Donor/Acceptor Metallocenes: a New Structure Principle in Catalyst Design
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COMMUNICATIONS metal complex inside their tunnels, which makes these [19] C. Cascales, E. GutieÂrrez-Puebla, M. A. Monge, C. Ruiz-Valero, materials a good point of departure for designing new Angew. Chem. 1998, 110, 135 ± 138; Angew. Chem. Int. Ed. 1998, 37, 129 ± 131. catalysts; a stable framework after removal of the transition [20] H. Li, M. Eddaaoudi, D. A. Richardson, O. M. Yaghi, J. Am. Chem. metal complex; and large distances between the active metal Soc. 1998, 120, 8567. centers, which allows unhindered access of reactants to these [21] Hailian Li, O. M. Yaghi, J. Am. Chem. Soc. 1998, 120, 10569. centers through uniformly sized 8Rc channels. [22] T. E. Gier, X. Bu, P. Feng, G. D. Stucky, Nature 1998, 395, 154. [23] X. Bu, P. Feng, G. D. Stucky, J. Am. Chem. Soc. 1998, 120, 11204. [24] X. Bu, P. Feng, T. E. Gier, D. Zhao, G. D. Stucky, J. Am. Chem. Soc. 1998, 120, 13389. [25] H. Brumer, K. Wutz, New J. Chem. 1992, 16,57. Experimental Section [26] A. Corma, V. ForneÂs, S. B. Pergher, T. L. Maesennn, J. G. Buglass, Nature 1998, 396, 353. [27] SHELXTL, Siemens Energy & Automation Inc., Analytical Instru- X-ray structure analysis of ICMM-2Cu, ICMM-2Ag, and ICMM-2H: mentation, 1996. Orthorhombic, space group Pnna,MoKa, dimensions of crystals: 0.2 Â 0.1 Â 0.05, 0.02 Â 0.08 Â 0.2, and 0.04 Â 0.16 Â 0.2 mm, respectively; see Table 1 for the cell parameters. Data were collected in a Siemens SMART- CCD diffractometer using w scans over the range 3 < q < 268. Of 4663, 5159, and 3518 reflections, 1301, 1651, and 1187 were independent for Cu, Ag and H compounds, respectively. The structures were solved by direct methods. In the Cu and Ag compounds, all the hydrogen atoms were located in difference Fourier maps and those of the NH4 cation refined with a model of disorder due to the special position of this N atom. Refinement was by full-matrix least-squares analysis with anisotropic thermal param- Donor/Acceptor Metallocenes: A New eters for all non-hydrogen atoms and isotropic thermal parameters for Structure Principle in Catalyst Design** hydrogen atoms.[27] Further details on the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 K. Aleksander Ostoja Starzewski,* W. Mark Kelly, Eggenstein-Leopoldshafen, Germany (fax: ( 49)7247-808-666; e-mail: Andreas Stumpf, and Dieter Freitag [email protected]), on quoting the depository numbers CSD- 410751 (ICMM-2Cu), -410752 (ICMM-2Ag), and -410753 (ICMM-2H). Dedicated to Dr. Pol Bamelis Cyclopropanation reactions: The sample of ICMM-2Cu was previously on the occasion of his 60th birthday dried at 100 8C. Ethyl diazoacetate (4.11 mmol) was added dropwise over a [1] period of 2 h in a N2 atmosphere at 508C to a stirred mixture of styrene Soon after their discovery and structure elucidation (3 mmol) and the catalyst (0.04 mmol). After the N evolution had ceased, 2 metallocenes were being applied as well-defined organo- the chemical yields were determined by gas chromatography. metallic species in transition metal catalyzed polymerization CAS-registry no. for ICMM-2: 9900953. with alkylaluminum halide cocatalysts.[2] However, it was only Received: March 17, 1999 [Z13179IE] after spectacular work by Sinn, Kaminsky, Brintzinger, Ewen, German version: Angew. Chem. 1999, 111, 2592 ± 2595 and others on the increase in catalyst activity in olefin polymerization by aluminoxanes[3] and on the realization of Keywords: germanium ´ microporosity ´ solid-state struc- stereospecificity in propene polymerization with homogene- tures ´ transition metals ´ zeolite analogues [4] ous stereorigid C2-symmetric ansa-metallocenes that the new era of worldwide polyolefin catalyst research began. The results have an impact on a current world market of more than [1] ªZeolites and Related Microporous Materialsº: State of the Art 1994, 170 million tonnes of polymers, of which almost half are Proceeding of the 10th International Zeolite Conference, Vol. 84 (Eds.: [5] J. Weitkamp, H. G. Karge, H. Pfeifer, W. Hölderich), Elsevier, polyolefins. Amsterdam, 1994. The metallocene catalysts developed up to now can be [2] A. Corma, Chem. Rev. 1995, 95, 559. divided into two large classes: 1) unbridged and 2) covalently [3] G. D. Stucky, Prog. Inorg. Chem. 1992, 40. bridged sandwich compounds.[6] [4] S. J. Weigel, J.-C. Gabriel, E. Gutierrez -Puebla, A. Monge-Bravo, The catalysts of the first group are highly active in the N. J. Henson, L. M. Bull, A. K. Cheetham, J. Am. Chem. Soc. 1996, [7a] 118, 2427. polymerization of the small ethylene molecule. A limited [5] R. H. Jones, J. M. Thomas, R. Xu, Q. Huo, A. K. Cheetham, A. V. Powell, J. Chem. Soc. Chem. Commun. 1991, 1266. [6] Q. Gao, S. Li, R. Xu , J. Chem. Soc. Chem. Commun. 