansa-metallocene that displays conventional solution behav- ior, but apparently loses its structural homogeneity in the solid state, as evidenced by diffuse X-ray scattering phenomena associated with a disordered placement of the transition metal. The disorder is reconciled by an unprecedented arrangement of organometallic pillars observed for both the zirconocene and hafnocene in the solid state. Results and Discussion The octamethyloctahydrodibenzofluorenyl ligand is a steri- cally expanded version of the fluorenyl ligand (14 vs 9 Å), which has recently been incorporated into metallocene dichlo- rides (CH 3 ) 2 C(C 5 H 4 )(C 29 H 36 )MCl 2 of zirconium (1-Zr) and hafnium (1-Hf). This simple steric modification generally results in markedly increased activity and syndioselectivity in the MAO-cocatalyzed (MAO ) methylaluminoxane) polymeriza- tion of propylene. 5 Pursuant to the study of these and related catalytic enhancements offered by the octamethyloctahydro- dibenzofluorenyl ligand, 6 derivative dimethyl metallocenes (CH 3 ) 2 C(C 5 H 4 )(C 29 H 36 )M(CH 3 ) 2 (2-Zr, 2-Hf) and the dibenzyl metallocene (CH 3 ) 2 C(C 5 H 4 )(C 29 H 36 )Zr(CH 2 C 6 H 5 ) 2 (3-Zr) were synthesized. Single-crystal X-ray diffraction studies of the isomorphic dichloro metallocenes (1-Zr and 1-Hf) and the dibenzyl metallocene (3-Zr) reveal bonding modes (η 5 ,η 5 ) and solid- state packing motifs typical of bent metallocenes (Figure 1). However, the X-ray diffraction patterns from single crystals of the isomorphic dimethyl metallocenes 2-Zr and 2-Hf present bands attributable to diffuse diffraction phenomena, which are not well documented for organometallic species and constitute very distinct diffuse scattering band patterns, reports of which are scarce for this class of compound. The bands are observable * To whom correspondence should be addressed. E-mail: samiller@ mail.chem.tamu.edu. (1) Welberry, T. R.; Butler, B. D. Chem. ReV. 1995, 95, 2369-2403. (2) Jagadzinski, H. Prog. Crystal Growth Charact. 1987, 14, 47-102. (3) (a) Welberry, T. R. Acta Crystallogr. 2001, A57, 244-255. (b) Welberry, T. R. Acta Crystallogr. 2000, A56, 348-358. (c) Welberry, T. R.; Goossens, D. J.; Edwards, A. J.; David, W. I. F. Acta Crystallogr. 2001, A57, 101-109. (d) Bu ¨rgi, H.-B.; Hostettler, M.; Birkedal, H.; Schwarzen- bach, D. Z. Kristallogr. 2005, 220, 1066-1075. (4) (a) The only apparent example for an organometallic single crystal is the polynuclear cluster compound Fe 3(CO)12. Welberry, T. R.; Proffen, T.; Bown, M. Acta Crystallogr. 1998, A54, 661-674. (b) An organometallic thin film (with no long-range lateral order) has also displayed diffuse diffraction. Salditt, T.; Ana, Q.; Plech, A.; Peisl, J.; Eschbaumer, C.; Weidl, C. H.; Schubert, U. S. Thin Solid Films 1999, 354, 208-214. (c) Iodine- doped phthalocyanine compounds, having uranium-nitrogen or ytterbium- nitrogen bonds, are examples of coordination compounds exhibiting diffuse diffraction. Krawczyk, J.; Pietraszko, A.; Kubiak, R.; Lukaszewicz K. Acta Crystallogr. 2003, B59, 384-392. (5) Miller, S. A.; Bercaw, J. E. Organometallics 2004, 23, 1777-1789. (6) (a) Irwin, L. J.; Reibenspies, J. H.; Miller, S. A. J. Am. Chem. Soc. 2004, 126, 16716-16717. (b) Irwin, L. J.; Miller, S. A. J. Am. Chem. Soc. 2005, 127, 9972-9973. (c) Irwin, L. J.; Reibenspies, J. H.; Miller, S. A. Polyhedron 2005, 24, 1314-1324. 1129 Organometallics 2007, 26, 1129-1133 10.1021/om060435g CCC: $37.00 © 2007 American Chemical Society Publication on Web 01/24/2007