1994, 1465. [*] Dr. Dr. habil. K. A. Ostoja Starzewski [7] M. P. Attfield, R. E. Morris, E. Gutierrez-Puebla, A. Monge-Bravo, Bayer AG, Zentrale Forschung A. K. Cheetham, J. Chem. Soc. Chem. Commun. 1995, 843. Wissenschaftliches Hauptlaboratorium [8] X. Bu, P. Feng, G. D. Stucky, Science 1997, 278, 2080. D-51368 Leverkusen (Germany) [9] M. A. Roberts, A. N. Fitch, J. Phys. Chem. Solids 1991, 52(10), 1209. Fax : ( 49) 214-30-81836 [10] J. Cheng, R. Xu, G. Yang J. Chem. Soc. Chem. Commun. 1991, 1553. E-mail: [email protected] [11] S. Feng, M. Greenblatt, Chem. Mater. 1994, 4, 462. Dr. W. M. Kelly,[] Dr. A. Stumpf, Dr. D. Freitag [12] S. Feng, M. Tsai, S. P. Szu, M. Greenblatt, Chem. Mater. 1992, 4, 468. Bayer AG (Germany) [13] S. Feng, M. Tsai, M. Greenblatt, Chem. Mater. 1992, 4, 338. [14] R. Bialek, V. Gramlich, Z. Kristallogr. 1992, 198,67. [] Current address: [15] M. A. Roberts, A. N. Fitch, A. V. Chadwick, J. Phys. Chem. Solids. NOVA Chemicals (Canada) 1995, 56, 1353. [**] We thank Dr. Stefan Altmann and Waltraud May for the temper- [16] M. A. Roberts, A. N. Fitch, Z. Kristallogr. 1996, 211, 378. ature-dependent NMR investigations, Dr. Thomas Fäcke and Diet- [17] J. Cheng, R. Xu, G. J. Yang, J. Chem. Soc. Dalton Trans. 1991, 1537. mar Wiegel for the 2D NMR investigations, and Dr. Jordi Benet- [18] R. Xu, S. Li, Y. Lu, G. Yang, Chem. Mater. 1992, 2, 808. Buchholz and Dr. Axel Göhrt for the X-ray structure analysis. Angew. Chem. Int. Ed. 1999, 38, No. 16 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 1433-7851/99/3816-2439 $ 17.50+.50/0 2439 COMMUNICATIONS incorporation of a-olefins (propene, butene, hexene) in the production of short-chain branched low-pressure poly- ethylene (LLDPE) is possible.[7d±g] Homopolymerization of a-olefins with three or more C atoms proceeds with much lower activity and predominantly results in products of low molecular weight.[7a,c] Possibilities for stereocontrol in this group are insufficient.[7b] The catalysts of the second group force and define a smaller centroid-metal-centroid angle through covalent bridging of the two rings, so that sterically demanding monomers can also be readily linked.[6] In the copolymerization, a high incorpo- ration of comonomer is achieved with a statistical distribution (very-low-density-polyethylene (VLDPE), cycloolefin-olefin- copolymers (COC), ethene-propene-ethylidene-norbornene (EPDM)).[6c, 7d,g] Such catalysts are particularly suitable for the homopolymerization of propene, but also of higher a- olefins. Structure-optimized ansa compounds of specific Figure 1. Molecular structure of 1 in the crystal. symmetry (C2 , Cs) allow near perfect stereocontrol for isotactic and syndiotactic polypro- the dynamic average on the NMR time scale, that is only two pylene (iPP and sPP, respective- signals are observed for each Cp ring and only one signal for ly).[8] the P-bound methyl groups. In the 13C{1H} NMR spectrum, In a continuation of our inves- the signal of the a-ring carbon atom adjacent to the four- tigations on ylide ± nickel polymer- coordinate P atom occurs at higher field (d 104), which is ization catalysts for linear and in agreement with a phosphonium cyclopentadienylide ligand. branched polyethylene[11b±g] we re- For a comparison with NMR data of free and complexed ylide port herein on a new class of ligands see references [11a, b, d]. The ring-bridging dative Scheme 1. Donor/accept- metallocene catalysts: the donor/ P !B interaction is directly visible in the 11B NMR spectrum or metallocenes. acceptor (D/A) metallocenes through a well-resolved 31P-11B coupling of 120 Hz. The low (Scheme 1). In these metallo- field shift of the 31P NMR signal compared to that of the cenes one p ligand of the sandwich complex bears a donor silylated donor (D) ligands and the high field shift of the 11B substituent with a lone pair of electrons and the other p ligand NMR signal relative to that of the silylated acceptor (A) an acceptor substituent with an electron pair vacancy. In this ligands of about 50 ppm is in agreement with a lower electron way a strongly polarized coordinative D !A bonding density at the phosphorus atom and a higher electron density interaction results spontaneously between the two p ligands. at the boron atom. The polar D ± A bridge in the present case The rotation of the rings with respect to each other is is thermally very stable; thus, even at 1008C the 1H NMR effectively hindered and at the same time the aperture angle spectrum in dideuterotetrachloroethane remains unchanged of the metallocene is influenced. This new structure concept in with regard to the previously described qualitative appear- metallocene catalysis offers a wide range of additional control ance and the size of the 31P-1H coupling.